Difference between revisions of "John's Linux page"

From ProgClub
Jump to: navigation, search
(Monitoring a ZFS server)
(File searching)
 
(52 intermediate revisions by the same user not shown)
Line 2: Line 2:
  
 
Note: I have some other disorganised notes on [http://www.jj5.net/sixsigma/UNIX UNIX], which include a few tips for MacOS. I also have some tips for [http://www.jj5.net/sixsigma/OS_X OS X].
 
Note: I have some other disorganised notes on [http://www.jj5.net/sixsigma/UNIX UNIX], which include a few tips for MacOS. I also have some tips for [http://www.jj5.net/sixsigma/OS_X 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.
  
 
= System =
 
= System =
Line 13: Line 15:
 
  $ lsb_release
 
  $ lsb_release
  
== Determining which Unix you are running ==
+
== Determining which Linux/Unix you are running ==
  
 
  $ uname
 
  $ uname
 +
 +
Or,
 +
 +
$ uname -mrs
  
 
Or,
 
Or,
Line 70: Line 76:
 
  RAID:      Devices: 1: /dev/md1 2: /dev/md0
 
  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
 
  Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5
 +
 +
= Power =
 +
 +
== Reporting on PowerShield DEFENDER UPS status ==
 +
 +
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
 +
 +
$ upsc defender
 +
 +
E.g.:
 +
 +
jj5@orac:~$ upsc defender
 +
Init SSL without certificate database
 +
battery.charge: 100
 +
battery.voltage: 27.40
 +
battery.voltage.high: 26.00
 +
battery.voltage.low: 20.80
 +
battery.voltage.nominal: 24.0
 +
device.type: ups
 +
driver.name: blazer_usb
 +
driver.parameter.pollinterval: 2
 +
driver.parameter.port: auto
 +
driver.parameter.synchronous: no
 +
driver.version: 2.7.4
 +
driver.version.internal: 0.12
 +
input.current.nominal: 5.0
 +
input.frequency: 50.1
 +
input.frequency.nominal: 50
 +
input.voltage: 242.6
 +
input.voltage.fault: 242.6
 +
input.voltage.nominal: 240
 +
output.voltage: 242.6
 +
ups.beeper.status: disabled
 +
ups.delay.shutdown: 30
 +
ups.delay.start: 180
 +
ups.load: 14
 +
ups.productid: 5161
 +
ups.status: OL
 +
ups.type: offline / line interactive
 +
ups.vendorid: 0665
 +
 +
== Run commands on PowerShield DEFENDER UPS batteries ==
 +
 +
You can run "instant commands" using the '''upscmd''' command.
 +
 +
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
 +
 +
diligence:/srv/salt/conf/app/defender-1200.sls
 +
 +
To see "instant commands" supported by the PowerShield DEFENDER:
 +
 +
$ upscmd -l defender
 +
 +
E.g.:
 +
 +
jj5@orac:~$ upscmd -l defender
 +
Instant commands supported on UPS [defender]:
 +
 +
beeper.toggle - Toggle the UPS beeper
 +
load.off - Turn off the load immediately
 +
load.on - Turn on the load immediately
 +
shutdown.return - Turn off the load and return when power is back
 +
shutdown.stayoff - Turn off the load and remain off
 +
shutdown.stop - Stop a shutdown in progress
 +
test.battery.start - Start a battery test
 +
test.battery.start.deep - Start a deep battery test
 +
test.battery.start.quick - Start a quick battery test
 +
test.battery.stop - Stop the battery test
  
 
= Environment =
 
= Environment =
Line 168: Line 242:
  
 
  $ sudo su -c "svn update" www-data
 
  $ sudo su -c "svn update" www-data
 +
 +
== Reporting user and group info for the current user ==
 +
 +
$ id
  
 
= Memory management =
 
= Memory management =
Line 176: Line 254:
  
 
  $ free -m
 
  $ free -m
 +
 +
== Check for swap thrashing ==
 +
 +
Check your virtual memory status with vmstat:
 +
 +
$ vmstat
  
 
= Video/display management =
 
= Video/display management =
Line 204: Line 288:
 
To see full command-line press 'c'.
 
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' ==
 
== Changing memory reporting in 'top' ==
  
Line 210: Line 298:
 
  $ top
 
  $ top
  
Press 'E' to switch between memory units (KiB, MiB, GiB, etc.)
+
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 sort by memory utilisation.
Line 261: Line 351:
 
  # watch free -h
 
  # watch free -h
 
  # watch slabtop -o
 
  # watch slabtop -o
 +
# slabtop
 
  # watch cat /proc/meminfo
 
  # watch cat /proc/meminfo
 +
# perf top
 
  # watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 
  # watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
 
  # watch zpool iostat -v
 
  # watch zpool iostat -v
 
  # zpool iostat -v 2
 
  # zpool iostat -v 2
  # watch 'zfs list; echo; zpool list'
+
  # watch 'zpool list; echo; zfs list'
 
  # watch zfs get compressratio -o all
 
  # watch zfs get compressratio -o all
 
  # watch cat /proc/spl/kstat/zfs/arcstats
 
  # watch cat /proc/spl/kstat/zfs/arcstats
Line 283: Line 375:
 
  # zfs get all data
 
  # zfs get all data
  
= Monitoring disk I/O =
+
If you want to get funky:
  
There's an app for that! iotop.
+
# cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
== Using iotop, top for disks ==
+
You can search for ZFS files like e.g. this:
  
  # iotop -oPa
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
= File management =
+
You can report history of a zpool:
  
== Listing only directories ==
+
# zpool history $poolname
  
$ ls -l | egrep '^d'
+
You can get a report on the dedup tables:
  
== Listing only files ==
+
# zpool status -D $poolname
  
$ ls -l | egrep -v '^d'
+
Or more detailed dedup table info:
  
== Listing hidden files ==
+
# zdb -DDD $poolname
  
$ ls -al .[!.]*
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
== Creating a symbolic link ==
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
$ ln -s /path/to/target link-name
+
== Measure data throughput ==
  
== Creating a hard-link ==
+
Use the 'pv' command from the 'pv' package, e.g.:
  
  $ ln /path/to/target file-name
+
  # cat /dev/sda | pv | cat > /dev/null
  
== Changing the owner of a file ==
+
Or for ZFS:
  
  $ chown user:group <files>
+
  # zfs send data/example | pv | cat > /dev/null
  
E.g.
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
$ chown jj5:staff README
+
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].
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
== Report hard disk usage ==
  
$ chown -R root:root /etc/*
+
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.
  
== Changing file permissions ==
+
== Report hard disk temperatures ==
  
{|class="wikitable"
+
E.g.
|+ Object codes
+
 
! User !! Group !! Other
+
# hddtemp /dev/sd[a-e]
|-
+
 
| u    || g    || o
+
= Monitoring disk I/O =
|}
+
 
 +
There's an app for that! iotop.
 +
 
 +
== Using iotop, top for disks ==
  
{|class="wikitable"
+
# iotop -oPa
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
== Monitor disk I/O for performance issues ==
|+ 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].
+
# watch iostat
  
$ chmod <user numeric code><group numeric code><other numeric code> <files>
+
Or e.g.
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
# watch iostat -xd /dev/sd[abc]
  
$ chmod 600 my-private-file
+
Or use groupings like this command for 'tact':
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
+
= Monitoring a system =
  
$ cp old.conf updated.conf
+
== Simple ZFS monitoring ==
$ 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
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
The merge program is a part of the RCS package. If you don't have it:
+
= Monitoring temperature =
  
$ sudo apt-get install rcs
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
== Listing open files ==
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
Use lsof to list open files. E.g.:
+
and:
  
  # lsof
+
  $ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
See man lsof for options.
+
== Monitoring CPU temperature ==
  
== List permissions on a whole directory path ==
+
$ watch sensors
  
E.g.:
+
== Monitoring HDD temperature ==
  
$ namei -om /home/jj5/workspace
+
For e.g. SATA drives sda to sdd:
  
Outputs:
+
# watch hddtemp /dev/sd[a-d]
  
f: /home/jj5/workspace/
+
= File management =
  drwxr-xr-x root root /
 
  drwxr-xr-x root root home
 
  drwxr-xr-x jj5  jj5  jj5
 
  drwxr-xr-x jj5  jj5  workspace
 
  
== Counting non-blank lines in a file ==
+
== Listing only directories ==
  
E.g.:
+
$ ls -l | egrep '^d'
  
$ cat foo.c | sed '/^\s*$/d' | wc -l
+
== Listing only files ==
  
== Cloning one directory to another with rsync ==
+
$ ls -l | egrep -v '^d'
  
E.g.:
+
== Listing hidden files ==
  
rsync --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse /data/source/ /data/target/
+
$ ls -al .[!.]*
  
= Symbolic-link management =
+
== Creating a symbolic link ==
  
== Data used by sym-linked files:
+
$ ln -s /path/to/target link-name
  
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:
+
== Creating a hard-link ==
  
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
  $ ln /path/to/target file-name
  
= File searching =
+
== Changing the owner of a file ==
  
== Finding a file with a particular name ==
+
$ chown user:group <files>
  
$ find -iname "*some-part-of-the-file-name*"
+
E.g.
  
Will start searching from the current directory, so maybe
+
$ chown jj5:staff README
 +
$ chown root:root *
  
$ cd /
+
To apply recursively into sub-directories use -R,
  
first. For a case-sensitive search:
+
$ chown -R root:root /etc/*
  
$ find -name "*eXaCT CaSE*"
+
== Changing file permissions ==
  
== Finding a file with particular content ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
To search in /etc/ for a file with particular content:
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
$ grep -R "search-string" /etc/*
+
{|class="wikitable"
 
+
|+ Numeric codes
To search the current directory for *.cs files containing the word "Up":
+
! 0
 
+
| None
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
|-
 
+
! 1
== Finding a list of files with particular content ==
+
| Execute
 +
|-
 +
! 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 ==
 
 
 
  $ locate part-of-filename
 
  
 
E.g.
 
E.g.
  
  $ locate texvc
+
  $ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
== Updating locate command's database ==
+
== Updating config files ==
  
# updatedb
+
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:
  
= Job control =
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
== Stopping a running process ==
+
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.
  
Press Ctrl+Z to stop a running process.
+
The merge program is a part of the RCS package. If you don't have it:
  
== Listing current jobs and their status ==
+
$ sudo apt-get install rcs
  
$ jobs
+
== Listing open files ==
  
== Resuming a stopped job in the backgroud ==
+
Use lsof to list open files. E.g.:
  
To resume a stopped process in the background
+
# lsof
  
$ bg %1
+
See man lsof for options.
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== List permissions on a whole directory path ==
  
== Resuming a stopped job in the foreground ==
+
E.g.:
  
To resume a stopped process in the foreground
+
$ namei -om /home/jj5/workspace
  
$ fg %1
+
Outputs:
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
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
  
== Killing a stopped job ==
+
== Counting non-blank lines in a file ==
  
To kill a job
+
E.g.:
  
  $ kill %1
+
  $ cat foo.c | sed '/^\s*$/d' | wc -l
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Cloning one directory to another with rsync ==
  
== Periodically run a program and watch its output ==
+
E.g.:
  
$ watch /your/command
+
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/
  
= Debian/Ubuntu package management =
+
== Counting number of files in current directory and all subdirectories ==
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
$ ls -AlhR . | egrep '^-' | wc -l
  
== configuring debconf ==
+
== Counting number of directories in current directory and all subdirectories ==
  
  # dpkg-reconfigure debconf
+
  $ ls -AlhR . | egrep '^d' | wc -l
  
Set priority to low to get asked detailed questions.
+
= Compression =
  
== Showing list of installed packages ==
+
== How to use pigz with tar ==
  
# dpkg --get-selections
+
See [https://stackoverflow.com/a/39904353 here]:
  
== Searching for installed package ==
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
# dpkg --get-selections | grep package-name
+
== Best parallel compression with pigz ==
  
or
+
$ pigz --best
  
# aptitude search package-name
+
== Best parallel compression with xz ==
  
== Showing which files are installed as part of a package ==
+
$ xz -9e -T 0
  
# dpkg -L package-name
+
== Reporting compression ratios with xz ==
  
== Installing a package ==
+
e.g.
  
  # apt-get install package-name
+
  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
  
== Uninstalling a package ==
+
= Symbolic-link management =
  
# apt-get remove package-name
+
== Data used by sym-linked files:
  
== Showing system architecture ==
+
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:
  
  $ dpkg --print-architecture
+
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
== Showing which package a file belongs to ==
+
= File searching =
  
$ which echo
+
== Finding a file with a particular name ==
/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 ==
+
$ find -iname "*some-part-of-the-file-name*"
  
$ apt-cache showpkg coreutils
+
Will start searching from the current directory, so maybe
  
Or for even more information:
+
$ cd /
  
$ apt-cache show coreutils
+
first. For a case-sensitive search:
  
== List all installed packages with package version info ==
+
$ find -name "*eXaCT CaSE*"
  
dpkg-query -l
+
== Finding a file with particular content ==
  
== Reporting which version of a package is installed ==
+
To search in /etc/ for a file with particular content:
  
  $ dpkg -l | grep package-name
+
  $ grep -R "search-string" /etc/*
  
E.g.:
+
To search the current directory for *.cs files containing the word "Up":
  
  root@hope:~/letsencrypt# dpkg -l | grep augeas
+
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
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 ==
+
== Finding a list of files with particular content ==
  
Try the following:
+
E.g. to find all the files with the word 'creativity':
  
  # apt-get update
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
= Networking =
+
== Using the locate command to find files ==
  
== net-tools vs iproute2 ==
+
$ locate part-of-filename
  
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"
+
  $ locate texvc
! 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 ==
+
== Updating locate command's database ==
  
For servers:
+
# updatedb
  
# service networking restart
+
== Select a random line from a text file ==
  
For desktops:
+
$ shuf -n 1 input.txt
  
# service network-manager restart
+
= Job control =
  
== Pinging with particular packet size ==
+
== Stopping a running process ==
  
$ ping -M do -s <packet size in bytes> <host>
+
Press Ctrl+Z to stop a running process.
  
E.g.
+
== Listing current jobs and their status ==
  
  $ ping -M do -s 1400 charity.progclub.org
+
  $ jobs
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Resuming a stopped job in the backgroud ==
  
# ip route add <host> dev <interface> advmss <packet size>
+
To resume a stopped process in the background
  
E.g.
+
$ bg %1
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Dropping configured MMS for a particular IP address ==
+
== Resuming a stopped job in the foreground ==
  
# ip route flush <host>
+
To resume a stopped process in the foreground
  
E.g.
+
$ fg %1
  
# ip route flush 10.0.0.1
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Listing open ports and socket information ==
+
== Killing a stopped job ==
  
Including which process is listening on which port.
+
To kill a job
  
  # netstat -tulpn
+
  $ kill %1
  
Or use the 'ss' command:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
# ss -s
+
== Periodically run a program and watch its output ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
$ watch /your/command
  
# lsof -Pnl +M -i4
+
= Debian/Ubuntu package management =
  
You might need to install the lsof package:
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
# apt-get install lsof
+
== configuring debconf ==
  
== Query for DNS MX record ==
+
# dpkg-reconfigure debconf
  
$ nslookup
+
Set priority to low to get asked detailed questions.
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
== Showing list of installed packages ==
  
  $ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
  # dpkg --get-selections
  
== Using nmap to list open ports on remote host ==
+
== Searching for installed package ==
  
To check the 1,000 most common ports:
+
# dpkg --get-selections | grep package-name
  
# nmap server.example.com
+
or
  
Or for a specific port range (e.g. 101 to 102):
+
# aptitude search package-name
  
# nmap -p 101-102 server.example.com
+
== Showing which files are installed as part of a package ==
  
Or for all ports (1 to 65,535):
+
# dpkg -L package-name
  
# nmap -p- server.example.com
+
== Installing a package ==
  
== Network monitoring ==
+
# apt-get install package-name
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
== Uninstalling a package ==
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
# apt-get remove package-name
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
== Showing system architecture ==
  
You can watch network traffic in real-time with nload:
+
$ dpkg --print-architecture
  
# nload -u M
+
== Showing which package a file belongs to ==
  
== Reporting network (NIC) speed ==
+
$ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
== Showing package information ==
  
  # dmesg | grep eth0
+
  $ apt-cache showpkg coreutils
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
Or for even more information:
  
== Path MTU discovery ==
+
$ apt-cache show coreutils
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
== List all installed packages with package version info ==
  
  # tracepath host.example.com
+
  dpkg-query -l
  
== Links ==
+
== Reporting which version of a package is installed ==
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
$ dpkg -l | grep package-name
  
= IPTables =
+
E.g.:
  
== Applying firewall rules ==
+
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
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
== Comprehensive upgrade ==
  
$ sudo vim /etc/iptables.test.rules
+
Try the following:
$ 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 =
+
# apt-get update
 +
# apt-get dist-upgrade
 +
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
== Denying hosts with ufw ==
+
== Searching all available packages ==
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
$ apt-cache search . | sort -d | less
  
= Bind9 =
+
= Networking =
  
== Viewing Bind9 querylog ==
+
== net-tools vs iproute2 ==
  
$ sudo rndc querylog
+
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].
$ tail -f /var/log/syslog
 
  
= IPSec =
+
{|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)
 +
|}
  
== Disabling IPSec ==
+
== Restart networking ==
  
# setkey -FP
+
For servers:
  
= OpenSSL =
+
# service networking restart
  
== Debugging IMAPS with OpenSSL ==
+
For desktops:
  
  # openssl s_client -connect localhost:993
+
  # service network-manager restart
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
== Pinging with particular packet size ==
  
  $ openssl s_client -connect www.example.com:443
+
  $ ping -M do -s <packet size in bytes> <host>
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
E.g.
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
$ ping -M do -s 1400 charity.progclub.org
  
= Pluggable Authentication Modules (PAM) =
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
== Links ==
+
# ip route add <host> dev <interface> advmss <packet size>
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
E.g.
  
= SSH =
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
== Configuring SSH key login ==
+
== Dropping configured MMS for a particular IP address ==
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
# ip route flush <host>
  
$ ssh-keygen -t rsa
+
E.g.
  
Copy the public key from the client to the server:
+
# ip route flush 10.0.0.1
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
== Listing open ports and socket information ==
  
Configure the authorized keys on the server:
+
Including which process is listening on which port.
  
  $ ssh user@example.org
+
  # netstat -tulpn
$ 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 ==
+
Or use the 'ss' command:
  
For example, connecting a remote MySQL server to the localhost:
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
== Listing open IPv4 connections ==
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
# lsof -Pnl +M -i4
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
You might need to install the lsof package:
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
# apt-get install lsof
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
== Query for DNS MX record ==
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
$ nslookup
 
+
> server 127.0.0.1
* run putty.exe
+
> set q=mx
* Connection -> SSH -> Tunnels
+
> mail.blackbrick.com
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
== Query for DNS SOA record ==
  
To see what's going on with your ssh connections,
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
$ ssh -v user@host
+
== Using nmap to list open ports on remote host ==
  
Or
+
To check the 1,000 most common ports:
  
  $ ssh -vv user@host
+
  # nmap server.example.com
  
== Unlocking SSH key for session ==
+
Or for a specific port range (e.g. 101 to 102):
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  # nmap -p 101-102 server.example.com
[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 ==
+
Or for all ports (1 to 65,535):
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
# nmap -p- server.example.com
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
== Network monitoring ==
  
== cat EOF ==
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
$ cat > output <<EOF
+
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
> text
+
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
> EOF
+
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 +
# Bandwidth per process: nethogs
  
$ cat output
+
== nload ==
text
 
  
= Script =
+
You can watch network traffic in real-time with nload:
  
== Creating a session log with script ==
+
# nload -u M
  
$ script -t 2> timing
+
== Reporting network (NIC) speed ==
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
== Replaying a scripted session ==
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
$ scriptreplay timing
+
Note: use ifconfig to get device name.
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
== Path MTU discovery ==
  
= Screen =
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
== Creating a new screen or reconnecting to a detached screen ==
+
# tracepath host.example.com
  
$ screen -R
+
== Listing available Ethernet devices ==
  
== Detaching a screen ==
+
To see a list of NICs available on the host:
  
  $ screen -D
+
  $ cat /proc/net/dev
  
== Reconnecting to screen ==
+
Also
  
  $ screen -D
+
  $ ip link
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
== 59 Linux Networking commands and scripts ==
  
#!/bin/bash
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
== Links ==
  
== Scrolling in screen ==
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
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.
+
= IPTables =
  
= Vim =
+
== Applying firewall rules ==
  
== First, why Vim? ==
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
$ 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
  
== Visual modes ==
+
= ufw =
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
== Denying hosts with ufw ==
  
== Configuring spaces instead of tabs ==
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
= Bind9 =
  
$ vim ~/.vimrc
+
== Viewing Bind9 querylog ==
  
and include the following lines:
+
$ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
set tabstop=2
+
= IPSec =
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
== Disabling IPSec ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
# setkey -FP
  
Use:
+
= OpenSSL =
  
:syntax on
+
== Debugging IMAPS with OpenSSL ==
  
to turn on syntax highlighting.
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
Use:
+
== Debugging HTTPS with OpenSSL ==
  
  :syntax off
+
  $ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
to turn off syntax highlighting.
+
== Links ==
  
To always use syntax highlighting:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
$ vim ~/.vimrc
+
= Pluggable Authentication Modules (PAM) =
  
and add:
+
== Links ==
  
syntax on
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
To get a list of supported colour schemes open vim and type:
+
= SSH =
  
:colorscheme[space][Ctrl+D]
+
== Configuring SSH key login ==
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
  colorscheme desert
+
  $ ssh-keygen -t rsa
  
== Inserting a TAB character when expandtab is on ==
+
Copy the public key from the client to the server:
  
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.
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
Press Ctrl+V TAB to insert a literal tab character.
+
Configure the authorized keys on the server:
  
Or you can disable tab expansion altogether with:
+
$ 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
  
:set expandtab!
+
== Tunneling over SSH ==
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
For example, connecting a remote MySQL server to the localhost:
  
  :%s/^\s*/&&/g
+
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
== Recording and replaying a macro ==
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
== Deleting to end of line ==
+
== Tunneling over SSH with PuTTY ==
  
d$
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
== Deleting to beginning of line ==
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
d^
+
== Enabling verbose SSH logging ==
  
== Finding text ==
+
To see what's going on with your ssh connections,
  
To search forward for "text":
+
$ ssh -v user@host
  
/text
+
Or
  
To search backward for "text":
+
$ ssh -vv user@host
  
?text
+
== Unlocking SSH key for session ==
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
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'
  
== Finding and replacing text ==
+
== Links ==
  
To replace the first instance of "search" on the current line with "destroy":
+
* [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]
  
:s/search/destroy/
+
= Standard IO =
  
To replace all instances of "search" on the current line with "destroy":
+
== cat EOF ==
  
  :s/search/destroy/g
+
  $ cat > output <<EOF
 +
> text
 +
> EOF
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
$ cat output
 +
text
  
:13,37 s/search/destroy/g
+
= Script =
  
To replace all instances of "search" in the entire file with "destroy":
+
== Creating a session log with script ==
  
  :%s/search/destroy/g
+
  $ script -t 2> timing
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
To set the line-ending to Unix line endings run the command:
+
== Replaying a scripted session ==
  
  :setlocal ff=unix
+
  $ scriptreplay timing
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
== Disabling auto-indent etc. to paste from clipboard ==
+
= Screen =
  
To disable smart indenting when you're going to paste in text:
+
== Creating a new screen or reconnecting to a detached screen ==
  
  :set paste
+
  $ screen -R
  
To turn it off again:
+
== Detaching a screen ==
  
  :set nopaste
+
  $ screen -D
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
== Reconnecting to screen ==
  
== Positioning windows ==
+
$ screen -D
 +
$ screen -R
  
Use -o for horizontal split, e.g.:
+
I have a script in ~/bin/reconnect like so,
  
  vim -o a.txt b.txt
+
  #!/bin/bash
 +
screen -D
 +
screen -R
  
Use -O for vertical split, e.g.:
+
This will detach your last screen, and reconnect it on the current terminal.
  
vim -o a.txt b.txt
+
== Scrolling in screen ==
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
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.
  
Use ^W and &lt; or &gt; to resize windows.
+
= Vim =
  
== To indent a block of text in Vim ==
+
== First, why Vim? ==
  
Use the > command. E.g. to indent five lines:
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
5 > >
+
== Visual modes ==
  
Press . (dot) to keep indenting.
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
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:
+
== Configuring spaces instead of tabs ==
  
> %
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
$ vim ~/.vimrc
  
== Open a file in a new window/tab ==
+
and include the following lines:
  
To open a file on the left hand side:
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
:vert new filename.ext
+
== Configuring syntax highlighting ==
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
To open a file at the top:
+
Use:
  
  :new filename.ext
+
  :syntax on
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
to turn on syntax highlighting.
  
== Explore files in Vim ==
+
Use:
  
Enter:
+
:syntax off
  
:Explore
+
to turn off syntax highlighting.
  
== Switch between Vim tabs ==
+
To always use syntax highlighting:
  
Use gt and gT.
+
$ vim ~/.vimrc
  
== Switch between Vim windows ==
+
and add:
  
To toggle between open windows use:
+
syntax on
  
Ctrl+W W
+
To get a list of supported colour schemes open vim and type:
  
To move in a direction use:
+
:colorscheme[space][Ctrl+D]
  
Ctrl+W h/j/k/l
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
colorscheme desert
  
== Insert block comment in Vim ==
+
== Inserting a TAB character when expandtab is on ==
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
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.
  
So it's:
+
Press Ctrl+V TAB to insert a literal tab character.
 +
 
 +
Or you can disable tab expansion altogether with:
  
# Ctrl+V (Note: not Shift+V!)
+
:set expandtab!
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
To navigate to the matching beginning or end tag use '%'.
+
:%s/^\s*/&&/g
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
== Auto-format HTML tags ==
+
== Recording and replaying a macro ==
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
  
# first join all the lines - ggVGgJ
+
== Deleting to end of line ==
# 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 ==
+
d$
  
* [http://www.vim.org/ Vim: the editor]
+
== Deleting to beginning of line ==
* [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 =
+
d^
  
== Talking to other users on the system ==
+
== Finding text ==
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
To search forward for "text":
  
1. SSH to <username>@<hostname> and login with your username and password.
+
/text
  
2. Issue the following command to find out who is logged onto the system:
+
To search backward for "text":
  
  $ who
+
  ?text
  
3. Issue the following command to talk to a specific user:
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
$ write <username>
+
== Finding and replacing text ==
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
To replace the first instance of "search" on the current line with "destroy":
  
= Date =
+
:s/search/destroy/
  
== Reporting the time on the server ==
+
To replace all instances of "search" on the current line with "destroy":
  
  $ date
+
  :s/search/destroy/g
  
== Reporting UTC time ==
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
  $ date --utc
+
  :13,37 s/search/destroy/g
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
To replace all instances of "search" in the entire file with "destroy":
  
  $ date="`date +%F-%H%M%S`"
+
  :%s/search/destroy/g
  
== Getting the year in four digits ==
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
$ year="`date +%Y`"
+
To set the line-ending to Unix line endings run the command:
  
== Getting the month in two digits ==
+
:setlocal ff=unix
  
$ month="`date +%m`"
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
== Getting the day of the month in two digits ==
+
== Disabling auto-indent etc. to paste from clipboard ==
  
$ day="`date +%d`"
+
To disable smart indenting when you're going to paste in text:
  
== Getting yesterday's date ==
+
:set paste
  
$ date --date='1 day ago' +%Y-%m-%d
+
To turn it off again:
  
== Converting Unix time (seconds since epoch) ==
+
:set nopaste
  
For timestamp '1501370200':
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
$ date -d @1501370200 +%F-%H%M%S
+
== Positioning windows ==
  
== Running timedatectl from systemd ==
+
Use -o for horizontal split, e.g.:
  
There's a new command bundled with systmed:
+
vim -o a.txt b.txt
  
# timedatectl
+
Use -O for vertical split, e.g.:
  
It reports on (and controls) how the system time is configured.
+
vim -o a.txt b.txt
  
= MySQL =
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
== Run mysql without authentication/authorisation ==
+
Use ^W and &lt; or &gt; to resize windows.
  
# service mysql stop
+
== To indent a block of text in Vim ==
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
Use the > command. E.g. to indent five lines:
  
  # mysql -u root mysql
+
  5 > >
  
To stop the unauthenticated service:
+
Press . (dot) to keep indenting.
  
# mysqladmin shutdown
+
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:
  
Then restart a normal service:
+
> %
  
# service mysql start
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
== Logging all database queries ==
+
== Open a file in a new window/tab ==
  
# vim /etc/mysql/my.cnf
+
To open a file on the left hand side:
  
In the [mysqld] section add:
+
:vert new filename.ext
  
log=/tmp/mysql.log
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
Then:
+
To open a file at the top:
  
  # service mysql restart
+
  :new filename.ext
  
Watch the log with:
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
# tail -f /tmp/mysql.log
+
== Explore files in Vim ==
  
== Dumping a MySQL database ==
+
Enter:
  
You can dump the database into a file using:  
+
:Explore
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
== Switch between Vim tabs ==
  
You can create a database using:
+
Use gt and gT.
  
$ echo create database databasename | mysql -h hostname -u user -p
+
== Switch between Vim windows ==
  
You can restore a database using:
+
To toggle between open windows use:
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
Ctrl+W W
  
# mysql -h localhost -u root --password=<password>
+
To move in a direction use:
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
Ctrl+W h/j/k/l
  
# mysql -h localhost -u root --password=<password>
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
== Insert block comment in Vim ==
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
So it's:
  
Check the SSL version in use:
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
show status like 'Ssl_version';
+
== Navigate to matching tag ==
  
Or check the cipher in use:
+
To navigate to the matching beginning or end tag use '%'.
  
show status like 'Ssl_cipher';
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
= Apache =
+
== Auto-format HTML tags ==
  
== Maintaining .htaccess passwords ==
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
To add or modify the password for a user:
+
# 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=
  
$ htpasswd /etc/apache2/passwd username
+
== Links ==
  
== Configuring PHP session timeout in .htaccess ==
+
* [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]
  
For a session timeout of 9 hours:
+
= Write =
  
php_value session.cookie_lifetime 32400
+
== Talking to other users on the system ==
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
php_flag magic_quotes_gpc Off
+
1. SSH to <username>@<hostname> and login with your username and password.
  
== Requiring HTTP Auth in .htaccess ==
+
2. Issue the following command to find out who is logged onto the system:
  
  AuthType Basic
+
  $ who
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
3. Issue the following command to talk to a specific user:
  
The hard way
+
$ write <username>
  
$ sudo /etc/init.d/apache2 restart
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
The graceful way (avoids dropping active connections)
+
= Date =
  
$ sudo apache2ctl graceful
+
== Reporting the time on the server ==
  
== Allowing directory browsing ==
+
$ date
  
To show directory index pages, in the apache config file:
+
== Reporting UTC time ==
  
  <Directory /var/www/data>
+
  $ date --utc
  Options Indexes
 
</Directory>
 
  
= C =
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
== Locating memset function ==
+
$ date="`date +%F-%H%M%S`"
  
The memset function is in &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
+
== Getting the year in four digits ==
  
== Links ==
+
$ year="`date +%Y`"
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
== Getting the month in two digits ==
  
= PHP =
+
$ month="`date +%m`"
  
== Including a file relative to the including file ==
+
== Getting the day of the month in two digits ==
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  $ day="`date +%d`"
  
== Enabling error reporting ==
+
== Getting yesterday's date ==
  
  error_reporting( E_ALL | E_STRICT );
+
  $ date --date='1 day ago' +%Y-%m-%d
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
== Converting Unix time (seconds since epoch) ==
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
For timestamp '1501370200':
  
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
  $ date -d @1501370200 +%F-%H%M%S
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
== Running timedatectl from systemd ==
  
ini_set( 'html_errors', 'off' );
+
There's a new command bundled with systmed:
  
= BASH scripting =
+
# timedatectl
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
It reports on (and controls) how the system time is configured.
  
== Telling a script to run in bash ==
+
= MySQL =
  
The first line of the file should be:
+
== Run mysql without authentication/authorisation ==
  
  #!/bin/bash
+
  # service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
== Checking if a command-line argument was passed in ==
+
Then you can connect without a password, e.g.:
  
  if [ -n "$1" ]; then
+
  # mysql -u root mysql
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
To stop the unauthenticated service:
  
  if [ "$1" = "" ]; then
+
  # mysqladmin shutdown
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
Then restart a normal service:
  
  if [ -z "$1" ]; then
+
  # service mysql start
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
== Logging all database queries ==
  
  cd /my/path
+
  # vim /etc/mysql/my.cnf
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
In the [mysqld] section add:
  
Check if file exists:
+
log=/tmp/mysql.log
  
if [ -f "/my/file" ]; then
+
Then:
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
# service mysql restart
  
if [ ! -f "/my/file" ]; then
+
Watch the log with:
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
# tail -f /tmp/mysql.log
  
Check if directory exists:
+
== Dumping a MySQL database ==
  
  if [ -d "/my/dir" ]; then
+
You can dump the database into a file using:
  rmdir /my/dir
+
   
  fi
+
  $ mysqldump -h hostname -u user --password=password databasename > filename
  
Check if directory doesn't exist:
+
== Loading a MySQL database from a dump file ==
  
if [ ! -d "/my/dir" ]; then
+
You can create a database using:
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
$ echo create database databasename | mysql -h hostname -u user -p
  
To keep only the latest five backups:
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
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
+
== Creating a MySQL user ==
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
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.
+
== Granting all MySQL user permissions ==
  
== Changing into the script's directory ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
cd "`dirname $0`"
+
== Select domain name from email address ==
  
== Getting the absolute path of a relative path ==
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
readlink -f ./some/path
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
== Creating a temp directory ==
+
Check the SSL version in use:
  
  dir=`mktemp -d` && cd $dir
+
  show status like 'Ssl_version';
  
== Reading secret input from stdin ==
+
Or check the cipher in use:
  
You can read a secret, such as a password, like this:
+
show status like 'Ssl_cipher';
  
echo -n "Enter passphrase: "
+
= Apache =
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Reporting loaded Apache modules ==
  
== String replacements in bash ==
+
# apache2ctl -M
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
== Maintaining .htaccess passwords ==
  
result=${var/find/replace}
+
To add or modify the password for a user:
  
To replace all occurrences:
+
$ htpasswd /etc/apache2/passwd username
  
  result=${var//find/replace}
+
== 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
  
A practical example, get an ISO date and turn it into a path:
+
== Disabling PHP magic quotes in .htaccess ==
  
  date="$(date +%Y-%m-%d)"
+
  php_flag magic_quotes_gpc Off
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
== Requiring HTTP Auth in .htaccess ==
  
  cat << EOF > /tmp/yourfilehere
+
  AuthType Basic
  These contents will be written to the file.
+
  AuthName "Speak Friend And Enter"
        This line is indented.
+
AuthUserFile /home/jj5/.htpasswd
  EOF
+
  Require valid-user
  
== Bash case/switch statement ==
+
== Restarting Apache ==
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
The hard way
  
  case $space in
+
  $ sudo /etc/init.d/apache2 restart
[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 ==
+
The graceful way (avoids dropping active connections)
  
To enable dot-file matching in globs, set the dotglob shell option:
+
$ sudo apache2ctl graceful
  
$ shopt -s dotglob
+
== Allowing directory browsing ==
  
= Sed =
+
To show directory index pages, in the apache config file:
  
== Find and replace with sed ==
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
To update the current file use '-i'. E.g.:
+
= C =
  
sed -i 's/search-text/replace-text/' file
+
== Locating memset function ==
  
= Awk =
+
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]
  
== Listing IP addresses in an Apache web log ==
+
== Links ==
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
== Printing space-separated field ==
+
= PHP =
  
echo 'no no yes no' | awk '{print $3}'
+
== Including a file relative to the including file ==
  
== Printing delimited field ==
+
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
== Enabling error reporting ==
  
= Subversion =
+
error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
== Setting svn:externals from the command-line ==
+
== Setting an error handler ==
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
To set an svn:externals from the command-line:
+
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
== Disable HTML content in var_dump ==
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
ini_set( 'html_errors', 'off' );
  
svn propset svn:externals -F svn.externals .
+
== Report PHP modules ==
  
== Setting svn:ignore from the command line ==
+
$ php -m
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
== PHP Security Best Practices For Sys Admins ==
  
$ svn propset svn:ignore [file|folder] [path]
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
Or use a file and apply recursively:
+
= BASH scripting =
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
= Git =
+
== Telling a script to run in bash ==
  
== Showing status of working copy ==
+
The first line of the file should be:
  
  git status
+
  #!/bin/bash
  
== Showing repo history ==
+
== Checking if a command-line argument was passed in ==
  
  git log
+
  if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
== Showing remote repositories (including 'origin') ==
+
== Checking if a command-line argument was not passed in ==
  
  git remote -v
+
  if [ "$1" = "" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
== Handy git aliases ==
+
Or:
  
Save these to your ~/.gitconfig file.
+
if [ -z "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
== Checking command exit status ==
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
To show only the files that have changed, rather than the full line-by-line content:
+
== Checking if a file does/doesn't exist ==
  
  dif  = !git diff --name-status
+
Check if file exists:
  
= IRC =
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
== Instructing ChanServ to op an admin ==
+
Check if file doesn't exist:
  
  /msg ChanServ op #channel user
+
  if [ ! -f "/my/file" ]; then
 +
  touch /my/file
 +
fi
 +
 
 +
== Checking if a directory does/doesn't exist ==
 +
 
 +
Check if directory exists:
  
E.g.
+
if [ -d "/my/dir" ]; then
 +
  rmdir /my/dir
 +
fi
  
/msg ChanServ op #gnurc jj5
+
Check if directory doesn't exist:
  
Sub 'op' for 'deop' to remove op privilege.
+
if [ ! -d "/my/dir" ]; then
 +
  mkdir /my/dir
 +
fi
  
= C++ =
+
== Deleting old backups ==
  
== C++ books ==
+
To keep only the latest five backups:
  
=== Books I want ===
+
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
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
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.
* [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 ===
+
== Changing into the script's directory ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
cd "`dirname $0`"
* [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 ===
+
== Getting the absolute path of a relative path ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
readlink -f ./some/path
** Note: 3ed is obsolete. Buy 4ed (above).
+
 
 +
== Creating a temp directory ==
 +
 
 +
dir=`mktemp -d` && cd $dir
 +
 
 +
== Reading secret input from stdin ==
  
=== Books I've read ===
+
You can read a secret, such as a password, like this:
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
echo -n "Enter passphrase: "
 +
stty -echo
 +
read passphrase;
 +
stty echo
 +
echo ""
  
== C++ blogs/articles ==
+
After running the above the secret will be in the $passphrase environment variable.
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
== String replacements in bash ==
* [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 ==
+
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
  
* ++c can be faster than c++.
+
result=${var/find/replace}
* 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 =
+
To replace all occurrences:
  
[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.
+
result=${var//find/replace}
  
== Following a service log ==
+
A practical example, get an ISO date and turn it into a path:
  
e.g. for bind9:
+
date="$(date +%Y-%m-%d)"
 +
work_dir=${date//-//}
  
# journalctl -f -u bind9
+
== Sending a HEREDOC to a file ==
  
or for everything:
+
cat << EOF > /tmp/yourfilehere
 +
These contents will be written to the file.
 +
        This line is indented.
 +
EOF
  
# journalctl -f
+
== Bash case/switch statement ==
  
== System status ==
+
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
  
To see spawned services hierarchy:
+
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
  
# systemctl status
+
== Make sure only one instance of a script is running at a time ==
  
Or for a specific service e.g.:
+
ephemeralDataDir=/var/run/something
 +
unlock() {
 +
  rmdir $ephemeralDataDir/lock
 +
}
 +
mkdir $ephemeralDataDir/lock || exit 1;
 +
trap unlock EXIT
  
  # systemctl status networking
+
== 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)].
 +
 
 +
= 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
 +
 
 +
= 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 ==
 +
 
 +
salt 'host' cmd.run 'update-locale'
 +
 
 +
== Running a command on all minions ==
 +
 
 +
salt '*' cmd.run 'update-locale'
 +
 
 +
== 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
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 +
|-
 +
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 +
|-
 +
| Konsole        || Meta+T  || konsole
 +
|-
 +
| Dolphin        || Meta+E  || dolphin
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|-
 +
| Firefox        || Ctrl+Shift+F10 || firefox
 +
|}
  
= SaltStack =
+
= VirtualBox =
  
== Running a command on specified minions ==
+
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
  
salt 'host' cmd.run 'update-locale'
+
Install qemu if necessary:
  
== Running a command on all minions ==
+
# apt install qemu
  
salt '*' cmd.run 'update-locale'
+
Then you'll need to load the network block device module:
  
== Listing active jobs ==
+
# rmmod nbd
 +
# modprobe nbd max_part=16
  
salt-run jobs.active
+
Attach the .vdi image to one of the nbd you just created:
  
== Listing available grains ==
+
# qemu-nbd -c /dev/nbd0 drive.vdi
  
salt 'example' grains.items
+
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
  
== Listing available pillar ==
+
# mount /dev/nbd0p1 /mnt
  
salt 'example' pillar.items
+
Once you are done, unmount everything and disconnect the device:
  
== Reporting a grain value ==
+
  # qemu-nbd -d /dev/nbd0
 
 
e.g. for the 'mem_total' grain:
 
 
 
  salt '*' grains.item mem_total
 
 
 
= 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'
 

Latest revision as of 04:21, 29 January 2020

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.

Contents

System

Determining which Debian/Ubuntu release your are running

$ lsb_release -r

Or for more information:

$ lsb_release

Determining which Linux/Unix you are running

$ uname

Or,

$ uname -mrs

Or,

$ uname -a

Configuring system swappiness

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

vm.swappiness = 0

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

echo 0 > /proc/sys/vm/swappiness

Hardware information

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

# lshw

And for CPUs:

# lscpu

And for PCI devices:

# lspci

And for DMI info:

# dmidecode

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

Power

Reporting on PowerShield DEFENDER UPS status

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

$ upsc defender

E.g.:

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

Run commands on PowerShield DEFENDER UPS batteries

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

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

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

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

$ upscmd -l defender

E.g.:

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

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

Environment

Configuring vim as your editor

Sometimes all you need is:

$ export EDITOR=/usr/bin/vim

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

Other times you need to run

# update-alternatives --config editor

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

Configuring your locale

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

User and group management

Adding a user

To add a new user on a linux system:

# useradd username
# passwd username

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

# adduser username

Adding a user to a group

To add an existing user to an existing group:

# gpasswd -a username group

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

# gpasswd -a jj5 sudo

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

# adduser username group

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

# adduser sclaughl staff

Disabling a user account

You can disable a user account with:

# passwd -l user

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

Enabling a disabled user account

To can re-enable a locked user account with:

# passwd -u user

Finding which user you are logged in as

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

$ whoami

Finding which groups you are a member of

To find which groups you are a member of:

$ groups

or

$ groups username

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

$ groups jj5

Finding who else is logged in to the system

To see who else is logged in,

$ who

Running a command as a particular user

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

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

Reporting user and group info for the current user

$ id

Memory management

Checking available memory

To report memory statistics in megabytes:

$ free -m

Check for swap thrashing

Check your virtual memory status with vmstat:

$ vmstat

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.

Disk management

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

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]

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]

File management

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

Compression

How to use pigz with tar

See here:

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

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

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

Networking

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

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.

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

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

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

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';

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).

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

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

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

Running a command on all minions

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

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

KDE

Running user login script (X11/XOrg/XWindows)

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

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

Standard KDE shortcut key bindings

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

VirtualBox

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