Difference between revisions of "John's Linux page"

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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.
 
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|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 44: Line 62:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 81: 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
  
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
+
=== RAM info ===
  
= Power =
+
# dmidecode --type memory
  
== Reporting on PowerShield DEFENDER UPS status ==
+
=== PCI info ===
  
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
+
# lspci -v
  
$ upsc defender
+
=== Drive info ===
  
E.g.:
+
# cat /proc/partitions
  
jj5@orac:~$ upsc defender
+
and:
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 ==
+
# hdparm -I /dev/sda
  
You can run "instant commands" using the '''upscmd''' command.
+
and:
  
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
+
# smartctl --info /dev/sda
  
diligence:/srv/salt/conf/app/defender-1200.sls
+
You can check if a drive is SSD or not with:
  
To see "instant commands" supported by the PowerShield DEFENDER:
+
# cat /sys/block/sde/queue/rotational
  
  $ upscmd -l defender
+
  0=SSD
 +
1=HDD
  
E.g.:
+
== Viewing syslog and other logs with KSystemLog ==
  
jj5@orac:~$ upscmd -l defender
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
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 =
+
= CPU =
  
== Configuring vim as your editor ==
+
== Monitoring CPU clock speed ==
  
Sometimes all you need is:
+
Try something like this:
  
  $ export EDITOR=/usr/bin/vim
+
  $ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
= Power =
  
Other times you need to run
+
== Reporting on PowerShield DEFENDER UPS status ==
  
# update-alternatives --config editor
+
Before running `upsc` ensure service is running:
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
# upsdrvctl start
  
== Configuring your locale ==
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
  
  $ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
  $ upsc defender
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
 
  
= User and group management =
+
E.g.:
  
== Adding a user ==
+
jj5@orac:~$ upsc defender
 
+
Init SSL without certificate database
To add a new user on a linux system:
+
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
  
# useradd username
+
== Run commands on PowerShield DEFENDER UPS batteries ==
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
You can run "instant commands" using the '''upscmd''' command.
  
# adduser username
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
== Adding a user to a group ==
+
diligence:/srv/salt/conf/app/defender-1200.sls
  
To add an existing user to an existing group:
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
  # gpasswd -a username group
+
  $ upscmd -l defender
  
e.g. to add user 'jj5' to the 'sudo' group:
+
E.g.:
  
  # gpasswd -a jj5 sudo
+
  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
  
Alternatively you can use adduser, passing the username and group:
+
= Environment =
  
# adduser username group
+
== Configuring vim as your editor ==
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
Sometimes all you need is:
  
  # adduser sclaughl staff
+
  $ export EDITOR=/usr/bin/vim
  
== Disabling a user account ==
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
You can disable a user account with:
+
Other times you need to run
  
  # passwd -l user
+
  # update-alternatives --config editor
  
Note: that's a lower-case L, not a one.
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
== Enabling a disabled user account ==
+
== Configuring your locale ==
  
To can re-enable a locked user account with:
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
# passwd -u user
+
= User and group management =
  
== Finding which user you are logged in as ==
+
== Adding a user ==
  
To determine which user you are running as enter the command:
+
To add a new user on a linux system:
  
  $ whoami
+
  # useradd username
 +
# passwd username
  
== Finding which groups you are a member of ==
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
To find which groups you are a member of:
+
# adduser username
  
$ groups
+
== Adding a user to a group ==
  
or
+
To add an existing user to an existing group:
  
  $ groups username
+
  # gpasswd -a username group
  
Where 'username' is the username of the user you are querying, e.g.:
+
e.g. to add user 'jj5' to the 'sudo' group:
  
  $ groups jj5
+
  # gpasswd -a jj5 sudo
  
== Finding who else is logged in to the system ==
+
Alternatively you can use adduser, passing the username and group:
  
To see who else is logged in,
+
# adduser username group
  
$ who
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
== Running a command as a particular user ==
+
# adduser sclaughl staff
  
To run "svn update" as the user www-data:
+
== Disabling a user account ==
  
$ sudo su -c "svn update" www-data
+
You can disable a user account with:
  
== Reporting user and group info for the current user ==
+
# passwd -l user
  
$ id
+
Note: that's a lower-case L, not a one.
  
= Memory management =
+
== Enabling a disabled user account ==
  
== Checking available memory ==
+
To can re-enable a locked user account with:
  
To report memory statistics in megabytes:
+
# passwd -u user
  
$ free -m
+
== Finding which user you are logged in as ==
  
== Check for swap thrashing ==
+
To determine which user you are running as enter the command:
  
Check your virtual memory status with vmstat:
+
$ whoami
  
$ vmstat
+
== Finding which groups you are a member of ==
  
== Report memory type ==
+
To find which groups you are a member of:
  
Report on RAM DIMMs:
+
$ groups
  
# dmidecode --type 17
+
or
  
Report on RAM and CPU cache:
+
$ groups username
  
# lshw -short -C memory
+
Where 'username' is the username of the user you are querying, e.g.:
  
Or for more detail:
+
$ groups jj5
  
# lshw -C memory
+
== Finding who else is logged in to the system ==
  
= Video/display management =
+
To see who else is logged in,
  
== Viewing EDID data for attached monitor ==
+
$ who
  
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):
+
== Running a command as a particular user ==
  
$ cd /sys/class/drm
+
To run "svn update" as the user www-data:
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
$ sudo su -c "svn update" www-data
  
== Using 'top' for dynamic resource usage reporting ==
+
== Reporting user and group info for the current user ==
  
To run top:
+
$ id
  
$ top
+
= Memory management =
  
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.
+
== Checking available memory ==
  
To see usage for a specific user run e.g.:
+
To report memory statistics in megabytes:
  
  $ top -u jj5
+
  $ free -m
  
To see full command-line press 'c'.
+
== Check for swap thrashing ==
  
When you're in 'top' you can:
+
Check your virtual memory status with vmstat:
  
* press '1' (one) to toggle CPU aggregation
+
$ vmstat
* press < and > to change the sort column
 
  
== Changing memory reporting in 'top' ==
+
== Report memory type ==
  
To run top:
+
Report on RAM DIMMs:
  
  $ top
+
  # dmidecode --type 17
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
# lshw -short -C memory
  
Press 'M' to sort by memory utilisation.
+
Or for more detail:
  
Press 'm' to switch between various display modes.
+
# lshw -C memory
  
== Showing full command-line in 'top' ==
+
= Video/display management =
  
To see the full command-line for processes run with -c:
+
== Viewing EDID data for attached monitor ==
  
$ top -c
+
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):
  
== Listing all processes currently running which were started in your current shell session ==
+
$ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
$ ps -fl
+
= Process management =
  
== Killing specific processes ==
+
== Using 'top' for dynamic resource usage reporting ==
  
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
+
To run top:
  
= Disk management =
+
$ top
  
== Creating a partition table ==
+
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.
  
# parted /dev/xvdf
+
To see usage for a specific user run e.g.:
  
  mktable msdos
+
  $ top -u jj5
  
== Creating a partition ==
+
To see full command-line press 'c'.
  
# parted /dev/xvdf
+
When you're in 'top' you can:
  
u MiB
+
* press '1' (one) to toggle CPU aggregation
mkpart primary 1 100%
+
* press < and > to change the sort column
  
== Creating an ext4 file-system ==
+
== Changing memory reporting in 'top' ==
  
# mkfs.ext4 /dev/xvdf1
+
To run top:
  
== Listing disk drives ==
+
$ top
  
# fdisk -l
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
(That's an L for "list")
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
 +
 
 +
Press 'M' to sort by memory utilisation.
  
== Checking available disk space ==
+
Press 'm' to switch between various display modes.
  
$ df -h
+
== Showing full command-line in 'top' ==
  
== Getting disk information ==
+
To see the full command-line for processes run with -c:
  
  # lsblk
+
  $ top -c
  
And
+
== Listing all processes currently running which were started in your current shell session ==
  
  # cat /proc/partitions
+
  $ ps -fl
  
Or the Grand Daddy of them all:
+
== Killing specific processes ==
  
  # lshw -class disk
+
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
(Requires the lshw package.)
+
== Run a command for a specified time using timeout ==
  
== Getting partition UUID and file-system type ==
+
$ timeout 3 ping jj5.net
  
# blkid
+
= Disk management =
  
== Checking for SSD vs magnetic disk ==
+
== Reporting ext4 file-systems mounted without noatime ==
  
  # cat /sys/block/sda/queue/rotational
+
  $ cat /proc/mounts | grep ext | grep -v noatime | sort
  
Will be 0 for SSD and 1 for magnetic.
+
== Creating a partition table ==
  
== Monitoring a ZFS server ==
+
# parted /dev/xvdf
  
So some commands I run to keep an eye on my new ZFS servers:
+
mktable msdos
  
# top
+
== Creating a partition ==
# iotop
+
 
# nethogs
+
  # parted /dev/xvdf
# 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:
+
u MiB
 +
mkpart primary 1 100%
  
# watch zpool status -v
+
== Creating an ext4 file-system ==
  
You can poke about in internals, e.g.:
+
# mkfs.ext4 /dev/xvdf1
  
# cat /proc/spl/kstat/zfs/arcstats
+
== Listing disk drives ==
  
  root@orac:/sys/module/zfs/parameters# tail *
+
  # fdisk -l
  
You can report on property values with e.g.:
+
(That's an L for "list")
  
# zfs get all data
+
== Checking available disk space ==
  
If you want to get funky:
+
$ df -h
  
# cd /tmp
+
== Getting disk information ==
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
# lsblk
  
root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
And
  
You can report history of a zpool:
+
# cat /proc/partitions
  
# zpool history $poolname
+
Or the Grand Daddy of them all:
  
You can get a report on the dedup tables:
+
# lshw -class disk
  
# zpool status -D $poolname
+
(Requires the lshw package.)
  
Or more detailed dedup table info:
+
== Getting partition UUID and file-system type ==
  
  # zdb -DDD $poolname
+
  # blkid
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
== Checking for SSD vs magnetic disk ==
  
{|class="wikitable"
+
  # cat /sys/block/sda/queue/rotational
! Abbr  !! Description
 
|-
 
| LSIZE || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== Measure data throughput ==
+
Will be 0 for SSD and 1 for magnetic.
  
Use the 'pv' command from the 'pv' package, e.g.:
+
== Monitoring a ZFS server ==
  
# cat /dev/sda | pv | cat > /dev/null
+
So some commands I run to keep an eye on my new ZFS servers:
  
Or for ZFS:
+
# 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
  
# zfs send data/example | pv | cat > /dev/null
+
If you have a scrub or resilvering in progress you can report on progress with:
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
# watch zpool status -v
  
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 poke about in internals, e.g.:
  
== Report hard disk usage ==
+
# cat /proc/spl/kstat/zfs/arcstats
  
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
+
root@orac:/sys/module/zfs/parameters# tail *
  
== Report hard disk temperatures ==
+
You can report on property values with e.g.:
  
E.g.
+
# zfs get all data
  
# hddtemp /dev/sd[a-e]
+
If you want to get funky:
  
== Burning an ISO image to USB on Mac ==
+
# cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
First insert your USB key and find the appropriate disk with:
+
You can search for ZFS files like e.g. this:
  
  # diskutil list
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
Then unmount it with:
+
You can report history of a zpool:
  
  # diskutil unmountDisk /dev/disk4
+
  # zpool history $poolname
  
Then copy ISO image with 'dd':
+
You can get a report on the dedup tables:
  
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
+
  # zpool status -D $poolname
  
You can get dd to report progress by sending it the SIGINFO signal:
+
Or more detailed dedup table info:
  
  # kill -s info 12345
+
  # zdb -DDD $poolname
  
== Listing all ext4 file systems ==
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
To see a list only of the mounted ext4 file systems:
+
{|class="wikitable"
 
+
! Abbr  !! Description
  # df -t ext4
+
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
 +
 
 +
== How to tell if zfs scrub is running ==
  
= Monitoring disk I/O =
+
You can get the status from the "scan:" line from:
  
There's an app for that! iotop.
+
$ zpool status
  
== Using iotop, top for disks ==
+
== Measure data throughput ==
  
# iotop -oPa
+
Use the 'pv' command from the 'pv' package, e.g.:
  
== Monitor disk I/O for performance issues ==
+
# cat /dev/sda | pv | cat > /dev/null
  
# watch iostat
+
Or for ZFS:
  
Or e.g.
+
# zfs send data/example | pv | cat > /dev/null
  
# watch iostat -xd /dev/sd[abc]
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
Or use groupings like this command for 'tact':
+
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].
  
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
== Report hard disk usage ==
  
= Monitoring a system =
+
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.
  
== Simple ZFS monitoring ==
+
== Report hard disk temperatures ==
  
# watch iostat
+
E.g.
# iotop
+
 
# zpool iostat -v 5
+
  # hddtemp /dev/sd[a-e]
  # watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
== Burning an ISO image to USB on Mac ==
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
First insert your USB key and find the appropriate disk with:
  
  $ cat /sys/class/thermal/thermal_zone*/temp
+
  # diskutil list
  
and:
+
Then unmount it with:
  
  $ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
  # diskutil unmountDisk /dev/disk4
  
== Monitoring CPU temperature ==
+
Then copy ISO image with 'dd':
  
  $ watch sensors
+
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
== Monitoring HDD temperature ==
+
You can get dd to report progress by sending it the SIGINFO signal:
  
For e.g. SATA drives sda to sdd:
+
# kill -s info 12345
  
# watch hddtemp /dev/sd[a-d]
+
== Listing all ext4 file systems ==
  
= ZFS =
+
To see a list only of the mounted ext4 file systems:
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
# df -t ext4
  
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?]
+
== Report hierarchical file system mount points and mount options ==
  
  $ cat /proc/spl/kstat/zfs/arcstats
+
  $ findmnt
  
Then:
+
== Report the mount point for the current working directory ==
  
  c is the target size of the ARC in bytes
+
  $ findmnt "$PWD"
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
= File management =
+
= Monitoring disk I/O =
  
== Listing files by size ==
+
There's an app for that! iotop.
  
Use capital S for Size:
+
== Using iotop, top for disks ==
  
  $ ls -S
+
  # iotop -oPa
  
== Listing only directories ==
+
== Monitor disk I/O for performance issues ==
  
  $ ls -l | egrep '^d'
+
  # watch iostat
  
== Listing only files ==
+
Or e.g.
  
  $ ls -l | egrep -v '^d'
+
  # watch iostat -xd /dev/sd[abc]
  
== Listing hidden files ==
+
Or use groupings like this command for 'tact':
  
  $ ls -al .[!.]*
+
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
== Creating a symbolic link ==
+
= Monitoring a system =
  
$ ln -s /path/to/target link-name
+
== Simple ZFS monitoring ==
  
== Creating a hard-link ==
+
# watch iostat
 
+
# iotop
  $ ln /path/to/target file-name
+
# zpool iostat -v 5
 +
  # watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
== Changing the owner of a file ==
+
= Monitoring temperature =
 +
 
 +
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
 +
 
 +
$ cat /sys/class/thermal/thermal_zone*/temp
  
$ chown user:group <files>
+
and:
  
E.g.
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
$ chown jj5:staff README
+
== Monitoring CPU temperature ==
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
$ watch sensors
  
$ chown -R root:root /etc/*
+
== Monitoring HDD temperature ==
  
== Changing file permissions ==
+
For e.g. SATA drives sda to sdd:
  
{|class="wikitable"
+
# watch hddtemp /dev/sd[a-d]
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
= ZFS =
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
|+ 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].
+
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?]
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  $ cat /proc/spl/kstat/zfs/arcstats
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
Then:
  
  $ chmod 600 my-private-file
+
  c is the target size of the ARC in bytes
  $ chmod go-rwx my-private-file
+
  c_max is the maximum size of the ARC in bytes
  $ chmod u+rw my-private-file
+
  size is the current size of the ARC in bytes
$ chmod +x my-script
 
  
== Updating config files ==
+
== Stopping a ZFS scrub in progress ==
  
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:
+
# zpool scrub -s $pool
  
$ cp old.conf updated.conf
+
e.g. for the 'data' pool:
$ 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.
+
# zpool scrub -s data
  
The merge program is a part of the RCS package. If you don't have it:
+
= File management =
  
$ sudo apt-get install rcs
+
== Listing files by size ==
  
== Listing open files ==
+
Use capital S for Size:
  
Use lsof to list open files. E.g.:
+
$ ls -S
  
# lsof
+
== Listing only directories ==
  
See man lsof for options.
+
$ ls -l | egrep '^d'
  
== List permissions on a whole directory path ==
+
== Listing only files ==
  
E.g.:
+
$ ls -l | egrep -v '^d'
  
$ namei -om /home/jj5/workspace
+
== Listing hidden files ==
  
Outputs:
+
$ ls -al .[!.]*
  
f: /home/jj5/workspace/
+
== Creating a symbolic link ==
  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 ==
+
$ ln -s /path/to/target link-name
  
E.g.:
+
== Creating a hard-link ==
  
  $ cat foo.c | sed '/^\s*$/d' | wc -l
+
  $ ln /path/to/target file-name
  
== Cloning one directory to another with rsync ==
+
== Changing the owner of a file ==
  
E.g.:
+
$ chown user:group <files>
  
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/
+
E.g.
  
== Counting number of files in current directory and all subdirectories ==
+
$ chown jj5:staff README
 +
$ chown root:root *
  
$ ls -AlhR . | egrep '^-' | wc -l
+
To apply recursively into sub-directories use -R,
  
== Counting number of directories in current directory and all subdirectories ==
+
$ chown -R root:root /etc/*
  
$ ls -AlhR . | egrep '^d' | wc -l
+
== Changing file permissions ==
  
== Getting the status of a 'dd' process ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
+
{|class="wikitable"
 
+
|+ Numeric codes
# kill -s info 40947
+
! 0
 
+
| None
The dd process will report its status in the terminal its running in.
+
|-
 
+
! 1
== Transferring a large file via FAT32 file system ==
+
| Execute
 
+
|-
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:
+
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
$ split -b 4000m input.tgz input.tgz-parts-
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
Then copy the small files and reassemble:
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
$ cat input.tgz-parts-* > output.tgz
+
E.g.
  
= NFS =
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== List NFS shares ==
+
== Updating config files ==
  
To e.g. show NFS shares on 'love':
+
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:
  
  $ showmount -e love
+
  $ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
= Compression =
+
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.
  
== How to use pigz with tar ==
+
The merge program is a part of the RCS package. If you don't have it:
  
See [https://stackoverflow.com/a/39904353 here]:
+
$ sudo apt-get install rcs
  
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
== Listing open files ==
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
Use lsof to list open files. E.g.:
  
== Best compression with tar ==
+
# lsof
  
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
+
See man lsof for options.
  
export GZIP=-9
+
== List permissions on a whole directory path ==
tar cvzf file.tar.gz /path/to/directory
 
  
or
+
E.g.:
  
  env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
+
  $ namei -om /home/jj5/workspace
  
== Best parallel compression with pigz ==
+
Outputs:
  
  $ pigz --best
+
  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
  
== Best parallel compression with xz ==
+
== Counting non-blank lines in a file ==
  
$ xz -9e -T 0
+
E.g.:
  
== Reporting compression ratios with xz ==
+
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
e.g.
+
== Cloning one directory to another with rsync ==
  
root@love:/data/image/archive# xz -l *
+
E.g.:
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 =
+
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/
  
== Data used by sym-linked files:
+
== Counting number of files in current directory and all subdirectories ==
  
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:
+
$ ls -AlhR . | egrep '^-' | wc -l
  
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
== Counting number of directories in current directory and all subdirectories ==
  
= File searching =
+
$ ls -AlhR . | egrep '^d' | wc -l
  
== Finding a file with a particular name ==
+
== Getting the status of a 'dd' process ==
  
$ find -iname "*some-part-of-the-file-name*"
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
Will start searching from the current directory, so maybe
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
  $ cd /
+
  # kill -s info 40947
  
first. For a case-sensitive search:
+
The dd process will report its status in the terminal its running in.
  
$ find -name "*eXaCT CaSE*"
+
== Transferring a large file via FAT32 file system ==
  
== Finding a file with particular content ==
+
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:
  
To search in /etc/ for a file with particular content:
+
$ split -b 4000m input.tgz input.tgz-parts-
  
$ grep -R "search-string" /etc/*
+
Then copy the small files and reassemble:
  
To search the current directory for *.cs files containing the word "Up":
+
$ cat input.tgz-parts-* > output.tgz
  
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
== Find the difference between two directories ==
  
== Finding a list of files with particular content ==
+
$ diif -qr $DIR_A $DIR_B
  
E.g. to find all the files with the word 'creativity':
+
= NFS =
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
== List NFS shares ==
  
== Using the locate command to find files ==
+
To e.g. show NFS shares on 'love':
  
  $ locate part-of-filename
+
  $ showmount -e love
  
E.g.
+
= Compression =
  
$ locate texvc
+
== How to use pigz with tar ==
  
== Updating locate command's database ==
+
See [https://stackoverflow.com/a/39904353 here]:
  
  # updatedb
+
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
== Select a random line from a text file ==
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
$ shuf -n 1 input.txt
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
== Extra context for grep ==
+
Fast pack:
  
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:
+
tar -I 'pigz --fast' -cf my.tar.gz whatver
  
$ grep -B 3 -A 1 ...
+
Best pack:
  
= Job control =
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
== Stopping a running process ==
+
Fast unpack:
  
Press Ctrl+Z to stop a running process.
+
tar -I pigz -xf my.tar.gz
  
== Listing current jobs and their status ==
+
== Best compression with tar ==
  
$ jobs
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
== Resuming a stopped job in the backgroud ==
+
export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
To resume a stopped process in the background
+
or
  
  $ bg %1
+
  env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Best parallel compression with pigz ==
  
== Resuming a stopped job in the foreground ==
+
$ pigz --best
  
To resume a stopped process in the foreground
+
== Best parallel compression with xz ==
  
  $ fg %1
+
  $ xz -9e -T 0
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Reporting compression ratios with xz ==
  
== Killing a stopped job ==
+
e.g.
  
To kill a job
+
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
  
$ kill %1
+
= Symbolic-link management =
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Data used by sym-linked files:
  
== Periodically run a program and watch its output ==
+
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:
  
  $ watch /your/command
+
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
= Debian/Ubuntu package management =
+
= File searching =
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
== Finding a file with a particular name ==
  
== configuring debconf ==
+
$ find -iname "*some-part-of-the-file-name*"
  
# dpkg-reconfigure debconf
+
Will start searching from the current directory, so maybe
  
Set priority to low to get asked detailed questions.
+
$ cd /
  
== Showing list of installed packages ==
+
first. For a case-sensitive search:
  
  # dpkg --get-selections
+
  $ find -name "*eXaCT CaSE*"
  
== Searching for installed package ==
+
== Finding a file with particular content ==
  
# dpkg --get-selections | grep package-name
+
To search in /etc/ for a file with particular content:
  
or
+
$ grep -R "search-string" /etc/*
  
# aptitude search package-name
+
To search the current directory for *.cs files containing the word "Up":
  
== Showing which files are installed as part of a package ==
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
# dpkg -L package-name
+
== Finding a list of files with particular content ==
  
== Installing a package ==
+
E.g. to find all the files with the word 'creativity':
  
  # apt-get install package-name
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
== Uninstalling a package ==
+
== Using the locate command to find files ==
  
  # apt-get remove package-name
+
  $ locate part-of-filename
  
== Showing system architecture ==
+
E.g.
  
  $ dpkg --print-architecture
+
  $ locate texvc
  
== Showing which package a file belongs to ==
+
== Updating locate command's database ==
  
  $ which echo
+
  # updatedb
/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 ==
+
== Select a random line from a text file ==
  
  $ apt-cache showpkg coreutils
+
  $ shuf -n 1 input.txt
  
Or for even more information:
+
== Extra context for grep ==
  
$ apt-cache show coreutils
+
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:
  
== List all installed packages with package version info ==
+
$ grep -B 3 -A 1 ...
  
dpkg-query -l
+
= Job control =
  
== Reporting which version of a package is installed ==
+
== Stopping a running process ==
  
$ dpkg -l | grep package-name
+
Press Ctrl+Z to stop a running process.
  
E.g.:
+
== Listing current jobs and their status ==
  
  root@hope:~/letsencrypt# dpkg -l | grep augeas
+
  $ jobs
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 ==
+
== 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').
  
Try the following:
+
== Resuming a stopped job in the foreground ==
  
# apt-get update
+
To resume a stopped process in the foreground
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
$ fg %1
  
$ apt-cache search . | sort -d | less
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
= Networking =
+
== Killing a stopped job ==
  
== net-tools vs iproute2 ==
+
To kill a job
  
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].
+
$ kill %1
  
{|class="wikitable"
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
! 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 ==
+
== Periodically run a program and watch its output ==
  
For servers:
+
$ watch /your/command
  
# service networking restart
+
= Debian/Ubuntu package management =
  
For desktops:
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
# service network-manager restart
+
== configuring debconf ==
  
== Pinging with particular packet size ==
+
# dpkg-reconfigure debconf
  
$ ping -M do -s <packet size in bytes> <host>
+
Set priority to low to get asked detailed questions.
  
E.g.
+
== Showing list of installed packages ==
  
  $ ping -M do -s 1400 charity.progclub.org
+
  # dpkg --get-selections
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Searching for installed package ==
  
  # ip route add <host> dev <interface> advmss <packet size>
+
  # dpkg --get-selections | grep package-name
  
E.g.
+
or
  
  # ip route add 10.0.0.1 dev eth0 advmss 1400
+
  # aptitude search package-name
  
== Dropping configured MMS for a particular IP address ==
+
== Showing which files are installed as part of a package ==
  
  # ip route flush <host>
+
  # dpkg -L package-name
  
E.g.
+
== Installing a package ==
  
  # ip route flush 10.0.0.1
+
  # apt-get install package-name
  
== Listing open ports and socket information ==
+
== Uninstalling a package ==
  
Including which process is listening on which port.
+
# apt-get remove package-name
  
# netstat -tulpn
+
== Showing system architecture ==
  
Or use the 'ss' command:
+
$ dpkg --print-architecture
  
# ss -s
+
== Showing which package a file belongs to ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
$ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
# lsof -Pnl +M -i4
+
== Showing package information ==
  
You might need to install the lsof package:
+
$ apt-cache showpkg coreutils
  
# apt-get install lsof
+
Or for even more information:
  
== Query for DNS MX record ==
+
$ apt-cache show coreutils
  
$ nslookup
+
== List all installed packages with package version info ==
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
dpkg-query -l
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
== Reporting which version of a package is installed ==
  
== Using nmap to list open ports on remote host ==
+
$ dpkg -l | grep package-name
  
To check the 1,000 most common ports:
+
E.g.:
  
  # nmap server.example.com
+
  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
  
Or for a specific port range (e.g. 101 to 102):
+
== Comprehensive upgrade ==
  
# nmap -p 101-102 server.example.com
+
Try the following:
  
Or for all ports (1 to 65,535):
+
# apt-get update
 
+
# apt-get dist-upgrade
  # nmap -p- server.example.com
+
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
  # update-flashplugin-nonfree --install
  
== Network monitoring ==
+
== Searching all available packages ==
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
$ apt-cache search . | sort -d | less
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
== Reporting unattended upgrades status ==
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
You can watch network traffic in real-time with nload:
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
# nload -u M
+
== Searching for Debian packages and versions ==
  
== Reporting network (NIC) speed ==
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
= Networking =
  
# dmesg | grep eth0
+
== Determining throughput between two hosts ==
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
# apt install iperf3
  
== Path MTU discovery ==
+
On the server:
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
# iperf3 -s
  
# tracepath host.example.com
+
On the client:
  
== Listing available Ethernet devices ==
+
# iperf3 -c $SERVER_IP
  
To see a list of NICs available on the host:
+
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].
  
$ cat /proc/net/dev
+
== net-tools vs iproute2 ==
  
Also
+
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].
  
  $ ip link
+
{|class="wikitable"
 +
! legacy net-tools commands
 +
! iproute2 replacement commands
 +
|-
 +
| arp      || ip n (ip neighbor)
 +
|-
 +
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 +
|-
 +
| iptunnel || ip tunnel
 +
|-
 +
| iwconfig || iw
 +
|-
 +
| nameif  || ip link, ifrename
 +
|-
 +
| netstat || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 +
|-
 +
| route    || ip r (ip route)
 +
|}
  
== 59 Linux Networking commands and scripts ==
+
== Restart networking ==
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
For servers:
  
== Links ==
+
# service networking restart
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
For desktops:
  
= IPTables =
+
# service network-manager restart
  
== Applying firewall rules ==
+
== Pinging with particular packet size ==
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
$ ping -M do -s <packet size in bytes> <host>
  
$ sudo vim /etc/iptables.test.rules
+
E.g.
$ 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 =
+
$ ping -M do -s 1400 charity.progclub.org
  
== Denying hosts with ufw ==
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
# ip route add <host> dev <interface> advmss <packet size>
  
= Bind9 =
+
E.g.
  
== Viewing Bind9 querylog ==
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
$ sudo rndc querylog
+
== Dropping configured MMS for a particular IP address ==
$ tail -f /var/log/syslog
 
  
= IPSec =
+
# ip route flush <host>
  
== Disabling IPSec ==
+
E.g.
  
  # setkey -FP
+
  # ip route flush 10.0.0.1
  
= OpenSSL =
+
== Listing open ports and socket information ==
  
== Debugging IMAPS with OpenSSL ==
+
Including which process is listening on which port.
  
  # openssl s_client -connect localhost:993
+
  # netstat -tulpn
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
Or use the 'ss' command:
  
  $ openssl s_client -connect www.example.com:443
+
  # ss -s
  GET /example.html HTTP/1.1
+
  # ss -l
  host: www.example.com
+
  # ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
== Links ==
+
== Listing open IPv4 connections ==
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
# lsof -Pnl +M -i4
  
= Pluggable Authentication Modules (PAM) =
+
You might need to install the lsof package:
  
== Links ==
+
# apt-get install lsof
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
== Query for DNS MX record ==
  
= SSH =
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
== Configuring SSH key login ==
+
== Query for DNS SOA record ==
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
$ ssh-keygen -t rsa
+
== Using nmap to list open ports on remote host ==
  
Copy the public key from the client to the server:
+
To check the 1,000 most common ports:
  
  $ scp ~/.ssh/id_rsa.pub user@example.org:
+
  # nmap server.example.com
 +
 
 +
Or for a specific port range (e.g. 101 to 102):
  
Configure the authorized keys on the server:
+
# nmap -p 101-102 server.example.com
  
$ ssh user@example.org
+
Or for all ports (1 to 65,535):
$ 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 ==
+
# nmap -p- server.example.com
  
For example, connecting a remote MySQL server to the localhost:
+
== Network monitoring ==
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
# 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
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
== nload ==
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
You can watch network traffic in real-time with nload:
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
# nload -u M
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
== Reporting network (NIC) speed ==
  
* run putty.exe
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
To see what's going on with your ssh connections,
+
Note: use ifconfig to get device name.
  
$ ssh -v user@host
+
== Path MTU discovery ==
  
Or
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
  $ ssh -vv user@host
+
  # tracepath host.example.com
  
== Unlocking SSH key for session ==
+
== Listing available Ethernet devices ==
  
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
To see a list of NICs available on the host:
[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 ==
+
$ cat /proc/net/dev
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
Also
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
$ ip link
  
== cat EOF ==
+
== 59 Linux Networking commands and scripts ==
  
$ cat > output <<EOF
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
> text
 
> EOF
 
  
$ cat output
+
== Links ==
text
 
  
= Script =
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
== Creating a session log with script ==
+
= IPTables =
  
$ script -t 2> timing
+
== Applying firewall rules ==
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
== Replaying a scripted session ==
+
$ 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
  
$ scriptreplay timing
+
== Blocking an IP address with iptables ==
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
To drop IP address 1.2.3.4:
  
= Screen =
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
== Creating a new screen or reconnecting to a detached screen ==
+
= ufw =
  
$ screen -R
+
== Denying hosts with ufw ==
  
== Detaching a screen ==
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
$ screen -D
+
= Bind9 =
  
== Reconnecting to screen ==
+
== Viewing Bind9 querylog ==
  
  $ screen -D
+
  $ sudo rndc querylog
  $ screen -R
+
  $ tail -f /var/log/syslog
  
I have a script in ~/bin/reconnect like so,
+
= IPSec =
  
#!/bin/bash
+
== Disabling IPSec ==
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
# setkey -FP
  
== Scrolling in screen ==
+
= OpenSSL =
  
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.
+
== Debugging IMAPS with OpenSSL ==
  
= tmux =
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
== Live collaboration with tmux ==
+
== Debugging HTTPS with OpenSSL ==
  
User A:
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
tmux -S /tmp/collab
+
== Links ==
chmod 777 /tmp/collab
 
  
User B:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
tmux -S /tmp/collab attach
+
= Pluggable Authentication Modules (PAM) =
  
= Vim =
+
== Links ==
  
== First, why Vim? ==
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
= SSH =
  
== Visual modes ==
+
== Configuring SSH key login ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
== Configuring spaces instead of tabs ==
+
$ ssh-keygen -t rsa
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
Copy the public key from the client to the server:
  
  $ vim ~/.vimrc
+
  $ scp ~/.ssh/id_rsa.pub user@example.org:
  
and include the following lines:
+
Configure the authorized keys on the server:
  
  set tabstop=2
+
  $ ssh user@example.org
  set shiftwidth=2
+
  $ mkdir ~/.ssh
  set expandtab
+
  $ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
== Configuring syntax highlighting ==
+
== Tunneling over SSH ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
For example, connecting a remote MySQL server to the localhost:
  
Use:
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
:syntax on
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
to turn on syntax highlighting.
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
Use:
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
:syntax off
+
== Tunneling over SSH with PuTTY ==
  
to turn off syntax highlighting.
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
To always use syntax highlighting:
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
$ vim ~/.vimrc
+
== Enabling verbose SSH logging ==
  
and add:
+
To see what's going on with your ssh connections,
  
  syntax on
+
  $ ssh -v user@host
  
To get a list of supported colour schemes open vim and type:
+
Or
  
  :colorscheme[space][Ctrl+D]
+
  $ ssh -vv user@host
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
== Unlocking SSH key for session ==
  
  colorscheme desert
+
  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'
  
== Inserting a TAB character when expandtab is on ==
+
== Links ==
  
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.
+
* [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]
  
Press Ctrl+V TAB to insert a literal tab character.
+
= Standard IO =
  
Or you can disable tab expansion altogether with:
+
== cat EOF ==
  
  :set expandtab!
+
  $ cat > output <<EOF
 +
> text
 +
> EOF
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
$ cat output
 +
text
  
:%s/^\s*/&&/g
+
= Script =
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
== Creating a session log with script ==
  
== Recording and replaying a macro ==
+
$ script -t 2> timing
  
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 "@@".
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
== Deleting to end of line ==
+
== Replaying a scripted session ==
  
  d$
+
  $ scriptreplay timing
  
== Deleting to beginning of line ==
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
d^
+
= Screen =
  
== Finding text ==
+
== Creating a new screen or reconnecting to a detached screen ==
  
To search forward for "text":
+
$ screen -R
  
/text
+
== Detaching a screen ==
  
To search backward for "text":
+
$ screen -D
  
?text
+
== Reconnecting to screen ==
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
$ screen -D
 +
$ screen -R
  
== Finding and replacing text ==
+
I have a script in ~/bin/reconnect like so,
  
To replace the first instance of "search" on the current line with "destroy":
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
:s/search/destroy/
+
This will detach your last screen, and reconnect it on the current terminal.
  
To replace all instances of "search" on the current line with "destroy":
+
== Scrolling in screen ==
  
:s/search/destroy/g
+
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.
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
= tmux =
  
:13,37 s/search/destroy/g
+
== Live collaboration with tmux ==
  
To replace all instances of "search" in the entire file with "destroy":
+
User A:
  
  :%s/search/destroy/g
+
  tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
User B:
  
To set the line-ending to Unix line endings run the command:
+
tmux -S /tmp/collab attach
  
:setlocal ff=unix
+
= Vim =
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
== First, why Vim? ==
  
== Disabling auto-indent etc. to paste from clipboard ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
To disable smart indenting when you're going to paste in text:
+
== Visual modes ==
  
:set paste
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
To turn it off again:
+
== Configuring spaces instead of tabs ==
  
:set nopaste
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
$ vim ~/.vimrc
  
== Positioning windows ==
+
and include the following lines:
  
Use -o for horizontal split, e.g.:
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
vim -o a.txt b.txt
+
== Configuring syntax highlighting ==
  
Use -O for vertical split, e.g.:
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
vim -o a.txt b.txt
+
Use:
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
:syntax on
  
Use ^W and &lt; or &gt; to resize windows.
+
to turn on syntax highlighting.
  
== To indent a block of text in Vim ==
+
Use:
  
Use the > command. E.g. to indent five lines:
+
:syntax off
  
5 > >
+
to turn off syntax highlighting.
  
Press . (dot) to keep indenting.
+
To always use syntax highlighting:
  
Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:
+
$ vim ~/.vimrc
  
> %
+
and add:
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
syntax on
  
== Open a file in a new window/tab ==
+
To get a list of supported colour schemes open vim and type:
  
To open a file on the left hand side:
+
:colorscheme[space][Ctrl+D]
  
:vert new filename.ext
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
colorscheme desert
  
To open a file at the top:
+
== Inserting a TAB character when expandtab is on ==
  
:new filename.ext
+
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
Press Ctrl+V TAB to insert a literal tab character.
  
== Explore files in Vim ==
+
Or you can disable tab expansion altogether with:
  
Enter:
+
:set expandtab!
  
:Explore
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
== Switch between Vim tabs ==
+
:%s/^\s*/&&/g
  
Use gt and gT.
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
== Switch between Vim windows ==
+
== Recording and replaying a macro ==
  
To toggle between open windows use:
+
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 "@@".
  
Ctrl+W W
+
== Deleting to end of line ==
  
To move in a direction use:
+
d$
  
Ctrl+W h/j/k/l
+
== Deleting to beginning of line ==
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
d^
  
== Insert block comment in Vim ==
+
== Finding text ==
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
To search forward for "text":
 +
 
 +
/text
 +
 
 +
To search backward for "text":
  
So it's:
+
?text
  
# Ctrl+V (Note: not Shift+V!)
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
== Finding and replacing text ==
  
To navigate to the matching beginning or end tag use '%'.
+
To replace the first instance of "search" on the current line with "destroy":
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
:s/search/destroy/
  
== Auto-format HTML tags ==
+
To replace all instances of "search" on the current line with "destroy":
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
:s/search/destroy/g
  
# first join all the lines - ggVGgJ
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
# 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 ==
+
:13,37 s/search/destroy/g
  
* [http://www.vim.org/ Vim: the editor]
+
To replace all instances of "search" in the entire file with "destroy":
* [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]
 
  
= Write =
+
:%s/search/destroy/g
  
== Talking to other users on the system ==
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
To set the line-ending to Unix line endings run the command:
  
1. SSH to <username>@<hostname> and login with your username and password.
+
:setlocal ff=unix
  
2. Issue the following command to find out who is logged onto the system:
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
$ who
+
== Disabling auto-indent etc. to paste from clipboard ==
  
3. Issue the following command to talk to a specific user:
+
To disable smart indenting when you're going to paste in text:
  
  $ write <username>
+
  :set paste
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
To turn it off again:
  
= Date =
+
:set nopaste
  
== Reporting the time on the server ==
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
$ date
+
== Positioning windows ==
  
== Reporting UTC time ==
+
Use -o for horizontal split, e.g.:
  
  $ date --utc
+
  vim -o a.txt b.txt
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
Use -O for vertical split, e.g.:
  
  $ date="`date +%F-%H%M%S`"
+
  vim -o a.txt b.txt
  
== Getting the year in four digits ==
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
$ year="`date +%Y`"
+
Use ^W and &lt; or &gt; to resize windows.
  
== Getting the month in two digits ==
+
== To indent a block of text in Vim ==
  
$ month="`date +%m`"
+
Use the > command. E.g. to indent five lines:
  
== Getting the day of the month in two digits ==
+
5 > >
  
$ day="`date +%d`"
+
Press . (dot) to keep indenting.
  
== Getting yesterday's date ==
+
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:
  
  $ date --date='1 day ago' +%Y-%m-%d
+
  > %
  
== Converting Unix time (seconds since epoch) ==
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
For timestamp '1501370200':
+
== Open a file in a new window/tab ==
  
$ date -d @1501370200 +%F-%H%M%S
+
To open a file on the left hand side:
  
== Running timedatectl from systemd ==
+
:vert new filename.ext
  
There's a new command bundled with systmed:
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
# timedatectl
+
To open a file at the top:
  
It reports on (and controls) how the system time is configured.
+
:new filename.ext
  
= MySQL =
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
== Run mysql without authentication/authorisation ==
+
== Explore files in Vim ==
  
# service mysql stop
+
Enter:
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
:Explore
  
# mysql -u root mysql
+
== Switch between Vim tabs ==
  
To stop the unauthenticated service:
+
Use gt and gT.
  
# mysqladmin shutdown
+
== Switch between Vim windows ==
  
Then restart a normal service:
+
To toggle between open windows use:
  
  # service mysql start
+
  Ctrl+W W
  
== Logging all database queries ==
+
To move in a direction use:
  
  # vim /etc/mysql/my.cnf
+
  Ctrl+W h/j/k/l
  
In the [mysqld] section add:
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
log=/tmp/mysql.log
+
== Insert block comment in Vim ==
  
Then:
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
# service mysql restart
+
So it's:
  
Watch the log with:
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
# tail -f /tmp/mysql.log
+
== Navigate to matching tag ==
  
== Dumping a MySQL database ==
+
To navigate to the matching beginning or end tag use '%'.
  
You can dump the database into a file using:
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
== Auto-format HTML tags ==
  
You can create a database using:
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
$ echo create database databasename | mysql -h hostname -u user -p
+
# 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=
  
You can restore a database using:
+
== Links ==
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
* [http://www.vim.org/ Vim: the editor]
 
+
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
# mysql -h localhost -u root --password=<password>
+
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
mysql> create user 'username'@'localhost' identified by '<password>';
+
* [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]
  
== Granting all MySQL user permissions ==
+
== Create PDF from text using Vim ==
  
# mysql -h localhost -u root --password=<password>
+
Generate PDF from input.txt with:
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
Examine output with:
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
$ okular doc.pdf
  
Check the SSL version in use:
+
= Write =
  
show status like 'Ssl_version';
+
== Talking to other users on the system ==
  
Or check the cipher in use:
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
show status like 'Ssl_cipher';
+
1. SSH to <username>@<hostname> and login with your username and password.
  
= Apache =
+
2. Issue the following command to find out who is logged onto the system:
  
== Reporting loaded Apache modules ==
+
$ who
  
# apache2ctl -M
+
3. Issue the following command to talk to a specific user:
  
== Maintaining .htaccess passwords ==
+
$ write <username>
  
To add or modify the password for a user:
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
$ htpasswd /etc/apache2/passwd username
+
= Date =
  
== Configuring PHP session timeout in .htaccess ==
+
== Reporting the time on the server ==
  
For a session timeout of 9 hours:
+
$ date
 +
 
 +
== Reporting UTC time ==
  
  php_value session.cookie_lifetime 32400
+
  $ date --utc
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
  php_flag magic_quotes_gpc Off
+
  $ date="`date +%F-%H%M%S`"
  
== Requiring HTTP Auth in .htaccess ==
+
== Getting the year in four digits ==
  
  AuthType Basic
+
  $ year="`date +%Y`"
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
== Getting the month in two digits ==
  
The hard way
+
$ month="`date +%m`"
  
$ sudo /etc/init.d/apache2 restart
+
== Getting the day of the month in two digits ==
  
The graceful way (avoids dropping active connections)
+
$ day="`date +%d`"
  
$ sudo apache2ctl graceful
+
== Getting yesterday's date ==
  
== Allowing directory browsing ==
+
$ date --date='1 day ago' +%Y-%m-%d
  
To show directory index pages, in the apache config file:
+
== Converting Unix time (seconds since epoch) ==
  
<Directory /var/www/data>
+
For timestamp '1501370200':
  Options Indexes
 
</Directory>
 
  
= C =
+
$ date -d @1501370200 +%F-%H%M%S
  
== Locating memset function ==
+
== Running timedatectl from systemd ==
  
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]
+
There's a new command bundled with systmed:
  
== Links ==
+
# timedatectl
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
It reports on (and controls) how the system time is configured.
  
= PHP =
+
= MySQL (and MariaDB) =
  
== Including a file relative to the including file ==
+
== Run mysql without authentication/authorisation ==
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  # service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
== Enabling error reporting ==
+
Then you can connect without a password, e.g.:
  
  error_reporting( E_ALL | E_STRICT );
+
  # mysql -u root mysql
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
To stop the unauthenticated service:
  
  set_error_handler( "error_handler", E_ALL | E_STRICT );
+
  # mysqladmin shutdown
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
Then restart a normal service:
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
# service mysql start
 +
 
 +
== Logging all database queries ==
  
  ini_set( 'html_errors', 'off' );
+
  # vim /etc/mysql/my.cnf
  
== Report PHP modules ==
+
In the [mysqld] section add:
  
  $ php -m
+
  log=/tmp/mysql.log
  
== PHP Security Best Practices For Sys Admins ==
+
Then:
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
# service mysql restart
  
= BASH scripting =
+
Watch the log with:
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
# tail -f /tmp/mysql.log
  
== Telling a script to run in bash ==
+
Or:
  
The first line of the file should be:
+
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
#!/bin/bash
+
my_logs.txt will be in /var/lib/mysql
  
== Checking if a command-line argument was passed in ==
+
== Dumping a MySQL database ==
  
  if [ -n "$1" ]; then
+
You can dump the database into a file using:
  echo "Missing parameter 1.";
+
   
  exit 1;
+
  $ mysqldump -h hostname -u user --password=password databasename > filename
  fi
 
  
== Checking if a command-line argument was not passed in ==
+
== Loading a MySQL database from a dump file ==
  
if [ "$1" = "" ]; then
+
You can create a database using:
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
$ echo create database databasename | mysql -h hostname -u user -p
  
  if [ -z "$1" ]; then
+
You can restore a database using:
  echo "Missing parameter 1.";
+
   
  exit 1;
+
  $ mysql -h hostname -u user --password=password databasename < filename
  fi
 
  
== Checking command exit status ==
+
== Creating a MySQL user ==
  
  cd /my/path
+
  # mysql -h localhost -u root --password=<password>
  if [ "$?" -ne "0" ]; then
+
  mysql> create user 'username'@'localhost' identified by '<password>';
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
== Granting all MySQL user permissions ==
  
Check if file exists:
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
if [ -f "/my/file" ]; then
+
== Select domain name from email address ==
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
if [ ! -f "/my/file" ]; then
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
Check the SSL version in use:
  
Check if directory exists:
+
show status like 'Ssl_version';
  
if [ -d "/my/dir" ]; then
+
Or check the cipher in use:
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
show status like 'Ssl_cipher';
  
if [ ! -d "/my/dir" ]; then
+
== Report on server config ==
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
  
To keep only the latest five backups:
+
SHOW VARIABLES
  
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
+
and
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
SHOW STATUS
  
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.
+
and
  
== Changing into the script's directory ==
+
SHOW PROCESSLIST
  
cd "`dirname $0`"
+
== Monitor MySQL activity ==
  
== Getting the absolute path of a relative path ==
+
$ watch "mysql -t -e 'show processlist'"
  
readlink -f ./some/path
+
= Apache =
  
== Creating a temp directory ==
+
== Reporting loaded Apache modules ==
  
  dir=`mktemp -d` && cd $dir
+
  # apache2ctl -M
  
== Reading secret input from stdin ==
+
== Maintaining .htaccess passwords ==
  
You can read a secret, such as a password, like this:
+
To add or modify the password for a user:
  
  echo -n "Enter passphrase: "
+
  $ htpasswd /etc/apache2/passwd username
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Configuring PHP session timeout in .htaccess ==
  
== String replacements in bash ==
+
For a session timeout of 9 hours:
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
result=${var/find/replace}
+
== Disabling PHP magic quotes in .htaccess ==
  
To replace all occurrences:
+
php_flag magic_quotes_gpc Off
  
result=${var//find/replace}
+
== Requiring HTTP Auth in .htaccess ==
  
A practical example, get an ISO date and turn it into a path:
+
AuthType Basic
 +
AuthName "Speak Friend And Enter"
 +
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
  
date="$(date +%Y-%m-%d)"
+
== Restarting Apache ==
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
The hard way
  
  cat << EOF > /tmp/yourfilehere
+
  $ sudo /etc/init.d/apache2 restart
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
The graceful way (avoids dropping active connections)
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
$ sudo apache2ctl graceful
  
case $space in
+
== Allowing directory browsing ==
[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 show directory index pages, in the apache config file:
  
To enable dot-file matching in globs, set the dotglob shell option:
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
$ shopt -s dotglob
+
= C =
  
== Stopping a script from running if it previously exited due to error ==
+
== Locating memset function ==
 +
 
 +
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]
  
persistentDataDir=/var/lib/something
+
== Links ==
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 ==
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
ephemeralDataDir=/var/run/something
+
= PHP =
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
== Including a file relative to the including file ==
  
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)].
+
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
== Run a command using arguments that come from an array ==
+
== Enabling error reporting ==
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
#!/bin/bash
+
== Setting an error handler ==
tabs=("first tab" "second tab")
 
args=()
 
for t in "${tabs[@]}" ; do
 
  args+=(-t "$t")
 
done
 
app "${args[@]}"
 
  
= Sed =
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
== Find and replace with sed ==
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
  
To update the current file use '-i'. E.g.:
+
== Disable HTML content in var_dump ==
  
  sed -i 's/search-text/replace-text/' file
+
  ini_set( 'html_errors', 'off' );
  
= Awk =
+
== Report PHP modules ==
  
== Listing IP addresses in an Apache web log ==
+
$ php -m
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
== PHP Security Best Practices For Sys Admins ==
  
== Printing space-separated field ==
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
echo 'no no yes no' | awk '{print $3}'
+
= BASH scripting =
  
== Printing delimited field ==
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
== Telling a script to run in bash ==
  
= Subversion =
+
The first line of the file should be:
  
== Setting svn:externals from the command-line ==
+
#!/bin/bash
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
== Checking if a command-line argument was passed in ==
  
To set an svn:externals from the command-line:
+
if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
== Checking if a command-line argument was not passed in ==
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
svn propset svn:externals -F svn.externals .
+
Or:
  
== Setting svn:ignore from the command line ==
+
if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
== Checking command exit status ==
  
  $ svn propset svn:ignore [file|folder] [path]
+
  cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
Or use a file and apply recursively:
+
== Checking if a file does/doesn't exist ==
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
Check if file exists:
  
= Git =
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
== Showing status of working copy ==
+
Check if file doesn't exist:
  
  git status
+
  if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
  
== Showing repo history ==
+
== Checking if a directory does/doesn't exist ==
  
git log
+
Check if directory exists:
  
== Showing remote repositories (including 'origin') ==
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
git remote -v
+
Check if directory doesn't exist:
  
== Handy git aliases ==
+
if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
Save these to your ~/.gitconfig file.
+
== Deleting old backups ==
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
To keep only the latest five backups:
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f
  
To show only the files that have changed, rather than the full line-by-line content:
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
  dif  = !git diff --name-status
+
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.
  
== Show git remote URL ==
+
== Changing into the script's directory ==
  
  git config --get remote.origin.url
+
  cd "`dirname $0`"
  
= IRC =
+
== Getting the absolute path of a relative path ==
  
== Instructing ChanServ to op an admin ==
+
readlink -f ./some/path
  
/msg ChanServ op #channel user
+
== Creating a temp directory ==
  
E.g.
+
dir=`mktemp -d` && cd $dir
  
/msg ChanServ op #gnurc jj5
+
== Reading secret input from stdin ==
  
Sub 'op' for 'deop' to remove op privilege.
+
You can read a secret, such as a password, like this:
  
= C++ =
+
echo -n "Enter passphrase: "
 +
stty -echo
 +
read passphrase;
 +
stty echo
 +
echo ""
  
== C++ books ==
+
After running the above the secret will be in the $passphrase environment variable.
  
=== Books I want ===
+
== String replacements in bash ==
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
result=${var/find/replace}
* [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 ===
+
To replace all occurrences:
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
result=${var//find/replace}
* [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;
 
  
=== Books I'm not reading ===
+
A practical example, get an ISO date and turn it into a path:
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
date="$(date +%Y-%m-%d)"
** Note: 3ed is obsolete. Buy 4ed (above).
+
work_dir=${date//-//}
  
=== Books I've read ===
+
== Sending a HEREDOC to a file ==
 +
 
 +
cat << EOF > /tmp/yourfilehere
 +
These contents will be written to the file.
 +
        This line is indented.
 +
EOF
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
== Bash case/switch statement ==
  
== C++ blogs/articles ==
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
case $space in
* [http://herbsutter.com/ Herb Sutter's personal blog]
+
[1-6]*)
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
+
  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
  
== C++ performance tips ==
+
== Using dotglob shopt to match dot-files ==
  
* ++c can be faster than c++.
+
To enable dot-file matching in globs, set the dotglob shell option:
* 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 =
+
$ shopt -s dotglob
  
[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.
+
== Stopping a script from running if it previously exited due to error ==
  
== Following a service log ==
+
persistentDataDir=/var/lib/something
 +
alarm() {
 +
  touch $persistentDataDir/alarm
 +
}
 +
trap alarm ERR
 +
[ -f $persistentDataDir/alarm ] && exit 1
  
e.g. for bind9:
+
== Make sure only one instance of a script is running at a time ==
  
  # journalctl -f -u bind9
+
  ephemeralDataDir=/var/run/something
 +
unlock() {
 +
  rmdir $ephemeralDataDir/lock
 +
}
 +
mkdir $ephemeralDataDir/lock || exit 1;
 +
trap unlock EXIT
  
or for everything:
+
== BASH programming advice ==
  
# journalctl -f
+
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)].
  
== System status ==
+
== Run a command using arguments that come from an array ==
  
To see spawned services hierarchy:
+
See [https://unix.stackexchange.com/a/412647/356289 here]:
  
  # systemctl status
+
  #!/bin/bash
 +
tabs=("first tab" "second tab")
 +
args=()
 +
for t in "${tabs[@]}" ; do
 +
  args+=(-t "$t")
 +
done
 +
app "${args[@]}"
  
Or for a specific service e.g.:
+
== Display a CSV in columnar or tabular format ==
  
  # systemctl status networking
+
  $ column -t -s , data.csv
  
= SaltStack =
+
== Maximum command line length ==
  
== Running a command on specified minions ==
+
Technically this is an operating system limit, not a BASH limit.
  
  salt 'host' cmd.run 'update-locale'
+
  $ getconf ARG_MAX    # Get argument limit in bytes/chars
  
== Running a command on all minions ==
+
= Sed =
  
salt '*' cmd.run 'update-locale'
+
== Find and replace with sed ==
  
== Listing active jobs ==
+
To update the current file use '-i'. E.g.:
  
  salt-run jobs.active
+
  sed -i 's/search-text/replace-text/' file
  
== Listing available grains ==
+
= Awk =
  
salt 'example' grains.items
+
== Listing IP addresses in an Apache web log ==
  
== Listing available pillar ==
+
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
  
salt 'example' pillar.items
+
== Printing space-separated field ==
  
== Reporting a grain value ==
+
echo 'no no yes no' | awk '{print $3}'
  
e.g. for the 'mem_total' grain:
+
== Printing delimited field ==
  
  salt '*' grains.item mem_total
+
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
= Subversion =
  
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
== Setting svn:externals from the command-line ==
  
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
  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 =
+
To set an svn:externals from the command-line:
  
== Running user login script (X11/XOrg/XWindows) ==
+
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
  
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:
+
Or to use a file:
  
  [Desktop Entry]
+
  svn propset svn:externals -F svn.externals .
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 ==
+
== Setting svn:ignore from the command line ==
  
{|class="wikitable"
+
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
! 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 =
+
$ svn propset svn:ignore [file|folder] [path]
  
== Mounting a VirtualBox VDI file ==
+
Or use a file and apply recursively:
  
Note: instead of doing this consider booting with a live CD.
+
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
  
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
= Git =
  
Install qemu if necessary:
+
== Showing status of working copy ==
  
  # apt install qemu
+
  git status
  
Then you'll need to load the network block device module:
+
== Showing repo history ==
  
  # rmmod nbd
+
  git log
# modprobe nbd max_part=16
 
  
Attach the .vdi image to one of the nbd you just created:
+
== Showing remote repositories (including 'origin') ==
  
  # qemu-nbd -c /dev/nbd0 drive.vdi
+
  git remote -v
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
== Handy git aliases ==
  
# mount /dev/nbd0p1 /mnt
+
Save these to your ~/.gitconfig file.
  
Once you are done, unmount everything and disconnect the device:
+
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
  
# qemu-nbd -d /dev/nbd0
+
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
  
= Elasticsearch =
+
To show only the files that have changed, rather than the full line-by-line content:
  
== Report on health of your Elasticsearch cluster ==
+
  dif  = !git diff --name-status
  
$ curl http://localhost:9200/_cluster/health?pretty
+
== Show git remote URL ==
  
= Zabbix =
+
git config --get remote.origin.url
  
== Zabbix Agent on Mac OS X ==
+
= 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 ==
  
Download and install agent.
+
=== Books I want ===
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
  
Unload agent with:
+
* [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
  
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
=== Books I own ===
 +
 
 +
* [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;
 +
 
 +
=== Books I'm not reading ===
 +
 
 +
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
 +
 
 +
=== Books I've read ===
 +
 
 +
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
 +
 
 +
== C++ blogs/articles ==
 +
 
 +
* [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]
 +
 
 +
== 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 [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 =
 +
 
 +
[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
 +
 
 +
== 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:
 +
 
 +
<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/