Difference between revisions of "John's Linux page"

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Quick jump to: [[#NetBeans|NetBeans]].
 
Quick jump to: [[#NetBeans|NetBeans]].
 +
 +
= References =
 +
 +
== Command-line ==
 +
 +
See [https://zaiste.net/posts/shell-commands-rust/ Shell Commands I Wish I Knew Earlier] for some interesting options.
  
 
= System =
 
= System =
 +
 +
== Reporting system specifications from the command-line ==
 +
 +
Try any of these:
 +
 +
# neofetch
 +
# inxi
 +
# hwinfo --short
 +
 +
You may need to install the relevant package.
  
 
== Determining which Debian/Ubuntu release your are running ==
 
== Determining which Debian/Ubuntu release your are running ==
Line 46: Line 62:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 83: Line 95:
 
  Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5
 
  Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5
  
== Viewing syslog and other logs with KSystemLog ==
+
=== Motherboard info ===
 +
 
 +
# dmidecode -t 2
 +
 
 +
=== CPU info ===
 +
 
 +
# lscpu
 +
 
 +
or:
 +
 
 +
# cat /proc/cpuinfo
 +
 
 +
=== RAM info ===
  
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
+
# dmidecode --type memory
  
= Power =
+
=== PCI info ===
  
== Reporting on PowerShield DEFENDER UPS status ==
+
# lspci -v
  
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
+
=== Drive info ===
  
  $ upsc defender
+
  # cat /proc/partitions
  
E.g.:
+
and:
  
  jj5@orac:~$ upsc defender
+
  # hdparm -I /dev/sda
Init SSL without certificate database
+
 
battery.charge: 100
+
and:
battery.voltage: 27.40
 
battery.voltage.high: 26.00
 
battery.voltage.low: 20.80
 
battery.voltage.nominal: 24.0
 
device.type: ups
 
driver.name: blazer_usb
 
driver.parameter.pollinterval: 2
 
driver.parameter.port: auto
 
driver.parameter.synchronous: no
 
driver.version: 2.7.4
 
driver.version.internal: 0.12
 
input.current.nominal: 5.0
 
input.frequency: 50.1
 
input.frequency.nominal: 50
 
input.voltage: 242.6
 
input.voltage.fault: 242.6
 
input.voltage.nominal: 240
 
output.voltage: 242.6
 
ups.beeper.status: disabled
 
ups.delay.shutdown: 30
 
ups.delay.start: 180
 
ups.load: 14
 
ups.productid: 5161
 
ups.status: OL
 
ups.type: offline / line interactive
 
ups.vendorid: 0665
 
  
== Run commands on PowerShield DEFENDER UPS batteries ==
+
# smartctl --info /dev/sda
  
You can run "instant commands" using the '''upscmd''' command.
+
You can check if a drive is SSD or not with:
  
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
+
# cat /sys/block/sde/queue/rotational
  
  diligence:/srv/salt/conf/app/defender-1200.sls
+
  0=SSD
 +
1=HDD
  
To see "instant commands" supported by the PowerShield DEFENDER:
+
== Viewing syslog and other logs with KSystemLog ==
  
$ upscmd -l defender
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
  
E.g.:
+
= CPU =
  
jj5@orac:~$ upscmd -l defender
+
== Monitoring CPU clock speed ==
Instant commands supported on UPS [defender]:
 
 
beeper.toggle - Toggle the UPS beeper
 
load.off - Turn off the load immediately
 
load.on - Turn on the load immediately
 
shutdown.return - Turn off the load and return when power is back
 
shutdown.stayoff - Turn off the load and remain off
 
shutdown.stop - Stop a shutdown in progress
 
test.battery.start - Start a battery test
 
test.battery.start.deep - Start a deep battery test
 
test.battery.start.quick - Start a quick battery test
 
test.battery.stop - Stop the battery test
 
  
= Environment =
+
Try something like this:
  
== Configuring vim as your editor ==
+
$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'
  
Sometimes all you need is:
+
= Power =
  
$ export EDITOR=/usr/bin/vim
+
== Reporting on PowerShield DEFENDER UPS status ==
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
Before running `upsc` ensure service is running:
  
Other times you need to run
+
# upsdrvctl start
  
# update-alternatives --config editor
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
$ upsc defender
  
== Configuring your locale ==
+
E.g.:
  
  $ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
  jj5@orac:~$ upsc defender
  $ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
+
Init SSL without certificate database
 
+
battery.charge: 100
= User and group management =
+
battery.voltage: 27.40
 +
battery.voltage.high: 26.00
 +
battery.voltage.low: 20.80
 +
battery.voltage.nominal: 24.0
 +
device.type: ups
 +
driver.name: blazer_usb
 +
driver.parameter.pollinterval: 2
 +
driver.parameter.port: auto
 +
driver.parameter.synchronous: no
 +
driver.version: 2.7.4
 +
driver.version.internal: 0.12
 +
input.current.nominal: 5.0
 +
input.frequency: 50.1
 +
input.frequency.nominal: 50
 +
input.voltage: 242.6
 +
input.voltage.fault: 242.6
 +
input.voltage.nominal: 240
 +
output.voltage: 242.6
 +
ups.beeper.status: disabled
 +
ups.delay.shutdown: 30
 +
ups.delay.start: 180
 +
ups.load: 14
 +
ups.productid: 5161
 +
  ups.status: OL
 +
ups.type: offline / line interactive
 +
ups.vendorid: 0665
  
== Adding a user ==
+
== Run commands on PowerShield DEFENDER UPS batteries ==
  
To add a new user on a linux system:
+
You can run "instant commands" using the '''upscmd''' command.
  
# useradd username
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
diligence:/srv/salt/conf/app/defender-1200.sls
  
# adduser username
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
== Adding a user to a group ==
+
$ upscmd -l defender
  
To add an existing user to an existing group:
+
E.g.:
  
  # gpasswd -a username group
+
  jj5@orac:~$ upscmd -l defender
 +
Instant commands supported on UPS [defender]:
 +
 +
beeper.toggle - Toggle the UPS beeper
 +
load.off - Turn off the load immediately
 +
load.on - Turn on the load immediately
 +
shutdown.return - Turn off the load and return when power is back
 +
shutdown.stayoff - Turn off the load and remain off
 +
shutdown.stop - Stop a shutdown in progress
 +
test.battery.start - Start a battery test
 +
test.battery.start.deep - Start a deep battery test
 +
test.battery.start.quick - Start a quick battery test
 +
test.battery.stop - Stop the battery test
  
e.g. to add user 'jj5' to the 'sudo' group:
+
= Environment =
  
# gpasswd -a jj5 sudo
+
== Configuring vim as your editor ==
  
Alternatively you can use adduser, passing the username and group:
+
Sometimes all you need is:
  
  # adduser username group
+
  $ export EDITOR=/usr/bin/vim
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
# adduser sclaughl staff
+
Other times you need to run
  
== Disabling a user account ==
+
# update-alternatives --config editor
  
You can disable a user account with:
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
# passwd -l user
+
== Configuring your locale ==
  
Note: that's a lower-case L, not a one.
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
== Enabling a disabled user account ==
+
= User and group management =
  
To can re-enable a locked user account with:
+
== Adding a user ==
  
# passwd -u user
+
To add a new user on a linux system:
  
== Finding which user you are logged in as ==
+
# useradd username
 +
# passwd username
  
To determine which user you are running as enter the command:
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
  $ whoami
+
  # adduser username
  
== Finding which groups you are a member of ==
+
== Adding a user to a group ==
  
To find which groups you are a member of:
+
To add an existing user to an existing group:
  
  $ groups
+
  # gpasswd -a username group
  
or
+
e.g. to add user 'jj5' to the 'sudo' group:
  
  $ groups username
+
  # gpasswd -a jj5 sudo
  
Where 'username' is the username of the user you are querying, e.g.:
+
Alternatively you can use adduser, passing the username and group:
  
  $ groups jj5
+
  # adduser username group
  
== Finding who else is logged in to the system ==
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
To see who else is logged in,
+
# adduser sclaughl staff
  
$ who
+
== Disabling a user account ==
  
== Running a command as a particular user ==
+
You can disable a user account with:
  
To run "svn update" as the user www-data:
+
# passwd -l user
  
$ sudo su -c "svn update" www-data
+
Note: that's a lower-case L, not a one.
  
== Reporting user and group info for the current user ==
+
== Enabling a disabled user account ==
  
$ id
+
To can re-enable a locked user account with:
  
= Memory management =
+
# passwd -u user
  
== Checking available memory ==
+
== Finding which user you are logged in as ==
  
To report memory statistics in megabytes:
+
To determine which user you are running as enter the command:
  
  $ free -m
+
  $ whoami
  
== Check for swap thrashing ==
+
== Finding which groups you are a member of ==
  
Check your virtual memory status with vmstat:
+
To find which groups you are a member of:
  
  $ vmstat
+
  $ groups
  
== Report memory type ==
+
or
  
Report on RAM DIMMs:
+
$ groups username
  
# dmidecode --type 17
+
Where 'username' is the username of the user you are querying, e.g.:
  
Report on RAM and CPU cache:
+
$ groups jj5
  
# lshw -short -C memory
+
== Finding who else is logged in to the system ==
  
Or for more detail:
+
To see who else is logged in,
  
  # lshw -C memory
+
  $ who
  
= Video/display management =
+
== Running a command as a particular user ==
  
== Viewing EDID data for attached monitor ==
+
To run "svn update" as the user www-data:
  
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
+
$ sudo su -c "svn update" www-data
  
$ cd /sys/class/drm
+
== Reporting user and group info for the current user ==
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
$ id
  
== Using 'top' for dynamic resource usage reporting ==
+
= Memory management =
  
To run top:
+
== Checking available memory ==
  
$ top
+
To report memory statistics in megabytes:
  
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
+
$ free -m
  
To see usage for a specific user run e.g.:
+
== Check for swap thrashing ==
  
$ top -u jj5
+
Check your virtual memory status with vmstat:
  
To see full command-line press 'c'.
+
$ vmstat
  
When you're in 'top' you can:
+
== Report memory type ==
  
* press '1' (one) to toggle CPU aggregation
+
Report on RAM DIMMs:
* press < and > to change the sort column
 
  
== Changing memory reporting in 'top' ==
+
# dmidecode --type 17
  
To run top:
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
  $ top
+
  # lshw -short -C memory
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
Or for more detail:
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
# lshw -C memory
  
Press 'M' to sort by memory utilisation.
+
= Video/display management =
  
Press 'm' to switch between various display modes.
+
== Viewing EDID data for attached monitor ==
  
== Showing full command-line in 'top' ==
+
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
  
To see the full command-line for processes run with -c:
+
$ cd /sys/class/drm
 
+
$ ls
  $ top -c
+
$ cd card0-HDMI-A-1
 +
  $ edid-decode edid
  
== Listing all processes currently running which were started in your current shell session ==
+
= Process management =
  
$ ps -fl
+
== Using 'top' for dynamic resource usage reporting ==
  
== Killing specific processes ==
+
To run top:
  
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
+
  $ top
  
== Run a command for a specified time using timeout ==
+
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
  
$ timeout 3 ping jj5.net
+
To see usage for a specific user run e.g.:
  
= Disk management =
+
$ top -u jj5
  
== Creating a partition table ==
+
To see full command-line press 'c'.
  
# parted /dev/xvdf
+
When you're in 'top' you can:
  
mktable msdos
+
* press '1' (one) to toggle CPU aggregation
 +
* press < and > to change the sort column
  
== Creating a partition ==
+
== Changing memory reporting in 'top' ==
  
# parted /dev/xvdf
+
To run top:
  
  u MiB
+
  $ top
mkpart primary 1 100%
 
  
== Creating an ext4 file-system ==
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
# mkfs.ext4 /dev/xvdf1
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
== Listing disk drives ==
+
Press 'M' to sort by memory utilisation.
  
# fdisk -l
+
Press 'm' to switch between various display modes.
  
(That's an L for "list")
+
== Showing full command-line in 'top' ==
  
== Checking available disk space ==
+
To see the full command-line for processes run with -c:
  
  $ df -h
+
  $ top -c
  
== Getting disk information ==
+
== Listing all processes currently running which were started in your current shell session ==
  
  # lsblk
+
  $ ps -fl
  
And
+
== Killing specific processes ==
  
  # cat /proc/partitions
+
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
Or the Grand Daddy of them all:
+
== Run a command for a specified time using timeout ==
  
  # lshw -class disk
+
  $ timeout 3 ping jj5.net
  
(Requires the lshw package.)
+
= Disk management =
  
== Getting partition UUID and file-system type ==
+
== Reporting ext4 file-systems mounted without noatime ==
  
  # blkid
+
  $ cat /proc/mounts | grep ext | grep -v noatime | sort
  
== Checking for SSD vs magnetic disk ==
+
== Creating a partition table ==
  
  # cat /sys/block/sda/queue/rotational
+
  # parted /dev/xvdf
  
Will be 0 for SSD and 1 for magnetic.
+
mktable msdos
  
== Monitoring a ZFS server ==
+
== Creating a partition ==
  
So some commands I run to keep an eye on my new ZFS servers:
+
# parted /dev/xvdf
  
  # top
+
  u MiB
  # iotop
+
  mkpart primary 1 100%
# nethogs
 
# watch free -h
 
# watch slabtop -o
 
# slabtop
 
# watch cat /proc/meminfo
 
# perf top
 
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 
# watch zpool iostat -v
 
# zpool iostat -v 2
 
# watch 'zpool list; echo; zfs list'
 
# watch zfs get compressratio -o all
 
# watch cat /proc/spl/kstat/zfs/arcstats
 
  
If you have a scrub or resilvering in progress you can report on progress with:
+
== Creating an ext4 file-system ==
  
  # watch zpool status -v
+
  # mkfs.ext4 /dev/xvdf1
  
You can poke about in internals, e.g.:
+
== Listing disk drives ==
  
  # cat /proc/spl/kstat/zfs/arcstats
+
  # fdisk -l
  
root@orac:/sys/module/zfs/parameters# tail *
+
(That's an L for "list")
  
You can report on property values with e.g.:
+
== Checking available disk space ==
  
  # zfs get all data
+
$ df -h
 +
 
 +
== Getting disk information ==
 +
 
 +
  # lsblk
  
If you want to get funky:
+
And
  
  # cd /tmp
+
  # cat /proc/partitions
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
Or the Grand Daddy of them all:
  
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
  # lshw -class disk
  
You can report history of a zpool:
+
(Requires the lshw package.)
  
# zpool history $poolname
+
== Getting partition UUID and file-system type ==
  
You can get a report on the dedup tables:
+
# blkid
  
# zpool status -D $poolname
+
== Checking for SSD vs magnetic disk ==
  
Or more detailed dedup table info:
+
# cat /sys/block/sda/queue/rotational
  
# zdb -DDD $poolname
+
Will be 0 for SSD and 1 for magnetic.
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
== Monitoring a ZFS server ==
  
{|class="wikitable"
+
So some commands I run to keep an eye on my new ZFS servers:
! Abbr  !! Description
 
|-
 
| LSIZE  || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== How to tell if zfs scrub is running ==
+
# top
 +
# iotop
 +
# nethogs
 +
# watch free -h
 +
# watch slabtop -o
 +
# slabtop
 +
# watch cat /proc/meminfo
 +
# perf top
 +
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 +
# watch zpool iostat -v
 +
# zpool iostat -v 2
 +
# watch 'zpool list; echo; zfs list'
 +
# watch zfs get compressratio -o all
 +
# watch cat /proc/spl/kstat/zfs/arcstats
  
You can get the status from the "scan:" line from:
+
If you have a scrub or resilvering in progress you can report on progress with:
  
  $ zpool status
+
  # watch zpool status -v
  
== Measure data throughput ==
+
You can poke about in internals, e.g.:
  
Use the 'pv' command from the 'pv' package, e.g.:
+
# cat /proc/spl/kstat/zfs/arcstats
  
  # cat /dev/sda | pv | cat > /dev/null
+
  root@orac:/sys/module/zfs/parameters# tail *
  
Or for ZFS:
+
You can report on property values with e.g.:
  
  # zfs send data/example | pv | cat > /dev/null
+
  # zfs get all data
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
If you want to get funky:
  
For notes on using smartctl see [https://www.lisenet.com/2014/using-smartctl-smartd-and-hddtemp-on-debian/ Using Smartctl, Smartd and Hddtemp on Debian].
+
# cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
== Report hard disk usage ==
+
You can search for ZFS files like e.g. this:
  
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
+
root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
== Report hard disk temperatures ==
+
You can report history of a zpool:
  
E.g.
+
# zpool history $poolname
  
# hddtemp /dev/sd[a-e]
+
You can get a report on the dedup tables:
  
== Burning an ISO image to USB on Mac ==
+
# zpool status -D $poolname
  
First insert your USB key and find the appropriate disk with:
+
Or more detailed dedup table info:
  
  # diskutil list
+
  # zdb -DDD $poolname
  
Then unmount it with:
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
  # diskutil unmountDisk /dev/disk4
+
{|class="wikitable"
 
+
! Abbr  !! Description
Then copy ISO image with 'dd':
+
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
+
== How to tell if zfs scrub is running ==
  
You can get dd to report progress by sending it the SIGINFO signal:
+
You can get the status from the "scan:" line from:
  
  # kill -s info 12345
+
  $ zpool status
  
== Listing all ext4 file systems ==
+
== Measure data throughput ==
  
To see a list only of the mounted ext4 file systems:
+
Use the 'pv' command from the 'pv' package, e.g.:
  
  # df -t ext4
+
  # cat /dev/sda | pv | cat > /dev/null
  
== Report hierarchical file system mount points and mount options ==
+
Or for ZFS:
  
  $ findmnt
+
  # zfs send data/example | pv | cat > /dev/null
  
== Report the mount point for the current working directory ==
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
$ findmnt "$PWD"
+
For notes on using smartctl see [https://www.lisenet.com/2014/using-smartctl-smartd-and-hddtemp-on-debian/ Using Smartctl, Smartd and Hddtemp on Debian].
  
= Monitoring disk I/O =
+
== Report hard disk usage ==
  
There's an app for that! iotop.
+
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
  
== Using iotop, top for disks ==
+
== Report hard disk temperatures ==
  
# iotop -oPa
+
E.g.
  
== Monitor disk I/O for performance issues ==
+
# hddtemp /dev/sd[a-e]
  
# watch iostat
+
== Burning an ISO image to USB on Mac ==
  
Or e.g.
+
First insert your USB key and find the appropriate disk with:
  
  # watch iostat -xd /dev/sd[abc]
+
  # diskutil list
  
Or use groupings like this command for 'tact':
+
Then unmount it with:
  
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
  # diskutil unmountDisk /dev/disk4
  
= Monitoring a system =
+
Then copy ISO image with 'dd':
  
== Simple ZFS monitoring ==
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
# watch iostat
+
You can get dd to report progress by sending it the SIGINFO signal:
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
# kill -s info 12345
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
== Listing all ext4 file systems ==
  
$ cat /sys/class/thermal/thermal_zone*/temp
+
To see a list only of the mounted ext4 file systems:
  
and:
+
# df -t ext4
  
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
== Report hierarchical file system mount points and mount options ==
  
== Monitoring CPU temperature ==
+
$ findmnt
  
$ watch sensors
+
== Report the mount point for the current working directory ==
  
== Monitoring HDD temperature ==
+
$ findmnt "$PWD"
  
For e.g. SATA drives sda to sdd:
+
= Monitoring disk I/O =
  
# watch hddtemp /dev/sd[a-d]
+
There's an app for that! iotop.
  
= ZFS =
+
== Using iotop, top for disks ==
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
# iotop -oPa
  
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
+
== Monitor disk I/O for performance issues ==
  
  $ cat /proc/spl/kstat/zfs/arcstats
+
  # watch iostat
  
Then:
+
Or e.g.
  
  c is the target size of the ARC in bytes
+
  # watch iostat -xd /dev/sd[abc]
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
== Stopping a ZFS scrub in progress ==
+
Or use groupings like this command for 'tact':
  
  # zpool scrub -s $pool
+
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
e.g. for the 'data' pool:
+
= Monitoring a system =
  
# zpool scrub -s data
+
== Simple ZFS monitoring ==
  
= File management =
+
# watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
== Listing files by size ==
+
= Monitoring temperature =
  
Use capital S for Size:
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
  $ ls -S
+
  $ cat /sys/class/thermal/thermal_zone*/temp
  
== Listing only directories ==
+
and:
  
  $ ls -l | egrep '^d'
+
  $ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
== Listing only files ==
+
== Monitoring CPU temperature ==
  
  $ ls -l | egrep -v '^d'
+
  $ watch sensors
  
== Listing hidden files ==
+
== Monitoring HDD temperature ==
  
$ ls -al .[!.]*
+
For e.g. SATA drives sda to sdd:
  
== Creating a symbolic link ==
+
# watch hddtemp /dev/sd[a-d]
  
$ ln -s /path/to/target link-name
+
= ZFS =
  
== Creating a hard-link ==
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
 +
 
 +
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
  
  $ ln /path/to/target file-name
+
  $ cat /proc/spl/kstat/zfs/arcstats
  
== Changing the owner of a file ==
+
Then:
  
  $ chown user:group <files>
+
  c is the target size of the ARC in bytes
 +
c_max is the maximum size of the ARC in bytes
 +
size is the current size of the ARC in bytes
  
E.g.
+
== Stopping a ZFS scrub in progress ==
  
  $ chown jj5:staff README
+
  # zpool scrub -s $pool
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
e.g. for the 'data' pool:
  
  $ chown -R root:root /etc/*
+
  # zpool scrub -s data
  
== Changing file permissions ==
+
= File management =
  
{|class="wikitable"
+
== Listing files by size ==
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
Use capital S for Size:
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
$ ls -S
|+ Numeric codes
 
! 0
 
| None
 
|-
 
! 1
 
| Execute
 
|-
 
! 2
 
| Write
 
|-
 
! 3
 
| Write, Execute
 
|-
 
! 4
 
| Read
 
|-
 
! 5
 
| Read, Execute
 
|-
 
! 6
 
| Read, Write
 
|-
 
! 7
 
| Read, Write, Execute
 
|}
 
  
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
+
== Listing only directories ==
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  $ ls -l | egrep '^d'
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
== Listing only files ==
  
  $ chmod 600 my-private-file
+
  $ ls -l | egrep -v '^d'
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
== Listing hidden files ==
  
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
+
$ ls -al .[!.]*
  
$ cp old.conf updated.conf
+
== Creating a symbolic link ==
$ merge -A updated.conf new.conf old.conf
 
  
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
+
$ ln -s /path/to/target link-name
  
The merge program is a part of the RCS package. If you don't have it:
+
== Creating a hard-link ==
  
  $ sudo apt-get install rcs
+
  $ ln /path/to/target file-name
  
== Listing open files ==
+
== Changing the owner of a file ==
  
Use lsof to list open files. E.g.:
+
$ chown user:group <files>
  
# lsof
+
E.g.
  
See man lsof for options.
+
$ chown jj5:staff README
 +
$ chown root:root *
  
== List permissions on a whole directory path ==
+
To apply recursively into sub-directories use -R,
  
E.g.:
+
$ chown -R root:root /etc/*
  
$ namei -om /home/jj5/workspace
+
== Changing file permissions ==
  
Outputs:
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
f: /home/jj5/workspace/
+
{|class="wikitable"
  drwxr-xr-x root root /
+
|+ Permission codes
  drwxr-xr-x root root home
+
! Read !! Write !! Exectue
  drwxr-xr-x jj5  jj5  jj5
+
|-
  drwxr-xr-x jj5  jj5  workspace
+
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
== Counting non-blank lines in a file ==
+
{|class="wikitable"
 
+
|+ Numeric codes
E.g.:
+
! 0
 +
| None
 +
|-
 +
! 1
 +
| Execute
 +
|-
 +
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
$ cat foo.c | sed '/^\s*$/d' | wc -l
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
== Cloning one directory to another with rsync ==
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
E.g.:
+
E.g.
  
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== Counting number of files in current directory and all subdirectories ==
+
== Updating config files ==
  
$ ls -AlhR . | egrep '^-' | wc -l
+
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
  
== Counting number of directories in current directory and all subdirectories ==
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
$ ls -AlhR . | egrep '^d' | wc -l
+
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
  
== Getting the status of a 'dd' process ==
+
The merge program is a part of the RCS package. If you don't have it:
  
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
+
$ sudo apt-get install rcs
  
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
+
== Listing open files ==
  
# kill -s info 40947
+
Use lsof to list open files. E.g.:
  
The dd process will report its status in the terminal its running in.
+
# lsof
  
== Transferring a large file via FAT32 file system ==
+
See man lsof for options.
  
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
+
== List permissions on a whole directory path ==
  
$ split -b 4000m input.tgz input.tgz-parts-
+
E.g.:
  
Then copy the small files and reassemble:
+
$ namei -om /home/jj5/workspace
  
$ cat input.tgz-parts-* > output.tgz
+
Outputs:
  
= NFS =
+
f: /home/jj5/workspace/
 +
  drwxr-xr-x root root /
 +
  drwxr-xr-x root root home
 +
  drwxr-xr-x jj5  jj5  jj5
 +
  drwxr-xr-x jj5  jj5  workspace
  
== List NFS shares ==
+
== Counting non-blank lines in a file ==
  
To e.g. show NFS shares on 'love':
+
E.g.:
  
  $ showmount -e love
+
  $ cat foo.c | sed '/^\s*$/d' | wc -l
  
= Compression =
+
== Cloning one directory to another with rsync ==
  
== How to use pigz with tar ==
+
E.g.:
  
See [https://stackoverflow.com/a/39904353 here]:
+
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
  
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
== Counting number of files in current directory and all subdirectories ==
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
$ ls -AlhR . | egrep '^-' | wc -l
  
Also from [https://stackoverflow.com/a/50586833 here]:
+
== Counting number of directories in current directory and all subdirectories ==
  
Fast pack:
+
$ ls -AlhR . | egrep '^d' | wc -l
  
tar -I 'pigz --fast' -cf my.tar.gz whatver
+
== Getting the status of a 'dd' process ==
  
Best pack:
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
tar -I 'pigz --best' -cf my.tar.gz whatver
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
Fast unpack:
+
# kill -s info 40947
  
  tar -I pigz -xf my.tar.gz
+
The dd process will report its status in the terminal its running in.
 +
 
 +
== Transferring a large file via FAT32 file system ==
 +
 
 +
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
 +
 
 +
  $ split -b 4000m input.tgz input.tgz-parts-
  
== Best compression with tar ==
+
Then copy the small files and reassemble:
  
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
+
$ cat input.tgz-parts-* > output.tgz
  
export GZIP=-9
+
== Find the difference between two directories ==
tar cvzf file.tar.gz /path/to/directory
 
  
or
+
$ diif -qr $DIR_A $DIR_B
  
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
+
= NFS =
  
== Best parallel compression with pigz ==
+
== List NFS shares ==
  
$ pigz --best
+
To e.g. show NFS shares on 'love':
  
== Best parallel compression with xz ==
+
$ showmount -e love
  
$ xz -9e -T 0
+
= Compression =
  
== Reporting compression ratios with xz ==
+
== How to use pigz with tar ==
  
e.g.
+
See [https://stackoverflow.com/a/39904353 here]:
  
  root@love:/data/image/archive# xz -l *
+
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
 
    1      3    372.2 MiB    442.3 MiB  0.841  CRC64  1999.txz
 
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64  2001.txz
 
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64  2002.txz
 
    1      9    568.5 MiB  1,660.2 MiB  0.342  CRC64  2003.txz
 
    1    639    66.8 GiB    119.6 GiB  0.558  CRC64  2004.txz
 
    1    313    12.7 GiB    58.6 GiB  0.217  CRC64  2005.txz
 
    1    414    35.0 GiB    77.4 GiB  0.452  CRC64  2006.txz
 
    1    485    44.5 GiB    90.9 GiB  0.490  CRC64  2007.txz
 
    1  1,690    150.0 GiB    316.8 GiB  0.473  CRC64  2008.txz
 
    1      3    457.9 MiB    526.0 MiB  0.871  CRC64  2009.txz
 
    1    168    27.3 GiB    31.4 GiB  0.868  CRC64  2010.txz
 
    1      4    477.1 MiB    702.8 MiB  0.679  CRC64  2011.txz
 
-------------------------------------------------------------------------------
 
    12  3,768    344.6 GiB    705.5 GiB  0.488  CRC64  12 files
 
  
= Symbolic-link management =
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
== Data used by sym-linked files:
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:
+
Fast pack:
  
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
  tar -I 'pigz --fast' -cf my.tar.gz whatver
  
= File searching =
+
Best pack:
  
== Finding a file with a particular name ==
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
$ find -iname "*some-part-of-the-file-name*"
+
Fast unpack:
  
Will start searching from the current directory, so maybe
+
tar -I pigz -xf my.tar.gz
  
$ cd /
+
== Best compression with tar ==
  
first. For a case-sensitive search:
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
  $ find -name "*eXaCT CaSE*"
+
  export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
== Finding a file with particular content ==
+
or
  
To search in /etc/ for a file with particular content:
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
$ grep -R "search-string" /etc/*
+
== Best parallel compression with pigz ==
  
To search the current directory for *.cs files containing the word "Up":
+
$ pigz --best
  
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
== Best parallel compression with xz ==
  
== Finding a list of files with particular content ==
+
$ xz -9e -T 0
  
E.g. to find all the files with the word 'creativity':
+
== Reporting compression ratios with xz ==
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
e.g.
  
== Using the locate command to find files ==
+
root@love:/data/image/archive# xz -l *
 
+
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
  $ locate part-of-filename
+
    1      3    372.2 MiB    442.3 MiB  0.841  CRC64  1999.txz
 
+
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64  2001.txz
E.g.
+
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64  2002.txz
 
+
    1      9    568.5 MiB  1,660.2 MiB  0.342  CRC64  2003.txz
  $ locate texvc
+
    1    639    66.8 GiB    119.6 GiB  0.558  CRC64  2004.txz
 +
    1    313    12.7 GiB    58.6 GiB  0.217  CRC64  2005.txz
 +
    1    414    35.0 GiB    77.4 GiB  0.452  CRC64  2006.txz
 +
    1    485    44.5 GiB    90.9 GiB 0.490  CRC64  2007.txz
 +
    1  1,690    150.0 GiB    316.8 GiB  0.473  CRC64  2008.txz
 +
    1      3    457.9 MiB    526.0 MiB  0.871  CRC64  2009.txz
 +
    1    168    27.3 GiB    31.4 GiB  0.868  CRC64  2010.txz
 +
    1      4    477.1 MiB    702.8 MiB 0.679  CRC64  2011.txz
 +
-------------------------------------------------------------------------------
 +
    12  3,768    344.6 GiB    705.5 GiB  0.488  CRC64  12 files
  
== Updating locate command's database ==
+
= Symbolic-link management =
  
# updatedb
+
== Data used by sym-linked files:
  
== Select a random line from a text file ==
+
This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:
  
  $ shuf -n 1 input.txt
+
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
== Extra context for grep ==
+
= File searching =
  
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
+
== Finding a file with a particular name ==
  
  $ grep -B 3 -A 1 ...
+
  $ find -iname "*some-part-of-the-file-name*"
  
= Job control =
+
Will start searching from the current directory, so maybe
  
== Stopping a running process ==
+
$ cd /
  
Press Ctrl+Z to stop a running process.
+
first. For a case-sensitive search:
  
== Listing current jobs and their status ==
+
$ find -name "*eXaCT CaSE*"
  
$ jobs
+
== Finding a file with particular content ==
  
== Resuming a stopped job in the backgroud ==
+
To search in /etc/ for a file with particular content:
  
To resume a stopped process in the background
+
$ grep -R "search-string" /etc/*
  
$ bg %1
+
To search the current directory for *.cs files containing the word "Up":
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
== Resuming a stopped job in the foreground ==
+
== Finding a list of files with particular content ==
  
To resume a stopped process in the foreground
+
E.g. to find all the files with the word 'creativity':
  
  $ fg %1
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Using the locate command to find files ==
  
== Killing a stopped job ==
+
$ locate part-of-filename
  
To kill a job
+
E.g.
  
  $ kill %1
+
  $ locate texvc
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Updating locate command's database ==
  
== Periodically run a program and watch its output ==
+
# updatedb
  
$ watch /your/command
+
== Select a random line from a text file ==
  
= Debian/Ubuntu package management =
+
$ shuf -n 1 input.txt
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
== Extra context for grep ==
  
== configuring debconf ==
+
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
  
  # dpkg-reconfigure debconf
+
  $ grep -B 3 -A 1 ...
  
Set priority to low to get asked detailed questions.
+
= Job control =
  
== Showing list of installed packages ==
+
== Stopping a running process ==
  
# dpkg --get-selections
+
Press Ctrl+Z to stop a running process.
  
== Searching for installed package ==
+
== Listing current jobs and their status ==
  
  # dpkg --get-selections | grep package-name
+
  $ jobs
  
or
+
== Resuming a stopped job in the backgroud ==
  
# aptitude search package-name
+
To resume a stopped process in the background
  
== Showing which files are installed as part of a package ==
+
$ bg %1
  
# dpkg -L package-name
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Installing a package ==
+
== Resuming a stopped job in the foreground ==
  
# apt-get install package-name
+
To resume a stopped process in the foreground
  
== Uninstalling a package ==
+
$ fg %1
  
# apt-get remove package-name
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Showing system architecture ==
+
== Killing a stopped job ==
  
$ dpkg --print-architecture
+
To kill a job
  
== Showing which package a file belongs to ==
+
$ kill %1
  
$ which echo
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
/bin/echo
 
$ dpkg -S /bin/echo
 
coreutils: /bin/echo
 
$ dpkg -l | grep coreutils
 
ii  coreutils                        6.10-6                  The GNU core utilities
 
  
== Showing package information ==
+
== Periodically run a program and watch its output ==
  
  $ apt-cache showpkg coreutils
+
  $ watch /your/command
  
Or for even more information:
+
= Debian/Ubuntu package management =
  
$ apt-cache show coreutils
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
== List all installed packages with package version info ==
+
== configuring debconf ==
  
  dpkg-query -l
+
  # dpkg-reconfigure debconf
  
== Reporting which version of a package is installed ==
+
Set priority to low to get asked detailed questions.
  
$ dpkg -l | grep package-name
+
== Showing list of installed packages ==
  
E.g.:
+
# dpkg --get-selections
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
== Searching for installed package ==
ii  augeas-lenses                  0.7.0-1ubuntu1                Set of lenses needed by libaugeas0 to parse
 
ii  libaugeas0                      0.7.0-1ubuntu1                The augeas configuration editing library and
 
  
== Comprehensive upgrade ==
+
# dpkg --get-selections | grep package-name
  
Try the following:
+
or
 +
 
 +
# aptitude search package-name
 +
 
 +
== Showing which files are installed as part of a package ==
 +
 
 +
# dpkg -L package-name
 +
 
 +
== Installing a package ==
  
  # apt-get update
+
  # apt-get install package-name
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
== Uninstalling a package ==
  
  $ apt-cache search . | sort -d | less
+
  # apt-get remove package-name
  
= Networking =
+
== Showing system architecture ==
  
== net-tools vs iproute2 ==
+
$ dpkg --print-architecture
  
The older 'net-tools' package has been replaced with 'iproute2' e.g. in [https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#iproute2 stretch].
+
== Showing which package a file belongs to ==
  
{|class="wikitable"
+
$ which echo
! legacy net-tools commands
+
/bin/echo
! iproute2 replacement commands
+
$ dpkg -S /bin/echo
|-
+
coreutils: /bin/echo
| arp      || ip n (ip neighbor)
+
$ dpkg -l | grep coreutils
|-
+
  ii  coreutils                        6.10-6                  The GNU core utilities
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 
|-
 
| iptunnel || ip tunnel
 
|-
 
| iwconfig || iw
 
|-
 
| nameif  || ip link, ifrename
 
|-
 
| netstat || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 
|-
 
| route    || ip r (ip route)
 
|}
 
  
== Restart networking ==
+
== Showing package information ==
  
For servers:
+
$ apt-cache showpkg coreutils
  
# service networking restart
+
Or for even more information:
  
For desktops:
+
$ apt-cache show coreutils
  
# service network-manager restart
+
== List all installed packages with package version info ==
  
== Pinging with particular packet size ==
+
dpkg-query -l
  
$ ping -M do -s <packet size in bytes> <host>
+
== Reporting which version of a package is installed ==
  
E.g.
+
$ dpkg -l | grep package-name
  
$ ping -M do -s 1400 charity.progclub.org
+
E.g.:
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
root@hope:~/letsencrypt# dpkg -l | grep augeas
 +
ii  augeas-lenses                  0.7.0-1ubuntu1                Set of lenses needed by libaugeas0 to parse
 +
ii  libaugeas0                      0.7.0-1ubuntu1                The augeas configuration editing library and
  
# ip route add <host> dev <interface> advmss <packet size>
+
== Comprehensive upgrade ==
  
E.g.
+
Try the following:
  
  # ip route add 10.0.0.1 dev eth0 advmss 1400
+
  # apt-get update
 +
# apt-get dist-upgrade
 +
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
== Dropping configured MMS for a particular IP address ==
+
== Searching all available packages ==
  
  # ip route flush <host>
+
  $ apt-cache search . | sort -d | less
  
E.g.
+
== Reporting unattended upgrades status ==
  
# ip route flush 10.0.0.1
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
== Listing open ports and socket information ==
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
Including which process is listening on which port.
+
== Searching for Debian packages and versions ==
  
# netstat -tulpn
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
Or use the 'ss' command:
+
= Networking =
  
# ss -s
+
== Determining throughput between two hosts ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
# apt install iperf3
  
# lsof -Pnl +M -i4
+
On the server:
  
You might need to install the lsof package:
+
# iperf3 -s
  
# apt-get install lsof
+
On the client:
  
== Query for DNS MX record ==
+
# iperf3 -c $SERVER_IP
  
$ nslookup
+
For more info see: [https://www.cyberciti.biz/faq/how-to-test-the-network-speedthroughput-between-two-linux-servers/ How to test the network speed/throughput between two Linux servers].
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
== net-tools vs iproute2 ==
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
The older 'net-tools' package has been replaced with 'iproute2' e.g. in [https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#iproute2 stretch].
  
== Using nmap to list open ports on remote host ==
+
{|class="wikitable"
 +
! legacy net-tools commands
 +
! iproute2 replacement commands
 +
|-
 +
| arp      || ip n (ip neighbor)
 +
|-
 +
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 +
|-
 +
| iptunnel || ip tunnel
 +
|-
 +
| iwconfig || iw
 +
|-
 +
| nameif  || ip link, ifrename
 +
|-
 +
| netstat  || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 +
|-
 +
| route    || ip r (ip route)
 +
|}
  
To check the 1,000 most common ports:
+
== Restart networking ==
  
# nmap server.example.com
+
For servers:
  
Or for a specific port range (e.g. 101 to 102):
+
# service networking restart
  
# nmap -p 101-102 server.example.com
+
For desktops:
  
Or for all ports (1 to 65,535):
+
# service network-manager restart
  
# nmap -p- server.example.com
+
== Pinging with particular packet size ==
  
== Network monitoring ==
+
$ ping -M do -s <packet size in bytes> <host>
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
E.g.
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
$ ping -M do -s 1400 charity.progclub.org
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
You can watch network traffic in real-time with nload:
+
# ip route add <host> dev <interface> advmss <packet size>
  
# nload -u M
+
E.g.
  
== Reporting network (NIC) speed ==
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
== Dropping configured MMS for a particular IP address ==
  
  # dmesg | grep eth0
+
  # ip route flush <host>
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
E.g.
  
== Path MTU discovery ==
+
# ip route flush 10.0.0.1
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
== Listing open ports and socket information ==
  
# tracepath host.example.com
+
Including which process is listening on which port.
  
== Listing available Ethernet devices ==
+
# netstat -tulpn
  
To see a list of NICs available on the host:
+
Or use the 'ss' command:
  
  $ cat /proc/net/dev
+
  # ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
Also
+
== Listing open IPv4 connections ==
  
  $ ip link
+
  # lsof -Pnl +M -i4
  
== 59 Linux Networking commands and scripts ==
+
You might need to install the lsof package:
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
# apt-get install lsof
  
== Links ==
+
== Query for DNS MX record ==
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
= IPTables =
+
== Query for DNS SOA record ==
  
== Applying firewall rules ==
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
== Using nmap to list open ports on remote host ==
  
$ sudo vim /etc/iptables.test.rules
+
To check the 1,000 most common ports:
$ sudo /sbin/iptables -F
 
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 
$ sudo iptables -L
 
$ sudo -s
 
# iptables-save > /etc/iptables.up.rules
 
# exit
 
  
= ufw =
+
# nmap server.example.com
  
== Denying hosts with ufw ==
+
Or for a specific port range (e.g. 101 to 102):
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
# nmap -p 101-102 server.example.com
  
= Bind9 =
+
Or for all ports (1 to 65,535):
  
== Viewing Bind9 querylog ==
+
# nmap -p- server.example.com
  
$ sudo rndc querylog
+
== Network monitoring ==
$ tail -f /var/log/syslog
 
  
= IPSec =
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
== Disabling IPSec ==
+
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
 +
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 +
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 +
# Bandwidth per process: nethogs
  
# setkey -FP
+
== nload ==
  
= OpenSSL =
+
You can watch network traffic in real-time with nload:
  
== Debugging IMAPS with OpenSSL ==
+
# nload -u M
  
# openssl s_client -connect localhost:993
+
== Reporting network (NIC) speed ==
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
  $ openssl s_client -connect www.example.com:443
+
  # dmesg | grep eth0
  GET /example.html HTTP/1.1
+
  # mii-tool -v eth0
  host: www.example.com
+
  # ethtool eth0
  
== Links ==
+
Note: use ifconfig to get device name.
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
== Path MTU discovery ==
  
= Pluggable Authentication Modules (PAM) =
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
== Links ==
+
# tracepath host.example.com
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
== Listing available Ethernet devices ==
  
= SSH =
+
To see a list of NICs available on the host:
  
== Configuring SSH key login ==
+
$ cat /proc/net/dev
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
Also
  
  $ ssh-keygen -t rsa
+
  $ ip link
  
Copy the public key from the client to the server:
+
== 59 Linux Networking commands and scripts ==
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
Configure the authorized keys on the server:
+
== Links ==
  
$ ssh user@example.org
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
$ mkdir ~/.ssh
 
$ chmod go-w .ssh
 
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 
$ chmod 600 ~/.ssh/authorized_keys
 
$ rm ~/id_rsa.pub
 
  
== Tunneling over SSH ==
+
= IPTables =
  
For example, connecting a remote MySQL server to the localhost:
+
== Applying firewall rules ==
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
$ sudo vim /etc/iptables.test.rules
 +
$ sudo /sbin/iptables -F
 +
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 +
$ sudo iptables -L
 +
$ sudo -s
 +
# iptables-save > /etc/iptables.up.rules
 +
# exit
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
== Blocking an IP address with iptables ==
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
To drop IP address 1.2.3.4:
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
= ufw =
  
* run putty.exe
+
== Denying hosts with ufw ==
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
To see what's going on with your ssh connections,
+
= Bind9 =
  
$ ssh -v user@host
+
== Viewing Bind9 querylog ==
  
Or
+
$ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
$ ssh -vv user@host
+
= IPSec =
  
== Unlocking SSH key for session ==
+
== Disabling IPSec ==
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  # setkey -FP
[Desktop Entry]
 
Type=Application
 
Name=ssh-add
 
Comment=Adds my private key to my session.
 
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Links ==
+
= OpenSSL =
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
== Debugging IMAPS with OpenSSL ==
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
== cat EOF ==
+
== Debugging HTTPS with OpenSSL ==
  
  $ cat > output <<EOF
+
  $ openssl s_client -connect www.example.com:443
  > text
+
  GET /example.html HTTP/1.1
  > EOF
+
  host: www.example.com
  
$ cat output
+
== Links ==
text
 
  
= Script =
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
== Creating a session log with script ==
+
= Pluggable Authentication Modules (PAM) =
  
$ script -t 2> timing
+
== Links ==
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
== Replaying a scripted session ==
+
= SSH =
  
$ scriptreplay timing
+
== Configuring SSH key login ==
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
= Screen =
+
$ ssh-keygen -t rsa
  
== Creating a new screen or reconnecting to a detached screen ==
+
Copy the public key from the client to the server:
  
  $ screen -R
+
  $ scp ~/.ssh/id_rsa.pub user@example.org:
  
== Detaching a screen ==
+
Configure the authorized keys on the server:
  
  $ screen -D
+
  $ ssh user@example.org
 +
$ mkdir ~/.ssh
 +
$ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
== Reconnecting to screen ==
+
== Tunneling over SSH ==
  
$ screen -D
+
For example, connecting a remote MySQL server to the localhost:
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
#!/bin/bash
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
== Scrolling in screen ==
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
See [https://www.saltycrane.com/blog/2008/01/how-to-scroll-in-gnu-screen/ How to scroll in GNU Screen]. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.
+
== Tunneling over SSH with PuTTY ==
  
= tmux =
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
== Live collaboration with tmux ==
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
User A:
+
== Enabling verbose SSH logging ==
  
tmux -S /tmp/collab
+
To see what's going on with your ssh connections,
chmod 777 /tmp/collab
 
  
User B:
+
$ ssh -v user@host
  
tmux -S /tmp/collab attach
+
Or
  
= Vim =
+
$ ssh -vv user@host
  
== First, why Vim? ==
+
== Unlocking SSH key for session ==
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
  
== Visual modes ==
+
== Links ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
 +
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
  
== Configuring spaces instead of tabs ==
+
= Standard IO =
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
== cat EOF ==
  
  $ vim ~/.vimrc
+
  $ cat > output <<EOF
 +
> text
 +
> EOF
  
and include the following lines:
+
$ cat output
 +
text
  
set tabstop=2
+
= Script =
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
== Creating a session log with script ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
$ script -t 2> timing
  
Use:
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
:syntax on
+
== Replaying a scripted session ==
  
to turn on syntax highlighting.
+
$ scriptreplay timing
  
Use:
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
:syntax off
+
= Screen =
  
to turn off syntax highlighting.
+
== Creating a new screen or reconnecting to a detached screen ==
  
To always use syntax highlighting:
+
$ screen -R
  
$ vim ~/.vimrc
+
== Detaching a screen ==
  
and add:
+
$ screen -D
  
syntax on
+
== Reconnecting to screen ==
  
To get a list of supported colour schemes open vim and type:
+
$ screen -D
 +
$ screen -R
  
:colorscheme[space][Ctrl+D]
+
I have a script in ~/bin/reconnect like so,
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
colorscheme desert
+
This will detach your last screen, and reconnect it on the current terminal.
  
== Inserting a TAB character when expandtab is on ==
+
== Scrolling in screen ==
  
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
+
See [https://www.saltycrane.com/blog/2008/01/how-to-scroll-in-gnu-screen/ How to scroll in GNU Screen]. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.
  
Press Ctrl+V TAB to insert a literal tab character.
+
= tmux =
  
Or you can disable tab expansion altogether with:
+
== Live collaboration with tmux ==
  
:set expandtab!
+
User A:
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
:%s/^\s*/&&/g
+
User B:
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
tmux -S /tmp/collab attach
  
== Recording and replaying a macro ==
+
= Vim =
  
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
+
== First, why Vim? ==
  
== Deleting to end of line ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
d$
+
== Visual modes ==
  
== Deleting to beginning of line ==
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
d^
+
== Configuring spaces instead of tabs ==
  
== Finding text ==
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
To search forward for "text":
+
$ vim ~/.vimrc
  
/text
+
and include the following lines:
  
To search backward for "text":
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
?text
+
== Configuring syntax highlighting ==
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
== Finding and replacing text ==
+
Use:
  
To replace the first instance of "search" on the current line with "destroy":
+
:syntax on
  
:s/search/destroy/
+
to turn on syntax highlighting.
  
To replace all instances of "search" on the current line with "destroy":
+
Use:
  
  :s/search/destroy/g
+
  :syntax off
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
to turn off syntax highlighting.
  
:13,37 s/search/destroy/g
+
To always use syntax highlighting:
  
To replace all instances of "search" in the entire file with "destroy":
+
$ vim ~/.vimrc
  
:%s/search/destroy/g
+
and add:
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
syntax on
  
To set the line-ending to Unix line endings run the command:
+
To get a list of supported colour schemes open vim and type:
  
  :setlocal ff=unix
+
  :colorscheme[space][Ctrl+D]
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
== Disabling auto-indent etc. to paste from clipboard ==
+
colorscheme desert
  
To disable smart indenting when you're going to paste in text:
+
== Inserting a TAB character when expandtab is on ==
  
:set paste
+
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
  
To turn it off again:
+
Press Ctrl+V TAB to insert a literal tab character.
  
:set nopaste
+
Or you can disable tab expansion altogether with:
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
:set expandtab!
  
== Positioning windows ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
Use -o for horizontal split, e.g.:
+
:%s/^\s*/&&/g
  
vim -o a.txt b.txt
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
Use -O for vertical split, e.g.:
+
== Recording and replaying a macro ==
  
vim -o a.txt b.txt
+
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
== Deleting to end of line ==
  
Use ^W and &lt; or &gt; to resize windows.
+
d$
  
== To indent a block of text in Vim ==
+
== Deleting to beginning of line ==
  
Use the > command. E.g. to indent five lines:
+
d^
  
5 > >
+
== Finding text ==
  
Press . (dot) to keep indenting.
+
To search forward for "text":
  
Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:
+
/text
  
> %
+
To search backward for "text":
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
?text
  
== Open a file in a new window/tab ==
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
To open a file on the left hand side:
+
== Finding and replacing text ==
  
:vert new filename.ext
+
To replace the first instance of "search" on the current line with "destroy":
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
:s/search/destroy/
  
To open a file at the top:
+
To replace all instances of "search" on the current line with "destroy":
  
  :new filename.ext
+
  :s/search/destroy/g
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
== Explore files in Vim ==
+
:13,37 s/search/destroy/g
  
Enter:
+
To replace all instances of "search" in the entire file with "destroy":
  
  :Explore
+
  :%s/search/destroy/g
  
== Switch between Vim tabs ==
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
Use gt and gT.
+
To set the line-ending to Unix line endings run the command:
  
== Switch between Vim windows ==
+
:setlocal ff=unix
  
To toggle between open windows use:
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
Ctrl+W W
+
== Disabling auto-indent etc. to paste from clipboard ==
  
To move in a direction use:
+
To disable smart indenting when you're going to paste in text:
  
  Ctrl+W h/j/k/l
+
  :set paste
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
To turn it off again:
  
== Insert block comment in Vim ==
+
:set nopaste
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
So it's:
+
== Positioning windows ==
  
# Ctrl+V (Note: not Shift+V!)
+
Use -o for horizontal split, e.g.:
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
vim -o a.txt b.txt
  
To navigate to the matching beginning or end tag use '%'.
+
Use -O for vertical split, e.g.:
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
vim -o a.txt b.txt
  
== Auto-format HTML tags ==
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
Use ^W and &lt; or &gt; to resize windows.
  
# first join all the lines - ggVGgJ
+
== To indent a block of text in Vim ==
# Now break tags to new lines - :%s/>\s*</>\r</g
 
# Now set filetype - :set ft=html (you can do this before too)
 
# Now Indent - ggVG=
 
  
== Links ==
+
Use the > command. E.g. to indent five lines:
  
* [http://www.vim.org/ Vim: the editor]
+
5 > >
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 
* [http://vim.wikia.com/wiki/File_format File format]
 
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
 
  
== Create PDF from text using Vim ==
+
Press . (dot) to keep indenting.
  
Generate PDF from input.txt with:
+
Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:
  
  $ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
+
  > %
  
Examine output with:
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
$ okular doc.pdf
+
== Open a file in a new window/tab ==
  
= Write =
+
To open a file on the left hand side:
  
== Talking to other users on the system ==
+
:vert new filename.ext
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
1. SSH to <username>@<hostname> and login with your username and password.
+
To open a file at the top:
  
2. Issue the following command to find out who is logged onto the system:
+
:new filename.ext
  
$ who
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
3. Issue the following command to talk to a specific user:
+
== Explore files in Vim ==
  
$ write <username>
+
Enter:
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
:Explore
  
= Date =
+
== Switch between Vim tabs ==
  
== Reporting the time on the server ==
+
Use gt and gT.
  
$ date
+
== Switch between Vim windows ==
  
== Reporting UTC time ==
+
To toggle between open windows use:
  
  $ date --utc
+
  Ctrl+W W
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
To move in a direction use:
  
  $ date="`date +%F-%H%M%S`"
+
  Ctrl+W h/j/k/l
  
== Getting the year in four digits ==
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
$ year="`date +%Y`"
+
== Insert block comment in Vim ==
  
== Getting the month in two digits ==
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
$ month="`date +%m`"
+
So it's:
  
== Getting the day of the month in two digits ==
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
$ day="`date +%d`"
+
== Navigate to matching tag ==
  
== Getting yesterday's date ==
+
To navigate to the matching beginning or end tag use '%'.
  
$ date --date='1 day ago' +%Y-%m-%d
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
== Converting Unix time (seconds since epoch) ==
+
== Auto-format HTML tags ==
  
For timestamp '1501370200':
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
$ date -d @1501370200 +%F-%H%M%S
+
# first join all the lines - ggVGgJ
 +
# Now break tags to new lines - :%s/>\s*</>\r</g
 +
# Now set filetype - :set ft=html (you can do this before too)
 +
# Now Indent - ggVG=
  
== Running timedatectl from systemd ==
+
== Links ==
  
There's a new command bundled with systmed:
+
* [http://www.vim.org/ Vim: the editor]
 +
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 +
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 +
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 +
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 +
* [http://vim.wikia.com/wiki/File_format File format]
 +
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 +
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
  
# timedatectl
+
== Create PDF from text using Vim ==
  
It reports on (and controls) how the system time is configured.
+
Generate PDF from input.txt with:
  
= MySQL =
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
== Run mysql without authentication/authorisation ==
+
Examine output with:
  
  # service mysql stop
+
  $ okular doc.pdf
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
= Write =
  
# mysql -u root mysql
+
== Talking to other users on the system ==
  
To stop the unauthenticated service:
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
# mysqladmin shutdown
+
1. SSH to <username>@<hostname> and login with your username and password.
  
Then restart a normal service:
+
2. Issue the following command to find out who is logged onto the system:
  
  # service mysql start
+
  $ who
  
== Logging all database queries ==
+
3. Issue the following command to talk to a specific user:
  
  # vim /etc/mysql/my.cnf
+
  $ write <username>
  
In the [mysqld] section add:
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
log=/tmp/mysql.log
+
= Date =
  
Then:
+
== Reporting the time on the server ==
  
  # service mysql restart
+
  $ date
  
Watch the log with:
+
== Reporting UTC time ==
  
  # tail -f /tmp/mysql.log
+
  $ date --utc
  
== Dumping a MySQL database ==
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
You can dump the database into a file using:
+
  $ date="`date +%F-%H%M%S`"
 
  $ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
== Getting the year in four digits ==
  
You can create a database using:
+
$ year="`date +%Y`"
  
$ echo create database databasename | mysql -h hostname -u user -p
+
== Getting the month in two digits ==
  
You can restore a database using:
+
  $ month="`date +%m`"
 
  $ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
== Getting the day of the month in two digits ==
  
  # mysql -h localhost -u root --password=<password>
+
  $ day="`date +%d`"
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
== Getting yesterday's date ==
  
  # mysql -h localhost -u root --password=<password>
+
  $ date --date='1 day ago' +%Y-%m-%d
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
== Converting Unix time (seconds since epoch) ==
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
For timestamp '1501370200':
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
$ date -d @1501370200 +%F-%H%M%S
  
Check the SSL version in use:
+
== Running timedatectl from systemd ==
  
show status like 'Ssl_version';
+
There's a new command bundled with systmed:
  
Or check the cipher in use:
+
# timedatectl
  
show status like 'Ssl_cipher';
+
It reports on (and controls) how the system time is configured.
  
= Apache =
+
= MySQL (and MariaDB) =
  
== Reporting loaded Apache modules ==
+
== Run mysql without authentication/authorisation ==
  
  # apache2ctl -M
+
  # service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
== Maintaining .htaccess passwords ==
+
Then you can connect without a password, e.g.:
  
To add or modify the password for a user:
+
# mysql -u root mysql
  
$ htpasswd /etc/apache2/passwd username
+
To stop the unauthenticated service:
  
== Configuring PHP session timeout in .htaccess ==
+
# mysqladmin shutdown
  
For a session timeout of 9 hours:
+
Then restart a normal service:
  
  php_value session.cookie_lifetime 32400
+
  # service mysql start
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
== Logging all database queries ==
  
  php_flag magic_quotes_gpc Off
+
  # vim /etc/mysql/my.cnf
  
== Requiring HTTP Auth in .htaccess ==
+
In the [mysqld] section add:
  
  AuthType Basic
+
  log=/tmp/mysql.log
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
Then:
  
The hard way
+
# service mysql restart
  
$ sudo /etc/init.d/apache2 restart
+
Watch the log with:
  
The graceful way (avoids dropping active connections)
+
# tail -f /tmp/mysql.log
  
$ sudo apache2ctl graceful
+
Or:
  
== Allowing directory browsing ==
+
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
To show directory index pages, in the apache config file:
+
my_logs.txt will be in /var/lib/mysql
  
<Directory /var/www/data>
+
== Dumping a MySQL database ==
  Options Indexes
 
</Directory>
 
  
= C =
+
You can dump the database into a file using:
 +
 +
$ mysqldump -h hostname -u user --password=password databasename > filename
  
== Locating memset function ==
+
== Loading a MySQL database from a dump file ==
  
The memset function is in &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
+
You can create a database using:
  
== Links ==
+
$ echo create database databasename | mysql -h hostname -u user -p
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
= PHP =
+
== Creating a MySQL user ==
  
== Including a file relative to the including file ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
== Granting all MySQL user permissions ==
  
== Enabling error reporting ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
error_reporting( E_ALL | E_STRICT );
+
== Select domain name from email address ==
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
Check the SSL version in use:
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
show status like 'Ssl_version';
  
ini_set( 'html_errors', 'off' );
+
Or check the cipher in use:
  
== Report PHP modules ==
+
show status like 'Ssl_cipher';
  
$ php -m
+
== Report on server config ==
  
== PHP Security Best Practices For Sys Admins ==
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
SHOW VARIABLES
  
= BASH scripting =
+
and
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
SHOW STATUS
  
== Telling a script to run in bash ==
+
and
  
The first line of the file should be:
+
SHOW PROCESSLIST
  
#!/bin/bash
+
== Monitor MySQL activity ==
  
== Checking if a command-line argument was passed in ==
+
$ watch "mysql -t -e 'show processlist'"
  
if [ -n "$1" ]; then
+
= Apache =
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
== Reporting loaded Apache modules ==
  
  if [ "$1" = "" ]; then
+
  # apache2ctl -M
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
== Maintaining .htaccess passwords ==
  
if [ -z "$1" ]; then
+
To add or modify the password for a user:
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
$ htpasswd /etc/apache2/passwd username
  
cd /my/path
+
== Configuring PHP session timeout in .htaccess ==
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
For a session timeout of 9 hours:
  
Check if file exists:
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
if [ -f "/my/file" ]; then
+
== Disabling PHP magic quotes in .htaccess ==
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
php_flag magic_quotes_gpc Off
  
if [ ! -f "/my/file" ]; then
+
== Requiring HTTP Auth in .htaccess ==
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
AuthType Basic
 +
AuthName "Speak Friend And Enter"
 +
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
  
Check if directory exists:
+
== Restarting Apache ==
  
if [ -d "/my/dir" ]; then
+
The hard way
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
$ sudo /etc/init.d/apache2 restart
  
if [ ! -d "/my/dir" ]; then
+
The graceful way (avoids dropping active connections)
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
$ sudo apache2ctl graceful
  
To keep only the latest five backups:
+
== Allowing directory browsing ==
  
find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f
+
To show directory index pages, in the apache config file:
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.
+
= C =
  
== Changing into the script's directory ==
+
== Locating memset function ==
  
cd "`dirname $0`"
+
The memset function is in &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
  
== Getting the absolute path of a relative path ==
+
== Links ==
  
readlink -f ./some/path
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
== Creating a temp directory ==
+
= PHP =
  
dir=`mktemp -d` && cd $dir
+
== Including a file relative to the including file ==
  
== Reading secret input from stdin ==
+
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
You can read a secret, such as a password, like this:
+
== Enabling error reporting ==
  
  echo -n "Enter passphrase: "
+
  error_reporting( E_ALL | E_STRICT );
stty -echo
+
  ini_set( 'display_errors', 'On' );
  read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Setting an error handler ==
  
== String replacements in bash ==
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
  
result=${var/find/replace}
+
== Disable HTML content in var_dump ==
  
To replace all occurrences:
+
ini_set( 'html_errors', 'off' );
  
result=${var//find/replace}
+
== Report PHP modules ==
  
A practical example, get an ISO date and turn it into a path:
+
$ php -m
 +
 
 +
== PHP Security Best Practices For Sys Admins ==
 +
 
 +
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
 +
 
 +
= BASH scripting =
  
date="$(date +%Y-%m-%d)"
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
== Telling a script to run in bash ==
  
cat << EOF > /tmp/yourfilehere
+
The first line of the file should be:
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
#!/bin/bash
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
== Checking if a command-line argument was passed in ==
  
  case $space in
+
  if [ -n "$1" ]; then
[1-6]*)
+
   echo "Missing parameter 1.";
  Message="All is quiet."
+
   exit 1;
  ;;
+
  fi
[7-8]*)
 
   Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
 
  ;;
 
9[1-8])
 
  Message="Better hurry with that new disk...  One partition is $space % full."
 
  ;;
 
99)
 
   Message="I'm drowning here!  There's a partition at $space %!"
 
  ;;
 
*)
 
  Message="I seem to be running with an nonexistent amount of disk space..."
 
  ;;
 
  esac
 
  
== Using dotglob shopt to match dot-files ==
+
== Checking if a command-line argument was not passed in ==
  
To enable dot-file matching in globs, set the dotglob shell option:
+
if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
$ shopt -s dotglob
+
Or:
  
== Stopping a script from running if it previously exited due to error ==
+
if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
persistentDataDir=/var/lib/something
+
== Checking command exit status ==
alarm() {
 
  touch $persistentDataDir/alarm
 
}
 
trap alarm ERR
 
[ -f $persistentDataDir/alarm ] && exit 1
 
  
== Make sure only one instance of a script is running at a time ==
+
cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
ephemeralDataDir=/var/run/something
+
== Checking if a file does/doesn't exist ==
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
Check if file exists:
  
See [https://blog.yossarian.net/2020/01/23/Anybody-can-write-good-bash-with-a-little-effort Anybody can write good bash (with a little effort)].
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
== Run a command using arguments that come from an array ==
+
Check if file doesn't exist:
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
  
#!/bin/bash
+
== Checking if a directory does/doesn't exist ==
tabs=("first tab" "second tab")
 
args=()
 
for t in "${tabs[@]}" ; do
 
  args+=(-t "$t")
 
done
 
app "${args[@]}"
 
  
== Display a CSV in columnar or tabular format ==
+
Check if directory exists:
  
  $ column -t -s , data.csv
+
  if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
= Sed =
+
Check if directory doesn't exist:
  
== Find and replace with sed ==
+
if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
To update the current file use '-i'. E.g.:
+
== Deleting old backups ==
  
sed -i 's/search-text/replace-text/' file
+
To keep only the latest five backups:
  
= Awk =
+
find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f
  
== Listing IP addresses in an Apache web log ==
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.
  
== Printing space-separated field ==
+
== Changing into the script's directory ==
  
  echo 'no no yes no' | awk '{print $3}'
+
  cd "`dirname $0`"
  
== Printing delimited field ==
+
== Getting the absolute path of a relative path ==
  
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
  readlink -f ./some/path
  
= Subversion =
+
== Creating a temp directory ==
  
== Setting svn:externals from the command-line ==
+
dir=`mktemp -d` && cd $dir
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
== Reading secret input from stdin ==
  
To set an svn:externals from the command-line:
+
You can read a secret, such as a password, like this:
  
  svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
  echo -n "Enter passphrase: "
  svn ci -m 'Adding svn:externals for rdfind-php...'
+
  stty -echo
  svn up
+
read passphrase;
 +
stty echo
 +
  echo ""
  
Or to use a file:
+
After running the above the secret will be in the $passphrase environment variable.
  
svn propset svn:externals -F svn.externals .
+
== String replacements in bash ==
  
== Setting svn:ignore from the command line ==
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
result=${var/find/replace}
  
$ svn propset svn:ignore [file|folder] [path]
+
To replace all occurrences:
  
Or use a file and apply recursively:
+
result=${var//find/replace}
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
A practical example, get an ISO date and turn it into a path:
  
= Git =
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
== Showing status of working copy ==
+
== Sending a HEREDOC to a file ==
  
  git status
+
  cat << EOF > /tmp/yourfilehere
 +
These contents will be written to the file.
 +
        This line is indented.
 +
EOF
  
== Showing repo history ==
+
== Bash case/switch statement ==
  
git log
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
== Showing remote repositories (including 'origin') ==
+
case $space in
 +
[1-6]*)
 +
  Message="All is quiet."
 +
  ;;
 +
[7-8]*)
 +
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
 +
  ;;
 +
9[1-8])
 +
  Message="Better hurry with that new disk...  One partition is $space % full."
 +
  ;;
 +
99)
 +
  Message="I'm drowning here!  There's a partition at $space %!"
 +
  ;;
 +
*)
 +
  Message="I seem to be running with an nonexistent amount of disk space..."
 +
  ;;
 +
esac
  
git remote -v
+
== Using dotglob shopt to match dot-files ==
  
== Handy git aliases ==
+
To enable dot-file matching in globs, set the dotglob shell option:
  
Save these to your ~/.gitconfig file.
+
$ shopt -s dotglob
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
== Stopping a script from running if it previously exited due to error ==
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
persistentDataDir=/var/lib/something
 +
alarm() {
 +
  touch $persistentDataDir/alarm
 +
}
 +
trap alarm ERR
 +
[ -f $persistentDataDir/alarm ] && exit 1
  
To show only the files that have changed, rather than the full line-by-line content:
+
== Make sure only one instance of a script is running at a time ==
  
  dif  = !git diff --name-status
+
ephemeralDataDir=/var/run/something
 +
unlock() {
 +
  rmdir $ephemeralDataDir/lock
 +
}
 +
mkdir $ephemeralDataDir/lock || exit 1;
 +
trap unlock EXIT
  
== Show git remote URL ==
+
== BASH programming advice ==
  
git config --get remote.origin.url
+
See [https://blog.yossarian.net/2020/01/23/Anybody-can-write-good-bash-with-a-little-effort Anybody can write good bash (with a little effort)].
  
= IRC =
+
== Run a command using arguments that come from an array ==
  
== Instructing ChanServ to op an admin ==
+
See [https://unix.stackexchange.com/a/412647/356289 here]:
  
  /msg ChanServ op #channel user
+
  #!/bin/bash
 +
tabs=("first tab" "second tab")
 +
args=()
 +
for t in "${tabs[@]}" ; do
 +
  args+=(-t "$t")
 +
done
 +
app "${args[@]}"
  
E.g.
+
== Display a CSV in columnar or tabular format ==
  
  /msg ChanServ op #gnurc jj5
+
  $ column -t -s , data.csv
 +
 
 +
== Maximum command line length ==
 +
 
 +
Technically this is an operating system limit, not a BASH limit.
  
Sub 'op' for 'deop' to remove op privilege.
+
$ getconf ARG_MAX    # Get argument limit in bytes/chars
  
= C++ =
+
= Sed =
  
== C++ books ==
+
== Find and replace with sed ==
  
=== Books I want ===
+
To update the current file use '-i'. E.g.:
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
sed -i 's/search-text/replace-text/' file
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
= Awk =
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
 
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
 
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
 
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
 
  
=== Books I own ===
+
== Listing IP addresses in an Apache web log ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
+
 
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
+
== Printing space-separated field ==
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
 
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
 
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
 
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
 
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
 
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
 
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
 
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
 
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
 
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
 
  
=== Books I'm not reading ===
+
echo 'no no yes no' | awk '{print $3}'
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
== Printing delimited field ==
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
= Subversion =
  
== C++ blogs/articles ==
+
== Setting svn:externals from the command-line ==
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
* [http://herbsutter.com/ Herb Sutter's personal blog]
 
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
 
  
== C++ performance tips ==
+
To set an svn:externals from the command-line:
  
* ++c can be faster than c++.
+
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
* use const for everything that you possibly can.
+
svn ci -m 'Adding svn:externals for rdfind-php...'
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
+
svn up
* don't use registers.
 
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 
  
= systemd =
+
Or to use a file:
  
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
+
svn propset svn:externals -F svn.externals .
  
== Following a service log ==
+
== Setting svn:ignore from the command line ==
  
e.g. for bind9:
+
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
  
  # journalctl -f -u bind9
+
  $ svn propset svn:ignore [file|folder] [path]
  
or for everything:
+
Or use a file and apply recursively:
  
  # journalctl -f
+
  $ svn propset svn:ignore -RF ./svn-ignore-list.txt .
  
== System status ==
+
= Git =
  
To see spawned services hierarchy:
+
== Showing status of working copy ==
  
  # systemctl status
+
  git status
  
Or for a specific service e.g.:
+
== Showing repo history ==
  
  # systemctl status networking
+
  git log
  
= SaltStack =
+
== Showing remote repositories (including 'origin') ==
  
== Running a command on specified minions ==
+
git remote -v
  
From the salt master:
+
== Handy git aliases ==
  
salt 'host' cmd.run 'update-locale'
+
Save these to your ~/.gitconfig file.
  
From the salt minion:
+
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
  
salt-call cmd.run 'update-locale'
+
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
  
== Running a command on all minions ==
+
To show only the files that have changed, rather than the full line-by-line content:
  
salt '*' cmd.run 'update-locale'
+
  dif  = !git diff --name-status
  
== Running a specific state file ==
+
== Show git remote URL ==
  
From the salt master:
+
git config --get remote.origin.url
  
salt $MINION_ID state.sls $STATE_FILE
+
= IRC =
  
From the salt minion:
+
== Instructing ChanServ to op an admin ==
  
  salt-call state.sls $STATE_FILE
+
  /msg ChanServ op #channel user
  
== Listing active jobs ==
+
E.g.
  
  salt-run jobs.active
+
  /msg ChanServ op #gnurc jj5
  
== Listing available grains ==
+
Sub 'op' for 'deop' to remove op privilege.
  
salt 'example' grains.items
+
= C++ =
  
== Listing available pillar ==
+
== C++ books ==
  
salt 'example' pillar.items
+
=== Books I want ===
  
== Reporting a grain value ==
+
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
  
e.g. for the 'mem_total' grain:
+
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
 +
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 +
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 +
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 +
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
  
salt '*' grains.item mem_total
+
=== Books I own ===
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
 
+
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 
+
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
  file.managed:
+
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
    - template: jinja
+
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
    - user: root
+
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
    - group: root
+
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
    - mode: 644
+
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
    - source: salt://file/srv/zabbix/release/source.txt
+
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
    - require:
+
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
      - file: /srv/zabbix/release
+
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
    - default:
 
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 
  
= KDE =
+
=== Books I'm not reading ===
  
== Running user login script (X11/XOrg/XWindows) ==
+
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
  
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
+
=== Books I've read ===
  
[Desktop Entry]
+
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
Type=Application
 
Name=ssh-add
 
Comment=Adds my private key to my session.
 
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Standard KDE shortcut key bindings ==
+
== C++ blogs/articles ==
  
{|class="wikitable"
+
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
! Name          !! Shortcut !! Command
+
* [http://herbsutter.com/ Herb Sutter's personal blog]
|-
+
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 
|-
 
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 
|-
 
| Konsole        || Meta+T  || konsole
 
|-
 
| Dolphin        || Meta+E  || dolphin
 
|-
 
| Kate          || Ctrl+Shift+F12 || kate
 
|-
 
| KCalc          || Ctrl+Shift+F11 || kcalc
 
|-
 
| Firefox        || Ctrl+Shift+F10 || firefox
 
|}
 
  
= VirtualBox =
+
== C++ performance tips ==
  
== Mounting a VirtualBox VDI file ==
+
* ++c can be faster than c++.
 
+
* use const for everything that you possibly can.
Note: instead of doing this consider booting with a live CD.
+
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
 
+
* don't use registers.
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 +
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 +
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 +
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 +
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 +
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 +
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 +
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 +
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
  
Install qemu if necessary:
+
= systemd =
  
# apt install qemu
+
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
  
Then you'll need to load the network block device module:
+
== Following a service log ==
  
# rmmod nbd
+
e.g. for bind9:
# modprobe nbd max_part=16
 
  
Attach the .vdi image to one of the nbd you just created:
+
# journalctl -f -u bind9
  
# qemu-nbd -c /dev/nbd0 drive.vdi
+
or for everything:
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
# journalctl -f
  
# mount /dev/nbd0p1 /mnt
+
== System status ==
  
Once you are done, unmount everything and disconnect the device:
+
To see spawned services hierarchy:
  
  # qemu-nbd -d /dev/nbd0
+
  # systemctl status
  
= Elasticsearch =
+
Or for a specific service e.g.:
  
== Report on health of your Elasticsearch cluster ==
+
# systemctl status networking
 +
 
 +
= SaltStack =
 +
 
 +
== Running a command on specified minions ==
 +
 
 +
From the salt master:
 +
 
 +
salt 'host' cmd.run 'update-locale'
 +
 
 +
From the salt minion:
 +
 
 +
salt-call cmd.run 'update-locale'
 +
 
 +
== Running a command on all minions ==
 +
 
 +
salt '*' cmd.run 'update-locale'
 +
 
 +
== Running a specific state file ==
 +
 
 +
From the salt master:
  
  $ curl http://localhost:9200/_cluster/health?pretty
+
  salt $MINION_ID state.sls $STATE_FILE
  
= Zabbix =
+
From the salt minion:
  
== Zabbix Agent on Mac OS X ==
+
salt-call state.sls $STATE_FILE
  
Download and install agent.
+
== Listing active jobs ==
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
salt-run jobs.active
  
Unload agent with:
+
== Listing available grains ==
  
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 +
|-
 +
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 +
|-
 +
| Konsole        || Meta+T  || konsole
 +
|-
 +
| Dolphin        || Meta+E  || dolphin
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|-
 +
| Firefox        || Ctrl+Shift+F10 || firefox
 +
|}
 +
 
 +
== Shutting down KDE/Plasma ==
 +
 
 +
# /etc/init.d/sddm stop
 +
 
 +
= VirtualBox =
 +
 
 +
== Mounting a VirtualBox VDI file ==
 +
 
 +
Note: instead of doing this consider booting with a live CD.
 +
 
 +
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
 +
 
 +
Install qemu if necessary:
 +
 
 +
# apt install qemu
 +
 
 +
Then you'll need to load the network block device module:
 +
 
 +
# rmmod nbd
 +
# modprobe nbd max_part=16
 +
 
 +
Attach the .vdi image to one of the nbd you just created:
 +
 
 +
# qemu-nbd -c /dev/nbd0 drive.vdi
 +
 
 +
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
 +
 
 +
# mount /dev/nbd0p1 /mnt
 +
 
 +
Once you are done, unmount everything and disconnect the device:
 +
 
 +
# qemu-nbd -d /dev/nbd0
 +
 
 +
= Elasticsearch =
 +
 
 +
== Report on health of your Elasticsearch cluster ==
 +
 
 +
$ curl http://localhost:9200/_cluster/health?pretty
 +
 
 +
= Zabbix =
 +
 
 +
== Zabbix Agent on Mac OS X ==
 +
 
 +
Download and install agent.
 +
 
 +
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
 +
 
 +
Unload agent with:
 +
 
 +
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 
 +
Load agent with:
 +
 
 +
# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 
 +
To add a 'pki' group:
 +
 
 +
# dseditgroup -o create pki
 +
 
 +
To monitor syslog on Mac OS X:
 +
 
 +
# tail -f /var/log/system.log
 +
 
 +
== Installing Zabbix Agent from source on Mac OS X ==
 +
 
 +
Download sources from https://www.zabbix.com/download_sources
 +
 
 +
$ brew update
 +
$ brew install openssl
 +
$ brew install pcre
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install
 +
 
 +
= NetBeans =
 +
 
 +
== NetBeans shortcut keys ==
 +
 
 +
{|class="wikitable sortable"
 +
! Keys        !! Action
 +
|-
 +
| Ctrl+W      || Close active window
 +
|-
 +
| Alt+Shift+K  || Open in Terminal
 +
|-
 +
| Ctrl+U U    || Convert selected text to uppercase
 +
|-
 +
| Ctrl+U L    || Convert selected text to lowercase
 +
|}
  
Load agent with:
+
= XML =
  
# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
== How to pretty-print an XML file ==
  
To add a 'pki' group:
+
$ xmllint --format input.xml > output.xml
  
# dseditgroup -o create pki
+
= ApacheBench =
  
To monitor syslog on Mac OS X:
+
== Run a benchmark with ApacheBench ==
 
 
# tail -f /var/log/system.log
 
  
== Installing Zabbix Agent from source on Mac OS X ==
+
$ ab -n 1000 -c 100 https://www.example.com/
 
 
Download sources from https://www.zabbix.com/download_sources
 
 
 
$ brew update
 
$ brew install openssl
 
$ brew install pcre
 
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
 
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install
 
 
 
= NetBeans =
 
 
 
== NetBeans shortcut keys ==
 
 
 
{|class="wikitable sortable"
 
! Keys        !! Action
 
|-
 
| Ctrl+W      || Close active window
 
|-
 
| Alt+Shift+K  || Open in Terminal
 
|-
 
| Ctrl+U U    || Convert selected text to uppercase
 
|-
 
| Ctrl+U L    || Convert selected text to lowercase
 
|}
 

Revision as of 00:05, 17 May 2022

Hi there, I'm John. I just wanted a page where I could document various Linux things that I bump into. This is that page. Thank you ProgClub. :)

Note: I have some other disorganised notes on UNIX, which include a few tips for MacOS. I also have some tips for OS X.

Note: the info on this page is probably Ubuntu (and Debian as an outside chance) specific, because I use Ubuntu pretty much everywhere these days.

You might also be interested in John's hacks.

Quick jump to: NetBeans.

References

Command-line

See Shell Commands I Wish I Knew Earlier for some interesting options.

System

Reporting system specifications from the command-line

Try any of these:

# neofetch
# inxi
# hwinfo --short

You may need to install the relevant package.

Determining which Debian/Ubuntu release your are running

$ lsb_release -r

Or for more information:

$ lsb_release

Determining which Linux/Unix you are running

$ uname

Or,

$ uname -mrs

Or,

$ uname -a

Configuring system swappiness

Swappiness is a number between 0 and 100 that regulates how much the system uses the swap file. I like setting this value to 0 to keep my apps as responsive as possible. Create a file /etc/sysctl.d/local.conf and add this line:

vm.swappiness = 0

If you want to set the value for the current session only:

echo 0 > /proc/sys/vm/swappiness

Hardware information

For information about the hardware attached to your system, check out:

# lshw

And for PCI devices:

# lspci

And for DMI info:

# dmidecode

Note that the dmidecode command (above) will give you information about your system's motherboard. For motherboard info look for 'System Information' and/or 'Base Board Information'.

Or the grand daddy of them all:

# hwinfo

There's also inxi, e.g.:

$ inxi -b

System:    Host: tact Kernel: 4.9.0-4-amd64 x86_64 (64 bit) Desktop: KDE Plasma 5.8.6
           Distro: Debian GNU/Linux 9 (stretch)
Machine:   Device: desktop Mobo: ASUSTeK model: STRIX Z270F GAMING v: Rev 1.xx
           UEFI [Legacy]: American Megatrends v: 0906 date: 03/22/2017
CPU:       Quad core Intel Core i7-7700K (-HT-MCP-) speed/max: 799/4600 MHz
Graphics:  Card: Intel Device 5912
           Display Server: X.Org 1.19.2 drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1920x1080@60.00hz, 1920x1080@60.00hz
           GLX Renderer: Mesa DRI Intel Kabylake GT2 GLX Version: 3.0 Mesa 13.0.6
Network:   Card: Intel Ethernet Connection (2) I219-V driver: e1000e
Drives:    HDD Total Size: 13026.6GB (42.0% used)
RAID:      Devices: 1: /dev/md1 2: /dev/md0
Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5

Motherboard info

# dmidecode -t 2

CPU info

# lscpu

or:

# cat /proc/cpuinfo

RAM info

# dmidecode --type memory

PCI info

# lspci -v

Drive info

# cat /proc/partitions

and:

# hdparm -I /dev/sda

and:

# smartctl --info /dev/sda

You can check if a drive is SSD or not with:

# cat /sys/block/sde/queue/rotational
0=SSD
1=HDD

Viewing syslog and other logs with KSystemLog

Run the 'KSystemLog' program under KDE for a handy log viewer GUI.

CPU

Monitoring CPU clock speed

Try something like this:

$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'

Power

Reporting on PowerShield DEFENDER UPS status

Before running `upsc` ensure service is running:

# upsdrvctl start

To see the status of the PowerShield DEFENDER systems on John's LAN:

$ upsc defender

E.g.:

jj5@orac:~$ upsc defender
Init SSL without certificate database
battery.charge: 100
battery.voltage: 27.40
battery.voltage.high: 26.00
battery.voltage.low: 20.80
battery.voltage.nominal: 24.0
device.type: ups
driver.name: blazer_usb
driver.parameter.pollinterval: 2
driver.parameter.port: auto
driver.parameter.synchronous: no
driver.version: 2.7.4
driver.version.internal: 0.12
input.current.nominal: 5.0
input.frequency: 50.1
input.frequency.nominal: 50
input.voltage: 242.6
input.voltage.fault: 242.6
input.voltage.nominal: 240
output.voltage: 242.6
ups.beeper.status: disabled
ups.delay.shutdown: 30
ups.delay.start: 180
ups.load: 14
ups.productid: 5161
ups.status: OL
ups.type: offline / line interactive
ups.vendorid: 0665

Run commands on PowerShield DEFENDER UPS batteries

You can run "instant commands" using the upscmd command.

We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:

diligence:/srv/salt/conf/app/defender-1200.sls

To see "instant commands" supported by the PowerShield DEFENDER:

$ upscmd -l defender

E.g.:

jj5@orac:~$ upscmd -l defender
Instant commands supported on UPS [defender]:

beeper.toggle - Toggle the UPS beeper
load.off - Turn off the load immediately
load.on - Turn on the load immediately
shutdown.return - Turn off the load and return when power is back
shutdown.stayoff - Turn off the load and remain off
shutdown.stop - Stop a shutdown in progress
test.battery.start - Start a battery test
test.battery.start.deep - Start a deep battery test
test.battery.start.quick - Start a quick battery test
test.battery.stop - Stop the battery test

Environment

Configuring vim as your editor

Sometimes all you need is:

$ export EDITOR=/usr/bin/vim

Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.

Other times you need to run

# update-alternatives --config editor

And then select vim from the list. This is what you do to configure your visudo editor.

Configuring your locale

$ sudo /usr/sbin/locale-gen en_AU.UTF-8
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8

User and group management

Adding a user

To add a new user on a linux system:

# useradd username
# passwd username

To have the home directory created from '/etc/skel' use the 'adduser' script instead:

# adduser username

Adding a user to a group

To add an existing user to an existing group:

# gpasswd -a username group

e.g. to add user 'jj5' to the 'sudo' group:

# gpasswd -a jj5 sudo

Alternatively you can use adduser, passing the username and group:

# adduser username group

e.g. to add user 'sclaughl' to the 'staff' group:

# adduser sclaughl staff

Disabling a user account

You can disable a user account with:

# passwd -l user

Note: that's a lower-case L, not a one.

Enabling a disabled user account

To can re-enable a locked user account with:

# passwd -u user

Finding which user you are logged in as

To determine which user you are running as enter the command:

$ whoami

Finding which groups you are a member of

To find which groups you are a member of:

$ groups

or

$ groups username

Where 'username' is the username of the user you are querying, e.g.:

$ groups jj5

Finding who else is logged in to the system

To see who else is logged in,

$ who

Running a command as a particular user

To run "svn update" as the user www-data:

$ sudo su -c "svn update" www-data

Reporting user and group info for the current user

$ id

Memory management

Checking available memory

To report memory statistics in megabytes:

$ free -m

Check for swap thrashing

Check your virtual memory status with vmstat:

$ vmstat

Report memory type

Report on RAM DIMMs:

# dmidecode --type 17

Report on RAM and CPU cache (including L1, L2, and L3):

# lshw -short -C memory

Or for more detail:

# lshw -C memory

Video/display management

Viewing EDID data for attached monitor

To view EDID data for an attached monitor (requires the edid-decode package):

$ cd /sys/class/drm
$ ls
$ cd card0-HDMI-A-1
$ edid-decode edid

Process management

Using 'top' for dynamic resource usage reporting

To run top:

$ top

See 15 Practical Linux Top Command Examples for some hints on usage.

To see usage for a specific user run e.g.:

$ top -u jj5

To see full command-line press 'c'.

When you're in 'top' you can:

  • press '1' (one) to toggle CPU aggregation
  • press < and > to change the sort column

Changing memory reporting in 'top'

To run top:

$ top

Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)

Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)

Press 'M' to sort by memory utilisation.

Press 'm' to switch between various display modes.

Showing full command-line in 'top'

To see the full command-line for processes run with -c:

$ top -c

Listing all processes currently running which were started in your current shell session

$ ps -fl

Killing specific processes

# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9

Run a command for a specified time using timeout

$ timeout 3 ping jj5.net

Disk management

Reporting ext4 file-systems mounted without noatime

$ cat /proc/mounts | grep ext | grep -v noatime | sort

Creating a partition table

# parted /dev/xvdf
mktable msdos

Creating a partition

# parted /dev/xvdf
u MiB
mkpart primary 1 100%

Creating an ext4 file-system

# mkfs.ext4 /dev/xvdf1

Listing disk drives

# fdisk -l

(That's an L for "list")

Checking available disk space

$ df -h

Getting disk information

# lsblk

And

# cat /proc/partitions

Or the Grand Daddy of them all:

# lshw -class disk

(Requires the lshw package.)

Getting partition UUID and file-system type

# blkid

Checking for SSD vs magnetic disk

# cat /sys/block/sda/queue/rotational

Will be 0 for SSD and 1 for magnetic.

Monitoring a ZFS server

So some commands I run to keep an eye on my new ZFS servers:

# top
# iotop
# nethogs
# watch free -h
# watch slabtop -o
# slabtop
# watch cat /proc/meminfo
# perf top
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
# watch zpool iostat -v
# zpool iostat -v 2
# watch 'zpool list; echo; zfs list'
# watch zfs get compressratio -o all
# watch cat /proc/spl/kstat/zfs/arcstats

If you have a scrub or resilvering in progress you can report on progress with:

# watch zpool status -v

You can poke about in internals, e.g.:

# cat /proc/spl/kstat/zfs/arcstats
root@orac:/sys/module/zfs/parameters# tail *

You can report on property values with e.g.:

# zfs get all data

If you want to get funky:

# cd /tmp
# perf record -ag #(Ctrl+C after ~15 seconds)
# perf report --stdio

You can search for ZFS files like e.g. this:

root@orac:/# find / -name '*zfs*' -or -name '*zpool*'

You can report history of a zpool:

# zpool history $poolname

You can get a report on the dedup tables:

# zpool status -D $poolname

Or more detailed dedup table info:

# zdb -DDD $poolname

Note in the output see here for details, basically:

Abbr Description
LSIZE logical size (in memory)
PSIZE physical size
DSIZE size on disk
refcnt reference count

How to tell if zfs scrub is running

You can get the status from the "scan:" line from:

$ zpool status

Measure data throughput

Use the 'pv' command from the 'pv' package, e.g.:

# cat /dev/sda | pv | cat > /dev/null

Or for ZFS:

# zfs send data/example | pv | cat > /dev/null

Using Smartctl, Smartd and Hddtemp on Debian

For notes on using smartctl see Using Smartctl, Smartd and Hddtemp on Debian.

Report hard disk usage

So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.

Report hard disk temperatures

E.g.

# hddtemp /dev/sd[a-e]

Burning an ISO image to USB on Mac

First insert your USB key and find the appropriate disk with:

# diskutil list

Then unmount it with:

# diskutil unmountDisk /dev/disk4

Then copy ISO image with 'dd':

# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4

You can get dd to report progress by sending it the SIGINFO signal:

# kill -s info 12345

Listing all ext4 file systems

To see a list only of the mounted ext4 file systems:

# df -t ext4

Report hierarchical file system mount points and mount options

$ findmnt

Report the mount point for the current working directory

$ findmnt "$PWD"

Monitoring disk I/O

There's an app for that! iotop.

Using iotop, top for disks

# iotop -oPa

Monitor disk I/O for performance issues

# watch iostat

Or e.g.

# watch iostat -xd /dev/sd[abc]

Or use groupings like this command for 'tact':

$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2

Monitoring a system

Simple ZFS monitoring

# watch iostat
# iotop
# zpool iostat -v 5
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
# nethogs
# top

Monitoring temperature

See temperature without third-party apps for:

$ cat /sys/class/thermal/thermal_zone*/temp

and:

$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'

Monitoring CPU temperature

$ watch sensors

Monitoring HDD temperature

For e.g. SATA drives sda to sdd:

# watch hddtemp /dev/sd[a-d]

ZFS

How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

See How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

$ cat /proc/spl/kstat/zfs/arcstats

Then:

c is the target size of the ARC in bytes
c_max is the maximum size of the ARC in bytes
size is the current size of the ARC in bytes

Stopping a ZFS scrub in progress

# zpool scrub -s $pool

e.g. for the 'data' pool:

# zpool scrub -s data

File management

Listing files by size

Use capital S for Size:

$ ls -S

Listing only directories

$ ls -l | egrep '^d'

Listing only files

$ ls -l | egrep -v '^d'

Listing hidden files

$ ls -al .[!.]*

Creating a symbolic link

$ ln -s /path/to/target link-name

Creating a hard-link

$ ln /path/to/target file-name

Changing the owner of a file

$ chown user:group <files>

E.g.

$ chown jj5:staff README
$ chown root:root *

To apply recursively into sub-directories use -R,

$ chown -R root:root /etc/*

Changing file permissions

Object codes
User Group Other
u g o
Permission codes
Read Write Exectue
r w x
4 2 1
Numeric codes
0 None
1 Execute
2 Write
3 Write, Execute
4 Read
5 Read, Execute
6 Read, Write
7 Read, Write, Execute

See Numeric Mode in Action.

$ chmod <user numeric code><group numeric code><other numeric code> <files>
$ chmod <object codes>+|-<permission codes> <files>

E.g.

$ chmod 600 my-private-file
$ chmod go-rwx my-private-file
$ chmod u+rw my-private-file
$ chmod +x my-script

Updating config files

If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:

$ cp old.conf updated.conf
$ merge -A updated.conf new.conf old.conf

Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.

The merge program is a part of the RCS package. If you don't have it:

$ sudo apt-get install rcs

Listing open files

Use lsof to list open files. E.g.:

# lsof

See man lsof for options.

List permissions on a whole directory path

E.g.:

$ namei -om /home/jj5/workspace

Outputs:

f: /home/jj5/workspace/
 drwxr-xr-x root root /
 drwxr-xr-x root root home
 drwxr-xr-x jj5  jj5  jj5
 drwxr-xr-x jj5  jj5  workspace

Counting non-blank lines in a file

E.g.:

$ cat foo.c | sed '/^\s*$/d' | wc -l

Cloning one directory to another with rsync

E.g.:

rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/

Counting number of files in current directory and all subdirectories

$ ls -AlhR . | egrep '^-' | wc -l

Counting number of directories in current directory and all subdirectories

$ ls -AlhR . | egrep '^d' | wc -l

Getting the status of a 'dd' process

First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'

Then send the dd process the SIGINFO signal, which for dd process 40947 would be:

# kill -s info 40947

The dd process will report its status in the terminal its running in.

Transferring a large file via FAT32 file system

So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:

$ split -b 4000m input.tgz input.tgz-parts-

Then copy the small files and reassemble:

$ cat input.tgz-parts-* > output.tgz

Find the difference between two directories

$ diif -qr $DIR_A $DIR_B

NFS

List NFS shares

To e.g. show NFS shares on 'love':

$ showmount -e love

Compression

How to use pigz with tar

See here:

$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz

Note: don't use --best unless you're being stingy, running without it will be much faster.

Also from here:

Fast pack:

tar -I 'pigz --fast' -cf my.tar.gz whatver

Best pack:

tar -I 'pigz --best' -cf my.tar.gz whatver

Fast unpack:

tar -I pigz -xf my.tar.gz

Best compression with tar

From here:

export GZIP=-9
tar cvzf file.tar.gz /path/to/directory

or

env GZIP=-9 tar cvzf file.tar.gz /path/to/directory

Best parallel compression with pigz

$ pigz --best

Best parallel compression with xz

$ xz -9e -T 0

Reporting compression ratios with xz

e.g.

root@love:/data/image/archive# xz -l *
Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
    1       3    372.2 MiB    442.3 MiB  0.841  CRC64   1999.txz
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64   2001.txz
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64   2002.txz
    1       9    568.5 MiB  1,660.2 MiB  0.342  CRC64   2003.txz
    1     639     66.8 GiB    119.6 GiB  0.558  CRC64   2004.txz
    1     313     12.7 GiB     58.6 GiB  0.217  CRC64   2005.txz
    1     414     35.0 GiB     77.4 GiB  0.452  CRC64   2006.txz
    1     485     44.5 GiB     90.9 GiB  0.490  CRC64   2007.txz
    1   1,690    150.0 GiB    316.8 GiB  0.473  CRC64   2008.txz
    1       3    457.9 MiB    526.0 MiB  0.871  CRC64   2009.txz
    1     168     27.3 GiB     31.4 GiB  0.868  CRC64   2010.txz
    1       4    477.1 MiB    702.8 MiB  0.679  CRC64   2011.txz
-------------------------------------------------------------------------------
   12   3,768    344.6 GiB    705.5 GiB  0.488  CRC64   12 files

Symbolic-link management

== Data used by sym-linked files:

This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:

jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h

File searching

Finding a file with a particular name

$ find -iname "*some-part-of-the-file-name*"

Will start searching from the current directory, so maybe

$ cd /

first. For a case-sensitive search:

$ find -name "*eXaCT CaSE*"

Finding a file with particular content

To search in /etc/ for a file with particular content:

$ grep -R "search-string" /etc/*

To search the current directory for *.cs files containing the word "Up":

$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;

Finding a list of files with particular content

E.g. to find all the files with the word 'creativity':

$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq

Using the locate command to find files

$ locate part-of-filename

E.g.

$ locate texvc

Updating locate command's database

# updatedb

Select a random line from a text file

$ shuf -n 1 input.txt

Extra context for grep

If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:

$ grep -B 3 -A 1 ...

Job control

Stopping a running process

Press Ctrl+Z to stop a running process.

Listing current jobs and their status

$ jobs

Resuming a stopped job in the backgroud

To resume a stopped process in the background

$ bg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Resuming a stopped job in the foreground

To resume a stopped process in the foreground

$ fg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Killing a stopped job

To kill a job

$ kill %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Periodically run a program and watch its output

$ watch /your/command

Debian/Ubuntu package management

Also see Where "is" it? on the Debian Wiki.

configuring debconf

# dpkg-reconfigure debconf 

Set priority to low to get asked detailed questions.

Showing list of installed packages

# dpkg --get-selections

Searching for installed package

# dpkg --get-selections | grep package-name

or

# aptitude search package-name

Showing which files are installed as part of a package

# dpkg -L package-name

Installing a package

# apt-get install package-name

Uninstalling a package

# apt-get remove package-name

Showing system architecture

$ dpkg --print-architecture

Showing which package a file belongs to

$ which echo
/bin/echo
$ dpkg -S /bin/echo
coreutils: /bin/echo
$ dpkg -l | grep coreutils
ii  coreutils                         6.10-6                   The GNU core utilities

Showing package information

$ apt-cache showpkg coreutils

Or for even more information:

$ apt-cache show coreutils

List all installed packages with package version info

dpkg-query -l

Reporting which version of a package is installed

$ dpkg -l | grep package-name

E.g.:

root@hope:~/letsencrypt# dpkg -l | grep augeas
ii  augeas-lenses                   0.7.0-1ubuntu1                 Set of lenses needed by libaugeas0 to parse 
ii  libaugeas0                      0.7.0-1ubuntu1                 The augeas configuration editing library and

Comprehensive upgrade

Try the following:

# apt-get update
# apt-get dist-upgrade
# apt-get autoremove
# apt-get remove $(deborphan)
# update-flashplugin-nonfree --install

Searching all available packages

$ apt-cache search . | sort -d | less

Reporting unattended upgrades status

See here for more info.

# tail -f /var/log/unattended-upgrades/unattended-upgrades.log

Searching for Debian packages and versions

Networking

Determining throughput between two hosts

# apt install iperf3

On the server:

# iperf3 -s

On the client:

# iperf3 -c $SERVER_IP

For more info see: How to test the network speed/throughput between two Linux servers.

net-tools vs iproute2

The older 'net-tools' package has been replaced with 'iproute2' e.g. in stretch.

legacy net-tools commands iproute2 replacement commands
arp ip n (ip neighbor)
ifconfig ip a (ip addr), ip link, ip -s (ip -stats)
iptunnel ip tunnel
iwconfig iw
nameif ip link, ifrename
netstat ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
route ip r (ip route)

Restart networking

For servers:

# service networking restart

For desktops:

# service network-manager restart

Pinging with particular packet size

$ ping -M do -s <packet size in bytes> <host>

E.g.

$ ping -M do -s 1400 charity.progclub.org

Setting MSS for a particular IP address on a particular interface

# ip route add <host> dev <interface> advmss <packet size>

E.g.

# ip route add 10.0.0.1 dev eth0 advmss 1400

Dropping configured MMS for a particular IP address

# ip route flush <host>

E.g.

# ip route flush 10.0.0.1

Listing open ports and socket information

Including which process is listening on which port.

# netstat -tulpn

Or use the 'ss' command:

# ss -s
# ss -l
# ss -pl
# ss -o state established '( dport = :smtp or sport = :smtp )'

Listing open IPv4 connections

# lsof -Pnl +M -i4

You might need to install the lsof package:

# apt-get install lsof

Query for DNS MX record

$ nslookup
> server 127.0.0.1
> set q=mx
> mail.blackbrick.com

Query for DNS SOA record

$ dig @ns2.staticmagic.net -t SOA staticmagic.net

Using nmap to list open ports on remote host

To check the 1,000 most common ports:

# nmap server.example.com

Or for a specific port range (e.g. 101 to 102):

# nmap -p 101-102 server.example.com

Or for all ports (1 to 65,535):

# nmap -p- server.example.com

Network monitoring

See here for details. Basically:

  1. Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
  2. Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
  3. Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
  4. Bandwidth per process: nethogs

nload

You can watch network traffic in real-time with nload:

# nload -u M

Reporting network (NIC) speed

From here:

# dmesg | grep eth0
# mii-tool -v eth0
# ethtool eth0

Note: use ifconfig to get device name.

Path MTU discovery

To do a Path MTU Discovery, from the iputils-tracepath package:

# tracepath host.example.com

Listing available Ethernet devices

To see a list of NICs available on the host:

$ cat /proc/net/dev

Also

$ ip link

59 Linux Networking commands and scripts

See 59 Linux Networking commands and scripts.

Links

IPTables

Applying firewall rules

For configuration info see this article.

$ sudo vim /etc/iptables.test.rules
$ sudo /sbin/iptables -F
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
$ sudo iptables -L
$ sudo -s
# iptables-save > /etc/iptables.up.rules
# exit

Blocking an IP address with iptables

To drop IP address 1.2.3.4:

# iptables -A INPUT -s 1.2.3.4 -j DROP

ufw

Denying hosts with ufw

See denying hosts with ufw.

Bind9

Viewing Bind9 querylog

$ sudo rndc querylog
$ tail -f /var/log/syslog

IPSec

Disabling IPSec

# setkey -FP

OpenSSL

Debugging IMAPS with OpenSSL

# openssl s_client -connect localhost:993
> a1 LOGIN username@host password
> a2 LOGOUT

Debugging HTTPS with OpenSSL

$ openssl s_client -connect www.example.com:443
GET /example.html HTTP/1.1
host: www.example.com

Links

Pluggable Authentication Modules (PAM)

Links

SSH

Configuring SSH key login

On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):

$ ssh-keygen -t rsa

Copy the public key from the client to the server:

$ scp ~/.ssh/id_rsa.pub user@example.org:

Configure the authorized keys on the server:

$ ssh user@example.org
$ mkdir ~/.ssh
$ chmod go-w .ssh
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ rm ~/id_rsa.pub

Tunneling over SSH

For example, connecting a remote MySQL server to the localhost:

$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org

If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,

 $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au

The -L stanza is localport:remotehost:remoteport where localport is a port on your machine, forwarded to remoteport on remotehost.

Tunneling over SSH with PuTTY

See Connecting to the MySQL database remotely (via an SSH Tunnel)

  • run putty.exe
  • Connection -> SSH -> Tunnels
    • Port forwarding: source port to 3306
    • destination: 127.0.0.1:3306
    • check Local
    • click Add

Enabling verbose SSH logging

To see what's going on with your ssh connections,

$ ssh -v user@host

Or

$ ssh -vv user@host

Unlocking SSH key for session

jj5@orac:~/.config/autostart$ cat ssh-add.desktop 
[Desktop Entry]
Type=Application
Name=ssh-add
Comment=Adds my private key to my session.
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'

Links

Standard IO

cat EOF

$ cat > output <<EOF
> text
> EOF
$ cat output
text

Script

Creating a session log with script

$ script -t 2> timing

The session log is in the file 'typescript' and the timing data is in 'timing'.

Replaying a scripted session

$ scriptreplay timing

Uses the default file 'typescript' and the 'timing' file as specified.

Screen

Creating a new screen or reconnecting to a detached screen

$ screen -R

Detaching a screen

$ screen -D

Reconnecting to screen

$ screen -D
$ screen -R

I have a script in ~/bin/reconnect like so,

#!/bin/bash
screen -D
screen -R

This will detach your last screen, and reconnect it on the current terminal.

Scrolling in screen

See How to scroll in GNU Screen. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.

tmux

Live collaboration with tmux

User A:

tmux -S /tmp/collab
chmod 777 /tmp/collab

User B:

tmux -S /tmp/collab attach

Vim

First, why Vim?

Read Why, oh WHY, do those #?@! nutheads use vi?

Visual modes

Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.

Configuring spaces instead of tabs

I use two spaces instead of tabs. To configure, edit your .vimrc file:

$ vim ~/.vimrc

and include the following lines:

set tabstop=2
set shiftwidth=2
set expandtab

Configuring syntax highlighting

See here.

Use:

:syntax on

to turn on syntax highlighting.

Use:

:syntax off

to turn off syntax highlighting.

To always use syntax highlighting:

$ vim ~/.vimrc

and add:

syntax on

To get a list of supported colour schemes open vim and type:

:colorscheme[space][Ctrl+D]

To always use a particular colorscheme edit ~/.vimrc and add (for example):

colorscheme desert

Inserting a TAB character when expandtab is on

The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.

Press Ctrl+V TAB to insert a literal tab character.

Or you can disable tab expansion altogether with:

:set expandtab!

Changing 2 space indent to 4 space indent (e.g. for python files)

:%s/^\s*/&&/g

For more information see here.

Recording and replaying a macro

To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".

Deleting to end of line

d$

Deleting to beginning of line

d^

Finding text

To search forward for "text":

/text

To search backward for "text":

?text

To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.

Finding and replacing text

To replace the first instance of "search" on the current line with "destroy":

:s/search/destroy/

To replace all instances of "search" on the current line with "destroy":

:s/search/destroy/g

To replace all instances of "search" on lines 13 to 37 with "destroy":

:13,37 s/search/destroy/g

To replace all instances of "search" in the entire file with "destroy":

:%s/search/destroy/g

Changing DOS/Windows line-endings (CRLF) to Unix line-endings

To set the line-ending to Unix line endings run the command:

:setlocal ff=unix

More information on managing file formats available here.

Disabling auto-indent etc. to paste from clipboard

To disable smart indenting when you're going to paste in text:

:set paste

To turn it off again:

:set nopaste

There's more info in this article: Toggle auto-indenting for code paste

Positioning windows

Use -o for horizontal split, e.g.:

vim -o a.txt b.txt

Use -O for vertical split, e.g.:

vim -o a.txt b.txt

Use ^W to navigate windows then use directional keys h, j, k, l, etc.

Use ^W and < or > to resize windows.

To indent a block of text in Vim

Use the > command. E.g. to indent five lines:

5 > >

Press . (dot) to keep indenting.

Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:

> %

See here for more.

Open a file in a new window/tab

To open a file on the left hand side:

:vert new filename.ext

Note: ':vnew filename.ext' and ':vsp filename.ext' also work.

To open a file at the top:

:new filename.ext

See here for more.

Explore files in Vim

Enter:

:Explore

Switch between Vim tabs

Use gt and gT.

Switch between Vim windows

To toggle between open windows use:

Ctrl+W W

To move in a direction use:

Ctrl+W h/j/k/l

See here for more.

Insert block comment in Vim

See here for line-commenting.

So it's:

  1. Ctrl+V (Note: not Shift+V!)
  2. Up/Down to select rows
  3. Shift+I
  4. Enter your text, e.g. '#' or '//'
  5. Ctrl+[ (or 'Esc')

Navigate to matching tag

To navigate to the matching beginning or end tag use '%'.

You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.

Auto-format HTML tags

Stolen from here.

  1. first join all the lines - ggVGgJ
  2. Now break tags to new lines - :%s/>\s*</>\r</g
  3. Now set filetype - :set ft=html (you can do this before too)
  4. Now Indent - ggVG=

Links

Create PDF from text using Vim

Generate PDF from input.txt with:

$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps

Examine output with:

$ okular doc.pdf

Write

Talking to other users on the system

write is a unix command for talking to other users on the system. To use write:

1. SSH to <username>@<hostname> and login with your username and password.

2. Issue the following command to find out who is logged onto the system:

$ who

3. Issue the following command to talk to a specific user:

$ write <username>

4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.

Date

Reporting the time on the server

$ date

Reporting UTC time

$ date --utc

Getting the date in yyyy-MM-dd-hhmmss format

$ date="`date +%F-%H%M%S`"

Getting the year in four digits

$ year="`date +%Y`"

Getting the month in two digits

$ month="`date +%m`"

Getting the day of the month in two digits

$ day="`date +%d`"

Getting yesterday's date

$ date --date='1 day ago' +%Y-%m-%d

Converting Unix time (seconds since epoch)

For timestamp '1501370200':

$ date -d @1501370200 +%F-%H%M%S

Running timedatectl from systemd

There's a new command bundled with systmed:

# timedatectl

It reports on (and controls) how the system time is configured.

MySQL (and MariaDB)

Run mysql without authentication/authorisation

# service mysql stop
# mysqld_safe --skip-grant-tables &

Then you can connect without a password, e.g.:

# mysql -u root mysql

To stop the unauthenticated service:

# mysqladmin shutdown

Then restart a normal service:

# service mysql start

Logging all database queries

# vim /etc/mysql/my.cnf

In the [mysqld] section add:

log=/tmp/mysql.log

Then:

# service mysql restart

Watch the log with:

# tail -f /tmp/mysql.log

Or:

SET GLOBAL log_output = 'FILE';
SET GLOBAL general_log_file = 'my_logs.txt';
SET GLOBAL general_log = 'ON';

my_logs.txt will be in /var/lib/mysql

Dumping a MySQL database

You can dump the database into a file using:

$ mysqldump -h hostname -u user --password=password databasename > filename

Loading a MySQL database from a dump file

You can create a database using:

$ echo create database databasename | mysql -h hostname -u user -p

You can restore a database using:

$ mysql -h hostname -u user --password=password databasename < filename

Creating a MySQL user

# mysql -h localhost -u root --password=<password>
mysql> create user 'username'@'localhost' identified by '<password>';

Granting all MySQL user permissions

# mysql -h localhost -u root --password=<password>
mysql> grant all privileges on dbname.* to user@host;

Select domain name from email address

SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )

Check if MySQL connection is encrypted with TLS/SSL

Check the SSL version in use:

show status like 'Ssl_version';

Or check the cipher in use:

show status like 'Ssl_cipher';

Report on server config

See SHOW Statements for the full list, but check out:

SHOW VARIABLES

and

SHOW STATUS

and

SHOW PROCESSLIST

Monitor MySQL activity

$ watch "mysql -t -e 'show processlist'"

Apache

Reporting loaded Apache modules

# apache2ctl -M

Maintaining .htaccess passwords

To add or modify the password for a user:

$ htpasswd /etc/apache2/passwd username

Configuring PHP session timeout in .htaccess

For a session timeout of 9 hours:

php_value session.cookie_lifetime 32400
php_value session.gc_maxlifetime 32400

Disabling PHP magic quotes in .htaccess

php_flag magic_quotes_gpc Off

Requiring HTTP Auth in .htaccess

AuthType Basic
AuthName "Speak Friend And Enter"
AuthUserFile /home/jj5/.htpasswd
Require valid-user

Restarting Apache

The hard way

$ sudo /etc/init.d/apache2 restart

The graceful way (avoids dropping active connections)

$ sudo apache2ctl graceful

Allowing directory browsing

To show directory index pages, in the apache config file:

<Directory /var/www/data>
  Options Indexes
</Directory>

C

Locating memset function

The memset function is in <string.h> as described in this article Using memset(), memcpy(), and memmove() in C

Links

PHP

Including a file relative to the including file

require_once( dirname( __FILE__ ) . '/relative/path/to.php' );

Enabling error reporting

error_reporting( E_ALL | E_STRICT );
ini_set( 'display_errors', 'On' );

Setting an error handler

set_error_handler( "error_handler", E_ALL | E_STRICT );
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
  // ...
}

Disable HTML content in var_dump

ini_set( 'html_errors', 'off' );

Report PHP modules

$ php -m

PHP Security Best Practices For Sys Admins

See Linux 25 PHP Security Best Practices For Sys Admins.

BASH scripting

For a primer on bash scripting see TFM: Erotic Fantasy: /bin/sh Programming.

Telling a script to run in bash

The first line of the file should be:

#!/bin/bash

Checking if a command-line argument was passed in

if [ -n "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking if a command-line argument was not passed in

if [ "$1" = "" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Or:

if [ -z "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking command exit status

cd /my/path
if [ "$?" -ne "0" ]; then
  echo "Cannot change dir.";
  exit 1;
fi

Checking if a file does/doesn't exist

Check if file exists:

if [ -f "/my/file" ]; then
  cat /my/file
fi

Check if file doesn't exist:

if [ ! -f "/my/file" ]; then
  touch /my/file
fi

Checking if a directory does/doesn't exist

Check if directory exists:

if [ -d "/my/dir" ]; then
  rmdir /my/dir
fi

Check if directory doesn't exist:

if [ ! -d "/my/dir" ]; then
  mkdir /my/dir
fi

Deleting old backups

To keep only the latest five backups:

find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f

This script stolen from stackoverflow.

Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.

Changing into the script's directory

cd "`dirname $0`"

Getting the absolute path of a relative path

readlink -f ./some/path

Creating a temp directory

dir=`mktemp -d` && cd $dir

Reading secret input from stdin

You can read a secret, such as a password, like this:

echo -n "Enter passphrase: "
stty -echo
read passphrase;
stty echo
echo ""

After running the above the secret will be in the $passphrase environment variable.

String replacements in bash

See the string manipulation doco. Basically, to replace first occurrence:

result=${var/find/replace}

To replace all occurrences:

result=${var//find/replace}

A practical example, get an ISO date and turn it into a path:

date="$(date +%Y-%m-%d)"
work_dir=${date//-//}

Sending a HEREDOC to a file

cat << EOF > /tmp/yourfilehere
These contents will be written to the file.
        This line is indented.
EOF

Bash case/switch statement

See using case statements, e.g.:

case $space in
[1-6]*)
  Message="All is quiet."
  ;;
[7-8]*)
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
  ;;
9[1-8])
  Message="Better hurry with that new disk...  One partition is $space % full."
  ;;
99)
  Message="I'm drowning here!  There's a partition at $space %!"
  ;;
*)
  Message="I seem to be running with an nonexistent amount of disk space..."
  ;;
esac

Using dotglob shopt to match dot-files

To enable dot-file matching in globs, set the dotglob shell option:

$ shopt -s dotglob

Stopping a script from running if it previously exited due to error

persistentDataDir=/var/lib/something
alarm() {
  touch $persistentDataDir/alarm
}
trap alarm ERR
[ -f $persistentDataDir/alarm ] && exit 1

Make sure only one instance of a script is running at a time

ephemeralDataDir=/var/run/something
unlock() {
  rmdir $ephemeralDataDir/lock
}
mkdir $ephemeralDataDir/lock || exit 1;
trap unlock EXIT

BASH programming advice

See Anybody can write good bash (with a little effort).

Run a command using arguments that come from an array

See here:

#!/bin/bash
tabs=("first tab" "second tab")
args=()
for t in "${tabs[@]}" ; do 
  args+=(-t "$t")
done
app "${args[@]}"

Display a CSV in columnar or tabular format

$ column -t -s , data.csv

Maximum command line length

Technically this is an operating system limit, not a BASH limit.

$ getconf ARG_MAX    # Get argument limit in bytes/chars

Sed

Find and replace with sed

To update the current file use '-i'. E.g.:

sed -i 's/search-text/replace-text/' file

Awk

Listing IP addresses in an Apache web log

awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq

Printing space-separated field

echo 'no no yes no' | awk '{print $3}'

Printing delimited field

echo 'no:no:yes:no' | awk -F ':' '{print $3}'

Subversion

Setting svn:externals from the command-line

See here.

To set an svn:externals from the command-line:

svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
svn ci -m 'Adding svn:externals for rdfind-php...'
svn up

Or to use a file:

svn propset svn:externals -F svn.externals .

Setting svn:ignore from the command line

See here.

$ svn propset svn:ignore [file|folder] [path]

Or use a file and apply recursively:

$ svn propset svn:ignore -RF ./svn-ignore-list.txt .

Git

Showing status of working copy

git status

Showing repo history

git log

Showing remote repositories (including 'origin')

git remote -v

Handy git aliases

Save these to your ~/.gitconfig file.

For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:

 graph = !git log --all --graph --color --abbrev-commit --pretty=oneline

To show only the files that have changed, rather than the full line-by-line content:

 dif   = !git diff --name-status

Show git remote URL

git config --get remote.origin.url

IRC

Instructing ChanServ to op an admin

/msg ChanServ op #channel user

E.g.

/msg ChanServ op #gnurc jj5

Sub 'op' for 'deop' to remove op privilege.

C++

C++ books

Books I want

Books I own

Books I'm not reading

Books I've read

C++ blogs/articles

C++ performance tips

  • ++c can be faster than c++.
  • use const for everything that you possibly can.
  • use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
  • don't use registers.
  • const rarely affects performance.
  • debunking a number of C++ myths that won't die.
  • std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
  • if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
  • read about performance cost of RTTI (Run Time Type Information) and how to disable it
  • don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
  • prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
  • Which is better, static or dynamic linking?
  • Integer vs Floating-Point performance

systemd

systemd is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.

Following a service log

e.g. for bind9:

# journalctl -f -u bind9

or for everything:

# journalctl -f

System status

To see spawned services hierarchy:

# systemctl status

Or for a specific service e.g.:

# systemctl status networking

SaltStack

Running a command on specified minions

From the salt master:

salt 'host' cmd.run 'update-locale'

From the salt minion:

salt-call cmd.run 'update-locale'

Running a command on all minions

salt '*' cmd.run 'update-locale'

Running a specific state file

From the salt master:

salt $MINION_ID state.sls $STATE_FILE

From the salt minion:

salt-call state.sls $STATE_FILE

Listing active jobs

salt-run jobs.active

Listing available grains

salt 'example' grains.items

Listing available pillar

salt 'example' pillar.items

Reporting a grain value

e.g. for the 'mem_total' grain:

salt '*' grains.item mem_total

Passing a variable into a Jinja template from a salt state (SLS)

e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:

/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:
  file.managed:
    - template: jinja
    - user: root
    - group: root
    - mode: 644
    - source: salt://file/srv/zabbix/release/source.txt
    - require:
      - file: /srv/zabbix/release
    - default:
      zabbix_deb_pkg: {{ zabbix_deb_pkg }}
      zabbix_deb_url: {{ zabbix_deb_url }}

KDE

Running user login script (X11/XOrg/XWindows)

A way to run user login scripts which works for KDE Plasma (and apparently other X.Org Server X Window System environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:

[Desktop Entry]
Type=Application
Name=ssh-add
Comment=Adds my private key to my session.
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'

Standard KDE shortcut key bindings

Name Shortcut Command
Insert comment F1 xdotool type "$(date +%Y-%m-%d ) $USER - "
Insert sydtime F4 xdotool type "$(date +%Y-%m-%d-%H%M%S)"
Konsole Meta+T konsole
Dolphin Meta+E dolphin
Kate Ctrl+Shift+F12 kate
KCalc Ctrl+Shift+F11 kcalc
Firefox Ctrl+Shift+F10 firefox

Shutting down KDE/Plasma

# /etc/init.d/sddm stop

VirtualBox

Mounting a VirtualBox VDI file

Note: instead of doing this consider booting with a live CD.

See here:

Install qemu if necessary:

# apt install qemu

Then you'll need to load the network block device module:

# rmmod nbd
# modprobe nbd max_part=16

Attach the .vdi image to one of the nbd you just created:

# qemu-nbd -c /dev/nbd0 drive.vdi

Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.

# mount /dev/nbd0p1 /mnt

Once you are done, unmount everything and disconnect the device:

# qemu-nbd -d /dev/nbd0

Elasticsearch

Report on health of your Elasticsearch cluster

$ curl http://localhost:9200/_cluster/health?pretty

Zabbix

Zabbix Agent on Mac OS X

Download and install agent.

Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf

Unload agent with:

# launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

Load agent with:

# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

To add a 'pki' group:

# dseditgroup -o create pki

To monitor syslog on Mac OS X:

# tail -f /var/log/system.log

Installing Zabbix Agent from source on Mac OS X

Download sources from https://www.zabbix.com/download_sources

$ brew update
$ brew install openssl
$ brew install pcre
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install

NetBeans

NetBeans shortcut keys

Keys Action
Ctrl+W Close active window
Alt+Shift+K Open in Terminal
Ctrl+U U Convert selected text to uppercase
Ctrl+U L Convert selected text to lowercase

XML

How to pretty-print an XML file

$ xmllint --format input.xml > output.xml

ApacheBench

Run a benchmark with ApacheBench

$ ab -n 1000 -c 100 https://www.example.com/