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 28: Line 46:
  
 
  $ uname -a
 
  $ uname -a
 +
 +
== Determining which Linux kernel you are running ==
 +
 +
$ uname -r
  
 
== Configuring system swappiness ==
 
== Configuring system swappiness ==
Line 44: Line 66:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 56: Line 74:
  
 
  # 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 99:
 
  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:
  
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
+
# cat /proc/cpuinfo
  
= Power =
+
=== RAM info ===
  
== Reporting on PowerShield DEFENDER UPS status ==
+
# dmidecode --type memory
  
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
+
=== PCI info ===
  
  $ upsc defender
+
  # lspci -v
  
E.g.:
+
=== Drive info ===
  
  jj5@orac:~$ upsc defender
+
  # cat /proc/partitions
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 ==
+
and:
  
You can run "instant commands" using the '''upscmd''' command.
+
# hdparm -I /dev/sda
  
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
+
and:
  
  diligence:/srv/salt/conf/app/defender-1200.sls
+
  # smartctl --info /dev/sda
  
To see "instant commands" supported by the PowerShield DEFENDER:
+
You can check if a drive is SSD or not with:
  
  $ upscmd -l defender
+
  # cat /sys/block/sde/queue/rotational
  
E.g.:
+
0=SSD
 +
1=HDD
  
jj5@orac:~$ upscmd -l defender
+
== Viewing syslog and other logs with KSystemLog ==
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 =
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
  
== Configuring vim as your editor ==
+
= CPU =
  
Sometimes all you need is:
+
== Monitoring CPU clock speed ==
  
$ export EDITOR=/usr/bin/vim
+
Try something like this:
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'
  
Other times you need to run
+
= Power =
  
# update-alternatives --config editor
+
== Reporting on PowerShield DEFENDER UPS status ==
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
Before running `upsc` ensure service is running:
  
== Configuring your locale ==
+
# upsdrvctl start
  
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
 
  
= User and group management =
+
$ upsc defender
  
== Adding a user ==
+
E.g.:
  
To add a new user on a linux system:
+
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
  
# useradd username
+
== Run commands on PowerShield DEFENDER UPS batteries ==
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
You can run "instant commands" using the '''upscmd''' command.
  
# adduser username
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
== Adding a user to a group ==
+
diligence:/srv/salt/conf/app/defender-1200.sls
  
To add an existing user to an existing group:
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
  # gpasswd -a username group
+
  $ upscmd -l defender
  
e.g. to add user 'jj5' to the 'sudo' group:
+
E.g.:
  
  # gpasswd -a jj5 sudo
+
  jj5@orac:~$ upscmd -l defender
 +
Instant commands supported on UPS [defender]:
 +
 +
beeper.toggle - Toggle the UPS beeper
 +
load.off - Turn off the load immediately
 +
load.on - Turn on the load immediately
 +
shutdown.return - Turn off the load and return when power is back
 +
shutdown.stayoff - Turn off the load and remain off
 +
shutdown.stop - Stop a shutdown in progress
 +
test.battery.start - Start a battery test
 +
test.battery.start.deep - Start a deep battery test
 +
test.battery.start.quick - Start a quick battery test
 +
test.battery.stop - Stop the battery test
  
Alternatively you can use adduser, passing the username and group:
+
= Service management =
  
# adduser username group
+
== Report running services ==
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
# service --status-all
  
# adduser sclaughl staff
+
= Environment =
  
== Disabling a user account ==
+
== Configuring vim as your editor ==
  
You can disable a user account with:
+
Sometimes all you need is:
  
  # passwd -l user
+
  $ export EDITOR=/usr/bin/vim
  
Note: that's a lower-case L, not a one.
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
== Enabling a disabled user account ==
+
Other times you need to run
  
To can re-enable a locked user account with:
+
# update-alternatives --config editor
  
# passwd -u user
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
== Finding which user you are logged in as ==
+
== Configuring your locale ==
  
To determine which user you are running as enter the command:
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
$ whoami
+
= User and group management =
  
== Finding which groups you are a member of ==
+
== Adding a user ==
  
To find which groups you are a member of:
+
To add a new user on a linux system:
  
  $ groups
+
  # useradd username
 +
# passwd username
  
or
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
  $ groups username
+
  # adduser username
  
Where 'username' is the username of the user you are querying, e.g.:
+
== Adding a user to a group ==
  
$ groups jj5
+
To add an existing user to an existing group:
  
== Finding who else is logged in to the system ==
+
# gpasswd -a username group
  
To see who else is logged in,
+
e.g. to add user 'jj5' to the 'sudo' group:
  
  $ who
+
  # gpasswd -a jj5 sudo
  
== Running a command as a particular user ==
+
Alternatively you can use adduser, passing the username and group:
  
To run "svn update" as the user www-data:
+
# adduser username group
  
$ sudo su -c "svn update" www-data
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
== Reporting user and group info for the current user ==
+
# adduser sclaughl staff
  
$ id
+
== Disabling a user account ==
  
= Memory management =
+
You can disable a user account with:
  
== Checking available memory ==
+
# passwd -l user
  
To report memory statistics in megabytes:
+
Note: that's a lower-case L, not a one.
  
$ free -m
+
== Enabling a disabled user account ==
  
== Check for swap thrashing ==
+
To can re-enable a locked user account with:
  
Check your virtual memory status with vmstat:
+
# passwd -u user
  
$ vmstat
+
== Finding which user you are logged in as ==
  
== Report memory type ==
+
To determine which user you are running as enter the command:
  
Report on RAM DIMMs:
+
$ whoami
  
# dmidecode --type 17
+
== Finding which groups you are a member of ==
  
Report on RAM and CPU cache:
+
To find which groups you are a member of:
  
  # lshw -short -C memory
+
  $ groups
  
Or for more detail:
+
or
  
  # lshw -C memory
+
  $ groups username
  
= Video/display management =
+
Where 'username' is the username of the user you are querying, e.g.:
  
== Viewing EDID data for attached monitor ==
+
$ groups jj5
  
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):
+
== Finding who else is logged in to the system ==
  
$ cd /sys/class/drm
+
To see who else is logged in,
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
$ who
  
== Using 'top' for dynamic resource usage reporting ==
+
== Running a command as a particular user ==
  
To run top:
+
To run "svn update" as the user www-data:
  
  $ top
+
  $ sudo su -c "svn update" www-data
  
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.
+
== Reporting user and group info for the current user ==
  
To see usage for a specific user run e.g.:
+
$ id
  
$ top -u jj5
+
= Memory management =
  
To see full command-line press 'c'.
+
== Checking available memory ==
  
When you're in 'top' you can:
+
To report memory statistics in megabytes:
  
* press '1' (one) to toggle CPU aggregation
+
$ free -m
* press < and > to change the sort column
 
  
== Changing memory reporting in 'top' ==
+
== Check for swap thrashing ==
  
To run top:
+
Check your virtual memory status with vmstat:
  
  $ top
+
  $ vmstat
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
== Report memory type ==
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
Report on RAM DIMMs:
  
Press 'M' to sort by memory utilisation.
+
# dmidecode --type 17
  
Press 'm' to switch between various display modes.
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
== Showing full command-line in 'top' ==
+
# lshw -short -C memory
  
To see the full command-line for processes run with -c:
+
Or for more detail:
  
  $ top -c
+
  # lshw -C memory
  
== Listing all processes currently running which were started in your current shell session ==
+
= Video/display management =
  
$ ps -fl
+
== Viewing EDID data for attached monitor ==
  
== Killing specific processes ==
+
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):
  
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
+
  $ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
= Disk management =
+
= Process management =
  
== Creating a partition table ==
+
== Using 'top' for dynamic resource usage reporting ==
  
# parted /dev/xvdf
+
To run top:
  
  mktable msdos
+
  $ top
  
== Creating a partition ==
+
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
  
# parted /dev/xvdf
+
To see usage for a specific user run e.g.:
  
  u MiB
+
  $ top -u jj5
mkpart primary 1 100%
 
  
== Creating an ext4 file-system ==
+
To see full command-line press 'c'.
  
# mkfs.ext4 /dev/xvdf1
+
When you're in 'top' you can:
  
== Listing disk drives ==
+
* press '1' (one) to toggle CPU aggregation
 +
* press < and > to change the sort column
  
# fdisk -l
+
== Changing memory reporting in 'top' ==
  
(That's an L for "list")
+
To run top:
  
== Checking available disk space ==
+
$ top
  
$ df -h
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
== Getting disk information ==
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
# lsblk
+
Press 'M' to sort by memory utilisation.
  
And
+
Press 'm' to switch between various display modes.
  
# cat /proc/partitions
+
== Showing full command-line in 'top' ==
  
Or the Grand Daddy of them all:
+
To see the full command-line for processes run with -c:
  
  # lshw -class disk
+
  $ top -c
  
(Requires the lshw package.)
+
== Listing all processes currently running which were started in your current shell session ==
  
== Getting partition UUID and file-system type ==
+
$ ps -fl
  
# blkid
+
== Killing specific processes ==
  
== Checking for SSD vs magnetic disk ==
+
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
# cat /sys/block/sda/queue/rotational
+
== Run a command for a specified time using timeout ==
  
Will be 0 for SSD and 1 for magnetic.
+
$ timeout 3 ping jj5.net
  
== Monitoring a ZFS server ==
+
= Disk management =
  
So some commands I run to keep an eye on my new ZFS servers:
+
== Power-off a hard drive ==
  
# top
+
For instance if it's a USB drive or in a mobile rack and you want to remove it.
# 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:
+
# udisksctl power-off -b /dev/sdi
  
# watch zpool status -v
+
== Reporting ext4 file-systems mounted without noatime ==
  
You can poke about in internals, e.g.:
+
$ cat /proc/mounts | grep ext | grep -v noatime | sort
  
# cat /proc/spl/kstat/zfs/arcstats
+
== Creating a partition table ==
  
  root@orac:/sys/module/zfs/parameters# tail *
+
  # parted /dev/xvdf
  
You can report on property values with e.g.:
+
mktable msdos
  
# zfs get all data
+
== Creating a partition ==
  
If you want to get funky:
+
# parted /dev/xvdf
 +
 
 +
u MiB
 +
mkpart primary 1 100%
 +
 
 +
== Creating an ext4 file-system ==
  
  # cd /tmp
+
  # mkfs.ext4 /dev/xvdf1
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
== Listing disk drives ==
  
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
  # fdisk -l
  
You can report history of a zpool:
+
(That's an L for "list")
  
# zpool history $poolname
+
== Checking available disk space ==
  
You can get a report on the dedup tables:
+
$ df -h
  
# zpool status -D $poolname
+
== Getting disk information ==
  
Or more detailed dedup table info:
+
# lsblk
  
# zdb -DDD $poolname
+
And
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
# cat /proc/partitions
  
{|class="wikitable"
+
Or the Grand Daddy of them all:
! Abbr  !! Description
 
|-
 
| LSIZE  || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== Measure data throughput ==
+
# lshw -class disk
  
Use the 'pv' command from the 'pv' package, e.g.:
+
(Requires the lshw package.)
  
# cat /dev/sda | pv | cat > /dev/null
+
== Getting partition UUID and file-system type ==
  
Or for ZFS:
+
# blkid
  
# zfs send data/example | pv | cat > /dev/null
+
== Checking for SSD vs magnetic disk ==
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
# cat /sys/block/sda/queue/rotational
  
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].
+
Will be 0 for SSD and 1 for magnetic.
  
== Report hard disk usage ==
+
== Monitoring a ZFS server ==
  
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.
+
So some commands I run to keep an eye on my new ZFS servers:
  
== Report hard disk temperatures ==
+
# top
 
+
# iotop
E.g.
+
# 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
  
# hddtemp /dev/sd[a-e]
+
If you have a scrub or resilvering in progress you can report on progress with:
  
= Monitoring disk I/O =
+
# watch zpool status -v
  
There's an app for that! iotop.
+
You can poke about in internals, e.g.:
  
== Using iotop, top for disks ==
+
# cat /proc/spl/kstat/zfs/arcstats
  
  # iotop -oPa
+
  root@orac:/sys/module/zfs/parameters# tail *
  
== Monitor disk I/O for performance issues ==
+
You can report on property values with e.g.:
  
  # watch iostat
+
  # zfs get all data
  
Or e.g.
+
If you want to get funky:
  
  # watch iostat -xd /dev/sd[abc]
+
  # cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
Or use groupings like this command for 'tact':
+
You can search for ZFS files like e.g. this:
  
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
= Monitoring a system =
+
You can report history of a zpool:
  
== Simple ZFS monitoring ==
+
# zpool history $poolname
  
# watch iostat
+
You can get a report on the dedup tables:
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= Monitoring temperature =
+
# zpool status -D $poolname
  
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
+
Or more detailed dedup table info:
  
  $ cat /sys/class/thermal/thermal_zone*/temp
+
  # zdb -DDD $poolname
  
and:
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
+
{|class="wikitable"
 
+
! Abbr  !! Description
== Monitoring CPU temperature ==
+
|-
 
+
| LSIZE  || logical size (in memory)
  $ watch sensors
+
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
== Monitoring HDD temperature ==
+
== How to tell if zfs scrub is running ==
  
For e.g. SATA drives sda to sdd:
+
You can get the status from the "scan:" line from:
  
  # watch hddtemp /dev/sd[a-d]
+
  $ zpool status
  
= ZFS =
+
== Measure data throughput ==
  
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
+
Use the 'pv' command from the 'pv' package, e.g.:
  
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
+
# cat /dev/sda | pv | cat > /dev/null
  
$ cat /proc/spl/kstat/zfs/arcstats
+
Or for ZFS:
  
Then:
+
# zfs send data/example | pv | cat > /dev/null
  
c is the target size of the ARC in bytes
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
c_max is the maximum size of the ARC in bytes
 
size is the current size of the ARC in bytes
 
  
= File management =
+
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].
  
== Listing only directories ==
+
== Report hard disk usage ==
  
$ ls -l | egrep '^d'
+
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.
  
== Listing only files ==
+
== Report hard disk temperatures ==
  
  $ ls -l | egrep -v '^d'
+
E.g.
 +
 
 +
  # hddtemp /dev/sd[a-e]
  
== Listing hidden files ==
+
== Burning an ISO image to USB on Mac ==
  
$ ls -al .[!.]*
+
First insert your USB key and find the appropriate disk with:
  
== Creating a symbolic link ==
+
# diskutil list
  
$ ln -s /path/to/target link-name
+
Then unmount it with:
  
== Creating a hard-link ==
+
# diskutil unmountDisk /dev/disk4
  
$ ln /path/to/target file-name
+
Then copy ISO image with 'dd':
  
== Changing the owner of a file ==
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
$ chown user:group <files>
+
You can get dd to report progress by sending it the SIGINFO signal:
  
E.g.
+
# kill -s info 12345
  
$ chown jj5:staff README
+
== Listing all ext4 file systems ==
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
To see a list only of the mounted ext4 file systems:
  
  $ chown -R root:root /etc/*
+
  # df -t ext4
  
== Changing file permissions ==
+
== Report hierarchical file system mount points and mount options ==
  
{|class="wikitable"
+
$ findmnt
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
== Report the mount point for the current working directory ==
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
$ findmnt "$PWD"
|+ Numeric codes
 
! 0
 
| None
 
|-
 
! 1
 
| Execute
 
|-
 
! 2
 
| Write
 
|-
 
! 3
 
| Write, Execute
 
|-
 
! 4
 
| Read
 
|-
 
! 5
 
| Read, Execute
 
|-
 
! 6
 
| Read, Write
 
|-
 
! 7
 
| Read, Write, Execute
 
|}
 
  
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
+
= Monitoring disk I/O =
  
$ chmod <user numeric code><group numeric code><other numeric code> <files>
+
There's an app for that! iotop.
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
== Using iotop, top for disks ==
  
  $ chmod 600 my-private-file
+
  # iotop -oPa
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
== Monitor disk I/O for performance issues ==
  
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:
+
# watch iostat
  
$ cp old.conf updated.conf
+
Or e.g.
$ 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 iostat -xd /dev/sd[abc]
  
The merge program is a part of the RCS package. If you don't have it:
+
Or use groupings like this command for 'tact':
  
  $ sudo apt-get install rcs
+
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
== Listing open files ==
+
= Monitoring a system =
  
Use lsof to list open files. E.g.:
+
== Simple ZFS monitoring ==
  
  # lsof
+
  # watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
See man lsof for options.
+
= Monitoring temperature =
  
== List permissions on a whole directory path ==
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
E.g.:
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
$ namei -om /home/jj5/workspace
+
and:
  
Outputs:
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
f: /home/jj5/workspace/
+
== Monitoring CPU temperature ==
  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 ==
+
$ watch sensors
  
E.g.:
+
== Monitoring HDD temperature ==
  
$ cat foo.c | sed '/^\s*$/d' | wc -l
+
For e.g. SATA drives sda to sdd:
  
== Cloning one directory to another with rsync ==
+
# watch hddtemp /dev/sd[a-d]
  
E.g.:
+
= ZFS =
  
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/
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
== Counting number of files in current directory and all subdirectories ==
+
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?]
  
  $ ls -AlhR . | egrep '^-' | wc -l
+
  $ cat /proc/spl/kstat/zfs/arcstats
  
== Counting number of directories in current directory and all subdirectories ==
+
Then:
  
  $ ls -AlhR . | egrep '^d' | wc -l
+
  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:
  
= Compression =
+
# zpool scrub -s data
  
== How to use pigz with tar ==
+
= File management =
  
See [https://stackoverflow.com/a/39904353 here]:
+
== Listing files by size ==
  
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
+
Use capital S for Size:
  
Note: don't use --best unless you're being stingy, running without it will be much faster.
+
$ ls -S
  
== Best parallel compression with pigz ==
+
== Listing only directories ==
  
  $ pigz --best
+
  $ ls -l | egrep '^d'
  
== Best parallel compression with xz ==
+
== Listing only files ==
  
  $ xz -9e -T 0
+
  $ ls -l | egrep -v '^d'
  
== Reporting compression ratios with xz ==
+
== Listing hidden files ==
  
e.g.
+
$ ls -al .[!.]*
  
root@love:/data/image/archive# xz -l *
+
== Creating a symbolic link ==
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 =
+
$ ln -s /path/to/target link-name
  
== Data used by sym-linked files:
+
== Creating a hard-link ==
  
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:
+
$ ln /path/to/target file-name
  
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
== Changing the owner of a file ==
  
= File searching =
+
$ chown user:group <files>
  
== Finding a file with a particular name ==
+
E.g.
  
  $ find -iname "*some-part-of-the-file-name*"
+
  $ chown jj5:staff README
 +
$ chown root:root *
  
Will start searching from the current directory, so maybe
+
To apply recursively into sub-directories use -R,
  
  $ cd /
+
  $ chown -R root:root /etc/*
  
first. For a case-sensitive search:
+
== Changing file permissions ==
  
$ find -name "*eXaCT CaSE*"
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
== Finding a file with particular content ==
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
To search in /etc/ for a file with particular content:
+
{|class="wikitable"
 
+
|+ Numeric codes
$ grep -R "search-string" /etc/*
+
! 0
 
+
| None
To search the current directory for *.cs files containing the word "Up":
+
|-
 
+
! 1
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
| Execute
 
+
|-
== Finding a list of files with particular content ==
+
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
E.g. to find all the files with the word 'creativity':
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
== Using the locate command to find files ==
+
E.g.
  
  $ locate part-of-filename
+
  $ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
E.g.
+
== Updating config files ==
  
$ locate texvc
+
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:
  
== Updating locate command's database ==
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
# updatedb
+
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.
  
== Select a random line from a text file ==
+
The merge program is a part of the RCS package. If you don't have it:
  
  $ shuf -n 1 input.txt
+
  $ sudo apt-get install rcs
  
== Extra context for grep ==
+
== Listing open files ==
  
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:
+
Use lsof to list open files. E.g.:
  
  $ grep -B 3 -A 1 ...
+
  # lsof
  
= Job control =
+
See man lsof for options.
  
== Stopping a running process ==
+
== List permissions on a whole directory path ==
  
Press Ctrl+Z to stop a running process.
+
E.g.:
  
== Listing current jobs and their status ==
+
$ namei -om /home/jj5/workspace
  
$ jobs
+
Outputs:
  
== Resuming a stopped job in the backgroud ==
+
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
  
To resume a stopped process in the background
+
== Counting non-blank lines in a file ==
  
$ bg %1
+
E.g.:
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
== Resuming a stopped job in the foreground ==
+
== Cloning one directory to another with rsync ==
  
To resume a stopped process in the foreground
+
E.g.:
  
$ fg %1
+
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Counting number of files in current directory and all subdirectories ==
  
== Killing a stopped job ==
+
$ ls -AlhR . | egrep '^-' | wc -l
  
To kill a job
+
== Counting number of directories in current directory and all subdirectories ==
  
  $ kill %1
+
  $ ls -AlhR . | egrep '^d' | wc -l
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Getting the status of a 'dd' process ==
  
== Periodically run a program and watch its output ==
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
$ watch /your/command
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
= Debian/Ubuntu package management =
+
# kill -s info 40947
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
The dd process will report its status in the terminal its running in.
  
== configuring debconf ==
+
== Transferring a large file via FAT32 file system ==
  
# dpkg-reconfigure debconf
+
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:
  
Set priority to low to get asked detailed questions.
+
$ split -b 4000m input.tgz input.tgz-parts-
  
== Showing list of installed packages ==
+
Then copy the small files and reassemble:
  
  # dpkg --get-selections
+
  $ cat input.tgz-parts-* > output.tgz
  
== Searching for installed package ==
+
== Find the difference between two directories ==
  
  # dpkg --get-selections | grep package-name
+
  $ diif -qr $DIR_A $DIR_B
  
or
+
== Merging two directories ==
 +
 
 +
$ cp -RT source/ destination/
  
# aptitude search package-name
+
Files from source will be merged into destination.
  
== Showing which files are installed as part of a package ==
+
== Generating a replacement file ==
  
# dpkg -L package-name
+
So you generate the file into a temp file, then hard link the temp file to where you want the replacement to go, then you delete the temp file:
  
== Installing a package ==
+
$ generate-file.sh > file.txt.tmp
 +
$ ln -f file.txt.tmp file.txt
 +
$ rm file.txt.tmp
  
# apt-get install package-name
+
= NFS =
  
== Uninstalling a package ==
+
== List NFS shares ==
  
# apt-get remove package-name
+
To e.g. show NFS shares on 'love':
  
== Showing system architecture ==
+
$ showmount -e love
  
$ dpkg --print-architecture
+
= Compression =
  
== Showing which package a file belongs to ==
+
== How to use pigz with tar ==
  
$ which echo
+
See [https://stackoverflow.com/a/39904353 here]:
/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 ==
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
$ apt-cache showpkg coreutils
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
Or for even more information:
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
$ apt-cache show coreutils
+
Fast pack:
  
== List all installed packages with package version info ==
+
tar -I 'pigz --fast' -cf my.tar.gz whatver
  
dpkg-query -l
+
Best pack:
  
== Reporting which version of a package is installed ==
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
$ dpkg -l | grep package-name
+
Fast unpack:
  
E.g.:
+
tar -I pigz -xf my.tar.gz
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
== Best compression with tar ==
  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
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
 +
 
 +
  export GZIP=-9
 +
  tar cvzf file.tar.gz /path/to/directory
  
== Comprehensive upgrade ==
+
or
  
Try the following:
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
# apt-get update
+
== Best parallel compression with pigz ==
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
$ pigz --best
  
$ apt-cache search . | sort -d | less
+
== Best parallel compression with xz ==
  
= Networking =
+
$ xz -9e -T 0
  
== net-tools vs iproute2 ==
+
== Reporting compression ratios with xz ==
  
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].
+
e.g.
  
{|class="wikitable"
+
root@love:/data/image/archive# xz -l *
! legacy net-tools commands
+
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
! iproute2 replacement commands
+
    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
| arp     || ip n (ip neighbor)
+
    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
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
+
    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
| iptunnel || ip tunnel
+
    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
| iwconfig || iw
+
    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
| nameif   || ip link, ifrename
+
    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
| netstat || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
+
  -------------------------------------------------------------------------------
|-
+
    12  3,768    344.6 GiB   705.5 GiB  0.488  CRC64  12 files
| route   || ip r (ip route)
 
|}
 
  
== Restart networking ==
+
= Symbolic-link management =
  
For servers:
+
== Data used by sym-linked files:
  
# service networking restart
+
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:
  
For desktops:
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
# service network-manager restart
+
= File searching =
  
== Pinging with particular packet size ==
+
== Finding a file with a particular name ==
  
  $ ping -M do -s <packet size in bytes> <host>
+
  $ find -iname "*some-part-of-the-file-name*"
  
E.g.
+
Will start searching from the current directory, so maybe
  
  $ ping -M do -s 1400 charity.progclub.org
+
  $ cd /
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
first. For a case-sensitive search:
  
  # ip route add <host> dev <interface> advmss <packet size>
+
  $ find -name "*eXaCT CaSE*"
  
E.g.
+
== Finding a file with particular content ==
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
To search in /etc/ for a file with particular content:
  
== Dropping configured MMS for a particular IP address ==
+
$ grep -R "search-string" /etc/*
  
# ip route flush <host>
+
To search the current directory for *.cs files containing the word "Up":
  
E.g.
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
# ip route flush 10.0.0.1
+
== Finding a list of files with particular content ==
  
== Listing open ports and socket information ==
+
E.g. to find all the files with the word 'creativity':
  
Including which process is listening on which port.
+
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
# netstat -tulpn
+
== Using the locate command to find files ==
  
Or use the 'ss' command:
+
$ locate part-of-filename
  
# ss -s
+
E.g.
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
$ locate texvc
  
# lsof -Pnl +M -i4
+
== Updating locate command's database ==
  
You might need to install the lsof package:
+
# updatedb
  
# apt-get install lsof
+
== Select a random line from a text file ==
  
== Query for DNS MX record ==
+
$ shuf -n 1 input.txt
  
$ nslookup
+
== Extra context for grep ==
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
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:
  
  $ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
  $ grep -B 3 -A 1 ...
  
== Using nmap to list open ports on remote host ==
+
= Job control =
  
To check the 1,000 most common ports:
+
== Stopping a running process ==
  
# nmap server.example.com
+
Press Ctrl+Z to stop a running process.
 +
 
 +
== Listing current jobs and their status ==
  
Or for a specific port range (e.g. 101 to 102):
+
$ jobs
  
# nmap -p 101-102 server.example.com
+
== Resuming a stopped job in the backgroud ==
  
Or for all ports (1 to 65,535):
+
To resume a stopped process in the background
  
  # nmap -p- server.example.com
+
  $ bg %1
  
== Network monitoring ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
== Resuming a stopped job in the foreground ==
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
To resume a stopped process in the foreground
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
$ fg %1
  
You can watch network traffic in real-time with nload:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
# nload -u M
+
== Killing a stopped job ==
  
== Reporting network (NIC) speed ==
+
To kill a job
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
$ kill %1
  
# dmesg | grep eth0
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
== Periodically run a program and watch its output ==
  
== Path MTU discovery ==
+
$ watch /your/command
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
= Debian/Ubuntu package management =
  
# tracepath host.example.com
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
== Listing available Ethernet devices ==
+
== configuring debconf ==
  
To see a list of NICs available on the host:
+
# dpkg-reconfigure debconf
  
$ cat /proc/net/dev
+
Set priority to low to get asked detailed questions.
  
Also
+
== Showing list of installed packages ==
  
  $ ip link
+
  # dpkg --get-selections
  
== 59 Linux Networking commands and scripts ==
+
== Searching for installed package ==
  
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
+
# dpkg --get-selections | grep package-name
  
== Links ==
+
or
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
# aptitude search package-name
  
= IPTables =
+
== Showing which files are installed as part of a package ==
  
== Applying firewall rules ==
+
# dpkg -L package-name
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
== Installing a package ==
  
  $ sudo vim /etc/iptables.test.rules
+
  # apt-get install package-name
$ 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 =
+
== Uninstalling a package ==
  
== Denying hosts with ufw ==
+
# apt-get remove package-name
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
== Showing system architecture ==
  
= Bind9 =
+
$ dpkg --print-architecture
  
== Viewing Bind9 querylog ==
+
== Showing which package a file belongs to ==
  
  $ sudo rndc querylog
+
  $ which echo
  $ tail -f /var/log/syslog
+
/bin/echo
 +
  $ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
= IPSec =
+
== Showing package information ==
  
== Disabling IPSec ==
+
$ apt-cache showpkg coreutils
  
# setkey -FP
+
Or for even more information:
  
= OpenSSL =
+
$ apt-cache show coreutils
  
== Debugging IMAPS with OpenSSL ==
+
== List all installed packages with package version info ==
  
  # openssl s_client -connect localhost:993
+
  dpkg-query -l
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
== Reporting which version of a package is installed ==
  
  $ openssl s_client -connect www.example.com:443
+
  $ dpkg -l | grep package-name
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
E.g.:
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
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
  
= Pluggable Authentication Modules (PAM) =
+
== Comprehensive upgrade ==
  
== Links ==
+
Try the following:
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
# apt-get update
 
+
# apt-get dist-upgrade
= SSH =
+
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
 +
 
 +
== Searching all available packages ==
  
== Configuring SSH key login ==
+
$ apt-cache search . | sort -d | less
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
== Reporting unattended upgrades status ==
  
$ ssh-keygen -t rsa
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
Copy the public key from the client to the server:
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
== Searching for Debian packages and versions ==
  
Configure the authorized keys on the server:
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
$ ssh user@example.org
+
= Networking =
$ 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 ==
+
== Determining throughput between two hosts ==
  
For example, connecting a remote MySQL server to the localhost:
+
# apt install iperf3
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
On the server:
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
# iperf3 -s
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
On the client:
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
# iperf3 -c $SERVER_IP
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
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].
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
== net-tools vs iproute2 ==
  
* run putty.exe
+
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].
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
{|class="wikitable"
 +
! legacy net-tools commands
 +
! iproute2 replacement commands
 +
|-
 +
| arp      || ip n (ip neighbor)
 +
|-
 +
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 +
|-
 +
| iptunnel || ip tunnel
 +
|-
 +
| iwconfig || iw
 +
|-
 +
| nameif  || ip link, ifrename
 +
|-
 +
| netstat  || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 +
|-
 +
| route    || ip r (ip route)
 +
|}
  
To see what's going on with your ssh connections,
+
== Restart networking ==
  
$ ssh -v user@host
+
For servers:
  
Or
+
# service networking restart
  
$ ssh -vv user@host
+
For desktops:
  
== Unlocking SSH key for session ==
+
# service network-manager restart
  
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
== Pinging with particular packet size ==
[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 ==
+
$ ping -M do -s <packet size in bytes> <host>
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
E.g.
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
$ ping -M do -s 1400 charity.progclub.org
  
== cat EOF ==
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
  $ cat > output <<EOF
+
  # ip route add <host> dev <interface> advmss <packet size>
> text
 
> EOF
 
  
$ cat output
+
E.g.
text
 
  
= Script =
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
== Creating a session log with script ==
+
== Dropping configured MMS for a particular IP address ==
  
  $ script -t 2> timing
+
  # ip route flush <host>
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
E.g.
  
== Replaying a scripted session ==
+
# ip route flush 10.0.0.1
  
$ scriptreplay timing
+
== Listing open ports and socket information ==
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
Including which process is listening on which port.
  
= Screen =
+
# netstat -tulpn
  
== Creating a new screen or reconnecting to a detached screen ==
+
Or use the 'ss' command:
  
  $ screen -R
+
  # ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
== Detaching a screen ==
+
== Listing open IPv4 connections ==
  
  $ screen -D
+
  # lsof -Pnl +M -i4
  
== Reconnecting to screen ==
+
You might need to install the lsof package:
  
  $ screen -D
+
  # apt-get install lsof
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
== Query for DNS MX record ==
  
  #!/bin/bash
+
  $ nslookup
  screen -D
+
  > server 127.0.0.1
  screen -R
+
  > set q=mx
 +
> mail.blackbrick.com
  
This will detach your last screen, and reconnect it on the current terminal.
+
== Query for DNS SOA record ==
  
== Scrolling in screen ==
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
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.
+
== Using nmap to list open ports on remote host ==
  
= Vim =
+
To check the 1,000 most common ports:
  
== First, why Vim? ==
+
# nmap server.example.com
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
Or for a specific port range (e.g. 101 to 102):
  
== Visual modes ==
+
# nmap -p 101-102 server.example.com
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
Or for all ports (1 to 65,535):
  
== Configuring spaces instead of tabs ==
+
# nmap -p- server.example.com
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
== Network monitoring ==
  
$ vim ~/.vimrc
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
and include the following lines:
+
# 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
  
set tabstop=2
+
== nload ==
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
You can watch network traffic in real-time with nload:
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
# nload -u M
  
Use:
+
== Reporting network (NIC) speed ==
  
:syntax on
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
to turn on syntax highlighting.
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
Use:
+
Note: use ifconfig to get device name.
  
:syntax off
+
== Path MTU discovery ==
  
to turn off syntax highlighting.
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
To always use syntax highlighting:
+
# tracepath host.example.com
  
$ vim ~/.vimrc
+
== Listing available Ethernet devices ==
  
and add:
+
To see a list of NICs available on the host:
  
  syntax on
+
  $ cat /proc/net/dev
  
To get a list of supported colour schemes open vim and type:
+
Also
  
  :colorscheme[space][Ctrl+D]
+
  $ ip link
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
== 59 Linux Networking commands and scripts ==
  
colorscheme desert
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
== Inserting a TAB character when expandtab is on ==
+
== Links ==
  
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
Press Ctrl+V TAB to insert a literal tab character.
+
= IPTables =
  
Or you can disable tab expansion altogether with:
+
== Applying firewall rules ==
  
:set expandtab!
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
$ 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
  
:%s/^\s*/&&/g
+
== Blocking an IP address with iptables ==
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
To drop IP address 1.2.3.4:
  
== Recording and replaying a macro ==
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
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 "@@".
+
= ufw =
  
== Deleting to end of line ==
+
== Denying hosts with ufw ==
  
d$
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
== Deleting to beginning of line ==
+
= Bind9 =
  
d^
+
== Viewing Bind9 querylog ==
  
== Finding text ==
+
$ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
To search forward for "text":
+
= IPSec =
  
/text
+
== Disabling IPSec ==
  
To search backward for "text":
+
# setkey -FP
  
?text
+
= OpenSSL =
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
== Debugging IMAPS with OpenSSL ==
  
== Finding and replacing text ==
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
To replace the first instance of "search" on the current line with "destroy":
+
== Debugging HTTPS with OpenSSL ==
  
  :s/search/destroy/
+
  $ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
To replace all instances of "search" on the current line with "destroy":
+
== Links ==
  
:s/search/destroy/g
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
= Pluggable Authentication Modules (PAM) =
  
:13,37 s/search/destroy/g
+
== Links ==
  
To replace all instances of "search" in the entire file with "destroy":
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
:%s/search/destroy/g
+
= SSH =
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
== Configuring SSH key login ==
  
To set the line-ending to Unix line endings run the command:
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
  :setlocal ff=unix
+
  $ ssh-keygen -t rsa
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
Copy the public key from the client to the server:
  
== Disabling auto-indent etc. to paste from clipboard ==
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
To disable smart indenting when you're going to paste in text:
+
Configure the authorized keys on the server:
  
  :set paste
+
  $ 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 turn it off again:
+
== Tunneling over SSH ==
  
:set nopaste
+
For example, connecting a remote MySQL server to the localhost:
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
== Positioning windows ==
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
Use -o for horizontal split, e.g.:
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
vim -o a.txt b.txt
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
Use -O for vertical split, e.g.:
+
== Tunneling over SSH with PuTTY ==
  
vim -o a.txt b.txt
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
Use ^W and &lt; or &gt; to resize windows.
+
== Enabling verbose SSH logging ==
  
== To indent a block of text in Vim ==
+
To see what's going on with your ssh connections,
  
Use the > command. E.g. to indent five lines:
+
$ ssh -v user@host
  
5 > >
+
Or
  
Press . (dot) to keep indenting.
+
$ ssh -vv user@host
  
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:
+
== Unlocking SSH key for session ==
  
  > %
+
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
 
+
[Desktop Entry]
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
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'
  
== Open a file in a new window/tab ==
+
== Links ==
  
To open a file on the left hand side:
+
* [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]
  
:vert new filename.ext
+
= Standard IO =
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
== cat EOF ==
  
To open a file at the top:
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  :new filename.ext
+
  $ cat output
 +
text
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
= Script =
  
== Explore files in Vim ==
+
== Creating a session log with script ==
  
Enter:
+
$ script -t 2> timing
  
:Explore
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
== Switch between Vim tabs ==
+
== Replaying a scripted session ==
  
Use gt and gT.
+
$ scriptreplay timing
  
== Switch between Vim windows ==
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
To toggle between open windows use:
+
= Screen =
  
Ctrl+W W
+
== Creating a new screen or reconnecting to a detached screen ==
  
To move in a direction use:
+
$ screen -R
  
Ctrl+W h/j/k/l
+
== Detaching a screen ==
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
$ screen -D
  
== Insert block comment in Vim ==
+
== Reconnecting to screen ==
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
$ screen -D
 +
$ screen -R
  
So it's:
+
I have a script in ~/bin/reconnect like so,
  
# Ctrl+V (Note: not Shift+V!)
+
#!/bin/bash
# Up/Down to select rows
+
screen -D
# Shift+I
+
screen -R
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
This will detach your last screen, and reconnect it on the current terminal.
  
To navigate to the matching beginning or end tag use '%'.
+
== Scrolling in screen ==
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
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.
  
== Auto-format HTML tags ==
+
= tmux =
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
== Live collaboration with tmux ==
  
# first join all the lines - ggVGgJ
+
User A:
# 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 ==
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
* [http://www.vim.org/ Vim: the editor]
+
User B:
* [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 =
+
tmux -S /tmp/collab attach
  
== Talking to other users on the system ==
+
= Vim =
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
== First, why Vim? ==
  
1. SSH to <username>@<hostname> and login with your username and password.
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
2. Issue the following command to find out who is logged onto the system:
+
== Visual modes ==
  
$ who
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
3. Issue the following command to talk to a specific user:
+
== Configuring spaces instead of tabs ==
  
$ write <username>
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
$ vim ~/.vimrc
  
= Date =
+
and include the following lines:
  
== Reporting the time on the server ==
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
$ date
+
== Configuring syntax highlighting ==
  
== Reporting UTC time ==
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
$ date --utc
+
Use:
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
:syntax on
  
$ date="`date +%F-%H%M%S`"
+
to turn on syntax highlighting.
  
== Getting the year in four digits ==
+
Use:
  
  $ year="`date +%Y`"
+
  :syntax off
  
== Getting the month in two digits ==
+
to turn off syntax highlighting.
  
$ month="`date +%m`"
+
To always use syntax highlighting:
  
== Getting the day of the month in two digits ==
+
$ vim ~/.vimrc
  
$ day="`date +%d`"
+
and add:
  
== Getting yesterday's date ==
+
syntax on
  
$ date --date='1 day ago' +%Y-%m-%d
+
To get a list of supported colour schemes open vim and type:
  
== Converting Unix time (seconds since epoch) ==
+
:colorscheme[space][Ctrl+D]
  
For timestamp '1501370200':
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
  $ date -d @1501370200 +%F-%H%M%S
+
  colorscheme desert
  
== Running timedatectl from systemd ==
+
== Inserting a TAB character when expandtab is on ==
  
There's a new command bundled with systmed:
+
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.
  
# timedatectl
+
Press Ctrl+V TAB to insert a literal tab character.
  
It reports on (and controls) how the system time is configured.
+
Or you can disable tab expansion altogether with:
  
= MySQL =
+
:set expandtab!
  
== Run mysql without authentication/authorisation ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
  # service mysql stop
+
  :%s/^\s*/&&/g
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
# mysql -u root mysql
+
== Recording and replaying a macro ==
  
To stop the unauthenticated service:
+
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 "@@".
  
# mysqladmin shutdown
+
== Deleting to end of line ==
  
Then restart a normal service:
+
d$
  
  # service mysql start
+
== Deleting to beginning of line ==
 +
 
 +
  d^
  
== Logging all database queries ==
+
== Finding text ==
  
# vim /etc/mysql/my.cnf
+
To search forward for "text":
  
In the [mysqld] section add:
+
/text
  
log=/tmp/mysql.log
+
To search backward for "text":
  
Then:
+
?text
  
# service mysql restart
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
Watch the log with:
+
== Finding and replacing text ==
  
# tail -f /tmp/mysql.log
+
To replace the first instance of "search" on the current line with "destroy":
  
== Dumping a MySQL database ==
+
:s/search/destroy/
  
You can dump the database into a file using:  
+
To replace all instances of "search" on the current line with "destroy":
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
:s/search/destroy/g
  
You can create a database using:
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
  $ echo create database databasename | mysql -h hostname -u user -p
+
  :13,37 s/search/destroy/g
  
You can restore a database using:
+
To replace all instances of "search" in the entire file with "destroy":
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
:%s/search/destroy/g
  
# mysql -h localhost -u root --password=<password>
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
To set the line-ending to Unix line endings run the command:
  
  # mysql -h localhost -u root --password=<password>
+
  :setlocal ff=unix
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
== Disabling auto-indent etc. to paste from clipboard ==
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
To disable smart indenting when you're going to paste in text:
  
Check the SSL version in use:
+
:set paste
  
show status like 'Ssl_version';
+
To turn it off again:
  
Or check the cipher in use:
+
:set nopaste
  
show status like 'Ssl_cipher';
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
= Apache =
+
== Positioning windows ==
  
== Reporting loaded Apache modules ==
+
Use -o for horizontal split, e.g.:
  
  # apache2ctl -M
+
  vim -o a.txt b.txt
  
== Maintaining .htaccess passwords ==
+
Use -O for vertical split, e.g.:
  
To add or modify the password for a user:
+
vim -o a.txt b.txt
  
$ htpasswd /etc/apache2/passwd username
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
== Configuring PHP session timeout in .htaccess ==
+
Use ^W and &lt; or &gt; to resize windows.
  
For a session timeout of 9 hours:
+
== To indent a block of text in Vim ==
  
php_value session.cookie_lifetime 32400
+
Use the > command. E.g. to indent five lines:
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
5 > >
  
php_flag magic_quotes_gpc Off
+
Press . (dot) to keep indenting.
  
== Requiring HTTP Auth in .htaccess ==
+
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:
  
  AuthType Basic
+
  > %
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
The hard way
+
== Open a file in a new window/tab ==
  
$ sudo /etc/init.d/apache2 restart
+
To open a file on the left hand side:
  
The graceful way (avoids dropping active connections)
+
:vert new filename.ext
  
$ sudo apache2ctl graceful
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
== Allowing directory browsing ==
+
To open a file at the top:
  
To show directory index pages, in the apache config file:
+
:new filename.ext
  
<Directory /var/www/data>
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  Options Indexes
 
</Directory>
 
  
= C =
+
== Explore files in Vim ==
  
== Locating memset function ==
+
Enter:
  
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]
+
:Explore
  
== Links ==
+
== Switch between Vim tabs ==
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
Use gt and gT.
  
= PHP =
+
== Switch between Vim windows ==
  
== Including a file relative to the including file ==
+
To toggle between open windows use:
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  Ctrl+W W
  
== Enabling error reporting ==
+
To move in a direction use:
  
  error_reporting( E_ALL | E_STRICT );
+
  Ctrl+W h/j/k/l
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
== Insert block comment in Vim ==
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
So it's:
  
ini_set( 'html_errors', 'off' );
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
== Report PHP modules ==
+
== Navigate to matching tag ==
  
$ php -m
+
To navigate to the matching beginning or end tag use '%'.
  
== PHP Security Best Practices For Sys Admins ==
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
+
== Auto-format HTML tags ==
  
= BASH scripting =
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
# 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=
  
== Telling a script to run in bash ==
+
== Links ==
  
The first line of the file should be:
+
* [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]
  
#!/bin/bash
+
== Create PDF from text using Vim ==
  
== Checking if a command-line argument was passed in ==
+
Generate PDF from input.txt with:
  
  if [ -n "$1" ]; then
+
  $ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
Examine output with:
  
  if [ "$1" = "" ]; then
+
  $ okular doc.pdf
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
= Write =
  
if [ -z "$1" ]; then
+
== Talking to other users on the system ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
cd /my/path
+
1. SSH to <username>@<hostname> and login with your username and password.
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
2. Issue the following command to find out who is logged onto the system:
  
Check if file exists:
+
$ who
  
if [ -f "/my/file" ]; then
+
3. Issue the following command to talk to a specific user:
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
$ write <username>
  
if [ ! -f "/my/file" ]; then
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
= Date =
  
Check if directory exists:
+
== Reporting the time on the server ==
  
  if [ -d "/my/dir" ]; then
+
  $ date
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
== Reporting UTC time ==
  
  if [ ! -d "/my/dir" ]; then
+
  $ date --utc
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
To keep only the latest five backups:
+
$ date="`date +%F-%H%M%S`"
  
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
+
== Getting the year in four digits ==
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
$ year="`date +%Y`"
  
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.
+
== Getting the month in two digits ==
  
== Changing into the script's directory ==
+
$ month="`date +%m`"
  
cd "`dirname $0`"
+
== Getting the day of the month in two digits ==
  
== Getting the absolute path of a relative path ==
+
$ day="`date +%d`"
  
readlink -f ./some/path
+
== Getting yesterday's date ==
  
== Creating a temp directory ==
+
$ date --date='1 day ago' +%Y-%m-%d
  
dir=`mktemp -d` && cd $dir
+
== Converting Unix time (seconds since epoch) ==
  
== Reading secret input from stdin ==
+
For timestamp '1501370200':
  
You can read a secret, such as a password, like this:
+
$ date -d @1501370200 +%F-%H%M%S
  
echo -n "Enter passphrase: "
+
== Running timedatectl from systemd ==
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
There's a new command bundled with systmed:
 +
 
 +
# timedatectl
  
== String replacements in bash ==
+
It reports on (and controls) how the system time is configured.
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
= MySQL (and MariaDB) =
  
result=${var/find/replace}
+
== Run mysql without authentication/authorisation ==
  
To replace all occurrences:
+
# service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
result=${var//find/replace}
+
Then you can connect without a password, e.g.:
  
A practical example, get an ISO date and turn it into a path:
+
# mysql -u root mysql
  
date="$(date +%Y-%m-%d)"
+
To stop the unauthenticated service:
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
# mysqladmin shutdown
  
cat << EOF > /tmp/yourfilehere
+
Then restart a normal service:
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
# service mysql start
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
== Logging all database queries ==
  
  case $space in
+
  # vim /etc/mysql/my.cnf
[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 ==
+
In the [mysqld] section add:
  
To enable dot-file matching in globs, set the dotglob shell option:
+
log=/tmp/mysql.log
  
$ shopt -s dotglob
+
Then:
  
== Stopping a script from running if it previously exited due to error ==
+
# service mysql restart
  
persistentDataDir=/var/lib/something
+
Watch the log with:
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 ==
+
# tail -f /tmp/mysql.log
  
ephemeralDataDir=/var/run/something
+
Or:
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
== BASH programming advice ==
+
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
  
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)].
+
my_logs.txt will be in /var/lib/mysql
  
== Run a command using arguments that come from an array ==
+
== Dumping a MySQL database ==
  
See [https://unix.stackexchange.com/a/412647/356289 here]:
+
You can dump the database into a file using:  
 +
 +
$ mysqldump -h hostname -u user --password=password databasename > filename
  
#!/bin/bash
+
== Loading a MySQL database from a dump file ==
tabs=("first tab" "second tab")
 
args=()
 
for t in "${tabs[@]}" ; do
 
  args+=(-t "$t")
 
done
 
app "${args[@]}"
 
  
= Sed =
+
You can create a database using:
  
== Find and replace with sed ==
+
$ echo create database databasename | mysql -h hostname -u user -p
  
To update the current file use '-i'. E.g.:
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
sed -i 's/search-text/replace-text/' file
+
== Creating a MySQL user ==
  
= Awk =
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
== Listing IP addresses in an Apache web log ==
+
== Granting all MySQL user permissions ==
  
  awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
  # mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
== Printing space-separated field ==
+
== Select domain name from email address ==
  
  echo 'no no yes no' | awk '{print $3}'
+
  SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
== Printing delimited field ==
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
Check the SSL version in use:
  
= Subversion =
+
show status like 'Ssl_version';
  
== Setting svn:externals from the command-line ==
+
Or check the cipher in use:
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
show status like 'Ssl_cipher';
  
To set an svn:externals from the command-line:
+
== Report on server config ==
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
SHOW VARIABLES
  
svn propset svn:externals -F svn.externals .
+
and
  
== Setting svn:ignore from the command line ==
+
SHOW STATUS
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
and
  
  $ svn propset svn:ignore [file|folder] [path]
+
  SHOW PROCESSLIST
  
Or use a file and apply recursively:
+
== Monitor MySQL activity ==
  
  $ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
  $ watch "mysql -t -e 'show processlist'"
  
= Git =
+
= Apache =
  
== Showing status of working copy ==
+
== Reporting loaded Apache modules ==
  
  git status
+
  # apache2ctl -M
  
== Showing repo history ==
+
== Maintaining .htaccess passwords ==
  
git log
+
To add or modify the password for a user:
  
== Showing remote repositories (including 'origin') ==
+
$ htpasswd /etc/apache2/passwd username
  
git remote -v
+
== Configuring PHP session timeout in .htaccess ==
  
== Handy git aliases ==
+
For a session timeout of 9 hours:
  
Save these to your ~/.gitconfig file.
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
== Disabling PHP magic quotes in .htaccess ==
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
php_flag magic_quotes_gpc Off
  
To show only the files that have changed, rather than the full line-by-line content:
+
== Requiring HTTP Auth in .htaccess ==
  
  dif  = !git diff --name-status
+
AuthType Basic
 
+
AuthName "Speak Friend And Enter"
== Show git remote URL ==
+
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
 +
 
 +
== Restarting Apache ==
  
git config --get remote.origin.url
+
The hard way
  
= IRC =
+
$ sudo /etc/init.d/apache2 restart
  
== Instructing ChanServ to op an admin ==
+
The graceful way (avoids dropping active connections)
  
  /msg ChanServ op #channel user
+
  $ sudo apache2ctl graceful
  
E.g.
+
== Allowing directory browsing ==
  
/msg ChanServ op #gnurc jj5
+
To show directory index pages, in the apache config file:
  
Sub 'op' for 'deop' to remove op privilege.
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
= C++ =
+
= C =
  
== C++ books ==
+
== Locating memset function ==
  
=== Books I want ===
+
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://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== Links ==
* [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.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
* [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 ===
+
= PHP =
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
== Including a file relative to the including file ==
* [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 ===
+
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
== Enabling error reporting ==
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
== Setting an error handler ==
  
== C++ blogs/articles ==
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
* [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 ==
+
== Disable HTML content in var_dump ==
  
* ++c can be faster than c++.
+
ini_set( 'html_errors', 'off' );
* 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 =
+
== Report PHP modules ==
  
[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.
+
$ php -m
  
== Following a service log ==
+
== PHP Security Best Practices For Sys Admins ==
  
e.g. for bind9:
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
# journalctl -f -u bind9
+
= BASH scripting =
  
or for everything:
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
# journalctl -f
+
== Telling a script to run in bash ==
  
== System status ==
+
The first line of the file should be:
  
To see spawned services hierarchy:
+
#!/bin/bash
  
# systemctl status
+
== Checking if a command-line argument was passed in ==
  
Or for a specific service e.g.:
+
if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
# systemctl status networking
+
== Checking if a command-line argument was not passed in ==
  
= SaltStack =
+
if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
== Running a command on specified minions ==
+
Or:
  
  salt 'host' cmd.run 'update-locale'
+
  if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
== Running a command on all minions ==
+
== Checking command exit status ==
  
  salt '*' cmd.run 'update-locale'
+
  cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
== Listing active jobs ==
+
== Checking if a file does/doesn't exist ==
  
salt-run jobs.active
+
Check if file exists:
  
== Listing available grains ==
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
salt 'example' grains.items
+
Check if file doesn't exist:
  
== Listing available pillar ==
+
if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
  
salt 'example' pillar.items
+
== Checking if a directory does/doesn't exist ==
  
== Reporting a grain value ==
+
Check if directory exists:
  
e.g. for the 'mem_total' grain:
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
 +
 
 +
Check if directory doesn't exist:
  
  salt '*' grains.item mem_total
+
  if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
== Passing a variable into a Jinja template from a salt state (SLS) ==
+
== Deleting old backups ==
  
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
+
To keep only the latest five backups:
  
  <nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
+
  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
  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 =
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
  
== Running user login script (X11/XOrg/XWindows) ==
+
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.
  
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:
+
== Changing into the script's directory ==
  
  [Desktop Entry]
+
  cd "`dirname $0`"
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 ==
+
== Getting the absolute path of a relative path ==
  
{|class="wikitable"
+
readlink -f ./some/path
! 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 =
+
== Creating a temp directory ==
  
== Mounting a VirtualBox VDI file ==
+
dir=`mktemp -d` && cd $dir
  
Note: instead of doing this consider booting with a live CD.
+
== Reading secret input from stdin ==
  
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
+
You can read a secret, such as a password, like this:
  
Install qemu if necessary:
+
echo -n "Enter passphrase: "
 +
stty -echo
 +
read passphrase;
 +
stty echo
 +
echo ""
  
# apt install qemu
+
After running the above the secret will be in the $passphrase environment variable.
  
Then you'll need to load the network block device module:
+
== String replacements in bash ==
  
# rmmod nbd
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
# modprobe nbd max_part=16
 
  
Attach the .vdi image to one of the nbd you just created:
+
result=${var/find/replace}
  
# qemu-nbd -c /dev/nbd0 drive.vdi
+
To replace all occurrences:
  
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
+
result=${var//find/replace}
  
# mount /dev/nbd0p1 /mnt
+
A practical example, get an ISO date and turn it into a path:
  
Once you are done, unmount everything and disconnect the device:
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
# qemu-nbd -d /dev/nbd0
+
== Sending a HEREDOC to a file ==
  
= Elasticsearch =
+
cat << EOF > /tmp/yourfilehere
 +
These contents will be written to the file.
 +
        This line is indented.
 +
EOF
  
== Report on health of your Elasticsearch cluster ==
+
== Bash case/switch statement ==
  
$ curl http://localhost:9200/_cluster/health?pretty
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
= Zabbix =
+
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
  
== Zabbix Agent on Mac OS X ==
+
== Using dotglob shopt to match dot-files ==
  
Download and install agent.
+
To enable dot-file matching in globs, set the dotglob shell option:
  
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
+
$ shopt -s dotglob
  
Unload agent with:
+
== 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 [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)].
 +
 
 +
== Run a command using arguments that come from an array ==
 +
 
 +
See [https://unix.stackexchange.com/a/412647/356289 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 [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 ==
 +
 
 +
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html 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 ===
 +
 
 +
* [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
 +
|-
 +
| Send Ctrl+D    || Pause    || xdotool key "ctrl+d"
 +
|-
 +
| 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
 +
|-
 +
| Firefox        || ScrollLock || firefox
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|}
 +
 
 +
== 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
 
|}
 

Latest revision as of 04:24, 28 February 2024

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

Determining which Linux kernel you are running

$ uname -r

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

Service management

Report running services

# service --status-all

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

Power-off a hard drive

For instance if it's a USB drive or in a mobile rack and you want to remove it.

# udisksctl power-off -b /dev/sdi

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

Merging two directories

$ cp -RT source/ destination/

Files from source will be merged into destination.

Generating a replacement file

So you generate the file into a temp file, then hard link the temp file to where you want the replacement to go, then you delete the temp file:

$ generate-file.sh > file.txt.tmp
$ ln -f file.txt.tmp file.txt
$ rm file.txt.tmp

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
Send Ctrl+D Pause xdotool key "ctrl+d"
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
Firefox ScrollLock firefox
Kate Ctrl+Shift+F12 kate
KCalc Ctrl+Shift+F11 kcalc

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/