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 56: Line 70:
  
 
  # dmidecode
 
  # 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:
 
Or the grand daddy of them all:
Line 79: 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
 +
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
  
To add a new user on a linux system:
+
== Run commands on PowerShield DEFENDER UPS batteries ==
  
# useradd username
+
You can run "instant commands" using the '''upscmd''' command.
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
  # adduser username
+
  diligence:/srv/salt/conf/app/defender-1200.sls
  
== Adding a user to a group ==
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
To add an existing user to an existing group:
+
$ upscmd -l defender
  
# gpasswd -a username group
+
E.g.:
  
e.g. to add user 'jj5' to the 'sudo' group:
+
jj5@orac:~$ upscmd -l defender
 +
Instant commands supported on UPS [defender]:
 +
 +
beeper.toggle - Toggle the UPS beeper
 +
load.off - Turn off the load immediately
 +
load.on - Turn on the load immediately
 +
shutdown.return - Turn off the load and return when power is back
 +
shutdown.stayoff - Turn off the load and remain off
 +
shutdown.stop - Stop a shutdown in progress
 +
test.battery.start - Start a battery test
 +
test.battery.start.deep - Start a deep battery test
 +
test.battery.start.quick - Start a quick battery test
 +
test.battery.stop - Stop the battery test
  
# gpasswd -a jj5 sudo
+
= Environment =
  
Alternatively you can use adduser, passing the username and group:
+
== Configuring vim as your editor ==
  
# adduser username group
+
Sometimes all you need is:
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
$ export EDITOR=/usr/bin/vim
  
# adduser sclaughl staff
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
== Disabling a user account ==
+
Other times you need to run
  
You can disable a user account with:
+
# update-alternatives --config editor
  
# passwd -l user
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
Note: that's a lower-case L, not a one.
+
== Configuring your locale ==
  
== Enabling a disabled user account ==
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
To can re-enable a locked user account with:
+
= User and group management =
  
# passwd -u user
+
== Adding a user ==
  
== Finding which user you are logged in as ==
+
To add a new user on a linux system:
  
To determine which user you are running as enter the command:
+
# useradd username
 +
# passwd username
  
$ whoami
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
== Finding which groups you are a member of ==
+
# adduser username
  
To find which groups you are a member of:
+
== Adding a user to a group ==
  
$ groups
+
To add an existing user to an existing group:
  
or
+
# gpasswd -a username group
  
$ groups username
+
e.g. to add user 'jj5' to the 'sudo' group:
  
Where 'username' is the username of the user you are querying, e.g.:
+
# gpasswd -a jj5 sudo
  
$ groups jj5
+
Alternatively you can use adduser, passing the username and group:
  
== Finding who else is logged in to the system ==
+
# adduser username group
  
To see who else is logged in,
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
  $ who
+
  # adduser sclaughl staff
  
== Running a command as a particular user ==
+
== Disabling a user account ==
  
To run "svn update" as the user www-data:
+
You can disable a user account with:
  
  $ sudo su -c "svn update" www-data
+
  # passwd -l user
  
== Reporting user and group info for the current user ==
+
Note: that's a lower-case L, not a one.
  
$ id
+
== Enabling a disabled user account ==
  
= Memory management =
+
To can re-enable a locked user account with:
  
== Checking available memory ==
+
# passwd -u user
  
To report memory statistics in megabytes:
+
== Finding which user you are logged in as ==
  
$ free -m
+
To determine which user you are running as enter the command:
  
== Check for swap thrashing ==
+
$ whoami
  
Check your virtual memory status with vmstat:
+
== Finding which groups you are a member of ==
  
$ vmstat
+
To find which groups you are a member of:
  
== Report memory type ==
+
$ groups
  
Report on RAM DIMMs:
+
or
  
  # dmidecode --type 17
+
  $ groups username
  
Report on RAM and CPU cache:
+
Where 'username' is the username of the user you are querying, e.g.:
  
  # lshw -short -C memory
+
  $ groups jj5
  
Or for more detail:
+
== Finding who else is logged in to the system ==
  
# lshw -C memory
+
To see who else is logged in,
  
= Video/display management =
+
$ who
  
== Viewing EDID data for attached monitor ==
+
== Running a command as a particular user ==
  
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
+
To run "svn update" as the user www-data:
  
  $ cd /sys/class/drm
+
  $ sudo su -c "svn update" www-data
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
== Reporting user and group info for the current user ==
  
== Using 'top' for dynamic resource usage reporting ==
+
$ id
  
To run top:
+
= Memory management =
  
$ top
+
== Checking available memory ==
  
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.
+
To report memory statistics in megabytes:
  
To see usage for a specific user run e.g.:
+
$ free -m
  
$ top -u jj5
+
== Check for swap thrashing ==
  
To see full command-line press 'c'.
+
Check your virtual memory status with vmstat:
  
When you're in 'top' you can:
+
$ vmstat
  
* press '1' (one) to toggle CPU aggregation
+
== Report memory type ==
* press < and > to change the sort column
 
  
== Changing memory reporting in 'top' ==
+
Report on RAM DIMMs:
  
To run top:
+
# dmidecode --type 17
  
$ top
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
# lshw -short -C memory
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
Or for more detail:
  
Press 'M' to sort by memory utilisation.
+
# lshw -C memory
  
Press 'm' to switch between various display modes.
+
= Video/display management =
  
== Showing full command-line in 'top' ==
+
== Viewing EDID data for attached monitor ==
  
To see the full command-line for processes run with -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):
  
  $ top -c
+
  $ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
== Listing all processes currently running which were started in your current shell session ==
+
= Process management =
  
$ ps -fl
+
== Using 'top' for dynamic resource usage reporting ==
  
== Killing specific processes ==
+
To run top:
  
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
+
  $ top
  
= Disk 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.
  
== Creating a partition table ==
+
To see usage for a specific user run e.g.:
  
  # parted /dev/xvdf
+
  $ top -u jj5
  
mktable msdos
+
To see full command-line press 'c'.
  
== Creating a partition ==
+
When you're in 'top' you can:
  
# parted /dev/xvdf
+
* press '1' (one) to toggle CPU aggregation
 +
* press < and > to change the sort column
  
u MiB
+
== Changing memory reporting in 'top' ==
mkpart primary 1 100%
 
  
== Creating an ext4 file-system ==
+
To run top:
  
  # mkfs.ext4 /dev/xvdf1
+
  $ top
  
== Listing disk drives ==
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
# fdisk -l
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
(That's an L for "list")
+
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
 
# 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:
+
# parted /dev/xvdf
  
  # watch zpool status -v
+
  u MiB
 +
mkpart primary 1 100%
  
You can poke about in internals, e.g.:
+
== Creating an ext4 file-system ==
  
  # cat /proc/spl/kstat/zfs/arcstats
+
  # mkfs.ext4 /dev/xvdf1
  
root@orac:/sys/module/zfs/parameters# tail *
+
== Listing disk drives ==
  
You can report on property values with e.g.:
+
# fdisk -l
  
# zfs get all data
+
(That's an L for "list")
  
If you want to get funky:
+
== Checking available disk space ==
  
  # cd /tmp
+
  $ df -h
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
== Getting disk information ==
  
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
  # lsblk
  
You can report history of a zpool:
+
And
  
  # zpool history $poolname
+
  # cat /proc/partitions
  
You can get a report on the dedup tables:
+
Or the Grand Daddy of them all:
  
  # zpool status -D $poolname
+
  # lshw -class disk
  
Or more detailed dedup table info:
+
(Requires the lshw package.)
  
# zdb -DDD $poolname
+
== Getting partition UUID and file-system type ==
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
# blkid
  
{|class="wikitable"
+
== Checking for SSD vs magnetic disk ==
! Abbr  !! Description
 
|-
 
| LSIZE  || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== Measure data throughput ==
+
# cat /sys/block/sda/queue/rotational
  
Use the 'pv' command from the 'pv' package, e.g.:
+
Will be 0 for SSD and 1 for magnetic.
  
# cat /dev/sda | pv | cat > /dev/null
+
== Monitoring a ZFS server ==
  
Or for ZFS:
+
So some commands I run to keep an eye on my new ZFS servers:
  
  # zfs send data/example | pv | cat > /dev/null
+
  # top
 
+
# iotop
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
# nethogs
 
+
# watch free -h
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].
+
# watch slabtop -o
 
+
# slabtop
== Report hard disk usage ==
+
# 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
  
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
+
If you have a scrub or resilvering in progress you can report on progress with:
  
== Report hard disk temperatures ==
+
# watch zpool status -v
  
E.g.
+
You can poke about in internals, e.g.:
  
  # hddtemp /dev/sd[a-e]
+
  # cat /proc/spl/kstat/zfs/arcstats
  
== Burning an ISO image to USB on Mac ==
+
root@orac:/sys/module/zfs/parameters# tail *
  
First find the appropriate disk with:
+
You can report on property values with e.g.:
  
  # diskutil list
+
  # zfs get all data
  
Then unmount it with:
+
If you want to get funky:
  
  # diskutil unmountDisk /dev/disk4
+
  # cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
Then copy ISO image with 'dd':
+
You can search for ZFS files like e.g. this:
  
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
= Monitoring disk I/O =
+
You can report history of a zpool:
  
There's an app for that! iotop.
+
# zpool history $poolname
 +
 
 +
You can get a report on the dedup tables:
  
== Using iotop, top for disks ==
+
# zpool status -D $poolname
  
# iotop -oPa
+
Or more detailed dedup table info:
  
== Monitor disk I/O for performance issues ==
+
# zdb -DDD $poolname
  
# watch iostat
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
Or e.g.
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
# watch iostat -xd /dev/sd[abc]
+
== How to tell if zfs scrub is running ==
  
Or use groupings like this command for 'tact':
+
You can get the status from the "scan:" line from:
  
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
  $ zpool status
  
= Monitoring a system =
+
== Measure data throughput ==
  
== Simple ZFS monitoring ==
+
Use the 'pv' command from the 'pv' package, e.g.:
  
  # watch iostat
+
  # cat /dev/sda | pv | cat > /dev/null
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
Or for ZFS:
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
# zfs send data/example | pv | cat > /dev/null
  
$ cat /sys/class/thermal/thermal_zone*/temp
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
and:
+
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].
  
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
== Report hard disk usage ==
  
== Monitoring CPU temperature ==
+
So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.
  
$ watch sensors
+
== Report hard disk temperatures ==
  
== Monitoring HDD temperature ==
+
E.g.
  
For e.g. SATA drives sda to sdd:
+
# hddtemp /dev/sd[a-e]
  
# watch hddtemp /dev/sd[a-d]
+
== Burning an ISO image to USB on Mac ==
  
= ZFS =
+
First insert your USB key and find the appropriate disk with:
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
# diskutil list
  
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?]
+
Then unmount it with:
  
  $ cat /proc/spl/kstat/zfs/arcstats
+
  # diskutil unmountDisk /dev/disk4
  
Then:
+
Then copy ISO image with 'dd':
  
  c is the target size of the ARC in bytes
+
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
= File management =
+
You can get dd to report progress by sending it the SIGINFO signal:
  
== Listing only directories ==
+
# kill -s info 12345
  
$ ls -l | egrep '^d'
+
== Listing all ext4 file systems ==
  
== Listing only files ==
+
To see a list only of the mounted ext4 file systems:
  
  $ ls -l | egrep -v '^d'
+
  # df -t ext4
  
== Listing hidden files ==
+
== Report hierarchical file system mount points and mount options ==
  
  $ ls -al .[!.]*
+
  $ findmnt
  
== Creating a symbolic link ==
+
== Report the mount point for the current working directory ==
  
  $ ln -s /path/to/target link-name
+
  $ findmnt "$PWD"
  
== Creating a hard-link ==
+
= Monitoring disk I/O =
  
$ ln /path/to/target file-name
+
There's an app for that! iotop.
  
== Changing the owner of a file ==
+
== Using iotop, top for disks ==
  
  $ chown user:group <files>
+
  # iotop -oPa
  
E.g.
+
== Monitor disk I/O for performance issues ==
  
  $ chown jj5:staff README
+
  # watch iostat
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
Or e.g.
  
  $ chown -R root:root /etc/*
+
  # watch iostat -xd /dev/sd[abc]
 +
 
 +
Or use groupings like this command for 'tact':
  
== Changing file permissions ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
{|class="wikitable"
+
= Monitoring a system =
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
== Simple ZFS monitoring ==
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
# watch iostat
|+ Numeric codes
+
# iotop
! 0
+
# zpool iostat -v 5
| None
+
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
|-
+
# nethogs
! 1
+
# top
| Execute
+
 
|-
+
= Monitoring temperature =
! 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://askubuntu.com/a/854029 temperature without third-party apps] for:
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  $ cat /sys/class/thermal/thermal_zone*/temp
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
and:
  
  $ chmod 600 my-private-file
+
  $ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
$ chmod go-rwx my-private-file
+
 
$ chmod u+rw my-private-file
+
== Monitoring CPU temperature ==
$ chmod +x my-script
 
  
== Updating config files ==
+
$ watch sensors
  
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:
+
== Monitoring HDD temperature ==
  
$ cp old.conf updated.conf
+
For e.g. SATA drives sda to sdd:
$ 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.
+
# watch hddtemp /dev/sd[a-d]
  
The merge program is a part of the RCS package. If you don't have it:
+
= ZFS =
  
$ sudo apt-get install rcs
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
== Listing open files ==
+
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?]
  
Use lsof to list open files. E.g.:
+
$ cat /proc/spl/kstat/zfs/arcstats
  
# lsof
+
Then:
  
See man lsof for options.
+
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
  
== List permissions on a whole directory path ==
+
== Stopping a ZFS scrub in progress ==
  
E.g.:
+
# zpool scrub -s $pool
  
$ namei -om /home/jj5/workspace
+
e.g. for the 'data' pool:
  
Outputs:
+
# zpool scrub -s data
  
f: /home/jj5/workspace/
+
= File management =
  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 ==
+
== Listing files by size ==
  
E.g.:
+
Use capital S for Size:
  
  $ cat foo.c | sed '/^\s*$/d' | wc -l
+
  $ ls -S
  
== Cloning one directory to another with rsync ==
+
== Listing only directories ==
  
E.g.:
+
$ ls -l | egrep '^d'
  
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/
+
== Listing only files ==
  
== Counting number of files in current directory and all subdirectories ==
+
$ ls -l | egrep -v '^d'
  
$ ls -AlhR . | egrep '^-' | wc -l
+
== Listing hidden files ==
  
== Counting number of directories in current directory and all subdirectories ==
+
$ ls -al .[!.]*
  
$ ls -AlhR . | egrep '^d' | wc -l
+
== Creating a symbolic link ==
  
== Getting the status of a 'dd' process ==
+
$ ln -s /path/to/target link-name
  
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
+
== Creating a hard-link ==
  
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
+
$ ln /path/to/target file-name
  
# kill -s info 40947
+
== Changing the owner of a file ==
  
The dd process will report its status in the terminal its running in.
+
$ chown user:group <files>
  
= Compression =
+
E.g.
  
== How to use pigz with tar ==
+
$ chown jj5:staff README
 +
$ chown root:root *
  
See [https://stackoverflow.com/a/39904353 here]:
+
To apply recursively into sub-directories use -R,
  
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
  $ chown -R root:root /etc/*
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
== Changing file permissions ==
  
== Best parallel compression with pigz ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
$ pigz --best
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
== Best parallel compression with xz ==
+
{|class="wikitable"
 
+
|+ Numeric codes
$ xz -9e -T 0
+
! 0
 +
| None
 +
|-
 +
! 1
 +
| Execute
 +
|-
 +
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
== Reporting compression ratios with xz ==
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
e.g.
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
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 =
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== Data used by sym-linked files:
+
== Updating config 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:
+
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:
  
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
  $ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
= File searching =
+
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.
  
== Finding a file with a particular name ==
+
The merge program is a part of the RCS package. If you don't have it:
  
  $ find -iname "*some-part-of-the-file-name*"
+
  $ sudo apt-get install rcs
  
Will start searching from the current directory, so maybe
+
== Listing open files ==
  
$ cd /
+
Use lsof to list open files. E.g.:
  
first. For a case-sensitive search:
+
# lsof
  
$ find -name "*eXaCT CaSE*"
+
See man lsof for options.
  
== Finding a file with particular content ==
+
== List permissions on a whole directory path ==
  
To search in /etc/ for a file with particular content:
+
E.g.:
  
  $ grep -R "search-string" /etc/*
+
  $ namei -om /home/jj5/workspace
  
To search the current directory for *.cs files containing the word "Up":
+
Outputs:
  
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
  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
  
== Finding a list of files with particular content ==
+
== Counting non-blank lines in a file ==
  
E.g. to find all the files with the word 'creativity':
+
E.g.:
  
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
  $ cat foo.c | sed '/^\s*$/d' | wc -l
  
== Using the locate command to find files ==
+
== Cloning one directory to another with rsync ==
  
$ locate part-of-filename
+
E.g.:
  
E.g.
+
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
  
$ locate texvc
+
== Counting number of files in current directory and all subdirectories ==
  
== Updating locate command's database ==
+
$ ls -AlhR . | egrep '^-' | wc -l
  
# updatedb
+
== Counting number of directories in current directory and all subdirectories ==
  
== Select a random line from a text file ==
+
$ ls -AlhR . | egrep '^d' | wc -l
  
$ shuf -n 1 input.txt
+
== Getting the status of a 'dd' process ==
  
== Extra context for grep ==
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
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:
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
  $ grep -B 3 -A 1 ...
+
  # kill -s info 40947
  
= Job control =
+
The dd process will report its status in the terminal its running in.
  
== Stopping a running process ==
+
== Transferring a large file via FAT32 file system ==
  
Press Ctrl+Z to stop a running process.
+
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
  
== Listing current jobs and their status ==
+
$ split -b 4000m input.tgz input.tgz-parts-
  
$ jobs
+
Then copy the small files and reassemble:
  
== Resuming a stopped job in the backgroud ==
+
$ cat input.tgz-parts-* > output.tgz
  
To resume a stopped process in the background
+
== Find the difference between two directories ==
  
  $ bg %1
+
  $ diif -qr $DIR_A $DIR_B
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
= NFS =
  
== Resuming a stopped job in the foreground ==
+
== List NFS shares ==
  
To resume a stopped process in the foreground
+
To e.g. show NFS shares on 'love':
  
  $ fg %1
+
  $ showmount -e love
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
= Compression =
  
== Killing a stopped job ==
+
== How to use pigz with tar ==
  
To kill a job
+
See [https://stackoverflow.com/a/39904353 here]:
  
  $ kill %1
+
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
 
 
== Periodically run a program and watch its output ==
 
  
$ watch /your/command
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
= Debian/Ubuntu package management =
+
Fast pack:
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
tar -I 'pigz --fast' -cf my.tar.gz whatver
  
== configuring debconf ==
+
Best pack:
  
  # dpkg-reconfigure debconf
+
  tar -I 'pigz --best' -cf my.tar.gz whatver
  
Set priority to low to get asked detailed questions.
+
Fast unpack:
  
== Showing list of installed packages ==
+
tar -I pigz -xf my.tar.gz
  
# dpkg --get-selections
+
== Best compression with tar ==
  
== Searching for installed package ==
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
  # dpkg --get-selections | grep package-name
+
  export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
 
or
 
or
  
  # aptitude search package-name
+
  env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
== Showing which files are installed as part of a package ==
+
== Best parallel compression with pigz ==
  
  # dpkg -L package-name
+
  $ pigz --best
  
== Installing a package ==
+
== Best parallel compression with xz ==
  
  # apt-get install package-name
+
  $ xz -9e -T 0
  
== Uninstalling a package ==
+
== Reporting compression ratios with xz ==
  
# apt-get remove package-name
+
e.g.
  
== Showing system architecture ==
+
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
  
$ dpkg --print-architecture
+
= Symbolic-link management =
  
== Showing which package a file belongs to ==
+
== Data used by sym-linked files:
  
$ which echo
+
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:
/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 ==
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
$ apt-cache showpkg coreutils
+
= File searching =
  
Or for even more information:
+
== Finding a file with a particular name ==
  
  $ apt-cache show coreutils
+
  $ find -iname "*some-part-of-the-file-name*"
  
== List all installed packages with package version info ==
+
Will start searching from the current directory, so maybe
  
  dpkg-query -l
+
  $ cd /
  
== Reporting which version of a package is installed ==
+
first. For a case-sensitive search:
  
  $ dpkg -l | grep package-name
+
  $ find -name "*eXaCT CaSE*"
  
E.g.:
+
== Finding a file with particular content ==
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
To search in /etc/ for a file with particular content:
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 ==
+
$ grep -R "search-string" /etc/*
  
Try the following:
+
To search the current directory for *.cs files containing the word "Up":
  
  # apt-get update
+
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
== Finding a list of files with particular content ==
  
$ apt-cache search . | sort -d | less
+
E.g. to find all the files with the word 'creativity':
  
= Networking =
+
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
== net-tools vs iproute2 ==
+
== Using the locate command to find files ==
  
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].
+
$ locate part-of-filename
  
{|class="wikitable"
+
E.g.
! 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 ==
+
$ locate texvc
  
For servers:
+
== Updating locate command's database ==
  
  # service networking restart
+
  # updatedb
  
For desktops:
+
== Select a random line from a text file ==
  
  # service network-manager restart
+
  $ shuf -n 1 input.txt
  
== Pinging with particular packet size ==
+
== Extra context for grep ==
  
$ ping -M do -s <packet size in bytes> <host>
+
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
  
E.g.
+
$ grep -B 3 -A 1 ...
  
$ ping -M do -s 1400 charity.progclub.org
+
= Job control =
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Stopping a running process ==
  
# ip route add <host> dev <interface> advmss <packet size>
+
Press Ctrl+Z to stop a running process.
  
E.g.
+
== Listing current jobs and their status ==
  
  # ip route add 10.0.0.1 dev eth0 advmss 1400
+
  $ jobs
  
== Dropping configured MMS for a particular IP address ==
+
== Resuming a stopped job in the backgroud ==
  
# ip route flush <host>
+
To resume a stopped process in the background
  
E.g.
+
$ bg %1
  
# ip route flush 10.0.0.1
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Listing open ports and socket information ==
+
== Resuming a stopped job in the foreground ==
  
Including which process is listening on which port.
+
To resume a stopped process in the foreground
  
  # netstat -tulpn
+
  $ fg %1
  
Or use the 'ss' command:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
# ss -s
+
== Killing a stopped job ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
To kill a job
  
  # lsof -Pnl +M -i4
+
  $ kill %1
  
You might need to install the lsof package:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
# apt-get install lsof
+
== Periodically run a program and watch its output ==
  
== Query for DNS MX record ==
+
$ watch /your/command
  
$ nslookup
+
= Debian/Ubuntu package management =
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
== configuring debconf ==
  
== Using nmap to list open ports on remote host ==
+
# dpkg-reconfigure debconf
  
To check the 1,000 most common ports:
+
Set priority to low to get asked detailed questions.
  
# nmap server.example.com
+
== Showing list of installed packages ==
  
Or for a specific port range (e.g. 101 to 102):
+
# dpkg --get-selections
  
# nmap -p 101-102 server.example.com
+
== Searching for installed package ==
  
Or for all ports (1 to 65,535):
+
# dpkg --get-selections | grep package-name
  
# nmap -p- server.example.com
+
or
  
== Network monitoring ==
+
# aptitude search package-name
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
== Showing which files are installed as part of a package ==
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
# dpkg -L package-name
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
== Installing a package ==
  
You can watch network traffic in real-time with nload:
+
# apt-get install package-name
  
# nload -u M
+
== Uninstalling a package ==
  
== Reporting network (NIC) speed ==
+
# apt-get remove package-name
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
== Showing system architecture ==
  
  # dmesg | grep eth0
+
  $ dpkg --print-architecture
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
== Showing which package a file belongs to ==
  
== Path MTU discovery ==
+
$ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
== Showing package information ==
  
  # tracepath host.example.com
+
  $ apt-cache showpkg coreutils
  
== Listing available Ethernet devices ==
+
Or for even more information:
  
To see a list of NICs available on the host:
+
$ apt-cache show coreutils
  
$ cat /proc/net/dev
+
== List all installed packages with package version info ==
  
Also
+
dpkg-query -l
  
$ ip link
+
== Reporting which version of a package is installed ==
  
== 59 Linux Networking commands and scripts ==
+
$ dpkg -l | grep package-name
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
E.g.:
  
== Links ==
+
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
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
== Comprehensive upgrade ==
  
= IPTables =
+
Try the following:
  
== Applying firewall rules ==
+
# apt-get update
 +
# apt-get dist-upgrade
 +
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
== Searching all available packages ==
  
  $ sudo vim /etc/iptables.test.rules
+
  $ apt-cache search . | sort -d | less
$ 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 =
+
== Reporting unattended upgrades status ==
  
== Denying hosts with ufw ==
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
= Bind9 =
+
== Searching for Debian packages and versions ==
  
== Viewing Bind9 querylog ==
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
$ sudo rndc querylog
+
= Networking =
$ tail -f /var/log/syslog
 
  
= IPSec =
+
== Determining throughput between two hosts ==
  
== Disabling IPSec ==
+
# apt install iperf3
  
# setkey -FP
+
On the server:
  
= OpenSSL =
+
# iperf3 -s
  
== Debugging IMAPS with OpenSSL ==
+
On the client:
  
  # openssl s_client -connect localhost:993
+
  # iperf3 -c $SERVER_IP
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
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].
  
$ openssl s_client -connect www.example.com:443
+
== net-tools vs iproute2 ==
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
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].
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
{|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)
 +
|}
  
= Pluggable Authentication Modules (PAM) =
+
== Restart networking ==
  
== Links ==
+
For servers:
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
# service networking restart
  
= SSH =
+
For desktops:
  
== Configuring SSH key login ==
+
# service network-manager restart
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
== Pinging with particular packet size ==
  
  $ ssh-keygen -t rsa
+
  $ ping -M do -s <packet size in bytes> <host>
  
Copy the public key from the client to the server:
+
E.g.
  
  $ scp ~/.ssh/id_rsa.pub user@example.org:
+
  $ ping -M do -s 1400 charity.progclub.org
  
Configure the authorized keys on the server:
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
  $ ssh user@example.org
+
  # ip route add <host> dev <interface> advmss <packet size>
$ 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 ==
+
E.g.
  
For example, connecting a remote MySQL server to the localhost:
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
== Dropping configured MMS for a particular IP address ==
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
# ip route flush <host>
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
E.g.
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
# ip route flush 10.0.0.1
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
== Listing open ports and socket information ==
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
Including which process is listening on which port.
  
* run putty.exe
+
# netstat -tulpn
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
Or use the 'ss' command:
  
To see what's going on with your ssh connections,
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
$ ssh -v user@host
+
== Listing open IPv4 connections ==
  
Or
+
# lsof -Pnl +M -i4
  
$ ssh -vv user@host
+
You might need to install the lsof package:
  
== Unlocking SSH key for session ==
+
# apt-get install lsof
  
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
== Query for DNS MX record ==
[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 ==
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
== Query for DNS SOA record ==
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
== cat EOF ==
+
== Using nmap to list open ports on remote host ==
  
$ cat > output <<EOF
+
To check the 1,000 most common ports:
> text
 
> EOF
 
  
  $ cat output
+
  # nmap server.example.com
text
 
  
= Script =
+
Or for a specific port range (e.g. 101 to 102):
  
== Creating a session log with script ==
+
# nmap -p 101-102 server.example.com
  
$ script -t 2> timing
+
Or for all ports (1 to 65,535):
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
# nmap -p- server.example.com
  
== Replaying a scripted session ==
+
== Network monitoring ==
  
$ scriptreplay timing
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
# 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
  
= Screen =
+
== nload ==
  
== Creating a new screen or reconnecting to a detached screen ==
+
You can watch network traffic in real-time with nload:
  
  $ screen -R
+
  # nload -u M
  
== Detaching a screen ==
+
== Reporting network (NIC) speed ==
  
$ screen -D
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
== Reconnecting to screen ==
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
$ screen -D
+
Note: use ifconfig to get device name.
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
== Path MTU discovery ==
  
#!/bin/bash
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
# tracepath host.example.com
  
== Scrolling in screen ==
+
== Listing available Ethernet devices ==
  
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 see a list of NICs available on the host:
  
= Vim =
+
$ cat /proc/net/dev
  
== First, why Vim? ==
+
Also
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
$ ip link
  
== Visual modes ==
+
== 59 Linux Networking commands and scripts ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
== Configuring spaces instead of tabs ==
+
== Links ==
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
$ vim ~/.vimrc
+
= IPTables =
  
and include the following lines:
+
== Applying firewall rules ==
  
set tabstop=2
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
$ 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
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
== Blocking an IP address with iptables ==
  
Use:
+
To drop IP address 1.2.3.4:
  
  :syntax on
+
  # iptables -A INPUT -s 1.2.3.4 -j DROP
  
to turn on syntax highlighting.
+
= ufw =
  
Use:
+
== Denying hosts with ufw ==
  
:syntax off
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
to turn off syntax highlighting.
+
= Bind9 =
  
To always use syntax highlighting:
+
== Viewing Bind9 querylog ==
  
  $ vim ~/.vimrc
+
  $ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
and add:
+
= IPSec =
  
syntax on
+
== Disabling IPSec ==
  
To get a list of supported colour schemes open vim and type:
+
# setkey -FP
  
:colorscheme[space][Ctrl+D]
+
= OpenSSL =
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
== Debugging IMAPS with OpenSSL ==
  
  colorscheme desert
+
  # openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
== Inserting a TAB character when expandtab is on ==
+
== Debugging HTTPS with OpenSSL ==
  
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.
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
Press Ctrl+V TAB to insert a literal tab character.
+
== Links ==
  
Or you can disable tab expansion altogether with:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
:set expandtab!
+
= Pluggable Authentication Modules (PAM) =
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
== Links ==
  
:%s/^\s*/&&/g
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
= SSH =
  
== Recording and replaying a macro ==
+
== Configuring SSH key login ==
  
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 "@@".
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
== Deleting to end of line ==
+
$ ssh-keygen -t rsa
  
d$
+
Copy the public key from the client to the server:
  
== Deleting to beginning of line ==
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
d^
+
Configure the authorized keys on the server:
  
== Finding text ==
+
$ 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
  
To search forward for "text":
+
== Tunneling over SSH ==
  
/text
+
For example, connecting a remote MySQL server to the localhost:
  
To search backward for "text":
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
?text
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
== Finding and replacing text ==
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
To replace the first instance of "search" on the current line with "destroy":
+
== Tunneling over SSH with PuTTY ==
  
:s/search/destroy/
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
To replace all instances of "search" on the current line with "destroy":
+
* run putty.exe
 
+
* Connection -> SSH -> Tunnels
:s/search/destroy/g
+
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
== Enabling verbose SSH logging ==
  
:13,37 s/search/destroy/g
+
To see what's going on with your ssh connections,
  
To replace all instances of "search" in the entire file with "destroy":
+
$ ssh -v user@host
  
:%s/search/destroy/g
+
Or
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
$ ssh -vv user@host
  
To set the line-ending to Unix line endings run the command:
+
== Unlocking SSH key for session ==
  
  :setlocal ff=unix
+
  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'
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
== Links ==
  
== Disabling auto-indent etc. to paste from clipboard ==
+
* [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]
  
To disable smart indenting when you're going to paste in text:
+
= Standard IO =
  
:set paste
+
== cat EOF ==
  
To turn it off again:
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  :set nopaste
+
  $ cat output
 +
text
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
= Script =
  
== Positioning windows ==
+
== Creating a session log with script ==
  
Use -o for horizontal split, e.g.:
+
$ script -t 2> timing
  
vim -o a.txt b.txt
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
Use -O for vertical split, e.g.:
+
== Replaying a scripted session ==
  
  vim -o a.txt b.txt
+
  $ scriptreplay timing
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
Use ^W and &lt; or &gt; to resize windows.
+
= Screen =
  
== To indent a block of text in Vim ==
+
== Creating a new screen or reconnecting to a detached screen ==
  
Use the > command. E.g. to indent five lines:
+
$ screen -R
  
5 > >
+
== Detaching a screen ==
  
Press . (dot) to keep indenting.
+
$ screen -D
  
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:
+
== Reconnecting to screen ==
  
  > %
+
  $ screen -D
 +
$ screen -R
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
I have a script in ~/bin/reconnect like so,
  
== Open a file in a new window/tab ==
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
To open a file on the left hand side:
+
This will detach your last screen, and reconnect it on the current terminal.
  
:vert new filename.ext
+
== Scrolling in screen ==
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
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 open a file at the top:
+
= tmux =
  
:new filename.ext
+
== Live collaboration with tmux ==
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
User A:
  
== Explore files in Vim ==
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
Enter:
+
User B:
  
  :Explore
+
  tmux -S /tmp/collab attach
  
== Switch between Vim tabs ==
+
= Vim =
  
Use gt and gT.
+
== First, why Vim? ==
  
== Switch between Vim windows ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
To toggle between open windows use:
+
== Visual modes ==
  
Ctrl+W W
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
To move in a direction use:
+
== Configuring spaces instead of tabs ==
  
Ctrl+W h/j/k/l
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
$ vim ~/.vimrc
  
== Insert block comment in Vim ==
+
and include the following lines:
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
So it's:
+
== Configuring syntax highlighting ==
  
# Ctrl+V (Note: not Shift+V!)
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
Use:
  
To navigate to the matching beginning or end tag use '%'.
+
:syntax on
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
to turn on syntax highlighting.
  
== Auto-format HTML tags ==
+
Use:
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
:syntax off
  
# first join all the lines - ggVGgJ
+
to turn off syntax highlighting.
# 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 ==
+
To always use syntax highlighting:
  
* [http://www.vim.org/ Vim: the editor]
+
$ vim ~/.vimrc
* [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 =
+
and add:
  
== Talking to other users on the system ==
+
syntax on
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
To get a list of supported colour schemes open vim and type:
  
1. SSH to <username>@<hostname> and login with your username and password.
+
:colorscheme[space][Ctrl+D]
  
2. Issue the following command to find out who is logged onto the system:
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
  $ who
+
  colorscheme desert
  
3. Issue the following command to talk to a specific user:
+
== Inserting a TAB character when expandtab is on ==
  
$ write <username>
+
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.
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
Press Ctrl+V TAB to insert a literal tab character.
  
= Date =
+
Or you can disable tab expansion altogether with:
  
== Reporting the time on the server ==
+
:set expandtab!
  
$ date
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
== Reporting UTC time ==
+
:%s/^\s*/&&/g
  
$ date --utc
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
== Recording and replaying a macro ==
  
$ date="`date +%F-%H%M%S`"
+
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 "@@".
  
== Getting the year in four digits ==
+
== Deleting to end of line ==
  
  $ year="`date +%Y`"
+
  d$
  
== Getting the month in two digits ==
+
== Deleting to beginning of line ==
  
  $ month="`date +%m`"
+
  d^
  
== Getting the day of the month in two digits ==
+
== Finding text ==
  
$ day="`date +%d`"
+
To search forward for "text":
  
== Getting yesterday's date ==
+
/text
  
$ date --date='1 day ago' +%Y-%m-%d
+
To search backward for "text":
  
== Converting Unix time (seconds since epoch) ==
+
?text
  
For timestamp '1501370200':
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
$ date -d @1501370200 +%F-%H%M%S
+
== Finding and replacing text ==
  
== Running timedatectl from systemd ==
+
To replace the first instance of "search" on the current line with "destroy":
  
There's a new command bundled with systmed:
+
:s/search/destroy/
  
# timedatectl
+
To replace all instances of "search" on the current line with "destroy":
  
It reports on (and controls) how the system time is configured.
+
:s/search/destroy/g
  
= MySQL =
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
== Run mysql without authentication/authorisation ==
+
:13,37 s/search/destroy/g
  
# service mysql stop
+
To replace all instances of "search" in the entire file with "destroy":
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
:%s/search/destroy/g
  
# mysql -u root mysql
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
To stop the unauthenticated service:
+
To set the line-ending to Unix line endings run the command:
  
  # mysqladmin shutdown
+
  :setlocal ff=unix
  
Then restart a normal service:
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
# service mysql start
+
== Disabling auto-indent etc. to paste from clipboard ==
  
== Logging all database queries ==
+
To disable smart indenting when you're going to paste in text:
  
  # vim /etc/mysql/my.cnf
+
  :set paste
  
In the [mysqld] section add:
+
To turn it off again:
  
  log=/tmp/mysql.log
+
  :set nopaste
  
Then:
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
# service mysql restart
+
== Positioning windows ==
  
Watch the log with:
+
Use -o for horizontal split, e.g.:
  
  # tail -f /tmp/mysql.log
+
  vim -o a.txt b.txt
  
== Dumping a MySQL database ==
+
Use -O for vertical split, e.g.:
  
You can dump the database into a file using:
+
  vim -o a.txt b.txt
   
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
You can create a database using:
+
Use ^W and &lt; or &gt; to resize windows.
  
$ echo create database databasename | mysql -h hostname -u user -p
+
== To indent a block of text in Vim ==
  
You can restore a database using:
+
Use the > command. E.g. to indent five lines:
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
5 > >
  
# mysql -h localhost -u root --password=<password>
+
Press . (dot) to keep indenting.
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
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:
  
  # mysql -h localhost -u root --password=<password>
+
  > %
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
== Open a file in a new window/tab ==
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
To open a file on the left hand side:
  
Check the SSL version in use:
+
:vert new filename.ext
  
show status like 'Ssl_version';
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
Or check the cipher in use:
+
To open a file at the top:
  
  show status like 'Ssl_cipher';
+
  :new filename.ext
  
= Apache =
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
== Reporting loaded Apache modules ==
+
== Explore files in Vim ==
  
# apache2ctl -M
+
Enter:
  
== Maintaining .htaccess passwords ==
+
:Explore
  
To add or modify the password for a user:
+
== Switch between Vim tabs ==
  
$ htpasswd /etc/apache2/passwd username
+
Use gt and gT.
  
== Configuring PHP session timeout in .htaccess ==
+
== Switch between Vim windows ==
  
For a session timeout of 9 hours:
+
To toggle between open windows use:
  
  php_value session.cookie_lifetime 32400
+
  Ctrl+W W
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
To move in a direction use:
  
  php_flag magic_quotes_gpc Off
+
  Ctrl+W h/j/k/l
  
== Requiring HTTP Auth in .htaccess ==
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
AuthType Basic
+
== Insert block comment in Vim ==
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
The hard way
+
So it's:
  
$ sudo /etc/init.d/apache2 restart
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
The graceful way (avoids dropping active connections)
+
== Navigate to matching tag ==
  
$ sudo apache2ctl graceful
+
To navigate to the matching beginning or end tag use '%'.
  
== Allowing directory browsing ==
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
To show directory index pages, in the apache config file:
+
== Auto-format HTML tags ==
  
<Directory /var/www/data>
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  Options Indexes
 
</Directory>
 
  
= C =
+
# 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=
  
== Locating memset function ==
+
== Links ==
  
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]
+
* [http://www.vim.org/ Vim: the editor]
 +
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 +
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 +
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 +
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 +
* [http://vim.wikia.com/wiki/File_format File format]
 +
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 +
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
  
== Links ==
+
== Create PDF from text using Vim ==
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
Generate PDF from input.txt with:
  
= PHP =
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
== Including a file relative to the including file ==
+
Examine output with:
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  $ okular doc.pdf
  
== Enabling error reporting ==
+
= Write =
  
error_reporting( E_ALL | E_STRICT );
+
== Talking to other users on the system ==
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
1. SSH to <username>@<hostname> and login with your username and password.
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
2. Issue the following command to find out who is logged onto the system:
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
$ who
  
ini_set( 'html_errors', 'off' );
+
3. Issue the following command to talk to a specific user:
  
== Report PHP modules ==
+
$ write <username>
  
$ php -m
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
== PHP Security Best Practices For Sys Admins ==
+
= Date =
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
== Reporting the time on the server ==
  
= BASH scripting =
+
$ date
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
== Reporting UTC time ==
  
== Telling a script to run in bash ==
+
$ date --utc
  
The first line of the file should be:
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
  #!/bin/bash
+
  $ date="`date +%F-%H%M%S`"
  
== Checking if a command-line argument was passed in ==
+
== Getting the year in four digits ==
  
  if [ -n "$1" ]; then
+
  $ year="`date +%Y`"
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
== Getting the month in two digits ==
  
  if [ "$1" = "" ]; then
+
  $ month="`date +%m`"
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
== Getting the day of the month in two digits ==
  
  if [ -z "$1" ]; then
+
  $ day="`date +%d`"
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
== Getting yesterday's date ==
  
  cd /my/path
+
  $ date --date='1 day ago' +%Y-%m-%d
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
== Converting Unix time (seconds since epoch) ==
  
Check if file exists:
+
For timestamp '1501370200':
  
  if [ -f "/my/file" ]; then
+
  $ date -d @1501370200 +%F-%H%M%S
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
== Running timedatectl from systemd ==
  
if [ ! -f "/my/file" ]; then
+
There's a new command bundled with systmed:
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
# timedatectl
  
Check if directory exists:
+
It reports on (and controls) how the system time is configured.
  
if [ -d "/my/dir" ]; then
+
= MySQL (and MariaDB) =
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
== Run mysql without authentication/authorisation ==
  
  if [ ! -d "/my/dir" ]; then
+
  # service mysql stop
  mkdir /my/dir
+
  # mysqld_safe --skip-grant-tables &
  fi
 
  
== Deleting old backups ==
+
Then you can connect without a password, e.g.:
  
To keep only the latest five backups:
+
# mysql -u root mysql
  
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 stop the unauthenticated service:
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
# mysqladmin shutdown
  
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.
+
Then restart a normal service:
  
== Changing into the script's directory ==
+
# service mysql start
  
cd "`dirname $0`"
+
== Logging all database queries ==
  
== Getting the absolute path of a relative path ==
+
# vim /etc/mysql/my.cnf
  
readlink -f ./some/path
+
In the [mysqld] section add:
  
== Creating a temp directory ==
+
log=/tmp/mysql.log
  
dir=`mktemp -d` && cd $dir
+
Then:
  
== Reading secret input from stdin ==
+
# service mysql restart
  
You can read a secret, such as a password, like this:
+
Watch the log with:
  
  echo -n "Enter passphrase: "
+
  # tail -f /tmp/mysql.log
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
Or:
  
== String replacements in bash ==
+
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
my_logs.txt will be in /var/lib/mysql
  
  result=${var/find/replace}
+
== Dumping a MySQL database ==
 +
 
 +
You can dump the database into a file using:
 +
   
 +
$ mysqldump -h hostname -u user --password=password databasename > filename
  
To replace all occurrences:
+
== Loading a MySQL database from a dump file ==
  
result=${var//find/replace}
+
You can create a database using:
  
A practical example, get an ISO date and turn it into a path:
+
$ echo create database databasename | mysql -h hostname -u user -p
  
  date="$(date +%Y-%m-%d)"
+
You can restore a database using:
work_dir=${date//-//}
+
 +
  $ mysql -h hostname -u user --password=password databasename < filename
  
== Sending a HEREDOC to a file ==
+
== Creating a MySQL user ==
  
  cat << EOF > /tmp/yourfilehere
+
  # mysql -h localhost -u root --password=<password>
  These contents will be written to the file.
+
  mysql> create user 'username'@'localhost' identified by '<password>';
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
== Granting all MySQL user permissions ==
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
case $space in
+
== Select domain name from email address ==
[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 ==
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
To enable dot-file matching in globs, set the dotglob shell option:
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
$ shopt -s dotglob
+
Check the SSL version in use:
  
== Stopping a script from running if it previously exited due to error ==
+
show status like 'Ssl_version';
  
persistentDataDir=/var/lib/something
+
Or check the cipher in use:
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 ==
+
show status like 'Ssl_cipher';
  
ephemeralDataDir=/var/run/something
+
== Report on server config ==
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
  
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)].
+
SHOW VARIABLES
  
== Run a command using arguments that come from an array ==
+
and
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
SHOW STATUS
  
#!/bin/bash
+
and
tabs=("first tab" "second tab")
 
args=()
 
for t in "${tabs[@]}" ; do
 
  args+=(-t "$t")
 
done
 
app "${args[@]}"
 
  
= Sed =
+
SHOW PROCESSLIST
  
== Find and replace with sed ==
+
== Monitor MySQL activity ==
  
To update the current file use '-i'. E.g.:
+
$ watch "mysql -t -e 'show processlist'"
  
sed -i 's/search-text/replace-text/' file
+
= Apache =
  
= Awk =
+
== Reporting loaded Apache modules ==
  
== Listing IP addresses in an Apache web log ==
+
# apache2ctl -M
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
== Maintaining .htaccess passwords ==
  
== Printing space-separated field ==
+
To add or modify the password for a user:
  
  echo 'no no yes no' | awk '{print $3}'
+
  $ htpasswd /etc/apache2/passwd username
  
== Printing delimited field ==
+
== Configuring PHP session timeout in .htaccess ==
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
For a session timeout of 9 hours:
  
= Subversion =
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
== Setting svn:externals from the command-line ==
+
== Disabling PHP magic quotes in .htaccess ==
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
php_flag magic_quotes_gpc Off
  
To set an svn:externals from the command-line:
+
== Requiring HTTP Auth in .htaccess ==
  
  svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
  AuthType Basic
  svn ci -m 'Adding svn:externals for rdfind-php...'
+
AuthName "Speak Friend And Enter"
svn up
+
AuthUserFile /home/jj5/.htpasswd
 +
  Require valid-user
  
Or to use a file:
+
== Restarting Apache ==
  
svn propset svn:externals -F svn.externals .
+
The hard way
  
== Setting svn:ignore from the command line ==
+
$ sudo /etc/init.d/apache2 restart
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
The graceful way (avoids dropping active connections)
  
  $ svn propset svn:ignore [file|folder] [path]
+
  $ sudo apache2ctl graceful
  
Or use a file and apply recursively:
+
== Allowing directory browsing ==
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
To show directory index pages, in the apache config file:
  
= Git =
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
== Showing status of working copy ==
+
= C =
  
git status
+
== Locating memset function ==
  
== Showing repo history ==
+
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]
  
git log
+
== Links ==
  
== Showing remote repositories (including 'origin') ==
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
git remote -v
+
= PHP =
  
== Handy git aliases ==
+
== Including a file relative to the including file ==
  
Save these to your ~/.gitconfig file.
+
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
== Enabling error reporting ==
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
To show only the files that have changed, rather than the full line-by-line content:
+
== Setting an error handler ==
  
  dif  = !git diff --name-status
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
== Show git remote URL ==
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
 +
 
 +
== Disable HTML content in var_dump ==
  
  git config --get remote.origin.url
+
  ini_set( 'html_errors', 'off' );
  
= IRC =
+
== Report PHP modules ==
  
== Instructing ChanServ to op an admin ==
+
$ php -m
  
/msg ChanServ op #channel user
+
== PHP Security Best Practices For Sys Admins ==
  
E.g.
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
/msg ChanServ op #gnurc jj5
+
= BASH scripting =
  
Sub 'op' for 'deop' to remove op privilege.
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
= C++ =
+
== Telling a script to run in bash ==
  
== C++ books ==
+
The first line of the file should be:
  
=== Books I want ===
+
#!/bin/bash
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== Checking if a command-line argument was passed in ==
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
if [ -n "$1" ]; then
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
+
  echo "Missing parameter 1.";
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
+
  exit 1;
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
+
fi
* [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 ===
+
== Checking if a command-line argument was not passed in ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
if [ "$1" = "" ]; then
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
+
  echo "Missing parameter 1.";
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
+
  exit 1;
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
+
fi
* [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 ===
+
Or:
 +
 
 +
if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
== Checking command exit status ==
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
== Checking if a file does/doesn't exist ==
  
== C++ blogs/articles ==
+
Check if file exists:
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
if [ -f "/my/file" ]; then
* [http://herbsutter.com/ Herb Sutter's personal blog]
+
  cat /my/file
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
+
fi
  
== C++ performance tips ==
+
Check if file doesn't exist:
  
* ++c can be faster than c++.
+
if [ ! -f "/my/file" ]; then
* use const for everything that you possibly can.
+
  touch /my/file
* 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.
+
fi
* 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 =
+
== Checking if a directory does/doesn't exist ==
  
[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.
+
Check if directory exists:
  
== Following a service log ==
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
e.g. for bind9:
+
Check if directory doesn't exist:
  
  # journalctl -f -u bind9
+
  if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
or for everything:
+
== Deleting old backups ==
  
# journalctl -f
+
To keep only the latest five backups:
  
== System status ==
+
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 see spawned services hierarchy:
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
# systemctl 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.
  
Or for a specific service e.g.:
+
== Changing into the script's directory ==
  
  # systemctl status networking
+
  cd "`dirname $0`"
  
= SaltStack =
+
== Getting the absolute path of a relative path ==
  
== Running a command on specified minions ==
+
readlink -f ./some/path
  
salt 'host' cmd.run 'update-locale'
+
== Creating a temp directory ==
  
== Running a command on all minions ==
+
dir=`mktemp -d` && cd $dir
  
salt '*' cmd.run 'update-locale'
+
== Reading secret input from stdin ==
  
== Listing active jobs ==
+
You can read a secret, such as a password, like this:
  
  salt-run jobs.active
+
  echo -n "Enter passphrase: "
 +
stty -echo
 +
read passphrase;
 +
stty echo
 +
echo ""
  
== Listing available grains ==
+
After running the above the secret will be in the $passphrase environment variable.
  
salt 'example' grains.items
+
== String replacements in bash ==
  
== Listing available pillar ==
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
  
  salt 'example' pillar.items
+
  result=${var/find/replace}
  
== Reporting a grain value ==
+
To replace all occurrences:
  
e.g. for the 'mem_total' grain:
+
result=${var//find/replace}
  
salt '*' grains.item mem_total
+
A practical example, get an ISO date and turn it into a path:
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
== Sending a HEREDOC to a file ==
  
  <nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
  cat << EOF > /tmp/yourfilehere
  file.managed:
+
These contents will be written to the file.
    - template: jinja
+
        This line is indented.
    - user: root
+
EOF
    - 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 =
+
== Bash case/switch statement ==
  
== Running user login script (X11/XOrg/XWindows) ==
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
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:
+
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 ==
  
[Desktop Entry]
+
To enable dot-file matching in globs, set the dotglob shell option:
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 ==
+
$ shopt -s dotglob
  
{|class="wikitable"
+
== Stopping a script from running if it previously exited due to error ==
! 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 =
+
persistentDataDir=/var/lib/something
 +
alarm() {
 +
  touch $persistentDataDir/alarm
 +
}
 +
trap alarm ERR
 +
[ -f $persistentDataDir/alarm ] && exit 1
  
== Mounting a VirtualBox VDI file ==
+
== Make sure only one instance of a script is running at a time ==
  
Note: instead of doing this consider booting with a live CD.
+
ephemeralDataDir=/var/run/something
 +
unlock() {
 +
  rmdir $ephemeralDataDir/lock
 +
}
 +
mkdir $ephemeralDataDir/lock || exit 1;
 +
trap unlock EXIT
  
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
== BASH programming advice ==
  
Install qemu if necessary:
+
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)].
  
# apt install qemu
+
== Run a command using arguments that come from an array ==
  
Then you'll need to load the network block device module:
+
See [https://unix.stackexchange.com/a/412647/356289 here]:
  
  # rmmod nbd
+
  #!/bin/bash
  # modprobe nbd max_part=16
+
  tabs=("first tab" "second tab")
 +
args=()
 +
for t in "${tabs[@]}" ; do
 +
  args+=(-t "$t")
 +
done
 +
app "${args[@]}"
  
Attach the .vdi image to one of the nbd you just created:
+
== Display a CSV in columnar or tabular format ==
  
  # qemu-nbd -c /dev/nbd0 drive.vdi
+
  $ column -t -s , data.csv
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
== Maximum command line length ==
  
# mount /dev/nbd0p1 /mnt
+
Technically this is an operating system limit, not a BASH limit.
  
Once you are done, unmount everything and disconnect the device:
+
$ getconf ARG_MAX    # Get argument limit in bytes/chars
  
# qemu-nbd -d /dev/nbd0
+
= Sed =
  
= Elasticsearch =
+
== Find and replace with sed ==
  
== Report on health of your Elasticsearch cluster ==
+
To update the current file use '-i'. E.g.:
  
  $ curl http://localhost:9200/_cluster/health?pretty
+
  sed -i 's/search-text/replace-text/' file
  
= Zabbix =
+
= Awk =
  
== Zabbix Agent on Mac OS X ==
+
== Listing IP addresses in an Apache web log ==
  
Download and install agent.
+
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 [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ 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 ==
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
  
Unload agent with:
+
$ 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 ===
 +
 
 +
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 +
 
 +
* [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
 +
 
 +
=== 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
 
  # launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
  
Load agent with:
+
Load agent with:
 
+
 
  # launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
+
  # launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 
+
 
To add a 'pki' group:
+
To add a 'pki' group:
 
+
 
  # dseditgroup -o create pki
+
  # dseditgroup -o create pki
 
+
 
To monitor syslog on Mac OS X:
+
To monitor syslog on Mac OS X:
 
+
 
  # tail -f /var/log/system.log
+
  # tail -f /var/log/system.log
 
+
 
== Installing Zabbix Agent from source on Mac OS X ==
+
== 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
 +
|}
 +
 
 +
= XML =
  
Download sources from https://www.zabbix.com/download_sources
+
== How to pretty-print an XML file ==
  
  $ brew update
+
  $ xmllint --format input.xml > output.xml
$ 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 =
+
= ApacheBench =
  
== NetBeans shortcut keys ==
+
== Run a benchmark with ApacheBench ==
  
{|class="wikitable sortable"
+
  $ ab -n 1000 -c 100 https://www.example.com/
! 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/