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
 
|}
 
  
== Measure data throughput ==
+
# 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
  
Use the 'pv' command from the 'pv' package, e.g.:
+
If you have a scrub or resilvering in progress you can report on progress with:
  
  # cat /dev/sda | pv | cat > /dev/null
+
  # watch zpool status -v
  
Or for ZFS:
+
You can poke about in internals, e.g.:
  
  # zfs send data/example | pv | cat > /dev/null
+
  # cat /proc/spl/kstat/zfs/arcstats
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
root@orac:/sys/module/zfs/parameters# tail *
  
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].
+
You can report on property values with e.g.:
  
== Report hard disk usage ==
+
# zfs get all data
  
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.
+
If you want to get funky:
  
== Report hard disk temperatures ==
+
# cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
E.g.
+
You can search for ZFS files like e.g. this:
  
  # hddtemp /dev/sd[a-e]
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
== Burning an ISO image to USB on Mac ==
+
You can report history of a zpool:
  
First insert your USB key and find the appropriate disk with:
+
# zpool history $poolname
  
# diskutil list
+
You can get a report on the dedup tables:
  
Then unmount it with:
+
# zpool status -D $poolname
  
# diskutil unmountDisk /dev/disk4
+
Or more detailed dedup table info:
  
Then copy ISO image with 'dd':
+
# zdb -DDD $poolname
  
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
You can get dd to report progress by sending it the SIGINFO signal:
+
{|class="wikitable"
 
+
! Abbr  !! Description
  # kill -s info 12345
+
|-
 +
| LSIZE || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
== Listing all ext4 file systems ==
+
== How to tell if zfs scrub is running ==
  
To see a list only of the mounted ext4 file systems:
+
You can get the status from the "scan:" line from:
  
  # df -t ext4
+
  $ zpool status
  
== Report hierarchical file system mount points and mount options ==
+
== Measure data throughput ==
  
$ findmnt
+
Use the 'pv' command from the 'pv' package, e.g.:
  
== Report the mount point for the current working directory ==
+
# cat /dev/sda | pv | cat > /dev/null
  
$ findmnt "$PWD"
+
Or for ZFS:
  
= Monitoring disk I/O =
+
# zfs send data/example | pv | cat > /dev/null
  
There's an app for that! iotop.
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
== Using iotop, top for disks ==
+
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].
  
# iotop -oPa
+
== Report hard disk usage ==
  
== Monitor disk I/O for performance issues ==
+
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.
  
# watch iostat
+
== Report hard disk temperatures ==
  
Or e.g.
+
E.g.
  
  # watch iostat -xd /dev/sd[abc]
+
  # hddtemp /dev/sd[a-e]
  
Or use groupings like this command for 'tact':
+
== Burning an ISO image to USB on Mac ==
  
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
First insert your USB key and find the appropriate disk with:
  
= Monitoring a system =
+
# diskutil list
  
== Simple ZFS monitoring ==
+
Then unmount it with:
  
  # watch iostat
+
  # diskutil unmountDisk /dev/disk4
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
Then copy ISO image with 'dd':
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
$ cat /sys/class/thermal/thermal_zone*/temp
+
You can get dd to report progress by sending it the SIGINFO signal:
  
and:
+
# kill -s info 12345
  
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
== Listing all ext4 file systems ==
  
== Monitoring CPU temperature ==
+
To see a list only of the mounted ext4 file systems:
  
  $ watch sensors
+
  # df -t ext4
  
== Monitoring HDD temperature ==
+
== Report hierarchical file system mount points and mount options ==
  
For e.g. SATA drives sda to sdd:
+
$ findmnt
  
# watch hddtemp /dev/sd[a-d]
+
== Report the mount point for the current working directory ==
  
= ZFS =
+
$ findmnt "$PWD"
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
= Monitoring disk I/O =
  
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?]
+
There's an app for that! iotop.
  
$ cat /proc/spl/kstat/zfs/arcstats
+
== Using iotop, top for disks ==
  
Then:
+
# iotop -oPa
  
c is the target size of the ARC in bytes
+
== Monitor disk I/O for performance issues ==
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
= File management =
+
# watch iostat
  
== Listing files by size ==
+
Or e.g.
  
Use capital S for Size:
+
# watch iostat -xd /dev/sd[abc]
  
$ ls -S
+
Or use groupings like this command for 'tact':
  
== Listing only directories ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
$ ls -l | egrep '^d'
+
= Monitoring a system =
  
== Listing only files ==
+
== Simple ZFS monitoring ==
  
  $ ls -l | egrep -v '^d'
+
  # watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
== Listing hidden files ==
+
= Monitoring temperature =
  
$ ls -al .[!.]*
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
== Creating a symbolic link ==
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
$ ln -s /path/to/target link-name
+
and:
  
== Creating a hard-link ==
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
$ ln /path/to/target file-name
+
== Monitoring CPU temperature ==
  
== Changing the owner of a file ==
+
$ watch sensors
  
$ chown user:group <files>
+
== Monitoring HDD temperature ==
  
E.g.
+
For e.g. SATA drives sda to sdd:
  
  $ chown jj5:staff README
+
  # watch hddtemp /dev/sd[a-d]
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
= ZFS =
  
$ chown -R root:root /etc/*
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
== Changing file permissions ==
+
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?]
 +
 
 +
$ 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
  
{|class="wikitable"
+
e.g. for the 'data' pool:
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g     || o
 
|}
 
  
{|class="wikitable"
+
# zpool scrub -s data
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
= File management =
|+ 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 files by size ==
  
$ chmod <user numeric code><group numeric code><other numeric code> <files>
+
Use capital S for Size:
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
$ ls -S
  
$ chmod 600 my-private-file
+
== Listing only directories ==
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
$ ls -l | egrep '^d'
 +
 
 +
== Listing only 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 -l | egrep -v '^d'
  
$ cp old.conf updated.conf
+
== Listing hidden files ==
$ 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.
+
$ ls -al .[!.]*
  
The merge program is a part of the RCS package. If you don't have it:
+
== Creating a symbolic link ==
  
  $ sudo apt-get install rcs
+
  $ ln -s /path/to/target link-name
  
== Listing open files ==
+
== Creating a hard-link ==
  
Use lsof to list open files. E.g.:
+
$ ln /path/to/target file-name
  
# lsof
+
== Changing the owner of a file ==
  
See man lsof for options.
+
$ chown user:group <files>
  
== List permissions on a whole directory path ==
+
E.g.
  
E.g.:
+
$ chown jj5:staff README
 +
$ chown root:root *
  
$ namei -om /home/jj5/workspace
+
To apply recursively into sub-directories use -R,
  
Outputs:
+
$ chown -R root:root /etc/*
  
f: /home/jj5/workspace/
+
== Changing file permissions ==
  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 ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
E.g.:
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
$ cat foo.c | sed '/^\s*$/d' | wc -l
+
{|class="wikitable"
 
+
|+ Numeric codes
== Cloning one directory to another with rsync ==
+
! 0
 
+
| None
E.g.:
+
|-
 
+
! 1
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/
+
| Execute
 +
|-
 +
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
== Counting number of files in current directory and all subdirectories ==
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
  $ ls -AlhR . | egrep '^-' | wc -l
+
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
== Counting number of directories in current directory and all subdirectories ==
+
E.g.
  
  $ ls -AlhR . | egrep '^d' | wc -l
+
  $ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== Getting the status of a 'dd' process ==
+
== Updating config files ==
  
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
+
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:
  
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
# kill -s info 40947
+
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 dd process will report its status in the terminal its running in.
+
The merge program is a part of the RCS package. If you don't have it:
  
== Transferring a large file via FAT32 file system ==
+
$ sudo apt-get install rcs
  
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:
+
== Listing open files ==
  
$ split -b 4000m input.tgz input.tgz-parts-
+
Use lsof to list open files. E.g.:
  
Then copy the small files and reassemble:
+
# lsof
  
$ cat input.tgz-parts-* > output.tgz
+
See man lsof for options.
  
= NFS =
+
== List permissions on a whole directory path ==
  
== List NFS shares ==
+
E.g.:
  
To e.g. show NFS shares on 'love':
+
$ namei -om /home/jj5/workspace
  
$ showmount -e love
+
Outputs:
  
= Compression =
+
f: /home/jj5/workspace/
 
+
  drwxr-xr-x root root /
== How to use pigz with tar ==
+
  drwxr-xr-x root root home
 +
  drwxr-xr-x jj5  jj5  jj5
 +
  drwxr-xr-x jj5  jj5  workspace
  
See [https://stackoverflow.com/a/39904353 here]:
+
== Counting non-blank lines in a file ==
  
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
E.g.:
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
Also from [https://stackoverflow.com/a/50586833 here]:
+
== Cloning one directory to another with rsync ==
  
Fast pack:
+
E.g.:
  
tar -I pigz -cf my.tar.gz whatver
+
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/
  
Fast unpack:
+
== Counting number of files in current directory and all subdirectories ==
  
  tar -I pigz -xf my.tar.gz
+
  $ ls -AlhR . | egrep '^-' | wc -l
  
== Best compression with tar ==
+
== Counting number of directories in current directory and all subdirectories ==
  
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
+
$ ls -AlhR . | egrep '^d' | wc -l
  
export GZIP=-9
+
== Getting the status of a 'dd' process ==
tar cvzf file.tar.gz /path/to/directory
 
  
or
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
== Best parallel compression with pigz ==
+
# kill -s info 40947
  
$ pigz --best
+
The dd process will report its status in the terminal its running in.
  
== Best parallel compression with xz ==
+
== Transferring a large file via FAT32 file system ==
  
$ xz -9e -T 0
+
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:
  
== Reporting compression ratios with xz ==
+
$ split -b 4000m input.tgz input.tgz-parts-
  
e.g.
+
Then copy the small files and reassemble:
  
  root@love:/data/image/archive# xz -l *
+
  $ cat input.tgz-parts-* > output.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 =
+
== Find the difference between two directories ==
  
== Data used by sym-linked files:
+
$ diif -qr $DIR_A $DIR_B
  
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:
+
= NFS =
  
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
== List NFS shares ==
  
= File searching =
+
To e.g. show NFS shares on 'love':
  
== Finding a file with a particular name ==
+
$ showmount -e love
  
$ find -iname "*some-part-of-the-file-name*"
+
= Compression =
  
Will start searching from the current directory, so maybe
+
== How to use pigz with tar ==
  
$ cd /
+
See [https://stackoverflow.com/a/39904353 here]:
  
first. For a case-sensitive search:
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
$ find -name "*eXaCT CaSE*"
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
== Finding a file with particular content ==
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
To search in /etc/ for a file with particular content:
+
Fast pack:
  
  $ grep -R "search-string" /etc/*
+
  tar -I 'pigz --fast' -cf my.tar.gz whatver
  
To search the current directory for *.cs files containing the word "Up":
+
Best pack:
  
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
  tar -I 'pigz --best' -cf my.tar.gz whatver
  
== Finding a list of files with particular content ==
+
Fast unpack:
  
E.g. to find all the files with the word 'creativity':
+
tar -I pigz -xf my.tar.gz
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
== Best compression with tar ==
  
== Using the locate command to find files ==
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
  $ locate part-of-filename
+
  export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
E.g.
+
or
  
  $ locate texvc
+
  env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
== Updating locate command's database ==
+
== Best parallel compression with pigz ==
  
  # updatedb
+
  $ pigz --best
  
== Select a random line from a text file ==
+
== Best parallel compression with xz ==
  
  $ shuf -n 1 input.txt
+
  $ xz -9e -T 0
  
== Extra context for grep ==
+
== Reporting compression ratios with xz ==
  
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:
+
e.g.
  
  $ grep -B 3 -A 1 ...
+
  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
  
= Job control =
+
= Symbolic-link management =
  
== Stopping a running process ==
+
== Data used by sym-linked files:
  
Press Ctrl+Z to stop a running process.
+
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:
  
== Listing current jobs and their status ==
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
$ jobs
+
= File searching =
  
== Resuming a stopped job in the backgroud ==
+
== Finding a file with a particular name ==
  
To resume a stopped process in the background
+
$ find -iname "*some-part-of-the-file-name*"
  
$ bg %1
+
Will start searching from the current directory, so maybe
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
$ cd /
  
== Resuming a stopped job in the foreground ==
+
first. For a case-sensitive search:
  
To resume a stopped process in the foreground
+
$ find -name "*eXaCT CaSE*"
  
$ fg %1
+
== Finding a file with particular content ==
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
To search in /etc/ for a file with particular content:
  
== Killing a stopped job ==
+
$ grep -R "search-string" /etc/*
  
To kill a job
+
To search the current directory for *.cs files containing the word "Up":
  
  $ kill %1
+
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Finding a list of files with particular content ==
  
== Periodically run a program and watch its output ==
+
E.g. to find all the files with the word 'creativity':
  
  $ watch /your/command
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
= Debian/Ubuntu package management =
+
== Using the locate command to find files ==
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
$ locate part-of-filename
  
== configuring debconf ==
+
E.g.
  
  # dpkg-reconfigure debconf
+
  $ locate texvc
  
Set priority to low to get asked detailed questions.
+
== Updating locate command's database ==
  
== Showing list of installed packages ==
+
# updatedb
  
# dpkg --get-selections
+
== Select a random line from a text file ==
  
== Searching for installed package ==
+
$ shuf -n 1 input.txt
  
# dpkg --get-selections | grep package-name
+
== Extra context for grep ==
  
or
+
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:
  
  # aptitude search package-name
+
  $ grep -B 3 -A 1 ...
  
== Showing which files are installed as part of a package ==
+
= Job control =
  
# dpkg -L package-name
+
== Stopping a running process ==
  
== Installing a package ==
+
Press Ctrl+Z to stop a running process.
  
# apt-get install package-name
+
== Listing current jobs and their status ==
  
== Uninstalling a package ==
+
$ jobs
  
# apt-get remove package-name
+
== Resuming a stopped job in the backgroud ==
  
== Showing system architecture ==
+
To resume a stopped process in the background
  
  $ dpkg --print-architecture
+
  $ bg %1
  
== Showing which package a file belongs to ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
$ which echo
+
== Resuming a stopped job in the foreground ==
/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 ==
+
To resume a stopped process in the foreground
  
  $ apt-cache showpkg coreutils
+
  $ fg %1
  
Or for even more information:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
$ apt-cache show coreutils
+
== Killing a stopped job ==
  
== List all installed packages with package version info ==
+
To kill a job
  
  dpkg-query -l
+
  $ kill %1
  
== Reporting which version of a package is installed ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
$ dpkg -l | grep package-name
+
== Periodically run a program and watch its output ==
  
E.g.:
+
$ watch /your/command
 +
 
 +
= Debian/Ubuntu package management =
 +
 
 +
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
== configuring debconf ==
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-reconfigure debconf
  
Try the following:
+
Set priority to low to get asked detailed questions.
  
# apt-get update
+
== Showing list of installed packages ==
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
# dpkg --get-selections
  
$ apt-cache search . | sort -d | less
+
== Searching for installed package ==
  
= Networking =
+
# dpkg --get-selections | grep package-name
  
== net-tools vs iproute2 ==
+
or
  
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].
+
# aptitude search package-name
  
{|class="wikitable"
+
== Showing which files are installed as part of a package ==
! 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 ==
+
# dpkg -L package-name
  
For servers:
+
== Installing a package ==
  
  # service networking restart
+
  # apt-get install package-name
  
For desktops:
+
== Uninstalling a package ==
  
  # service network-manager restart
+
  # apt-get remove package-name
  
== Pinging with particular packet size ==
+
== Showing system architecture ==
  
  $ ping -M do -s <packet size in bytes> <host>
+
  $ dpkg --print-architecture
  
E.g.
+
== Showing which package a file belongs to ==
  
  $ ping -M do -s 1400 charity.progclub.org
+
  $ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Showing package information ==
  
  # ip route add <host> dev <interface> advmss <packet size>
+
  $ apt-cache showpkg coreutils
  
E.g.
+
Or for even more information:
  
  # ip route add 10.0.0.1 dev eth0 advmss 1400
+
  $ apt-cache show coreutils
  
== Dropping configured MMS for a particular IP address ==
+
== List all installed packages with package version info ==
  
  # ip route flush <host>
+
  dpkg-query -l
  
E.g.
+
== Reporting which version of a package is installed ==
  
  # ip route flush 10.0.0.1
+
  $ dpkg -l | grep package-name
  
== Listing open ports and socket information ==
+
E.g.:
  
Including which process is listening on which port.
+
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
  
# netstat -tulpn
+
== Comprehensive upgrade ==
  
Or use the 'ss' command:
+
Try the following:
  
  # ss -s
+
  # apt-get update
  # ss -l
+
  # apt-get dist-upgrade
  # ss -pl
+
  # apt-get autoremove
  # ss -o state established '( dport = :smtp or sport = :smtp )'
+
  # apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
== Listing open IPv4 connections ==
+
== Searching all available packages ==
  
  # lsof -Pnl +M -i4
+
  $ apt-cache search . | sort -d | less
  
You might need to install the lsof package:
+
== Reporting unattended upgrades status ==
  
# apt-get install lsof
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
== Query for DNS MX record ==
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
$ nslookup
+
== Searching for Debian packages and versions ==
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
= Networking =
  
== Using nmap to list open ports on remote host ==
+
== Determining throughput between two hosts ==
  
To check the 1,000 most common ports:
+
# apt install iperf3
  
# nmap server.example.com
+
On the server:
  
Or for a specific port range (e.g. 101 to 102):
+
# iperf3 -s
  
# nmap -p 101-102 server.example.com
+
On the client:
  
Or for all ports (1 to 65,535):
+
# iperf3 -c $SERVER_IP
  
# nmap -p- server.example.com
+
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].
  
== Network monitoring ==
+
== net-tools vs iproute2 ==
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
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].
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
{|class="wikitable"
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
+
! legacy net-tools commands
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
+
! iproute2 replacement commands
# Bandwidth per process: nethogs
+
|-
 +
| 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)
 +
|}
  
== nload ==
+
== Restart networking ==
  
You can watch network traffic in real-time with nload:
+
For servers:
  
  # nload -u M
+
  # service networking restart
  
== Reporting network (NIC) speed ==
+
For desktops:
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
# service network-manager restart
  
# dmesg | grep eth0
+
== Pinging with particular packet size ==
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
$ ping -M do -s <packet size in bytes> <host>
  
== Path MTU discovery ==
+
E.g.
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
$ ping -M do -s 1400 charity.progclub.org
  
# tracepath host.example.com
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
== Listing available Ethernet devices ==
+
# ip route add <host> dev <interface> advmss <packet size>
  
To see a list of NICs available on the host:
+
E.g.
  
  $ cat /proc/net/dev
+
  # ip route add 10.0.0.1 dev eth0 advmss 1400
  
Also
+
== Dropping configured MMS for a particular IP address ==
  
  $ ip link
+
  # ip route flush <host>
  
== 59 Linux Networking commands and scripts ==
+
E.g.
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
# ip route flush 10.0.0.1
  
== Links ==
+
== Listing open ports and socket information ==
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
Including which process is listening on which port.
  
= IPTables =
+
# netstat -tulpn
  
== Applying firewall rules ==
+
Or use the 'ss' command:
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
$ sudo vim /etc/iptables.test.rules
+
== Listing open IPv4 connections ==
$ 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 =
+
# lsof -Pnl +M -i4
  
== Denying hosts with ufw ==
+
You might need to install the lsof package:
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
# apt-get install lsof
  
= Bind9 =
+
== Query for DNS MX record ==
  
== Viewing Bind9 querylog ==
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
$ sudo rndc querylog
+
== Query for DNS SOA record ==
$ tail -f /var/log/syslog
 
  
= IPSec =
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
== Disabling IPSec ==
+
== Using nmap to list open ports on remote host ==
  
# setkey -FP
+
To check the 1,000 most common ports:
  
= OpenSSL =
+
# nmap server.example.com
  
== Debugging IMAPS with OpenSSL ==
+
Or for a specific port range (e.g. 101 to 102):
  
  # openssl s_client -connect localhost:993
+
  # nmap -p 101-102 server.example.com
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
Or for all ports (1 to 65,535):
  
  $ openssl s_client -connect www.example.com:443
+
  # nmap -p- server.example.com
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
== Network monitoring ==
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
= Pluggable Authentication Modules (PAM) =
+
# 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
  
== Links ==
+
== nload ==
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
You can watch network traffic in real-time with nload:
  
= SSH =
+
# nload -u M
  
== Configuring SSH key login ==
+
== Reporting network (NIC) speed ==
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
  $ ssh-keygen -t rsa
+
  # dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
Copy the public key from the client to the server:
+
Note: use ifconfig to get device name.
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
== Path MTU discovery ==
  
Configure the authorized keys on the server:
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
  $ ssh user@example.org
+
  # tracepath host.example.com
$ 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 ==
+
== Listing available Ethernet devices ==
  
For example, connecting a remote MySQL server to the localhost:
+
To see a list of NICs available on the host:
  
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
  $ cat /proc/net/dev
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
Also
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
$ ip link
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
== 59 Linux Networking commands and scripts ==
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
== Links ==
  
* run putty.exe
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
= IPTables =
  
To see what's going on with your ssh connections,
+
== Applying firewall rules ==
  
$ ssh -v user@host
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
Or
+
$ 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 -vv user@host
+
== Blocking an IP address with iptables ==
  
== Unlocking SSH key for session ==
+
To drop IP address 1.2.3.4:
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  # iptables -A INPUT -s 1.2.3.4 -j DROP
[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 ==
+
= ufw =
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
== Denying hosts with ufw ==
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
== cat EOF ==
+
= Bind9 =
  
$ cat > output <<EOF
+
== Viewing Bind9 querylog ==
> text
 
> EOF
 
  
  $ cat output
+
  $ sudo rndc querylog
  text
+
  $ tail -f /var/log/syslog
  
= Script =
+
= IPSec =
  
== Creating a session log with script ==
+
== Disabling IPSec ==
  
  $ script -t 2> timing
+
  # setkey -FP
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
= OpenSSL =
  
== Replaying a scripted session ==
+
== Debugging IMAPS with OpenSSL ==
  
  $ scriptreplay timing
+
  # openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
== Debugging HTTPS with OpenSSL ==
  
= Screen =
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
== Creating a new screen or reconnecting to a detached screen ==
+
== Links ==
  
$ screen -R
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
== Detaching a screen ==
+
= Pluggable Authentication Modules (PAM) =
  
$ screen -D
+
== Links ==
  
== Reconnecting to screen ==
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
$ screen -D
+
= SSH =
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
== Configuring SSH key login ==
  
#!/bin/bash
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
$ ssh-keygen -t rsa
  
== Scrolling in screen ==
+
Copy the public key from the client to the server:
  
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.
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
= tmux =
+
Configure the authorized keys on the server:
  
== Live collaboration with tmux ==
+
$ ssh user@example.org
 
+
$ mkdir ~/.ssh
User A:
+
$ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
tmux -S /tmp/collab
+
== Tunneling over SSH ==
chmod 777 /tmp/collab
 
  
User B:
+
For example, connecting a remote MySQL server to the localhost:
  
  tmux -S /tmp/collab attach
+
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
= Vim =
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
== First, why Vim? ==
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
== Visual modes ==
+
== Tunneling over SSH with PuTTY ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
== Configuring spaces instead of tabs ==
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
== Enabling verbose SSH logging ==
  
$ vim ~/.vimrc
+
To see what's going on with your ssh connections,
  
and include the following lines:
+
$ ssh -v user@host
  
set tabstop=2
+
Or
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
$ ssh -vv user@host
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
== Unlocking SSH key for session ==
  
Use:
+
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'
  
:syntax on
+
== Links ==
  
to turn on syntax highlighting.
+
* [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]
  
Use:
+
= Standard IO =
  
:syntax off
+
== cat EOF ==
  
to turn off syntax highlighting.
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
To always use syntax highlighting:
+
$ cat output
 +
text
  
$ vim ~/.vimrc
+
= Script =
  
and add:
+
== Creating a session log with script ==
  
  syntax on
+
  $ script -t 2> timing
  
To get a list of supported colour schemes open vim and type:
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
:colorscheme[space][Ctrl+D]
+
== Replaying a scripted session ==
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
$ scriptreplay timing
  
colorscheme desert
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
== Inserting a TAB character when expandtab is on ==
+
= 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.
+
== Creating a new screen or reconnecting to a detached screen ==
  
Press Ctrl+V TAB to insert a literal tab character.
+
$ screen -R
  
Or you can disable tab expansion altogether with:
+
== Detaching a screen ==
  
  :set expandtab!
+
  $ screen -D
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
== Reconnecting to screen ==
  
  :%s/^\s*/&&/g
+
  $ screen -D
 +
$ screen -R
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
I have a script in ~/bin/reconnect like so,
  
== Recording and replaying a macro ==
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
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 "@@".
+
This will detach your last screen, and reconnect it on the current terminal.
  
== Deleting to end of line ==
+
== Scrolling in screen ==
  
d$
+
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.
  
== Deleting to beginning of line ==
+
= tmux =
  
d^
+
== Live collaboration with tmux ==
  
== Finding text ==
+
User A:
  
To search forward for "text":
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
/text
+
User B:
  
To search backward for "text":
+
tmux -S /tmp/collab attach
  
?text
+
= Vim =
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
== First, why Vim? ==
  
== Finding and replacing text ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
To replace the first instance of "search" on the current line with "destroy":
+
== Visual modes ==
  
:s/search/destroy/
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
To replace all instances of "search" on the current line with "destroy":
+
== Configuring spaces instead of tabs ==
  
:s/search/destroy/g
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
$ vim ~/.vimrc
  
:13,37 s/search/destroy/g
+
and include the following lines:
  
To replace all instances of "search" in the entire file with "destroy":
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
:%s/search/destroy/g
+
== Configuring syntax highlighting ==
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
To set the line-ending to Unix line endings run the command:
+
Use:
  
  :setlocal ff=unix
+
  :syntax on
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
to turn on syntax highlighting.
  
== Disabling auto-indent etc. to paste from clipboard ==
+
Use:
  
To disable smart indenting when you're going to paste in text:
+
:syntax off
  
:set paste
+
to turn off syntax highlighting.
  
To turn it off again:
+
To always use syntax highlighting:
  
  :set nopaste
+
  $ vim ~/.vimrc
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
and add:
  
== Positioning windows ==
+
syntax on
  
Use -o for horizontal split, e.g.:
+
To get a list of supported colour schemes open vim and type:
  
  vim -o a.txt b.txt
+
  :colorscheme[space][Ctrl+D]
  
Use -O for vertical split, e.g.:
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
  vim -o a.txt b.txt
+
  colorscheme desert
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
== Inserting a TAB character when expandtab is on ==
  
Use ^W and &lt; or &gt; to resize windows.
+
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 indent a block of text in Vim ==
+
Press Ctrl+V TAB to insert a literal tab character.
  
Use the > command. E.g. to indent five lines:
+
Or you can disable tab expansion altogether with:
  
  5 > >
+
  :set expandtab!
  
Press . (dot) to keep indenting.
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
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:
+
:%s/^\s*/&&/g
  
> %
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
== Recording and replaying a macro ==
  
== Open a file in a new window/tab ==
+
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 "@@".
  
To open a file on the left hand side:
+
== Deleting to end of line ==
  
  :vert new filename.ext
+
  d$
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
== Deleting to beginning of line ==
  
To open a file at the top:
+
d^
  
:new filename.ext
+
== Finding text ==
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
To search forward for "text":
  
== Explore files in Vim ==
+
/text
  
Enter:
+
To search backward for "text":
  
  :Explore
+
  ?text
  
== Switch between Vim tabs ==
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
Use gt and gT.
+
== Finding and replacing text ==
  
== Switch between Vim windows ==
+
To replace the first instance of "search" on the current line with "destroy":
  
To toggle between open windows use:
+
:s/search/destroy/
  
Ctrl+W W
+
To replace all instances of "search" on the current line with "destroy":
  
To move in a direction use:
+
:s/search/destroy/g
  
Ctrl+W h/j/k/l
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
:13,37 s/search/destroy/g
  
== Insert block comment in Vim ==
+
To replace all instances of "search" in the entire file with "destroy":
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
:%s/search/destroy/g
 +
 
 +
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
So it's:
+
To set the line-ending to Unix line endings run the command:
  
# Ctrl+V (Note: not Shift+V!)
+
:setlocal ff=unix
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
To navigate to the matching beginning or end tag use '%'.
+
== Disabling auto-indent etc. to paste from clipboard ==
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
To disable smart indenting when you're going to paste in text:
  
== Auto-format HTML tags ==
+
:set paste
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
To turn it off again:
  
# first join all the lines - ggVGgJ
+
:set nopaste
# 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 ==
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
* [http://www.vim.org/ Vim: the editor]
+
== Positioning windows ==
* [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 ==
+
Use -o for horizontal split, e.g.:
  
Generate PDF from input.txt with:
+
vim -o a.txt b.txt
  
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
+
Use -O for vertical split, e.g.:
  
Examine output with:
+
vim -o a.txt b.txt
  
$ okular doc.pdf
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
= Write =
+
Use ^W and &lt; or &gt; to resize windows.
  
== Talking to other users on the system ==
+
== To indent a block of text in Vim ==
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
Use the > command. E.g. to indent five lines:
  
1. SSH to <username>@<hostname> and login with your username and password.
+
5 > >
  
2. Issue the following command to find out who is logged onto the system:
+
Press . (dot) to keep indenting.
  
$ who
+
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:
  
3. Issue the following command to talk to a specific user:
+
> %
  
$ write <username>
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
== Open a file in a new window/tab ==
  
= Date =
+
To open a file on the left hand side:
  
== Reporting the time on the server ==
+
:vert new filename.ext
  
$ date
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
== Reporting UTC time ==
+
To open a file at the top:
  
  $ date --utc
+
  :new filename.ext
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
$ date="`date +%F-%H%M%S`"
+
== Explore files in Vim ==
  
== Getting the year in four digits ==
+
Enter:
  
  $ year="`date +%Y`"
+
  :Explore
  
== Getting the month in two digits ==
+
== Switch between Vim tabs ==
  
$ month="`date +%m`"
+
Use gt and gT.
  
== Getting the day of the month in two digits ==
+
== Switch between Vim windows ==
  
$ day="`date +%d`"
+
To toggle between open windows use:
  
== Getting yesterday's date ==
+
Ctrl+W W
  
$ date --date='1 day ago' +%Y-%m-%d
+
To move in a direction use:
  
== Converting Unix time (seconds since epoch) ==
+
Ctrl+W h/j/k/l
  
For timestamp '1501370200':
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
$ date -d @1501370200 +%F-%H%M%S
+
== Insert block comment in Vim ==
  
== Running timedatectl from systemd ==
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
There's a new command bundled with systmed:
+
So it's:
  
# timedatectl
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
It reports on (and controls) how the system time is configured.
+
== Navigate to matching tag ==
  
= MySQL =
+
To navigate to the matching beginning or end tag use '%'.
  
== Run mysql without authentication/authorisation ==
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
# service mysql stop
+
== Auto-format HTML tags ==
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
# mysql -u root mysql
+
# 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=
  
To stop the unauthenticated service:
+
== Links ==
  
# mysqladmin shutdown
+
* [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]
  
Then restart a normal service:
+
== Create PDF from text using Vim ==
  
# service mysql start
+
Generate PDF from input.txt with:
  
== Logging all database queries ==
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
# vim /etc/mysql/my.cnf
+
Examine output with:
  
In the [mysqld] section add:
+
$ okular doc.pdf
  
log=/tmp/mysql.log
+
= Write =
  
Then:
+
== Talking to other users on the system ==
  
# service mysql restart
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
Watch the log with:
+
1. SSH to <username>@<hostname> and login with your username and password.
  
# tail -f /tmp/mysql.log
+
2. Issue the following command to find out who is logged onto the system:
  
== Dumping a MySQL database ==
+
$ who
  
You can dump the database into a file using:  
+
3. Issue the following command to talk to a specific user:
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
$ write <username>
  
You can create a database using:
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
$ echo create database databasename | mysql -h hostname -u user -p
+
= Date =
  
You can restore a database using:
+
== Reporting the time on the server ==
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
$ date
  
# mysql -h localhost -u root --password=<password>
+
== Reporting UTC time ==
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
$ date --utc
  
# mysql -h localhost -u root --password=<password>
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
$ date="`date +%F-%H%M%S`"
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
== Getting the year in four digits ==
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
$ year="`date +%Y`"
  
Check the SSL version in use:
+
== Getting the month in two digits ==
  
  show status like 'Ssl_version';
+
  $ month="`date +%m`"
  
Or check the cipher in use:
+
== Getting the day of the month in two digits ==
  
  show status like 'Ssl_cipher';
+
  $ day="`date +%d`"
  
= Apache =
+
== Getting yesterday's date ==
  
== Reporting loaded Apache modules ==
+
$ date --date='1 day ago' +%Y-%m-%d
  
# apache2ctl -M
+
== Converting Unix time (seconds since epoch) ==
  
== Maintaining .htaccess passwords ==
+
For timestamp '1501370200':
  
To add or modify the password for a user:
+
$ date -d @1501370200 +%F-%H%M%S
  
$ htpasswd /etc/apache2/passwd username
+
== Running timedatectl from systemd ==
  
== Configuring PHP session timeout in .htaccess ==
+
There's a new command bundled with systmed:
  
For a session timeout of 9 hours:
+
# timedatectl
  
php_value session.cookie_lifetime 32400
+
It reports on (and controls) how the system time is configured.
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
= MySQL (and MariaDB) =
  
php_flag magic_quotes_gpc Off
+
== Run mysql without authentication/authorisation ==
  
== Requiring HTTP Auth in .htaccess ==
+
# service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
AuthType Basic
+
Then you can connect without a password, e.g.:
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
# mysql -u root mysql
  
The hard way
+
To stop the unauthenticated service:
  
  $ sudo /etc/init.d/apache2 restart
+
  # mysqladmin shutdown
  
The graceful way (avoids dropping active connections)
+
Then restart a normal service:
  
  $ sudo apache2ctl graceful
+
  # service mysql start
  
== Allowing directory browsing ==
+
== Logging all database queries ==
  
To show directory index pages, in the apache config file:
+
# vim /etc/mysql/my.cnf
  
<Directory /var/www/data>
+
In the [mysqld] section add:
  Options Indexes
 
</Directory>
 
  
= C =
+
log=/tmp/mysql.log
  
== Locating memset function ==
+
Then:
  
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]
+
# service mysql restart
  
== Links ==
+
Watch the log with:
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
# tail -f /tmp/mysql.log
  
= PHP =
+
Or:
  
== Including a file relative to the including file ==
+
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
my_logs.txt will be in /var/lib/mysql
  
== Enabling error reporting ==
+
== Dumping a MySQL database ==
  
  error_reporting( E_ALL | E_STRICT );
+
You can dump the database into a file using:
  ini_set( 'display_errors', 'On' );
+
   
 +
  $ mysqldump -h hostname -u user --password=password databasename > filename
  
== Setting an error handler ==
+
== Loading a MySQL database from a dump file ==
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
You can create a database using:
  
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
  $ echo create database databasename | mysql -h hostname -u user -p
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
ini_set( 'html_errors', 'off' );
+
== Creating a MySQL user ==
  
== Report PHP modules ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
$ php -m
+
== Granting all MySQL user permissions ==
  
== PHP Security Best Practices For Sys Admins ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
== Select domain name from email address ==
  
= BASH scripting =
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
== Telling a script to run in bash ==
+
Check the SSL version in use:
  
The first line of the file should be:
+
show status like 'Ssl_version';
  
#!/bin/bash
+
Or check the cipher in use:
  
== Checking if a command-line argument was passed in ==
+
show status like 'Ssl_cipher';
  
if [ -n "$1" ]; then
+
== Report on server config ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
  
  if [ "$1" = "" ]; then
+
  SHOW VARIABLES
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
and
  
  if [ -z "$1" ]; then
+
  SHOW STATUS
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
and
  
  cd /my/path
+
  SHOW PROCESSLIST
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
== Monitor MySQL activity ==
  
Check if file exists:
+
$ watch "mysql -t -e 'show processlist'"
  
if [ -f "/my/file" ]; then
+
= Apache =
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
== Reporting loaded Apache modules ==
  
  if [ ! -f "/my/file" ]; then
+
  # apache2ctl -M
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
== Maintaining .htaccess passwords ==
  
Check if directory exists:
+
To add or modify the password for a user:
  
  if [ -d "/my/dir" ]; then
+
  $ htpasswd /etc/apache2/passwd username
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
== Configuring PHP session timeout in .htaccess ==
  
if [ ! -d "/my/dir" ]; then
+
For a session timeout of 9 hours:
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
To keep only the latest five backups:
+
== Disabling PHP magic quotes in .htaccess ==
  
  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
+
  php_flag magic_quotes_gpc Off
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
== Requiring HTTP Auth in .htaccess ==
  
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.
+
AuthType Basic
 +
AuthName "Speak Friend And Enter"
 +
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
  
== Changing into the script's directory ==
+
== Restarting Apache ==
  
cd "`dirname $0`"
+
The hard way
  
== Getting the absolute path of a relative path ==
+
$ sudo /etc/init.d/apache2 restart
  
readlink -f ./some/path
+
The graceful way (avoids dropping active connections)
  
== Creating a temp directory ==
+
$ sudo apache2ctl graceful
  
dir=`mktemp -d` && cd $dir
+
== Allowing directory browsing ==
  
== Reading secret input from stdin ==
+
To show directory index pages, in the apache config file:
  
You can read a secret, such as a password, like this:
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
echo -n "Enter passphrase: "
+
= C =
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Locating memset function ==
  
== String replacements in bash ==
+
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]
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
== Links ==
  
result=${var/find/replace}
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
To replace all occurrences:
+
= PHP =
 +
 
 +
== Including a file relative to the including file ==
 +
 
 +
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
 +
 
 +
== Enabling error reporting ==
  
  result=${var//find/replace}
+
  error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
A practical example, get an ISO date and turn it into a path:
+
== Setting an error handler ==
  
  date="$(date +%Y-%m-%d)"
+
  set_error_handler( "error_handler", E_ALL | E_STRICT );
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
  
cat << EOF > /tmp/yourfilehere
+
== Disable HTML content in var_dump ==
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
ini_set( 'html_errors', 'off' );
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
== Report PHP modules ==
  
  case $space in
+
  $ php -m
[1-6]*)
+
 
  Message="All is quiet."
+
== PHP Security Best Practices For Sys Admins ==
  ;;
 
[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 ==
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
To enable dot-file matching in globs, set the dotglob shell option:
+
= BASH scripting =
  
$ shopt -s dotglob
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
== Stopping a script from running if it previously exited due to error ==
+
== Telling a script to run in bash ==
  
persistentDataDir=/var/lib/something
+
The first line of the file should be:
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 ==
+
#!/bin/bash
  
ephemeralDataDir=/var/run/something
+
== Checking if a command-line argument was passed in ==
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
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)].
+
== Checking if a command-line argument was not passed in ==
  
== Run a command using arguments that come from an array ==
+
if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
Or:
  
  #!/bin/bash
+
  if [ -z "$1" ]; then
tabs=("first tab" "second tab")
+
   echo "Missing parameter 1.";
args=()
+
  exit 1;
for t in "${tabs[@]}" ; do
+
  fi
   args+=(-t "$t")
 
done
 
  app "${args[@]}"
 
  
== Display a CSV in columnar or tabular format ==
+
== Checking command exit status ==
  
  $ column -t -s , data.csv
+
  cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
= Sed =
+
== Checking if a file does/doesn't exist ==
  
== Find and replace with sed ==
+
Check if file exists:
  
To update the current file use '-i'. E.g.:
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
sed -i 's/search-text/replace-text/' file
+
Check if file doesn't exist:
  
= Awk =
+
if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
  
== Listing IP addresses in an Apache web log ==
+
== Checking if a directory does/doesn't exist ==
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
Check if directory exists:
  
== Printing space-separated field ==
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
echo 'no no yes no' | awk '{print $3}'
+
Check if directory doesn't exist:
  
== Printing delimited field ==
+
if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
== Deleting old backups ==
  
= Subversion =
+
To keep only the latest five backups:
  
== Setting svn:externals from the command-line ==
+
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
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
To set an svn:externals from the command-line:
+
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.
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
== Changing into the script's directory ==
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
cd "`dirname $0`"
  
svn propset svn:externals -F svn.externals .
+
== Getting the absolute path of a relative path ==
  
== Setting svn:ignore from the command line ==
+
readlink -f ./some/path
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
== Creating a temp directory ==
  
  $ svn propset svn:ignore [file|folder] [path]
+
  dir=`mktemp -d` && cd $dir
  
Or use a file and apply recursively:
+
== Reading secret input from stdin ==
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
You can read a secret, such as a password, like this:
  
= Git =
+
echo -n "Enter passphrase: "
 
+
stty -echo
== Showing status of working copy ==
+
read passphrase;
 +
stty echo
 +
echo ""
  
git status
+
After running the above the secret will be in the $passphrase environment variable.
  
== Showing repo history ==
+
== String replacements in bash ==
  
git log
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
  
== Showing remote repositories (including 'origin') ==
+
result=${var/find/replace}
  
git remote -v
+
To replace all occurrences:
  
== Handy git aliases ==
+
result=${var//find/replace}
  
Save these to your ~/.gitconfig file.
+
A practical example, get an ISO date and turn it into a path:
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
== Sending a HEREDOC to a file ==
  
To show only the files that have changed, rather than the full line-by-line content:
+
cat << EOF > /tmp/yourfilehere
 +
These contents will be written to the file.
 +
        This line is indented.
 +
EOF
  
  dif  = !git diff --name-status
+
== Bash case/switch statement ==
  
== Show git remote URL ==
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
  git config --get remote.origin.url
+
  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
  
= IRC =
+
== Using dotglob shopt to match dot-files ==
  
== Instructing ChanServ to op an admin ==
+
To enable dot-file matching in globs, set the dotglob shell option:
  
  /msg ChanServ op #channel user
+
  $ shopt -s dotglob
  
E.g.
+
== Stopping a script from running if it previously exited due to error ==
  
  /msg ChanServ op #gnurc jj5
+
  persistentDataDir=/var/lib/something
 +
alarm() {
 +
  touch $persistentDataDir/alarm
 +
}
 +
trap alarm ERR
 +
[ -f $persistentDataDir/alarm ] && exit 1
  
Sub 'op' for 'deop' to remove op privilege.
+
== Make sure only one instance of a script is running at a time ==
  
= C++ =
+
ephemeralDataDir=/var/run/something
 +
unlock() {
 +
  rmdir $ephemeralDataDir/lock
 +
}
 +
mkdir $ephemeralDataDir/lock || exit 1;
 +
trap unlock EXIT
  
== C++ books ==
+
== BASH programming advice ==
  
=== Books I want ===
+
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)].
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== Run a command using arguments that come from an array ==
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
See [https://unix.stackexchange.com/a/412647/356289 here]:
* [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 ===
+
#!/bin/bash
 
+
tabs=("first tab" "second tab")
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
args=()
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
+
for t in "${tabs[@]}" ; do
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
+
  args+=(-t "$t")
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
+
done
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
+
app "${args[@]}"
* [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;
+
== Display a CSV in columnar or tabular format ==
* [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 ===
+
$ column -t -s , data.csv
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
== Maximum command line length ==
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
Technically this is an operating system limit, not a BASH limit.
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
$ getconf ARG_MAX    # Get argument limit in bytes/chars
  
== C++ blogs/articles ==
+
= Sed =
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
== Find and replace with sed ==
* [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 update the current file use '-i'. E.g.:
  
* ++c can be faster than c++.
+
sed -i 's/search-text/replace-text/' file
* 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 [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 =
+
= Awk =
  
[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.
+
== Listing IP addresses in an Apache web log ==
  
== Following a service log ==
+
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
  
e.g. for bind9:
+
== Printing space-separated field ==
  
  # journalctl -f -u bind9
+
  echo 'no no yes no' | awk '{print $3}'
  
or for everything:
+
== Printing delimited field ==
  
  # journalctl -f
+
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
  
== System status ==
+
= Subversion =
  
To see spawned services hierarchy:
+
== Setting svn:externals from the command-line ==
  
# systemctl status
+
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
  
Or for a specific service e.g.:
+
To set an svn:externals from the command-line:
  
  # systemctl status networking
+
  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
  
= SaltStack =
+
Or to use a file:
  
== Running a command on specified minions ==
+
svn propset svn:externals -F svn.externals .
  
From the salt master:
+
== Setting svn:ignore from the command line ==
  
salt 'host' cmd.run 'update-locale'
+
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
  
From the salt minion:
+
$ svn propset svn:ignore [file|folder] [path]
  
salt-call cmd.run 'update-locale'
+
Or use a file and apply recursively:
  
== Running a command on all minions ==
+
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
  
salt '*' cmd.run 'update-locale'
+
= Git =
  
== Running a specific state file ==
+
== Showing status of working copy ==
  
From the salt master:
+
git status
  
salt $MINION_ID state.sls $STATE_FILE
+
== Showing repo history ==
  
From the salt minion:
+
git log
  
salt-call state.sls $STATE_FILE
+
== Showing remote repositories (including 'origin') ==
  
== Listing active jobs ==
+
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:
  
salt-run jobs.active
+
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
  
== Listing available grains ==
+
To show only the files that have changed, rather than the full line-by-line content:
  
salt 'example' grains.items
+
  dif  = !git diff --name-status
  
== Listing available pillar ==
+
== Show git remote URL ==
  
  salt 'example' pillar.items
+
  git config --get remote.origin.url
  
== Reporting a grain value ==
+
= IRC =
  
e.g. for the 'mem_total' grain:
+
== Instructing ChanServ to op an admin ==
  
  salt '*' grains.item mem_total
+
  /msg ChanServ op #channel user
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
E.g.
  
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
/msg ChanServ op #gnurc jj5
  
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
Sub 'op' for 'deop' to remove op privilege.
  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 =
+
= C++ =
  
== Running user login script (X11/XOrg/XWindows) ==
+
== C++ books ==
  
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 want ===
  
[Desktop Entry]
+
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
Type=Application
+
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
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 ==
+
* [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
  
{|class="wikitable"
+
=== Books I own ===
! 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
 
|}
 
  
= VirtualBox =
+
* [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]
 +
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 +
* [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;
  
== Mounting a VirtualBox VDI file ==
+
=== Books I'm not reading ===
  
Note: instead of doing this consider booting with a live CD.
+
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
  
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
=== Books I've read ===
  
Install qemu if necessary:
+
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
  
# apt install qemu
+
== C++ blogs/articles ==
  
Then you'll need to load the network block device module:
+
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
 +
* [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]
  
# rmmod nbd
+
== C++ performance tips ==
# modprobe nbd max_part=16
 
  
Attach the .vdi image to one of the nbd you just created:
+
* ++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 [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]
  
# qemu-nbd -c /dev/nbd0 drive.vdi
+
= systemd =
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
[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.
 +
 
 +
== Following a service log ==
 +
 
 +
e.g. for bind9:
 +
 
 +
# journalctl -f -u bind9
 +
 
 +
or for everything:
 +
 
 +
# 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
  
$ curl http://localhost:9200/_cluster/health?pretty
+
= SaltStack =
  
= Zabbix =
+
== Running a command on specified minions ==
  
== Zabbix Agent on Mac OS X ==
+
From the salt master:
  
Download and install agent.
+
salt 'host' cmd.run 'update-locale'
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
From the salt minion:
  
Unload agent with:
+
salt-call cmd.run 'update-locale'
  
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
== 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:
 +
 
 +
<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/