Difference between revisions of "John's Linux page"

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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.
 +
 +
You might also be interested in [[John's hacks]].
 +
 +
Quick jump to: [[#NetBeans|NetBeans]].
  
 
= System =
 
= System =
Line 13: Line 19:
 
  $ 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 48: Line 58:
  
 
  # dmidecode
 
  # dmidecode
 +
 +
Note that the dmidecode command (above) will give you information about your system's motherboard. For motherboard info look for 'System Information' and/or 'Base Board Information'.
  
 
Or the grand daddy of them all:
 
Or the grand daddy of them all:
Line 70: Line 82:
 
  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
 +
 +
== Viewing syslog and other logs with KSystemLog ==
 +
 +
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
 +
 +
= 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 252:
  
 
  $ 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 177: Line 265:
 
  $ free -m
 
  $ free -m
  
= Video/display management =
+
== Check for swap thrashing ==
 +
 
 +
Check your virtual memory status with vmstat:
 +
 
 +
$ vmstat
 +
 
 +
== Report memory type ==
 +
 
 +
Report on RAM DIMMs:
 +
 
 +
# dmidecode --type 17
 +
 
 +
Report on RAM and CPU cache (including L1, L2, and L3):
 +
 
 +
# lshw -short -C memory
 +
 
 +
Or for more detail:
 +
 
 +
# lshw -C memory
 +
 
 +
= Video/display management =
  
 
== Viewing EDID data for attached monitor ==
 
== Viewing EDID data for attached monitor ==
Line 208: Line 316:
 
* press '1' (one) to toggle CPU aggregation
 
* press '1' (one) to toggle CPU aggregation
 
* press < and > to change the sort column
 
* press < and > to change the sort column
 +
 
== Changing memory reporting in 'top' ==
 
== Changing memory reporting in 'top' ==
  
Line 221: Line 330:
  
 
Press 'm' to switch between various display modes.
 
Press 'm' to switch between various display modes.
 +
 +
== Showing full command-line in 'top' ==
 +
 +
To see the full command-line for processes run with -c:
 +
 +
$ top -c
 +
 +
== Listing all processes currently running which were started in your current shell session ==
 +
 +
$ ps -fl
 +
 +
== Killing specific processes ==
 +
 +
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
 +
 +
== Run a command for a specified time using timeout ==
 +
 +
$ timeout 3 ping jj5.net
  
 
= Disk management =
 
= Disk management =
 +
 +
== Creating a partition table ==
 +
 +
# parted /dev/xvdf
 +
 +
mktable msdos
 +
 +
== Creating a partition ==
 +
 +
# parted /dev/xvdf
 +
 +
u MiB
 +
mkpart primary 1 100%
 +
 +
== Creating an ext4 file-system ==
 +
 +
# mkfs.ext4 /dev/xvdf1
  
 
== Listing disk drives ==
 
== Listing disk drives ==
Line 273: Line 417:
 
  # 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 297: Line 441:
 
  # perf report --stdio
 
  # perf report --stdio
  
= Monitoring disk I/O =
+
You can search for ZFS files like e.g. this:
  
There's an app for that! iotop.
+
root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
== Using iotop, top for disks ==
+
You can report history of a zpool:
  
  # iotop -oPa
+
  # zpool history $poolname
  
= File management =
+
You can get a report on the dedup tables:
  
== Listing only directories ==
+
# zpool status -D $poolname
  
$ ls -l | egrep '^d'
+
Or more detailed dedup table info:
  
== Listing only files ==
+
# zdb -DDD $poolname
  
$ ls -l | egrep -v '^d'
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
== Listing hidden files ==
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
$ ls -al .[!.]*
+
== How to tell if zfs scrub is running ==
  
== Creating a symbolic link ==
+
You can get the status from the "scan:" line from:
  
  $ ln -s /path/to/target link-name
+
  $ zpool status
  
== Creating a hard-link ==
+
== Measure data throughput ==
  
$ ln /path/to/target file-name
+
Use the 'pv' command from the 'pv' package, e.g.:
  
== Changing the owner of a file ==
+
# cat /dev/sda | pv | cat > /dev/null
  
$ chown user:group <files>
+
Or for ZFS:
  
E.g.
+
# zfs send data/example | pv | cat > /dev/null
  
$ chown jj5:staff README
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
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 -R root:root /etc/*
+
== Report hard disk usage ==
  
== Changing file permissions ==
+
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.
  
{|class="wikitable"
+
== Report hard disk temperatures ==
|+ Object codes
+
 
! User !! Group !! Other
+
E.g.
|-
+
 
| u    || g    || o
+
# hddtemp /dev/sd[a-e]
|}
+
 
 +
== Burning an ISO image to USB on Mac ==
 +
 
 +
First insert your USB key and find the appropriate disk with:
 +
 
 +
# diskutil list
 +
 
 +
Then unmount it with:
 +
 
 +
# diskutil unmountDisk /dev/disk4
  
{|class="wikitable"
+
Then copy ISO image with 'dd':
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
|+ 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].
+
You can get dd to report progress by sending it the SIGINFO signal:
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  # kill -s info 12345
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
== Listing all ext4 file systems ==
  
$ chmod 600 my-private-file
+
To see a list only of the mounted ext4 file systems:
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
# df -t ext4
  
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:
+
== Report hierarchical file system mount points and mount options ==
  
  $ cp old.conf updated.conf
+
  $ findmnt
$ 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.
+
== Report the mount point for the current working directory ==
  
The merge program is a part of the RCS package. If you don't have it:
+
$ findmnt "$PWD"
  
$ sudo apt-get install rcs
+
= Monitoring disk I/O =
  
== Listing open files ==
+
There's an app for that! iotop.
  
Use lsof to list open files. E.g.:
+
== Using iotop, top for disks ==
  
  # lsof
+
  # iotop -oPa
  
See man lsof for options.
+
== Monitor disk I/O for performance issues ==
  
== List permissions on a whole directory path ==
+
# watch iostat
  
E.g.:
+
Or e.g.
  
  $ namei -om /home/jj5/workspace
+
  # watch iostat -xd /dev/sd[abc]
  
Outputs:
+
Or use groupings like this command for 'tact':
  
  f: /home/jj5/workspace/
+
  $ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  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 ==
+
= Monitoring a system =
  
E.g.:
+
== Simple ZFS monitoring ==
  
  $ cat foo.c | sed '/^\s*$/d' | wc -l
+
  # watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
== Cloning one directory to another with rsync ==
+
= Monitoring temperature =
  
E.g.:
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
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/
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
= Symbolic-link management =
+
and:
  
== Data used by sym-linked files:
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
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:
+
== Monitoring CPU temperature ==
  
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
  $ watch sensors
  
= File searching =
+
== Monitoring HDD temperature ==
  
== Finding a file with a particular name ==
+
For e.g. SATA drives sda to sdd:
  
  $ find -iname "*some-part-of-the-file-name*"
+
  # watch hddtemp /dev/sd[a-d]
  
Will start searching from the current directory, so maybe
+
= ZFS =
  
$ cd /
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
first. For a case-sensitive search:
+
See [https://superuser.com/q/1137416 How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?]
  
  $ find -name "*eXaCT CaSE*"
+
  $ cat /proc/spl/kstat/zfs/arcstats
  
== Finding a file with particular content ==
+
Then:
  
To search in /etc/ for a file with particular content:
+
c is the target size of the ARC in bytes
 +
c_max is the maximum size of the ARC in bytes
 +
size is the current size of the ARC in bytes
  
$ grep -R "search-string" /etc/*
+
== Stopping a ZFS scrub in progress ==
  
To search the current directory for *.cs files containing the word "Up":
+
# zpool scrub -s $pool
  
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
e.g. for the 'data' pool:
  
== Finding a list of files with particular content ==
+
# zpool scrub -s data
  
E.g. to find all the files with the word 'creativity':
+
= File management =
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
== Listing files by size ==
  
== Using the locate command to find files ==
+
Use capital S for Size:
  
  $ locate part-of-filename
+
  $ ls -S
  
E.g.
+
== Listing only directories ==
  
  $ locate texvc
+
  $ ls -l | egrep '^d'
  
== Updating locate command's database ==
+
== Listing only files ==
  
  # updatedb
+
  $ ls -l | egrep -v '^d'
  
= Job control =
+
== Listing hidden files ==
  
== Stopping a running process ==
+
$ ls -al .[!.]*
  
Press Ctrl+Z to stop a running process.
+
== Creating a symbolic link ==
  
== Listing current jobs and their status ==
+
$ ln -s /path/to/target link-name
  
$ jobs
+
== Creating a hard-link ==
  
== Resuming a stopped job in the backgroud ==
+
$ ln /path/to/target file-name
  
To resume a stopped process in the background
+
== Changing the owner of a file ==
  
  $ bg %1
+
  $ chown user:group <files>
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
E.g.
  
== Resuming a stopped job in the foreground ==
+
$ chown jj5:staff README
 +
$ chown root:root *
  
To resume a stopped process in the foreground
+
To apply recursively into sub-directories use -R,
  
  $ fg %1
+
  $ chown -R root:root /etc/*
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Changing file permissions ==
  
== Killing a stopped job ==
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
To kill a job
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
$ kill %1
+
{|class="wikitable"
 
+
|+ Numeric codes
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
! 0
 
+
| None
== Periodically run a program and watch its output ==
+
|-
 +
! 1
 +
| Execute
 +
|-
 +
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
$ watch /your/command
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
= Debian/Ubuntu package management =
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
E.g.
  
== configuring debconf ==
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
# dpkg-reconfigure debconf
+
== Updating config files ==
  
Set priority to low to get asked detailed questions.
+
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:
  
== Showing list of installed packages ==
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
# dpkg --get-selections
+
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.
  
== Searching for installed package ==
+
The merge program is a part of the RCS package. If you don't have it:
  
  # dpkg --get-selections | grep package-name
+
  $ sudo apt-get install rcs
  
or
+
== Listing open files ==
  
# aptitude search package-name
+
Use lsof to list open files. E.g.:
  
== Showing which files are installed as part of a package ==
+
# lsof
  
# dpkg -L package-name
+
See man lsof for options.
  
== Installing a package ==
+
== List permissions on a whole directory path ==
  
# apt-get install package-name
+
E.g.:
  
== Uninstalling a package ==
+
$ namei -om /home/jj5/workspace
  
# apt-get remove package-name
+
Outputs:
  
== Showing system architecture ==
+
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
  
$ dpkg --print-architecture
+
== Counting non-blank lines in a file ==
  
== Showing which package a file belongs to ==
+
E.g.:
  
  $ which echo
+
  $ cat foo.c | sed '/^\s*$/d' | wc -l
/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 ==
+
== Cloning one directory to another with rsync ==
  
$ apt-cache showpkg coreutils
+
E.g.:
  
Or for even more information:
+
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/
  
$ apt-cache show coreutils
+
== Counting number of files in current directory and all subdirectories ==
  
== List all installed packages with package version info ==
+
$ ls -AlhR . | egrep '^-' | wc -l
  
dpkg-query -l
+
== Counting number of directories in current directory and all subdirectories ==
  
== Reporting which version of a package is installed ==
+
$ ls -AlhR . | egrep '^d' | wc -l
 +
 
 +
== Getting the status of a 'dd' process ==
 +
 
 +
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
 +
 
 +
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
 +
 
 +
# kill -s info 40947
 +
 
 +
The dd process will report its status in the terminal its running in.
 +
 
 +
== Transferring a large file via FAT32 file system ==
 +
 
 +
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
  
  $ dpkg -l | grep package-name
+
  $ split -b 4000m input.tgz input.tgz-parts-
  
E.g.:
+
Then copy the small files and reassemble:
  
  root@hope:~/letsencrypt# dpkg -l | grep augeas
+
  $ cat input.tgz-parts-* > output.tgz
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 ==
+
= NFS =
  
Try the following:
+
== List NFS shares ==
  
# apt-get update
+
To e.g. show NFS shares on 'love':
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
= Networking =
+
$ showmount -e love
  
== net-tools vs iproute2 ==
+
= Compression =
  
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].
+
== How to use pigz with tar ==
  
{|class="wikitable"
+
See [https://stackoverflow.com/a/39904353 here]:
! 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 ==
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
For servers:
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
# service networking restart
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
For desktops:
+
Fast pack:
  
  # service network-manager restart
+
  tar -I 'pigz --fast' -cf my.tar.gz whatver
  
== Pinging with particular packet size ==
+
Best pack:
  
  $ ping -M do -s <packet size in bytes> <host>
+
  tar -I 'pigz --best' -cf my.tar.gz whatver
  
E.g.
+
Fast unpack:
  
  $ ping -M do -s 1400 charity.progclub.org
+
  tar -I pigz -xf my.tar.gz
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
== Best compression with tar ==
  
# ip route add <host> dev <interface> advmss <packet size>
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
E.g.
+
export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
or
  
== Dropping configured MMS for a particular IP address ==
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
# ip route flush <host>
+
== Best parallel compression with pigz ==
  
E.g.
+
$ pigz --best
  
# ip route flush 10.0.0.1
+
== Best parallel compression with xz ==
  
== Listing open ports and socket information ==
+
$ xz -9e -T 0
  
Including which process is listening on which port.
+
== Reporting compression ratios with xz ==
  
# netstat -tulpn
+
e.g.
  
Or use the 'ss' command:
+
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
  
# ss -s
+
= Symbolic-link management =
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
== Data used by sym-linked files:
  
# lsof -Pnl +M -i4
+
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:
  
You might need to install the lsof package:
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
# apt-get install lsof
+
= File searching =
  
== Query for DNS MX record ==
+
== Finding a file with a particular name ==
  
  $ nslookup
+
  $ find -iname "*some-part-of-the-file-name*"
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
Will start searching from the current directory, so maybe
  
  $ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
  $ cd /
  
== Using nmap to list open ports on remote host ==
+
first. For a case-sensitive search:
  
To check the 1,000 most common ports:
+
$ find -name "*eXaCT CaSE*"
  
# nmap server.example.com
+
== Finding a file with particular content ==
  
Or for a specific port range (e.g. 101 to 102):
+
To search in /etc/ for a file with particular content:
  
  # nmap -p 101-102 server.example.com
+
  $ grep -R "search-string" /etc/*
  
Or for all ports (1 to 65,535):
+
To search the current directory for *.cs files containing the word "Up":
  
  # nmap -p- server.example.com
+
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
== Network monitoring ==
+
== Finding a list of files with particular content ==
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
E.g. to find all the files with the word 'creativity':
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
== Using the locate command to find files ==
  
You can watch network traffic in real-time with nload:
+
$ locate part-of-filename
  
# nload -u M
+
E.g.
  
== Reporting network (NIC) speed ==
+
$ locate texvc
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
== Updating locate command's database ==
  
  # dmesg | grep eth0
+
  # updatedb
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
== Select a random line from a text file ==
  
== Path MTU discovery ==
+
$ shuf -n 1 input.txt
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
== Extra context for grep ==
  
# tracepath host.example.com
+
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
  
== Listing available Ethernet devices ==
+
$ grep -B 3 -A 1 ...
  
To see a list of NICs available on the host:
+
= Job control =
  
$ cat /proc/net/dev
+
== Stopping a running process ==
  
Also
+
Press Ctrl+Z to stop a running process.
  
$ ip link
+
== Listing current jobs and their status ==
  
== Links ==
+
$ jobs
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
== Resuming a stopped job in the backgroud ==
  
= IPTables =
+
To resume a stopped process in the background
  
== Applying firewall rules ==
+
$ bg %1
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
$ sudo vim /etc/iptables.test.rules
+
== Resuming a stopped job in the foreground ==
$ 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 =
+
To resume a stopped process in the foreground
  
== Denying hosts with ufw ==
+
$ fg %1
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
= Bind9 =
+
== Killing a stopped job ==
  
== Viewing Bind9 querylog ==
+
To kill a job
  
  $ sudo rndc querylog
+
  $ kill %1
$ tail -f /var/log/syslog
 
  
= IPSec =
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Disabling IPSec ==
+
== Periodically run a program and watch its output ==
  
  # setkey -FP
+
  $ watch /your/command
  
= OpenSSL =
+
= Debian/Ubuntu package management =
  
== Debugging IMAPS with OpenSSL ==
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
# openssl s_client -connect localhost:993
+
== configuring debconf ==
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
# dpkg-reconfigure debconf
  
$ openssl s_client -connect www.example.com:443
+
Set priority to low to get asked detailed questions.
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
== Showing list of installed packages ==
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
# dpkg --get-selections
  
= Pluggable Authentication Modules (PAM) =
+
== Searching for installed package ==
  
== Links ==
+
# dpkg --get-selections | grep package-name
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
or
  
= SSH =
+
# aptitude search package-name
  
== Configuring SSH key login ==
+
== Showing which files are installed as part of a package ==
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
# dpkg -L package-name
  
$ ssh-keygen -t rsa
+
== Installing a package ==
  
Copy the public key from the client to the server:
+
# apt-get install package-name
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
== Uninstalling a package ==
  
Configure the authorized keys on the server:
+
# apt-get remove package-name
  
$ ssh user@example.org
+
== Showing system architecture ==
$ 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 ==
+
$ dpkg --print-architecture
  
For example, connecting a remote MySQL server to the localhost:
+
== Showing which package a file belongs to ==
  
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
  $ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
== Showing package information ==
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
$ apt-cache showpkg coreutils
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
Or for even more information:
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
$ apt-cache show coreutils
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
== List all installed packages with package version info ==
  
* run putty.exe
+
dpkg-query -l
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
== Reporting which version of a package is installed ==
  
To see what's going on with your ssh connections,
+
$ dpkg -l | grep package-name
  
$ ssh -v user@host
+
E.g.:
  
Or
+
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
  
$ ssh -vv user@host
+
== Comprehensive upgrade ==
  
== Unlocking SSH key for session ==
+
Try the following:
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  # apt-get update
  [Desktop Entry]
+
  # apt-get dist-upgrade
  Type=Application
+
  # apt-get autoremove
  Name=ssh-add
+
  # apt-get remove $(deborphan)
  Comment=Adds my private key to my session.
+
  # update-flashplugin-nonfree --install
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Links ==
+
== Searching all available packages ==
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
$ apt-cache search . | sort -d | less
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
= Networking =
  
== cat EOF ==
+
== net-tools vs iproute2 ==
  
$ cat > output <<EOF
+
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].
> text
 
> EOF
 
  
  $ cat output
+
{|class="wikitable"
text
+
! legacy net-tools commands
 
+
! iproute2 replacement commands
= Script =
+
|-
 +
| 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)
 +
|}
  
== Creating a session log with script ==
+
== Restart networking ==
  
$ script -t 2> timing
+
For servers:
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
# service networking restart
  
== Replaying a scripted session ==
+
For desktops:
  
  $ scriptreplay timing
+
  # service network-manager restart
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
== Pinging with particular packet size ==
  
= Screen =
+
$ ping -M do -s <packet size in bytes> <host>
  
== Creating a new screen or reconnecting to a detached screen ==
+
E.g.
  
  $ screen -R
+
  $ ping -M do -s 1400 charity.progclub.org
  
== Detaching a screen ==
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
  $ screen -D
+
  # ip route add <host> dev <interface> advmss <packet size>
  
== Reconnecting to screen ==
+
E.g.
  
  $ screen -D
+
  # ip route add 10.0.0.1 dev eth0 advmss 1400
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
== Dropping configured MMS for a particular IP address ==
  
  #!/bin/bash
+
  # ip route flush <host>
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
E.g.
  
== Scrolling in screen ==
+
# ip route flush 10.0.0.1
  
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.
+
== Listing open ports and socket information ==
  
= Vim =
+
Including which process is listening on which port.
  
== First, why Vim? ==
+
# netstat -tulpn
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
Or use the 'ss' command:
  
== Visual modes ==
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
== Listing open IPv4 connections ==
  
== Configuring spaces instead of tabs ==
+
# lsof -Pnl +M -i4
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
You might need to install the lsof package:
  
  $ vim ~/.vimrc
+
  # apt-get install lsof
  
and include the following lines:
+
== Query for DNS MX record ==
  
  set tabstop=2
+
  $ nslookup
  set shiftwidth=2
+
> server 127.0.0.1
  set expandtab
+
  > set q=mx
 +
  > mail.blackbrick.com
  
== Configuring syntax highlighting ==
+
== Query for DNS SOA record ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
Use:
+
== Using nmap to list open ports on remote host ==
  
:syntax on
+
To check the 1,000 most common ports:
  
to turn on syntax highlighting.
+
# nmap server.example.com
  
Use:
+
Or for a specific port range (e.g. 101 to 102):
  
  :syntax off
+
  # nmap -p 101-102 server.example.com
  
to turn off syntax highlighting.
+
Or for all ports (1 to 65,535):
  
To always use syntax highlighting:
+
# nmap -p- server.example.com
  
$ vim ~/.vimrc
+
== Network monitoring ==
  
and add:
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
syntax on
+
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
 +
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 +
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 +
# Bandwidth per process: nethogs
  
To get a list of supported colour schemes open vim and type:
+
== nload ==
  
:colorscheme[space][Ctrl+D]
+
You can watch network traffic in real-time with nload:
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
# nload -u M
  
colorscheme desert
+
== Reporting network (NIC) speed ==
  
== Inserting a TAB character when expandtab is on ==
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
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.
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
Press Ctrl+V TAB to insert a literal tab character.
+
Note: use ifconfig to get device name.
  
Or you can disable tab expansion altogether with:
+
== Path MTU discovery ==
  
:set expandtab!
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
# tracepath host.example.com
  
:%s/^\s*/&&/g
+
== Listing available Ethernet devices ==
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
To see a list of NICs available on the host:
  
== Recording and replaying a macro ==
+
$ cat /proc/net/dev
  
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 "@@".
+
Also
  
== Deleting to end of line ==
+
$ ip link
  
d$
+
== 59 Linux Networking commands and scripts ==
  
== Deleting to beginning of line ==
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
d^
+
== Links ==
  
== Finding text ==
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
To search forward for "text":
+
= IPTables =
  
/text
+
== Applying firewall rules ==
  
To search backward for "text":
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
  ?text
+
  $ 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
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
= ufw =
  
== Finding and replacing text ==
+
== Denying hosts with ufw ==
  
To replace the first instance of "search" on the current line with "destroy":
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
:s/search/destroy/
+
= Bind9 =
  
To replace all instances of "search" on the current line with "destroy":
+
== Viewing Bind9 querylog ==
  
  :s/search/destroy/g
+
  $ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
= IPSec =
  
:13,37 s/search/destroy/g
+
== Disabling IPSec ==
  
To replace all instances of "search" in the entire file with "destroy":
+
# setkey -FP
  
:%s/search/destroy/g
+
= OpenSSL =
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
== Debugging IMAPS with OpenSSL ==
  
To set the line-ending to Unix line endings run the command:
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
:setlocal ff=unix
+
== Debugging HTTPS with OpenSSL ==
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
== Disabling auto-indent etc. to paste from clipboard ==
+
== Links ==
  
To disable smart indenting when you're going to paste in text:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
:set paste
+
= Pluggable Authentication Modules (PAM) =
  
To turn it off again:
+
== Links ==
  
:set nopaste
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
= SSH =
  
== Positioning windows ==
+
== Configuring SSH key login ==
  
Use -o for horizontal split, e.g.:
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
  vim -o a.txt b.txt
+
  $ ssh-keygen -t rsa
  
Use -O for vertical split, e.g.:
+
Copy the public key from the client to the server:
  
  vim -o a.txt b.txt
+
  $ scp ~/.ssh/id_rsa.pub user@example.org:
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
Configure the authorized keys on the server:
  
Use ^W and &lt; or &gt; to resize windows.
+
$ ssh user@example.org
 +
$ mkdir ~/.ssh
 +
$ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
== To indent a block of text in Vim ==
+
== Tunneling over SSH ==
  
Use the > command. E.g. to indent five lines:
+
For example, connecting a remote MySQL server to the localhost:
  
  5 > >
+
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
Press . (dot) to keep indenting.
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
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:
+
  $ 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.
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
== Tunneling over SSH with PuTTY ==
  
== Open a file in a new window/tab ==
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
To open a file on the left hand side:
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
:vert new filename.ext
+
== Enabling verbose SSH logging ==
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
To see what's going on with your ssh connections,
  
To open a file at the top:
+
$ ssh -v user@host
  
:new filename.ext
+
Or
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
$ ssh -vv user@host
  
== Explore files in Vim ==
+
== Unlocking SSH key for session ==
  
Enter:
+
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'
  
:Explore
+
== Links ==
  
== Switch between Vim tabs ==
+
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
 +
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
  
Use gt and gT.
+
= Standard IO =
  
== Switch between Vim windows ==
+
== cat EOF ==
  
To toggle between open windows use:
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  Ctrl+W W
+
  $ cat output
 +
text
  
To move in a direction use:
+
= Script =
  
Ctrl+W h/j/k/l
+
== Creating a session log with script ==
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
$ script -t 2> timing
  
== Insert block comment in Vim ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
== Replaying a scripted session ==
  
So it's:
+
$ scriptreplay timing
  
# Ctrl+V (Note: not Shift+V!)
+
Uses the default file 'typescript' and the 'timing' file as specified.
# Up/Down to select rows
 
# Shift+I
 
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
= Screen =
  
To navigate to the matching beginning or end tag use '%'.
+
== Creating a new screen or reconnecting to a detached screen ==
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
$ screen -R
  
== Auto-format HTML tags ==
+
== Detaching a screen ==
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
$ screen -D
  
# first join all the lines - ggVGgJ
+
== Reconnecting to screen ==
# 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 ==
+
$ screen -D
 +
$ screen -R
  
* [http://www.vim.org/ Vim: the editor]
+
I have a script in ~/bin/reconnect like so,
* [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 =
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
== Talking to other users on the system ==
+
This will detach your last screen, and reconnect it on the current terminal.
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
== Scrolling in screen ==
  
1. SSH to <username>@<hostname> and login with your username and password.
+
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.
  
2. Issue the following command to find out who is logged onto the system:
+
= tmux =
  
$ who
+
== Live collaboration with tmux ==
  
3. Issue the following command to talk to a specific user:
+
User A:
  
  $ write <username>
+
  tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
User B:
  
= Date =
+
tmux -S /tmp/collab attach
  
== Reporting the time on the server ==
+
= Vim =
  
$ date
+
== First, why Vim? ==
  
== Reporting UTC time ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
$ date --utc
+
== Visual modes ==
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
$ date="`date +%F-%H%M%S`"
+
== Configuring spaces instead of tabs ==
  
== Getting the year in four digits ==
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
  $ year="`date +%Y`"
+
  $ vim ~/.vimrc
  
== Getting the month in two digits ==
+
and include the following lines:
  
  $ month="`date +%m`"
+
  set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
== Getting the day of the month in two digits ==
+
== Configuring syntax highlighting ==
  
$ day="`date +%d`"
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
== Getting yesterday's date ==
+
Use:
  
  $ date --date='1 day ago' +%Y-%m-%d
+
  :syntax on
  
== Converting Unix time (seconds since epoch) ==
+
to turn on syntax highlighting.
  
For timestamp '1501370200':
+
Use:
  
  $ date -d @1501370200 +%F-%H%M%S
+
  :syntax off
  
== Running timedatectl from systemd ==
+
to turn off syntax highlighting.
  
There's a new command bundled with systmed:
+
To always use syntax highlighting:
  
  # timedatectl
+
  $ vim ~/.vimrc
  
It reports on (and controls) how the system time is configured.
+
and add:
  
= MySQL =
+
syntax on
  
== Run mysql without authentication/authorisation ==
+
To get a list of supported colour schemes open vim and type:
  
  # service mysql stop
+
  :colorscheme[space][Ctrl+D]
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
  # mysql -u root mysql
+
  colorscheme desert
  
To stop the unauthenticated service:
+
== Inserting a TAB character when expandtab is on ==
  
# mysqladmin shutdown
+
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.
  
Then restart a normal service:
+
Press Ctrl+V TAB to insert a literal tab character.
  
# service mysql start
+
Or you can disable tab expansion altogether with:
  
== Logging all database queries ==
+
:set expandtab!
  
# vim /etc/mysql/my.cnf
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
In the [mysqld] section add:
+
:%s/^\s*/&&/g
  
log=/tmp/mysql.log
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
Then:
+
== Recording and replaying a macro ==
  
# service mysql restart
+
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 "@@".
  
Watch the log with:
+
== Deleting to end of line ==
  
  # tail -f /tmp/mysql.log
+
  d$
  
== Dumping a MySQL database ==
+
== Deleting to beginning of line ==
  
You can dump the database into a file using:
+
  d^
   
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
== Finding text ==
  
You can create a database using:
+
To search forward for "text":
  
  $ echo create database databasename | mysql -h hostname -u user -p
+
  /text
  
You can restore a database using:
+
To search backward for "text":
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
?text
  
# mysql -h localhost -u root --password=<password>
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
== Finding and replacing text ==
  
# mysql -h localhost -u root --password=<password>
+
To replace the first instance of "search" on the current line with "destroy":
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
:s/search/destroy/
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
To replace all instances of "search" on the current line with "destroy":
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
:s/search/destroy/g
  
Check the SSL version in use:
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  
  show status like 'Ssl_version';
+
  :13,37 s/search/destroy/g
  
Or check the cipher in use:
+
To replace all instances of "search" in the entire file with "destroy":
  
  show status like 'Ssl_cipher';
+
  :%s/search/destroy/g
  
= Apache =
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  
== Maintaining .htaccess passwords ==
+
To set the line-ending to Unix line endings run the command:
  
To add or modify the password for a user:
+
:setlocal ff=unix
  
$ htpasswd /etc/apache2/passwd username
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
== Configuring PHP session timeout in .htaccess ==
+
== Disabling auto-indent etc. to paste from clipboard ==
  
For a session timeout of 9 hours:
+
To disable smart indenting when you're going to paste in text:
  
  php_value session.cookie_lifetime 32400
+
  :set paste
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
To turn it off again:
  
  php_flag magic_quotes_gpc Off
+
  :set nopaste
  
== Requiring HTTP Auth in .htaccess ==
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
AuthType Basic
+
== Positioning windows ==
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
Use -o for horizontal split, e.g.:
  
The hard way
+
vim -o a.txt b.txt
  
$ sudo /etc/init.d/apache2 restart
+
Use -O for vertical split, e.g.:
  
The graceful way (avoids dropping active connections)
+
vim -o a.txt b.txt
  
$ sudo apache2ctl graceful
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
== Allowing directory browsing ==
+
Use ^W and &lt; or &gt; to resize windows.
  
To show directory index pages, in the apache config file:
+
== To indent a block of text in Vim ==
  
<Directory /var/www/data>
+
Use the > command. E.g. to indent five lines:
  Options Indexes
 
</Directory>
 
  
= C =
+
5 > >
  
== Locating memset function ==
+
Press . (dot) to keep indenting.
  
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]
+
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:
  
== Links ==
+
> %
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
= PHP =
+
== Open a file in a new window/tab ==
  
== Including a file relative to the including file ==
+
To open a file on the left hand side:
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  :vert new filename.ext
  
== Enabling error reporting ==
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
  
error_reporting( E_ALL | E_STRICT );
+
To open a file at the top:
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
:new filename.ext
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
== Explore files in Vim ==
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
Enter:
  
  ini_set( 'html_errors', 'off' );
+
  :Explore
  
= BASH scripting =
+
== Switch between Vim tabs ==
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
Use gt and gT.
  
== Telling a script to run in bash ==
+
== Switch between Vim windows ==
  
The first line of the file should be:
+
To toggle between open windows use:
  
  #!/bin/bash
+
  Ctrl+W W
  
== Checking if a command-line argument was passed in ==
+
To move in a direction use:
  
  if [ -n "$1" ]; then
+
  Ctrl+W h/j/k/l
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
if [ "$1" = "" ]; then
+
== Insert block comment in Vim ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
if [ -z "$1" ]; then
+
So it's:
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# Ctrl+[ (or 'Esc')
  
cd /my/path
+
== Navigate to matching tag ==
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
To navigate to the matching beginning or end tag use '%'.
  
Check if file exists:
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
if [ -f "/my/file" ]; then
+
== Auto-format HTML tags ==
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
if [ ! -f "/my/file" ]; then
+
# first join all the lines - ggVGgJ
  touch /my/file
+
# Now break tags to new lines - :%s/>\s*</>\r</g
fi
+
# Now set filetype - :set ft=html (you can do this before too)
 +
# Now Indent - ggVG=
  
== Checking if a directory does/doesn't exist ==
+
== Links ==
  
Check if directory exists:
+
* [http://www.vim.org/ Vim: the editor]
 
+
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
if [ -d "/my/dir" ]; then
+
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
  rmdir /my/dir
+
* [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]
fi
+
* [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]
  
Check if directory doesn't exist:
+
== Create PDF from text using Vim ==
  
if [ ! -d "/my/dir" ]; then
+
Generate PDF from input.txt with:
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
To keep only the latest five backups:
+
Examine output with:
  
  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
+
  $ okular doc.pdf
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
= Write =
  
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.
+
== Talking to other users on the system ==
  
== Changing into the script's directory ==
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
cd "`dirname $0`"
+
1. SSH to <username>@<hostname> and login with your username and password.
  
== Getting the absolute path of a relative path ==
+
2. Issue the following command to find out who is logged onto the system:
  
  readlink -f ./some/path
+
  $ who
  
== Creating a temp directory ==
+
3. Issue the following command to talk to a specific user:
  
  dir=`mktemp -d` && cd $dir
+
  $ write <username>
  
== Reading secret input from stdin ==
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
You can read a secret, such as a password, like this:
+
= Date =
  
echo -n "Enter passphrase: "
+
== Reporting the time on the server ==
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
$ date
  
== String replacements in bash ==
+
== Reporting UTC time ==
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
$ date --utc
  
result=${var/find/replace}
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
To replace all occurrences:
+
$ date="`date +%F-%H%M%S`"
  
result=${var//find/replace}
+
== Getting the year in four digits ==
  
A practical example, get an ISO date and turn it into a path:
+
$ year="`date +%Y`"
  
date="$(date +%Y-%m-%d)"
+
== Getting the month in two digits ==
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
$ month="`date +%m`"
  
cat << EOF > /tmp/yourfilehere
+
== Getting the day of the month in two digits ==
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
$ day="`date +%d`"
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
== Getting yesterday's date ==
  
  case $space in
+
  $ date --date='1 day ago' +%Y-%m-%d
[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 ==
+
== Converting Unix time (seconds since epoch) ==
  
To enable dot-file matching in globs, set the dotglob shell option:
+
For timestamp '1501370200':
  
  $ shopt -s dotglob
+
  $ date -d @1501370200 +%F-%H%M%S
  
= Sed =
+
== Running timedatectl from systemd ==
  
== Find and replace with sed ==
+
There's a new command bundled with systmed:
  
To update the current file use '-i'. E.g.:
+
# timedatectl
  
sed -i 's/search-text/replace-text/' file
+
It reports on (and controls) how the system time is configured.
  
= Awk =
+
= MySQL =
  
== Listing IP addresses in an Apache web log ==
+
== Run mysql without authentication/authorisation ==
  
  awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
  # service mysql stop
 +
# mysqld_safe --skip-grant-tables &
  
== Printing space-separated field ==
+
Then you can connect without a password, e.g.:
  
  echo 'no no yes no' | awk '{print $3}'
+
  # mysql -u root mysql
  
== Printing delimited field ==
+
To stop the unauthenticated service:
  
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
  # mysqladmin shutdown
  
= Subversion =
+
Then restart a normal service:
  
== Setting svn:externals from the command-line ==
+
# service mysql start
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
== Logging all database queries ==
  
To set an svn:externals from the command-line:
+
# vim /etc/mysql/my.cnf
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
In the [mysqld] section add:
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
log=/tmp/mysql.log
  
svn propset svn:externals -F svn.externals .
+
Then:
  
== Setting svn:ignore from the command line ==
+
# service mysql restart
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
Watch the log with:
  
  $ svn propset svn:ignore [file|folder] [path]
+
  # tail -f /tmp/mysql.log
  
Or use a file and apply recursively:
+
== Dumping a MySQL database ==
  
  $ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
You can dump the database into a file using:
 +
 +
  $ mysqldump -h hostname -u user --password=password databasename > filename
  
= Git =
+
== Loading a MySQL database from a dump file ==
  
== Showing status of working copy ==
+
You can create a database using:
  
  git status
+
  $ echo create database databasename | mysql -h hostname -u user -p
  
== Showing repo history ==
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
git log
+
== Creating a MySQL user ==
  
== Showing remote repositories (including 'origin') ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
git remote -v
+
== Granting all MySQL user permissions ==
  
== Handy git aliases ==
+
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
  
Save these to your ~/.gitconfig file.
+
== Select domain name from email address ==
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
== Check if MySQL connection is encrypted with TLS/SSL ==
  
To show only the files that have changed, rather than the full line-by-line content:
+
Check the SSL version in use:
  
  dif  = !git diff --name-status
+
show status like 'Ssl_version';
  
= IRC =
+
Or check the cipher in use:
 +
 
 +
show status like 'Ssl_cipher';
 +
 
 +
= Apache =
  
== Instructing ChanServ to op an admin ==
+
== Reporting loaded Apache modules ==
  
  /msg ChanServ op #channel user
+
  # apache2ctl -M
  
E.g.
+
== Maintaining .htaccess passwords ==
  
/msg ChanServ op #gnurc jj5
+
To add or modify the password for a user:
  
Sub 'op' for 'deop' to remove op privilege.
+
$ htpasswd /etc/apache2/passwd username
  
= C++ =
+
== Configuring PHP session timeout in .htaccess ==
  
== C++ books ==
+
For a session timeout of 9 hours:
  
=== Books I want ===
+
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== Disabling PHP magic quotes in .htaccess ==
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
php_flag magic_quotes_gpc Off
* [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 ===
+
== Requiring HTTP Auth in .htaccess ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
AuthType Basic
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
+
AuthName "Speak Friend And Enter"
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
+
AuthUserFile /home/jj5/.htpasswd
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
+
Require valid-user
* [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 ===
+
== Restarting Apache ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
The hard way
** Note: 3ed is obsolete. Buy 4ed (above).
+
 
 +
$ sudo /etc/init.d/apache2 restart
 +
 
 +
The graceful way (avoids dropping active connections)
 +
 
 +
$ sudo apache2ctl graceful
  
=== Books I've read ===
+
== Allowing directory browsing ==
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
To show directory index pages, in the apache config file:
  
== C++ blogs/articles ==
+
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
= C =
* [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 ==
+
== Locating memset function ==
  
* ++c can be faster than c++.
+
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]
* 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 =
+
== Links ==
  
[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.
+
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
  
== Following a service log ==
+
= PHP =
  
e.g. for bind9:
+
== Including a file relative to the including file ==
  
  # journalctl -f -u bind9
+
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
  
or for everything:
+
== Enabling error reporting ==
  
  # journalctl -f
+
  error_reporting( E_ALL | E_STRICT );
 +
ini_set( 'display_errors', 'On' );
  
== System status ==
+
== Setting an error handler ==
  
To see spawned services hierarchy:
+
set_error_handler( "error_handler", E_ALL | E_STRICT );
  
  # systemctl status
+
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
 +
  // ...
 +
}
  
Or for a specific service e.g.:
+
== Disable HTML content in var_dump ==
  
  # systemctl status networking
+
  ini_set( 'html_errors', 'off' );
  
= SaltStack =
+
== Report PHP modules ==
  
== Running a command on specified minions ==
+
$ php -m
  
salt 'host' cmd.run 'update-locale'
+
== PHP Security Best Practices For Sys Admins ==
  
== Running a command on all minions ==
+
See [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
  
salt '*' cmd.run 'update-locale'
+
= BASH scripting =
  
== Listing active jobs ==
+
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
  
salt-run jobs.active
+
== Telling a script to run in bash ==
  
== Listing available grains ==
+
The first line of the file should be:
  
  salt 'example' grains.items
+
  #!/bin/bash
  
== Listing available pillar ==
+
== Checking if a command-line argument was passed in ==
  
  salt 'example' pillar.items
+
  if [ -n "$1" ]; then
 +
  echo "Missing parameter 1.";
 +
  exit 1;
 +
fi
  
== Reporting a grain value ==
+
== Checking if a command-line argument was not passed in ==
  
e.g. for the 'mem_total' grain:
+
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 ==
  
  salt '*' grains.item mem_total
+
  cd /my/path
 +
if [ "$?" -ne "0" ]; then
 +
  echo "Cannot change dir.";
 +
  exit 1;
 +
fi
  
= KDE =
+
== Checking if a file does/doesn't exist ==
  
== Running user login script (X11/XOrg/XWindows) ==
+
Check if file exists:
  
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:
+
if [ -f "/my/file" ]; then
 +
  cat /my/file
 +
fi
  
  [Desktop Entry]
+
Check if file doesn't exist:
  Type=Application
+
 
  Name=ssh-add
+
if [ ! -f "/my/file" ]; then
  Comment=Adds my private key to my session.
+
  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 [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash 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 [http://www.tldp.org/LDP/abs/html/string-manipulation.html 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 [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html 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 [https://blog.yossarian.net/2020/01/23/Anybody-can-write-good-bash-with-a-little-effort Anybody can write good bash (with a little effort)].
 +
 
 +
== Run a command using arguments that come from an array ==
 +
 
 +
See [https://unix.stackexchange.com/a/412647/356289 here]:
 +
 
 +
#!/bin/bash
 +
tabs=("first tab" "second tab")
 +
args=()
 +
for t in "${tabs[@]}" ; do
 +
  args+=(-t "$t")
 +
done
 +
app "${args[@]}"
 +
 
 +
== Display a CSV in columnar or tabular format ==
 +
 
 +
$ column -t -s , data.csv
 +
 
 +
= Sed =
 +
 
 +
== Find and replace with sed ==
 +
 
 +
To update the current file use '-i'. E.g.:
 +
 
 +
sed -i 's/search-text/replace-text/' file
 +
 
 +
= Awk =
 +
 
 +
== Listing IP addresses in an Apache web log ==
 +
 
 +
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
 +
 
 +
== Printing space-separated field ==
 +
 
 +
echo 'no no yes no' | awk '{print $3}'
 +
 
 +
== Printing delimited field ==
 +
 
 +
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
 +
 
 +
= Subversion =
 +
 
 +
== Setting svn:externals from the command-line ==
 +
 
 +
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
 +
 
 +
To set an svn:externals from the command-line:
 +
 
 +
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
 +
svn ci -m 'Adding svn:externals for rdfind-php...'
 +
svn up
 +
 
 +
Or to use a file:
 +
 
 +
svn propset svn:externals -F svn.externals .
 +
 
 +
== Setting svn:ignore from the command line ==
 +
 
 +
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
 +
 
 +
$ svn propset svn:ignore [file|folder] [path]
 +
 
 +
Or use a file and apply recursively:
 +
 
 +
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
 +
 
 +
= Git =
 +
 
 +
== Showing status of working copy ==
 +
 
 +
git status
 +
 
 +
== Showing repo history ==
 +
 
 +
git log
 +
 
 +
== Showing remote repositories (including 'origin') ==
 +
 
 +
git remote -v
 +
 
 +
== Handy git aliases ==
 +
 
 +
Save these to your ~/.gitconfig file.
 +
 
 +
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
 +
 
 +
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
 +
 
 +
To show only the files that have changed, rather than the full line-by-line content:
 +
 
 +
  dif  = !git diff --name-status
 +
 
 +
== Show git remote URL ==
 +
 
 +
git config --get remote.origin.url
 +
 
 +
= IRC =
 +
 
 +
== Instructing ChanServ to op an admin ==
 +
 
 +
/msg ChanServ op #channel user
 +
 
 +
E.g.
 +
 
 +
/msg ChanServ op #gnurc jj5
 +
 
 +
Sub 'op' for 'deop' to remove op privilege.
 +
 
 +
= C++ =
 +
 
 +
== C++ books ==
 +
 
 +
=== Books I want ===
 +
 
 +
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 +
 
 +
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
 +
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 +
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 +
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 +
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
 +
 
 +
=== Books I own ===
 +
 
 +
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
 +
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
 +
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 +
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
 +
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
 +
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
 +
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
 +
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
 +
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
 +
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
 +
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
 +
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
 +
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
 +
 
 +
=== Books I'm not reading ===
 +
 
 +
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
 +
 
 +
=== Books I've read ===
 +
 
 +
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
 +
 
 +
== C++ blogs/articles ==
 +
 
 +
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
 +
* [http://herbsutter.com/ Herb Sutter's personal blog]
 +
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
 +
 
 +
== C++ performance tips ==
 +
 
 +
* ++c can be faster than c++.
 +
* use const for everything that you possibly can.
 +
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
 +
* don't use registers.
 +
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 +
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 +
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 +
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 +
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 +
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 +
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 +
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 +
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 +
 
 +
= systemd =
 +
 
 +
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
 +
 
 +
== Following a service log ==
 +
 
 +
e.g. for bind9:
 +
 
 +
# journalctl -f -u bind9
 +
 
 +
or for everything:
 +
 
 +
# journalctl -f
 +
 
 +
== System status ==
 +
 
 +
To see spawned services hierarchy:
 +
 
 +
# systemctl status
 +
 
 +
Or for a specific service e.g.:
 +
 
 +
# systemctl status networking
 +
 
 +
= SaltStack =
 +
 
 +
== Running a command on specified minions ==
 +
 
 +
From the salt master:
 +
 
 +
salt 'host' cmd.run 'update-locale'
 +
 
 +
From the salt minion:
 +
 
 +
salt-call cmd.run 'update-locale'
 +
 
 +
== Running a command on all minions ==
 +
 
 +
salt '*' cmd.run 'update-locale'
 +
 
 +
== Running a specific state file ==
 +
 
 +
From the salt master:
 +
 
 +
salt $MINION_ID state.sls $STATE_FILE
 +
 
 +
From the salt minion:
 +
 
 +
salt-call state.sls $STATE_FILE
 +
 
 +
== Listing active jobs ==
 +
 
 +
salt-run jobs.active
 +
 
 +
== Listing available grains ==
 +
 
 +
salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
  [Desktop Entry]
 +
  Type=Application
 +
  Name=ssh-add
 +
  Comment=Adds my private key to my session.
 
  Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  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
 +
|}
 +
 +
= VirtualBox =
 +
 +
== Mounting a VirtualBox VDI file ==
 +
 +
Note: instead of doing this consider booting with a live CD.
 +
 +
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
 +
 +
Install qemu if necessary:
 +
 +
# apt install qemu
 +
 +
Then you'll need to load the network block device module:
 +
 +
# rmmod nbd
 +
# modprobe nbd max_part=16
 +
 +
Attach the .vdi image to one of the nbd you just created:
 +
 +
# qemu-nbd -c /dev/nbd0 drive.vdi
 +
 +
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
 +
 +
# mount /dev/nbd0p1 /mnt
 +
 +
Once you are done, unmount everything and disconnect the device:
 +
 +
# qemu-nbd -d /dev/nbd0
 +
 +
= Elasticsearch =
 +
 +
== Report on health of your Elasticsearch cluster ==
 +
 +
$ curl http://localhost:9200/_cluster/health?pretty
 +
 +
= Zabbix =
 +
 +
== Zabbix Agent on Mac OS X ==
 +
 +
Download and install agent.
 +
 +
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
 +
 +
Unload agent with:
 +
 +
# launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 +
Load agent with:
 +
 +
# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 +
To add a 'pki' group:
 +
 +
# dseditgroup -o create pki
 +
 +
To monitor syslog on Mac OS X:
 +
 +
# tail -f /var/log/system.log
 +
 +
== Installing Zabbix Agent from source on Mac OS X ==
 +
 +
Download sources from https://www.zabbix.com/download_sources
 +
 +
$ brew update
 +
$ brew install openssl
 +
$ brew install pcre
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
 +
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install
 +
 +
= NetBeans =
 +
 +
== NetBeans shortcut keys ==
 +
 +
{|class="wikitable sortable"
 +
! Keys        !! Action
 +
|-
 +
| Ctrl+W      || Close active window
 +
|-
 +
| Alt+Shift+K  || Open in Terminal
 +
|-
 +
| Ctrl+U U    || Convert selected text to uppercase
 +
|-
 +
| Ctrl+U L    || Convert selected text to lowercase
 +
|}

Latest revision as of 04:18, 16 June 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.

You might also be interested in John's hacks.

Quick jump to: NetBeans.

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

Note that the dmidecode command (above) will give you information about your system's motherboard. For motherboard info look for 'System Information' and/or 'Base Board Information'.

Or the grand daddy of them all:

# hwinfo

There's also inxi, e.g.:

$ inxi -b

System:    Host: tact Kernel: 4.9.0-4-amd64 x86_64 (64 bit) Desktop: KDE Plasma 5.8.6
           Distro: Debian GNU/Linux 9 (stretch)
Machine:   Device: desktop Mobo: ASUSTeK model: STRIX Z270F GAMING v: Rev 1.xx
           UEFI [Legacy]: American Megatrends v: 0906 date: 03/22/2017
CPU:       Quad core Intel Core i7-7700K (-HT-MCP-) speed/max: 799/4600 MHz
Graphics:  Card: Intel Device 5912
           Display Server: X.Org 1.19.2 drivers: modesetting (unloaded: fbdev,vesa)
           Resolution: 1920x1080@60.00hz, 1920x1080@60.00hz
           GLX Renderer: Mesa DRI Intel Kabylake GT2 GLX Version: 3.0 Mesa 13.0.6
Network:   Card: Intel Ethernet Connection (2) I219-V driver: e1000e
Drives:    HDD Total Size: 13026.6GB (42.0% used)
RAID:      Devices: 1: /dev/md1 2: /dev/md0
Info:      Processes: 355 Uptime: 11 days Memory: 21198.3/32043.3MB Client: Shell (bash) inxi: 2.3.5

Viewing syslog and other logs with KSystemLog

Run the 'KSystemLog' program under KDE for a handy log viewer GUI.

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

Report memory type

Report on RAM DIMMs:

# dmidecode --type 17

Report on RAM and CPU cache (including L1, L2, and L3):

# lshw -short -C memory

Or for more detail:

# lshw -C memory

Video/display management

Viewing EDID data for attached monitor

To view EDID data for an attached monitor (requires the edid-decode package):

$ cd /sys/class/drm
$ ls
$ cd card0-HDMI-A-1
$ edid-decode edid

Process management

Using 'top' for dynamic resource usage reporting

To run top:

$ top

See 15 Practical Linux Top Command Examples for some hints on usage.

To see usage for a specific user run e.g.:

$ top -u jj5

To see full command-line press 'c'.

When you're in 'top' you can:

  • press '1' (one) to toggle CPU aggregation
  • press < and > to change the sort column

Changing memory reporting in 'top'

To run top:

$ top

Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)

Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)

Press 'M' to sort by memory utilisation.

Press 'm' to switch between various display modes.

Showing full command-line in 'top'

To see the full command-line for processes run with -c:

$ top -c

Listing all processes currently running which were started in your current shell session

$ ps -fl

Killing specific processes

# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9

Run a command for a specified time using timeout

$ timeout 3 ping jj5.net

Disk management

Creating a partition table

# parted /dev/xvdf
mktable msdos

Creating a partition

# parted /dev/xvdf
u MiB
mkpart primary 1 100%

Creating an ext4 file-system

# mkfs.ext4 /dev/xvdf1

Listing disk drives

# fdisk -l

(That's an L for "list")

Checking available disk space

$ df -h

Getting disk information

# lsblk

And

# cat /proc/partitions

Or the Grand Daddy of them all:

# lshw -class disk

(Requires the lshw package.)

Getting partition UUID and file-system type

# blkid

Checking for SSD vs magnetic disk

# cat /sys/block/sda/queue/rotational

Will be 0 for SSD and 1 for magnetic.

Monitoring a ZFS server

So some commands I run to keep an eye on my new ZFS servers:

# top
# iotop
# nethogs
# watch free -h
# watch slabtop -o
# slabtop
# watch cat /proc/meminfo
# perf top
# watch "df -h | grep -v -e tmpfs -e udev -e by-uuid"
# watch zpool iostat -v
# zpool iostat -v 2
# watch 'zpool list; echo; zfs list'
# watch zfs get compressratio -o all
# watch cat /proc/spl/kstat/zfs/arcstats

If you have a scrub or resilvering in progress you can report on progress with:

# watch zpool status -v

You can poke about in internals, e.g.:

# cat /proc/spl/kstat/zfs/arcstats
root@orac:/sys/module/zfs/parameters# tail *

You can report on property values with e.g.:

# zfs get all data

If you want to get funky:

# cd /tmp
# perf record -ag #(Ctrl+C after ~15 seconds)
# perf report --stdio

You can search for ZFS files like e.g. this:

root@orac:/# find / -name '*zfs*' -or -name '*zpool*'

You can report history of a zpool:

# zpool history $poolname

You can get a report on the dedup tables:

# zpool status -D $poolname

Or more detailed dedup table info:

# zdb -DDD $poolname

Note in the output see here for details, basically:

Abbr Description
LSIZE logical size (in memory)
PSIZE physical size
DSIZE size on disk
refcnt reference count

How to tell if zfs scrub is running

You can get the status from the "scan:" line from:

$ zpool status

Measure data throughput

Use the 'pv' command from the 'pv' package, e.g.:

# cat /dev/sda | pv | cat > /dev/null

Or for ZFS:

# zfs send data/example | pv | cat > /dev/null

Using Smartctl, Smartd and Hddtemp on Debian

For notes on using smartctl see Using Smartctl, Smartd and Hddtemp on Debian.

Report hard disk usage

So you might want to know how much data a process reads or writes to a hard disk. You can monitor process total disk utilisation with the 'iotop' command. Run 'iotop' and then press 'a' for --accumulated.

Report hard disk temperatures

E.g.

# hddtemp /dev/sd[a-e]

Burning an ISO image to USB on Mac

First insert your USB key and find the appropriate disk with:

# diskutil list

Then unmount it with:

# diskutil unmountDisk /dev/disk4

Then copy ISO image with 'dd':

# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4

You can get dd to report progress by sending it the SIGINFO signal:

# kill -s info 12345

Listing all ext4 file systems

To see a list only of the mounted ext4 file systems:

# df -t ext4

Report hierarchical file system mount points and mount options

$ findmnt

Report the mount point for the current working directory

$ findmnt "$PWD"

Monitoring disk I/O

There's an app for that! iotop.

Using iotop, top for disks

# iotop -oPa

Monitor disk I/O for performance issues

# watch iostat

Or e.g.

# watch iostat -xd /dev/sd[abc]

Or use groupings like this command for 'tact':

$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2

Monitoring a system

Simple ZFS monitoring

# watch iostat
# iotop
# zpool iostat -v 5
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
# nethogs
# top

Monitoring temperature

See temperature without third-party apps for:

$ cat /sys/class/thermal/thermal_zone*/temp

and:

$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'

Monitoring CPU temperature

$ watch sensors

Monitoring HDD temperature

For e.g. SATA drives sda to sdd:

# watch hddtemp /dev/sd[a-d]

ZFS

How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

See How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory?

$ cat /proc/spl/kstat/zfs/arcstats

Then:

c is the target size of the ARC in bytes
c_max is the maximum size of the ARC in bytes
size is the current size of the ARC in bytes

Stopping a ZFS scrub in progress

# zpool scrub -s $pool

e.g. for the 'data' pool:

# zpool scrub -s data

File management

Listing files by size

Use capital S for Size:

$ ls -S

Listing only directories

$ ls -l | egrep '^d'

Listing only files

$ ls -l | egrep -v '^d'

Listing hidden files

$ ls -al .[!.]*

Creating a symbolic link

$ ln -s /path/to/target link-name

Creating a hard-link

$ ln /path/to/target file-name

Changing the owner of a file

$ chown user:group <files>

E.g.

$ chown jj5:staff README
$ chown root:root *

To apply recursively into sub-directories use -R,

$ chown -R root:root /etc/*

Changing file permissions

Object codes
User Group Other
u g o
Permission codes
Read Write Exectue
r w x
4 2 1
Numeric codes
0 None
1 Execute
2 Write
3 Write, Execute
4 Read
5 Read, Execute
6 Read, Write
7 Read, Write, Execute

See Numeric Mode in Action.

$ chmod <user numeric code><group numeric code><other numeric code> <files>
$ chmod <object codes>+|-<permission codes> <files>

E.g.

$ chmod 600 my-private-file
$ chmod go-rwx my-private-file
$ chmod u+rw my-private-file
$ chmod +x my-script

Updating config files

If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:

$ cp old.conf updated.conf
$ merge -A updated.conf new.conf old.conf

Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.

The merge program is a part of the RCS package. If you don't have it:

$ sudo apt-get install rcs

Listing open files

Use lsof to list open files. E.g.:

# lsof

See man lsof for options.

List permissions on a whole directory path

E.g.:

$ namei -om /home/jj5/workspace

Outputs:

f: /home/jj5/workspace/
 drwxr-xr-x root root /
 drwxr-xr-x root root home
 drwxr-xr-x jj5  jj5  jj5
 drwxr-xr-x jj5  jj5  workspace

Counting non-blank lines in a file

E.g.:

$ cat foo.c | sed '/^\s*$/d' | wc -l

Cloning one directory to another with rsync

E.g.:

rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/

Counting number of files in current directory and all subdirectories

$ ls -AlhR . | egrep '^-' | wc -l

Counting number of directories in current directory and all subdirectories

$ ls -AlhR . | egrep '^d' | wc -l

Getting the status of a 'dd' process

First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'

Then send the dd process the SIGINFO signal, which for dd process 40947 would be:

# kill -s info 40947

The dd process will report its status in the terminal its running in.

Transferring a large file via FAT32 file system

So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:

$ split -b 4000m input.tgz input.tgz-parts-

Then copy the small files and reassemble:

$ cat input.tgz-parts-* > output.tgz

NFS

List NFS shares

To e.g. show NFS shares on 'love':

$ showmount -e love

Compression

How to use pigz with tar

See here:

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

Note: don't use --best unless you're being stingy, running without it will be much faster.

Also from here:

Fast pack:

tar -I 'pigz --fast' -cf my.tar.gz whatver

Best pack:

tar -I 'pigz --best' -cf my.tar.gz whatver

Fast unpack:

tar -I pigz -xf my.tar.gz

Best compression with tar

From here:

export GZIP=-9
tar cvzf file.tar.gz /path/to/directory

or

env GZIP=-9 tar cvzf file.tar.gz /path/to/directory

Best parallel compression with pigz

$ pigz --best

Best parallel compression with xz

$ xz -9e -T 0

Reporting compression ratios with xz

e.g.

root@love:/data/image/archive# xz -l *
Strms  Blocks   Compressed Uncompressed  Ratio  Check   Filename
    1       3    372.2 MiB    442.3 MiB  0.841  CRC64   1999.txz
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64   2001.txz
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64   2002.txz
    1       9    568.5 MiB  1,660.2 MiB  0.342  CRC64   2003.txz
    1     639     66.8 GiB    119.6 GiB  0.558  CRC64   2004.txz
    1     313     12.7 GiB     58.6 GiB  0.217  CRC64   2005.txz
    1     414     35.0 GiB     77.4 GiB  0.452  CRC64   2006.txz
    1     485     44.5 GiB     90.9 GiB  0.490  CRC64   2007.txz
    1   1,690    150.0 GiB    316.8 GiB  0.473  CRC64   2008.txz
    1       3    457.9 MiB    526.0 MiB  0.871  CRC64   2009.txz
    1     168     27.3 GiB     31.4 GiB  0.868  CRC64   2010.txz
    1       4    477.1 MiB    702.8 MiB  0.679  CRC64   2011.txz
-------------------------------------------------------------------------------
   12   3,768    344.6 GiB    705.5 GiB  0.488  CRC64   12 files

Symbolic-link management

== Data used by sym-linked files:

This will de-reference the sym-links in the current directory and tell you how much data the files pointed to by the sym-links are using:

jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h

File searching

Finding a file with a particular name

$ find -iname "*some-part-of-the-file-name*"

Will start searching from the current directory, so maybe

$ cd /

first. For a case-sensitive search:

$ find -name "*eXaCT CaSE*"

Finding a file with particular content

To search in /etc/ for a file with particular content:

$ grep -R "search-string" /etc/*

To search the current directory for *.cs files containing the word "Up":

$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;

Finding a list of files with particular content

E.g. to find all the files with the word 'creativity':

$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq

Using the locate command to find files

$ locate part-of-filename

E.g.

$ locate texvc

Updating locate command's database

# updatedb

Select a random line from a text file

$ shuf -n 1 input.txt

Extra context for grep

If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:

$ grep -B 3 -A 1 ...

Job control

Stopping a running process

Press Ctrl+Z to stop a running process.

Listing current jobs and their status

$ jobs

Resuming a stopped job in the backgroud

To resume a stopped process in the background

$ bg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Resuming a stopped job in the foreground

To resume a stopped process in the foreground

$ fg %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Killing a stopped job

To kill a job

$ kill %1

where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').

Periodically run a program and watch its output

$ watch /your/command

Debian/Ubuntu package management

Also see Where "is" it? on the Debian Wiki.

configuring debconf

# dpkg-reconfigure debconf 

Set priority to low to get asked detailed questions.

Showing list of installed packages

# dpkg --get-selections

Searching for installed package

# dpkg --get-selections | grep package-name

or

# aptitude search package-name

Showing which files are installed as part of a package

# dpkg -L package-name

Installing a package

# apt-get install package-name

Uninstalling a package

# apt-get remove package-name

Showing system architecture

$ dpkg --print-architecture

Showing which package a file belongs to

$ which echo
/bin/echo
$ dpkg -S /bin/echo
coreutils: /bin/echo
$ dpkg -l | grep coreutils
ii  coreutils                         6.10-6                   The GNU core utilities

Showing package information

$ apt-cache showpkg coreutils

Or for even more information:

$ apt-cache show coreutils

List all installed packages with package version info

dpkg-query -l

Reporting which version of a package is installed

$ dpkg -l | grep package-name

E.g.:

root@hope:~/letsencrypt# dpkg -l | grep augeas
ii  augeas-lenses                   0.7.0-1ubuntu1                 Set of lenses needed by libaugeas0 to parse 
ii  libaugeas0                      0.7.0-1ubuntu1                 The augeas configuration editing library and

Comprehensive upgrade

Try the following:

# apt-get update
# apt-get dist-upgrade
# apt-get autoremove
# apt-get remove $(deborphan)
# update-flashplugin-nonfree --install

Searching all available packages

$ apt-cache search . | sort -d | less

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.

tmux

Live collaboration with tmux

User A:

tmux -S /tmp/collab
chmod 777 /tmp/collab

User B:

tmux -S /tmp/collab attach

Vim

First, why Vim?

Read Why, oh WHY, do those #?@! nutheads use vi?

Visual modes

Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.

Configuring spaces instead of tabs

I use two spaces instead of tabs. To configure, edit your .vimrc file:

$ vim ~/.vimrc

and include the following lines:

set tabstop=2
set shiftwidth=2
set expandtab

Configuring syntax highlighting

See here.

Use:

:syntax on

to turn on syntax highlighting.

Use:

:syntax off

to turn off syntax highlighting.

To always use syntax highlighting:

$ vim ~/.vimrc

and add:

syntax on

To get a list of supported colour schemes open vim and type:

:colorscheme[space][Ctrl+D]

To always use a particular colorscheme edit ~/.vimrc and add (for example):

colorscheme desert

Inserting a TAB character when expandtab is on

The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.

Press Ctrl+V TAB to insert a literal tab character.

Or you can disable tab expansion altogether with:

:set expandtab!

Changing 2 space indent to 4 space indent (e.g. for python files)

:%s/^\s*/&&/g

For more information see here.

Recording and replaying a macro

To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".

Deleting to end of line

d$

Deleting to beginning of line

d^

Finding text

To search forward for "text":

/text

To search backward for "text":

?text

To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.

Finding and replacing text

To replace the first instance of "search" on the current line with "destroy":

:s/search/destroy/

To replace all instances of "search" on the current line with "destroy":

:s/search/destroy/g

To replace all instances of "search" on lines 13 to 37 with "destroy":

:13,37 s/search/destroy/g

To replace all instances of "search" in the entire file with "destroy":

:%s/search/destroy/g

Changing DOS/Windows line-endings (CRLF) to Unix line-endings

To set the line-ending to Unix line endings run the command:

:setlocal ff=unix

More information on managing file formats available here.

Disabling auto-indent etc. to paste from clipboard

To disable smart indenting when you're going to paste in text:

:set paste

To turn it off again:

:set nopaste

There's more info in this article: Toggle auto-indenting for code paste

Positioning windows

Use -o for horizontal split, e.g.:

vim -o a.txt b.txt

Use -O for vertical split, e.g.:

vim -o a.txt b.txt

Use ^W to navigate windows then use directional keys h, j, k, l, etc.

Use ^W and < or > to resize windows.

To indent a block of text in Vim

Use the > command. E.g. to indent five lines:

5 > >

Press . (dot) to keep indenting.

Or inside a block (e.g. curly brace, HTML/XML element, etc.) you can put your cursor in the element on on the curly brace and then:

> %

See here for more.

Open a file in a new window/tab

To open a file on the left hand side:

:vert new filename.ext

Note: ':vnew filename.ext' and ':vsp filename.ext' also work.

To open a file at the top:

:new filename.ext

See here for more.

Explore files in Vim

Enter:

:Explore

Switch between Vim tabs

Use gt and gT.

Switch between Vim windows

To toggle between open windows use:

Ctrl+W W

To move in a direction use:

Ctrl+W h/j/k/l

See here for more.

Insert block comment in Vim

See here for line-commenting.

So it's:

  1. Ctrl+V (Note: not Shift+V!)
  2. Up/Down to select rows
  3. Shift+I
  4. Enter your text, e.g. '#' or '//'
  5. Ctrl+[ (or 'Esc')

Navigate to matching tag

To navigate to the matching beginning or end tag use '%'.

You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.

Auto-format HTML tags

Stolen from here.

  1. first join all the lines - ggVGgJ
  2. Now break tags to new lines - :%s/>\s*</>\r</g
  3. Now set filetype - :set ft=html (you can do this before too)
  4. Now Indent - ggVG=

Links

Create PDF from text using Vim

Generate PDF from input.txt with:

$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps

Examine output with:

$ okular doc.pdf

Write

Talking to other users on the system

write is a unix command for talking to other users on the system. To use write:

1. SSH to <username>@<hostname> and login with your username and password.

2. Issue the following command to find out who is logged onto the system:

$ who

3. Issue the following command to talk to a specific user:

$ write <username>

4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.

Date

Reporting the time on the server

$ date

Reporting UTC time

$ date --utc

Getting the date in yyyy-MM-dd-hhmmss format

$ date="`date +%F-%H%M%S`"

Getting the year in four digits

$ year="`date +%Y`"

Getting the month in two digits

$ month="`date +%m`"

Getting the day of the month in two digits

$ day="`date +%d`"

Getting yesterday's date

$ date --date='1 day ago' +%Y-%m-%d

Converting Unix time (seconds since epoch)

For timestamp '1501370200':

$ date -d @1501370200 +%F-%H%M%S

Running timedatectl from systemd

There's a new command bundled with systmed:

# timedatectl

It reports on (and controls) how the system time is configured.

MySQL

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).

Run a command using arguments that come from an array

See here:

#!/bin/bash
tabs=("first tab" "second tab")
args=()
for t in "${tabs[@]}" ; do 
  args+=(-t "$t")
done
app "${args[@]}"

Display a CSV in columnar or tabular format

$ column -t -s , data.csv

Sed

Find and replace with sed

To update the current file use '-i'. E.g.:

sed -i 's/search-text/replace-text/' file

Awk

Listing IP addresses in an Apache web log

awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq

Printing space-separated field

echo 'no no yes no' | awk '{print $3}'

Printing delimited field

echo 'no:no:yes:no' | awk -F ':' '{print $3}'

Subversion

Setting svn:externals from the command-line

See here.

To set an svn:externals from the command-line:

svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
svn ci -m 'Adding svn:externals for rdfind-php...'
svn up

Or to use a file:

svn propset svn:externals -F svn.externals .

Setting svn:ignore from the command line

See here.

$ svn propset svn:ignore [file|folder] [path]

Or use a file and apply recursively:

$ svn propset svn:ignore -RF ./svn-ignore-list.txt .

Git

Showing status of working copy

git status

Showing repo history

git log

Showing remote repositories (including 'origin')

git remote -v

Handy git aliases

Save these to your ~/.gitconfig file.

For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:

 graph = !git log --all --graph --color --abbrev-commit --pretty=oneline

To show only the files that have changed, rather than the full line-by-line content:

 dif   = !git diff --name-status

Show git remote URL

git config --get remote.origin.url

IRC

Instructing ChanServ to op an admin

/msg ChanServ op #channel user

E.g.

/msg ChanServ op #gnurc jj5

Sub 'op' for 'deop' to remove op privilege.

C++

C++ books

Books I want

Books I own

Books I'm not reading

Books I've read

C++ blogs/articles

C++ performance tips

  • ++c can be faster than c++.
  • use const for everything that you possibly can.
  • use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
  • don't use registers.
  • const rarely affects performance.
  • debunking a number of C++ myths that won't die.
  • std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
  • if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
  • read about performance cost of RTTI (Run Time Type Information) and how to disable it
  • don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
  • prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
  • Which is better, static or dynamic linking?
  • Integer vs Floating-Point performance

systemd

systemd is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.

Following a service log

e.g. for bind9:

# journalctl -f -u bind9

or for everything:

# journalctl -f

System status

To see spawned services hierarchy:

# systemctl status

Or for a specific service e.g.:

# systemctl status networking

SaltStack

Running a command on specified minions

From the salt master:

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

From the salt minion:

salt-call cmd.run 'update-locale'

Running a command on all minions

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

Running a specific state file

From the salt master:

salt $MINION_ID state.sls $STATE_FILE

From the salt minion:

salt-call state.sls $STATE_FILE

Listing active jobs

salt-run jobs.active

Listing available grains

salt 'example' grains.items

Listing available pillar

salt 'example' pillar.items

Reporting a grain value

e.g. for the 'mem_total' grain:

salt '*' grains.item mem_total

Passing a variable into a Jinja template from a salt state (SLS)

e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:

/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:
  file.managed:
    - template: jinja
    - user: root
    - group: root
    - mode: 644
    - source: salt://file/srv/zabbix/release/source.txt
    - require:
      - file: /srv/zabbix/release
    - default:
      zabbix_deb_pkg: {{ zabbix_deb_pkg }}
      zabbix_deb_url: {{ zabbix_deb_url }}

KDE

Running user login script (X11/XOrg/XWindows)

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

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

Standard KDE shortcut key bindings

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

VirtualBox

Mounting a VirtualBox VDI file

Note: instead of doing this consider booting with a live CD.

See here:

Install qemu if necessary:

# apt install qemu

Then you'll need to load the network block device module:

# rmmod nbd
# modprobe nbd max_part=16

Attach the .vdi image to one of the nbd you just created:

# qemu-nbd -c /dev/nbd0 drive.vdi

Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.

# mount /dev/nbd0p1 /mnt

Once you are done, unmount everything and disconnect the device:

# qemu-nbd -d /dev/nbd0

Elasticsearch

Report on health of your Elasticsearch cluster

$ curl http://localhost:9200/_cluster/health?pretty

Zabbix

Zabbix Agent on Mac OS X

Download and install agent.

Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf

Unload agent with:

# launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

Load agent with:

# launchctl load /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist

To add a 'pki' group:

# dseditgroup -o create pki

To monitor syslog on Mac OS X:

# tail -f /var/log/system.log

Installing Zabbix Agent from source on Mac OS X

Download sources from https://www.zabbix.com/download_sources

$ brew update
$ brew install openssl
$ brew install pcre
jj5@condor:~/Desktop/zabbix-4.4.7$ ./configure --enable-agent --with-openssl=/usr/local/opt/openssl/
jj5@condor:~/Desktop/zabbix-4.4.7$ sudo make install

NetBeans

NetBeans shortcut keys

Keys Action
Ctrl+W Close active window
Alt+Shift+K Open in Terminal
Ctrl+U U Convert selected text to uppercase
Ctrl+U L Convert selected text to lowercase