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]].
 +
 +
= References =
 +
 +
== Command-line ==
 +
 +
See [https://zaiste.net/posts/shell-commands-rust/ Shell Commands I Wish I Knew Earlier] for some interesting options.
  
 
= System =
 
= System =
Line 13: Line 25:
 
  $ 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 36: Line 52:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 48: Line 60:
  
 
  # 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 71: Line 85:
 
  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
  
= Environment =
+
=== Motherboard info ===
 +
 
 +
# dmidecode -t 2
  
== Configuring vim as your editor ==
+
=== CPU info ===
  
Sometimes all you need is:
+
# lscpu
  
$ export EDITOR=/usr/bin/vim
+
or:
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
# cat /proc/cpuinfo
  
Other times you need to run
+
=== RAM info ===
  
  # update-alternatives --config editor
+
  # dmidecode --type memory
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
=== PCI info ===
  
== Configuring your locale ==
+
# lspci -v
  
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
=== Drive info ===
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
 
  
= User and group management =
+
# cat /proc/partitions
  
== Adding a user ==
+
and:
  
To add a new user on a linux system:
+
# hdparm -I /dev/sda
  
# useradd username
+
and:
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
# smartctl --info /dev/sda
  
# adduser username
+
You can check if a drive is SSD or not with:
  
== Adding a user to a group ==
+
# cat /sys/block/sde/queue/rotational
  
To add an existing user to an existing group:
+
0=SSD
 +
1=HDD
  
# gpasswd -a username group
+
== Viewing syslog and other logs with KSystemLog ==
  
e.g. to add user 'jj5' to the 'sudo' group:
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
  
# gpasswd -a jj5 sudo
+
= Power =
  
Alternatively you can use adduser, passing the username and group:
+
== Reporting on PowerShield DEFENDER UPS status ==
  
# adduser username group
+
Before running `upsc` ensure service is running:
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
# upsdrvctl start
  
# adduser sclaughl staff
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
  
== Disabling a user account ==
+
$ upsc defender
  
You can disable a user account with:
+
E.g.:
  
  # passwd -l user
+
  jj5@orac:~$ upsc defender
 +
Init SSL without certificate database
 +
battery.charge: 100
 +
battery.voltage: 27.40
 +
battery.voltage.high: 26.00
 +
battery.voltage.low: 20.80
 +
battery.voltage.nominal: 24.0
 +
device.type: ups
 +
driver.name: blazer_usb
 +
driver.parameter.pollinterval: 2
 +
driver.parameter.port: auto
 +
driver.parameter.synchronous: no
 +
driver.version: 2.7.4
 +
driver.version.internal: 0.12
 +
input.current.nominal: 5.0
 +
input.frequency: 50.1
 +
input.frequency.nominal: 50
 +
input.voltage: 242.6
 +
input.voltage.fault: 242.6
 +
input.voltage.nominal: 240
 +
output.voltage: 242.6
 +
ups.beeper.status: disabled
 +
ups.delay.shutdown: 30
 +
ups.delay.start: 180
 +
ups.load: 14
 +
ups.productid: 5161
 +
ups.status: OL
 +
ups.type: offline / line interactive
 +
ups.vendorid: 0665
  
Note: that's a lower-case L, not a one.
+
== Run commands on PowerShield DEFENDER UPS batteries ==
  
== Enabling a disabled user account ==
+
You can run "instant commands" using the '''upscmd''' command.
  
To can re-enable a locked user account with:
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
  # passwd -u user
+
  diligence:/srv/salt/conf/app/defender-1200.sls
  
== Finding which user you are logged in as ==
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
To determine which user you are running as enter the command:
+
$ upscmd -l defender
  
$ whoami
+
E.g.:
  
== Finding which groups you are a member of ==
+
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
  
To find which groups you are a member of:
+
= Environment =
  
$ groups
+
== Configuring vim as your editor ==
  
or
+
Sometimes all you need is:
  
  $ groups username
+
  $ export EDITOR=/usr/bin/vim
  
Where 'username' is the username of the user you are querying, e.g.:
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
$ groups jj5
+
Other times you need to run
  
== Finding who else is logged in to the system ==
+
# update-alternatives --config editor
  
To see who else is logged in,
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
$ who
+
== Configuring your locale ==
  
== Running a command as a particular user ==
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
To run "svn update" as the user www-data:
+
= User and group management =
  
$ sudo su -c "svn update" www-data
+
== Adding a user ==
  
= Memory management =
+
To add a new user on a linux system:
  
== Checking available memory ==
+
# useradd username
 +
# passwd username
  
To report memory statistics in megabytes:
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
  $ free -m
+
  # adduser username
  
= Video/display management =
+
== Adding a user to a group ==
  
== Viewing EDID data for attached monitor ==
+
To add an existing user to an existing group:
  
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
+
# gpasswd -a username group
  
$ cd /sys/class/drm
+
e.g. to add user 'jj5' to the 'sudo' group:
$ ls
 
$ cd card0-HDMI-A-1
 
$ edid-decode edid
 
  
= Process management =
+
# gpasswd -a jj5 sudo
  
== Using 'top' for dynamic resource usage reporting ==
+
Alternatively you can use adduser, passing the username and group:
  
To run top:
+
# adduser username group
  
$ top
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
+
# adduser sclaughl staff
  
To see usage for a specific user run e.g.:
+
== Disabling a user account ==
  
$ top -u jj5
+
You can disable a user account with:
  
To see full command-line press 'c'.
+
# passwd -l user
  
When you're in 'top' you can:
+
Note: that's a lower-case L, not a one.
  
* press '1' (one) to toggle CPU aggregation
+
== Enabling a disabled user account ==
* press < and > to change the sort column
 
== Changing memory reporting in 'top' ==
 
  
To run top:
+
To can re-enable a locked user account with:
  
  $ top
+
  # passwd -u user
  
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
+
== Finding which user you are logged in as ==
  
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
+
To determine which user you are running as enter the command:
  
Press 'M' to sort by memory utilisation.
+
$ whoami
  
Press 'm' to switch between various display modes.
+
== Finding which groups you are a member of ==
  
= Disk management =
+
To find which groups you are a member of:
  
== Listing disk drives ==
+
$ groups
  
# fdisk -l
+
or
  
(That's an L for "list")
+
$ groups username
  
== Checking available disk space ==
+
Where 'username' is the username of the user you are querying, e.g.:
  
  $ df -h
+
  $ groups jj5
  
== Getting disk information ==
+
== Finding who else is logged in to the system ==
  
  # lsblk
+
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
  
And
+
== Reporting user and group info for the current user ==
  
  # cat /proc/partitions
+
  $ id
  
Or the Grand Daddy of them all:
+
= Memory management =
  
# lshw -class disk
+
== Checking available memory ==
  
(Requires the lshw package.)
+
To report memory statistics in megabytes:
  
== Getting partition UUID and file-system type ==
+
$ free -m
  
# blkid
+
== Check for swap thrashing ==
  
== Checking for SSD vs magnetic disk ==
+
Check your virtual memory status with vmstat:
  
  # cat /sys/block/sda/queue/rotational
+
  $ vmstat
  
Will be 0 for SSD and 1 for magnetic.
+
== Report memory type ==
  
== Monitoring a ZFS server ==
+
Report on RAM DIMMs:
  
So some commands I run to keep an eye on my new ZFS servers:
+
# dmidecode --type 17
  
# top
+
Report on RAM and CPU cache (including L1, L2, and L3):
# 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:
+
# lshw -short -C memory
  
# watch zpool status -v
+
Or for more detail:
  
You can poke about in internals, e.g.:
+
# lshw -C memory
  
# cat /proc/spl/kstat/zfs/arcstats
+
= Video/display management =
  
root@orac:/sys/module/zfs/parameters# tail *
+
== Viewing EDID data for attached monitor ==
  
You can report on property values with e.g.:
+
To view [https://en.wikipedia.org/wiki/Extended_Display_Identification_Data EDID] data for an attached monitor (requires the [https://packages.debian.org/stable/main/edid-decode edid-decode] package):
  
  # zfs get all data
+
  $ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
If you want to get funky:
+
= Process management =
  
# cd /tmp
+
== Using 'top' for dynamic resource usage reporting ==
# perf record -ag #(Ctrl+C after ~15 seconds)
 
# perf report --stdio
 
  
You can search for ZFS files like e.g. this:
+
To run top:
 +
 
 +
$ top
 +
 
 +
See [https://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/ 15 Practical Linux Top Command Examples] for some hints on usage.
 +
 
 +
To see usage for a specific user run e.g.:
  
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
+
  $ top -u jj5
  
You can report history of a zpool:
+
To see full command-line press 'c'.
  
# zpool history $poolname
+
When you're in 'top' you can:
  
You can get a report on the dedup tables:
+
* press '1' (one) to toggle CPU aggregation
 +
* press < and > to change the sort column
  
# zpool status -D $poolname
+
== Changing memory reporting in 'top' ==
  
Or more detailed dedup table info:
+
To run top:
  
  # zdb -DDD $poolname
+
  $ top
  
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
{|class="wikitable"
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
! Abbr  !! Description
 
|-
 
| LSIZE  || logical size (in memory)
 
|-
 
| PSIZE  || physical size
 
|-
 
| DSIZE  || size on disk
 
|-
 
| refcnt || reference count
 
|}
 
  
== Measure data throughput ==
+
Press 'M' to sort by memory utilisation.
  
Use the 'pv' command from the 'pv' package, e.g.:
+
Press 'm' to switch between various display modes.
  
# cat /dev/sda | pv | cat > /dev/null
+
== Showing full command-line in 'top' ==
  
Or for ZFS:
+
To see the full command-line for processes run with -c:
  
  # zfs send data/example | pv | cat > /dev/null
+
  $ top -c
  
== Using Smartctl, Smartd and Hddtemp on Debian ==
+
== Listing all processes currently running which were started in your current shell session ==
  
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].
+
$ ps -fl
  
== Report hard disk usage ==
+
== Killing specific processes ==
  
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.
+
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
== Report hard disk temperatures ==
+
== Run a command for a specified time using timeout ==
  
E.g.
+
$ timeout 3 ping jj5.net
  
# hddtemp /dev/sd[a-e]
+
= Disk management =
  
= Monitoring disk I/O =
+
== Creating a partition table ==
  
There's an app for that! iotop.
+
# parted /dev/xvdf
  
== Using iotop, top for disks ==
+
mktable msdos
  
# iotop -oPa
+
== Creating a partition ==
  
== Monitor disk I/O for performance issues ==
+
# parted /dev/xvdf
  
  # watch iostat
+
  u MiB
 +
mkpart primary 1 100%
  
Or e.g.
+
== Creating an ext4 file-system ==
  
  # watch iostat -xd /dev/sd[abc]
+
  # mkfs.ext4 /dev/xvdf1
  
= Monitoring a system =
+
== Listing disk drives ==
  
== Simple ZFS monitoring ==
+
# fdisk -l
  
# watch iostat
+
(That's an L for "list")
# iotop
 
# zpool iostat -v 5
 
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 
# nethogs
 
# top
 
  
= File management =
+
== Checking available disk space ==
  
== Listing only directories ==
+
$ df -h
  
$ ls -l | egrep '^d'
+
== Getting disk information ==
  
== Listing only files ==
+
# lsblk
  
$ ls -l | egrep -v '^d'
+
And
  
== Listing hidden files ==
+
# cat /proc/partitions
  
$ ls -al .[!.]*
+
Or the Grand Daddy of them all:
  
== Creating a symbolic link ==
+
# lshw -class disk
  
$ ln -s /path/to/target link-name
+
(Requires the lshw package.)
  
== Creating a hard-link ==
+
== Getting partition UUID and file-system type ==
  
  $ ln /path/to/target file-name
+
  # blkid
  
== Changing the owner of a file ==
+
== Checking for SSD vs magnetic disk ==
  
  $ chown user:group <files>
+
  # cat /sys/block/sda/queue/rotational
  
E.g.
+
Will be 0 for SSD and 1 for magnetic.
  
$ chown jj5:staff README
+
== Monitoring a ZFS server ==
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
So some commands I run to keep an eye on my new ZFS servers:
  
  $ chown -R root:root /etc/*
+
  # 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
  
== Changing file permissions ==
+
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
  
{|class="wikitable"
+
root@orac:/sys/module/zfs/parameters# tail *
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
You can report on property values with e.g.:
|+ Permission codes
 
! Read !! Write !! Exectue
 
|-
 
| r    || w    || x
 
|-
 
| 4    || 2    || 1
 
|}
 
  
{|class="wikitable"
+
# zfs get all data
|+ 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].
+
If you want to get funky:
  
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
+
  # cd /tmp
  $ chmod <object codes>+|-<permission codes> <files>
+
  # perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
E.g.
+
You can search for ZFS files like e.g. this:
  
  $ chmod 600 my-private-file
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
You can report history of a zpool:
  
If you get given a new config file called new.conf and you want to integrate it with your old config file old.conf then:
+
# zpool history $poolname
  
$ cp old.conf updated.conf
+
You can get a report on the dedup tables:
$ merge -A updated.conf new.conf old.conf
 
  
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
+
# zpool status -D $poolname
  
The merge program is a part of the RCS package. If you don't have it:
+
Or more detailed dedup table info:
  
  $ sudo apt-get install rcs
+
  # zdb -DDD $poolname
  
== Listing open files ==
+
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
Use lsof to list open files. E.g.:
+
{|class="wikitable"
 
+
! Abbr  !! Description
  # lsof
+
|-
 
+
| LSIZE  || logical size (in memory)
See man lsof for options.
+
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
== List permissions on a whole directory path ==
+
== How to tell if zfs scrub is running ==
  
E.g.:
+
You can get the status from the "scan:" line from:
  
  $ namei -om /home/jj5/workspace
+
  $ zpool status
  
Outputs:
+
== Measure data throughput ==
  
f: /home/jj5/workspace/
+
Use the 'pv' command from the 'pv' package, e.g.:
  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 ==
+
# cat /dev/sda | pv | cat > /dev/null
  
E.g.:
+
Or for ZFS:
  
  $ cat foo.c | sed '/^\s*$/d' | wc -l
+
  # zfs send data/example | pv | cat > /dev/null
  
== Cloning one directory to another with rsync ==
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
E.g.:
+
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].
  
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/
+
== Report hard disk usage ==
  
== Counting number of files in current directory and all subdirectories ==
+
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.
  
$ ls -AlhR . | egrep '^-' | wc -l
+
== Report hard disk temperatures ==
  
== Counting number of directories in current directory and all subdirectories ==
+
E.g.
  
  $ ls -AlhR . | egrep '^d' | wc -l
+
  # hddtemp /dev/sd[a-e]
  
= Symbolic-link management =
+
== Burning an ISO image to USB on Mac ==
  
== Data used by sym-linked files:
+
First insert your USB key and find the appropriate disk with:
  
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:
+
# diskutil list
  
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
+
Then unmount it with:
  
= File searching =
+
# diskutil unmountDisk /dev/disk4
  
== Finding a file with a particular name ==
+
Then copy ISO image with 'dd':
  
  $ find -iname "*some-part-of-the-file-name*"
+
  # dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
Will start searching from the current directory, so maybe
+
You can get dd to report progress by sending it the SIGINFO signal:
  
  $ cd /
+
  # kill -s info 12345
  
first. For a case-sensitive search:
+
== Listing all ext4 file systems ==
  
$ find -name "*eXaCT CaSE*"
+
To see a list only of the mounted ext4 file systems:
  
== Finding a file with particular content ==
+
# df -t ext4
  
To search in /etc/ for a file with particular content:
+
== Report hierarchical file system mount points and mount options ==
  
  $ grep -R "search-string" /etc/*
+
  $ findmnt
  
To search the current directory for *.cs files containing the word "Up":
+
== Report the mount point for the current working directory ==
  
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
  $ findmnt "$PWD"
  
== Finding a list of files with particular content ==
+
= Monitoring disk I/O =
  
E.g. to find all the files with the word 'creativity':
+
There's an app for that! iotop.
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
== Using iotop, top for disks ==
  
== Using the locate command to find files ==
+
# iotop -oPa
  
$ locate part-of-filename
+
== Monitor disk I/O for performance issues ==
  
E.g.
+
# watch iostat
  
$ locate texvc
+
Or e.g.
  
== Updating locate command's database ==
+
# watch iostat -xd /dev/sd[abc]
  
# updatedb
+
Or use groupings like this command for 'tact':
  
= Job control =
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
== Stopping a running process ==
+
= Monitoring a system =
  
Press Ctrl+Z to stop a running process.
+
== Simple ZFS monitoring ==
  
== Listing current jobs and their status ==
+
# watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
$ jobs
+
= Monitoring temperature =
  
== Resuming a stopped job in the backgroud ==
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
To resume a stopped process in the background
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
$ bg %1
+
and:
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
== Resuming a stopped job in the foreground ==
+
== Monitoring CPU temperature ==
  
To resume a stopped process in the foreground
+
$ watch sensors
  
$ fg %1
+
== Monitoring HDD temperature ==
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
For e.g. SATA drives sda to sdd:
  
== Killing a stopped job ==
+
# watch hddtemp /dev/sd[a-d]
  
To kill a job
+
= ZFS =
  
$ kill %1
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
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?]
  
== Periodically run a program and watch its output ==
+
$ cat /proc/spl/kstat/zfs/arcstats
  
$ watch /your/command
+
Then:
  
= Debian/Ubuntu package management =
+
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
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
== Stopping a ZFS scrub in progress ==
  
== configuring debconf ==
+
# zpool scrub -s $pool
  
# dpkg-reconfigure debconf
+
e.g. for the 'data' pool:
  
Set priority to low to get asked detailed questions.
+
# zpool scrub -s data
  
== Showing list of installed packages ==
+
= File management =
  
# dpkg --get-selections
+
== Listing files by size ==
  
== Searching for installed package ==
+
Use capital S for Size:
  
  # dpkg --get-selections | grep package-name
+
  $ ls -S
  
or
+
== Listing only directories ==
  
  # aptitude search package-name
+
  $ ls -l | egrep '^d'
  
== Showing which files are installed as part of a package ==
+
== Listing only files ==
  
  # dpkg -L package-name
+
  $ ls -l | egrep -v '^d'
  
== Installing a package ==
+
== Listing hidden files ==
  
  # apt-get install package-name
+
  $ ls -al .[!.]*
  
== Uninstalling a package ==
+
== Creating a symbolic link ==
  
  # apt-get remove package-name
+
  $ ln -s /path/to/target link-name
  
== Showing system architecture ==
+
== Creating a hard-link ==
  
  $ dpkg --print-architecture
+
  $ ln /path/to/target file-name
  
== Showing which package a file belongs to ==
+
== Changing the owner of a file ==
  
  $ which echo
+
  $ chown user:group <files>
/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 ==
+
E.g.
  
  $ apt-cache showpkg coreutils
+
  $ chown jj5:staff README
 +
$ chown root:root *
  
Or for even more information:
+
To apply recursively into sub-directories use -R,
  
  $ apt-cache show coreutils
+
  $ chown -R root:root /etc/*
  
== List all installed packages with package version info ==
+
== Changing file permissions ==
  
dpkg-query -l
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
== Reporting which version of a package is installed ==
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
$ dpkg -l | grep package-name
+
{|class="wikitable"
 
+
|+ Numeric codes
E.g.:
+
! 0
 
+
| None
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
|-
ii  augeas-lenses                  0.7.0-1ubuntu1                Set of lenses needed by libaugeas0 to parse
+
! 1
ii  libaugeas0                      0.7.0-1ubuntu1                The augeas configuration editing library and
+
| Execute
 
+
|-
== Comprehensive upgrade ==
+
! 2
 +
| Write
 +
|-
 +
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
Try the following:
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
  # apt-get update
+
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
# apt-get dist-upgrade
+
  $ chmod <object codes>+|-<permission codes> <files>
  # apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
== Searching all available packages ==
+
E.g.
  
  $ apt-cache search . | sort -d | less
+
  $ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
= Networking =
+
== Updating config files ==
  
== net-tools vs iproute2 ==
+
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:
  
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].
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
{|class="wikitable"
+
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.
! 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 ==
+
The merge program is a part of the RCS package. If you don't have it:
  
For servers:
+
$ sudo apt-get install rcs
  
# service networking restart
+
== Listing open files ==
  
For desktops:
+
Use lsof to list open files. E.g.:
  
  # service network-manager restart
+
  # lsof
  
== Pinging with particular packet size ==
+
See man lsof for options.
  
$ ping -M do -s <packet size in bytes> <host>
+
== List permissions on a whole directory path ==
  
E.g.
+
E.g.:
  
  $ ping -M do -s 1400 charity.progclub.org
+
  $ namei -om /home/jj5/workspace
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
Outputs:
  
  # ip route add <host> dev <interface> advmss <packet size>
+
  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
  
E.g.
+
== Counting non-blank lines in a file ==
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
E.g.:
  
== Dropping configured MMS for a particular IP address ==
+
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
# ip route flush <host>
+
== Cloning one directory to another with rsync ==
  
E.g.
+
E.g.:
  
# ip route flush 10.0.0.1
+
rsync --acls --xattrs --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse --compress-level=0 /data/source/ hostname:/data/target/
  
== Listing open ports and socket information ==
+
== Counting number of files in current directory and all subdirectories ==
  
Including which process is listening on which port.
+
$ ls -AlhR . | egrep '^-' | wc -l
  
# netstat -tulpn
+
== Counting number of directories in current directory and all subdirectories ==
  
Or use the 'ss' command:
+
$ ls -AlhR . | egrep '^d' | wc -l
  
# ss -s
+
== Getting the status of a 'dd' process ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
# lsof -Pnl +M -i4
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
You might need to install the lsof package:
+
# kill -s info 40947
  
# apt-get install lsof
+
The dd process will report its status in the terminal its running in.
  
== Query for DNS MX record ==
+
== Transferring a large file via FAT32 file system ==
  
$ nslookup
+
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:
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
$ split -b 4000m input.tgz input.tgz-parts-
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
Then copy the small files and reassemble:
  
== Using nmap to list open ports on remote host ==
+
$ cat input.tgz-parts-* > output.tgz
  
To check the 1,000 most common ports:
+
== Find the difference between two directories ==
  
  # nmap server.example.com
+
  $ diif -qr $DIR_A $DIR_B
  
Or for a specific port range (e.g. 101 to 102):
+
= NFS =
  
# nmap -p 101-102 server.example.com
+
== List NFS shares ==
  
Or for all ports (1 to 65,535):
+
To e.g. show NFS shares on 'love':
  
  # nmap -p- server.example.com
+
  $ showmount -e love
  
== Network monitoring ==
+
= Compression =
  
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
+
== How to use pigz with tar ==
  
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
+
See [https://stackoverflow.com/a/39904353 here]:
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 
# Bandwidth per process: nethogs
 
  
== nload ==
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
You can watch network traffic in real-time with nload:
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
# nload -u M
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
== Reporting network (NIC) speed ==
+
Fast pack:
  
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
+
tar -I 'pigz --fast' -cf my.tar.gz whatver
  
# dmesg | grep eth0
+
Best pack:
# mii-tool -v eth0
 
# ethtool eth0
 
  
Note: use ifconfig to get device name.
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
== Path MTU discovery ==
+
Fast unpack:
  
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
+
tar -I pigz -xf my.tar.gz
  
# tracepath host.example.com
+
== Best compression with tar ==
  
== Listing available Ethernet devices ==
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
To see a list of NICs available on the host:
+
export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
$ cat /proc/net/dev
+
or
  
Also
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
$ ip link
+
== Best parallel compression with pigz ==
  
== Links ==
+
$ pigz --best
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
== Best parallel compression with xz ==
  
= IPTables =
+
$ xz -9e -T 0
  
== Applying firewall rules ==
+
== Reporting compression ratios with xz ==
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
e.g.
  
  $ sudo vim /etc/iptables.test.rules
+
  root@love:/data/image/archive# xz -l *
  $ sudo /sbin/iptables -F
+
Strms  Blocks  Compressed Uncompressed  Ratio  Check  Filename
  $ sudo /sbin/iptables-restore < /etc/iptables.test.rules
+
    1      3    372.2 MiB    442.3 MiB  0.841  CRC64  1999.txz
  $ sudo iptables -L
+
    1      29  5,281.3 MiB  5,542.5 MiB  0.953  CRC64  2001.txz
  $ sudo -s
+
    1      11  1,364.3 MiB  2,084.3 MiB  0.655  CRC64  2002.txz
  # iptables-save > /etc/iptables.up.rules
+
    1      9    568.5 MiB  1,660.2 MiB 0.342  CRC64  2003.txz
  # exit
+
    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
  
= ufw =
+
= Symbolic-link management =
  
== Denying hosts with ufw ==
+
== Data used by sym-linked files:
  
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
+
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:
  
= Bind9 =
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
== Viewing Bind9 querylog ==
+
= File searching =
  
$ sudo rndc querylog
+
== Finding a file with a particular name ==
$ tail -f /var/log/syslog
 
  
= IPSec =
+
$ find -iname "*some-part-of-the-file-name*"
  
== Disabling IPSec ==
+
Will start searching from the current directory, so maybe
  
  # setkey -FP
+
  $ cd /
  
= OpenSSL =
+
first. For a case-sensitive search:
  
== Debugging IMAPS with OpenSSL ==
+
$ find -name "*eXaCT CaSE*"
  
# openssl s_client -connect localhost:993
+
== Finding a file with particular content ==
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
To search in /etc/ for a file with particular content:
  
  $ openssl s_client -connect www.example.com:443
+
  $ grep -R "search-string" /etc/*
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
To search the current directory for *.cs files containing the word "Up":
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
= Pluggable Authentication Modules (PAM) =
+
== Finding a list of files with particular content ==
  
== Links ==
+
E.g. to find all the files with the word 'creativity':
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
= SSH =
+
== Using the locate command to find files ==
  
== Configuring SSH key login ==
+
$ locate part-of-filename
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
E.g.
  
  $ ssh-keygen -t rsa
+
  $ locate texvc
  
Copy the public key from the client to the server:
+
== Updating locate command's database ==
  
  $ scp ~/.ssh/id_rsa.pub user@example.org:
+
  # updatedb
  
Configure the authorized keys on the server:
+
== Select a random line from a text file ==
  
  $ ssh user@example.org
+
  $ shuf -n 1 input.txt
$ 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 ==
+
== Extra context for grep ==
  
For example, connecting a remote MySQL server to the localhost:
+
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:
  
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
  $ grep -B 3 -A 1 ...
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
= Job control =
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
== Stopping a running process ==
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
Press Ctrl+Z to stop a running process.
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
== Listing current jobs and their status ==
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
$ jobs
  
* run putty.exe
+
== Resuming a stopped job in the backgroud ==
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
To resume a stopped process in the background
  
To see what's going on with your ssh connections,
+
$ bg %1
  
$ ssh -v user@host
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
Or
+
== Resuming a stopped job in the foreground ==
  
$ ssh -vv user@host
+
To resume a stopped process in the foreground
  
== Unlocking SSH key for session ==
+
$ fg %1
  
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
[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 ==
+
== Killing a stopped job ==
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
To kill a job
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
$ kill %1
  
== cat EOF ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
$ cat > output <<EOF
+
== Periodically run a program and watch its output ==
> text
 
> EOF
 
  
  $ cat output
+
  $ watch /your/command
text
 
  
= Script =
+
= Debian/Ubuntu package management =
  
== Creating a session log with script ==
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
$ script -t 2> timing
+
== configuring debconf ==
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
# dpkg-reconfigure debconf
  
== Replaying a scripted session ==
+
Set priority to low to get asked detailed questions.
  
$ scriptreplay timing
+
== Showing list of installed packages ==
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
# dpkg --get-selections
  
= Screen =
+
== Searching for installed package ==
  
== Creating a new screen or reconnecting to a detached screen ==
+
# dpkg --get-selections | grep package-name
  
$ screen -R
+
or
  
== Detaching a screen ==
+
# aptitude search package-name
  
$ screen -D
+
== Showing which files are installed as part of a package ==
  
== Reconnecting to screen ==
+
# dpkg -L package-name
  
$ screen -D
+
== Installing a package ==
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
# apt-get install package-name
  
#!/bin/bash
+
== Uninstalling a package ==
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
# apt-get remove package-name
  
== Scrolling in screen ==
+
== Showing system architecture ==
  
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.
+
$ dpkg --print-architecture
  
= Vim =
+
== Showing which package a file belongs to ==
  
== First, why Vim? ==
+
$ which echo
 
+
/bin/echo
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
== Visual modes ==
+
== Showing package information ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
$ apt-cache showpkg coreutils
  
== Configuring spaces instead of tabs ==
+
Or for even more information:
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
$ apt-cache show coreutils
  
$ vim ~/.vimrc
+
== List all installed packages with package version info ==
  
and include the following lines:
+
dpkg-query -l
  
set tabstop=2
+
== Reporting which version of a package is installed ==
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
$ dpkg -l | grep package-name
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
E.g.:
  
Use:
+
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
  
:syntax on
+
== Comprehensive upgrade ==
  
to turn on syntax highlighting.
+
Try the following:
  
Use:
+
# apt-get update
 +
# apt-get dist-upgrade
 +
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
:syntax off
+
== Searching all available packages ==
  
to turn off syntax highlighting.
+
$ apt-cache search . | sort -d | less
  
To always use syntax highlighting:
+
= Networking =
  
$ vim ~/.vimrc
+
== net-tools vs iproute2 ==
  
and add:
+
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].
  
syntax on
+
{|class="wikitable"
 
+
! legacy net-tools commands
To get a list of supported colour schemes open vim and type:
+
! iproute2 replacement commands
 
+
|-
  :colorscheme[space][Ctrl+D]
+
| arp      || ip n (ip neighbor)
 
+
|-
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
| 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)
 +
|}
  
colorscheme desert
+
== Restart networking ==
  
== Inserting a TAB character when expandtab is on ==
+
For servers:
  
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.
+
# service networking restart
  
Press Ctrl+V TAB to insert a literal tab character.
+
For desktops:
  
Or you can disable tab expansion altogether with:
+
# service network-manager restart
  
:set expandtab!
+
== Pinging with particular packet size ==
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
$ ping -M do -s <packet size in bytes> <host>
  
:%s/^\s*/&&/g
+
E.g.
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
$ ping -M do -s 1400 charity.progclub.org
  
== Recording and replaying a macro ==
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
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 "@@".
+
# ip route add <host> dev <interface> advmss <packet size>
  
== Deleting to end of line ==
+
E.g.
  
  d$
+
  # ip route add 10.0.0.1 dev eth0 advmss 1400
  
== Deleting to beginning of line ==
+
== Dropping configured MMS for a particular IP address ==
  
  d^
+
  # ip route flush <host>
  
== Finding text ==
+
E.g.
  
To search forward for "text":
+
# ip route flush 10.0.0.1
  
/text
+
== Listing open ports and socket information ==
  
To search backward for "text":
+
Including which process is listening on which port.
  
  ?text
+
  # netstat -tulpn
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
Or use the 'ss' command:
  
== Finding and replacing text ==
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
To replace the first instance of "search" on the current line with "destroy":
+
== Listing open IPv4 connections ==
  
  :s/search/destroy/
+
  # lsof -Pnl +M -i4
  
To replace all instances of "search" on the current line with "destroy":
+
You might need to install the lsof package:
  
  :s/search/destroy/g
+
  # apt-get install lsof
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
== Query for DNS MX record ==
  
  :13,37 s/search/destroy/g
+
  $ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
To replace all instances of "search" in the entire file with "destroy":
+
== Query for DNS SOA record ==
  
  :%s/search/destroy/g
+
  $ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
== Using nmap to list open ports on remote host ==
  
To set the line-ending to Unix line endings run the command:
+
To check the 1,000 most common ports:
  
  :setlocal ff=unix
+
  # nmap server.example.com
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
Or for a specific port range (e.g. 101 to 102):
  
== Disabling auto-indent etc. to paste from clipboard ==
+
# nmap -p 101-102 server.example.com
  
To disable smart indenting when you're going to paste in text:
+
Or for all ports (1 to 65,535):
  
  :set paste
+
  # nmap -p- server.example.com
  
To turn it off again:
+
== Network monitoring ==
  
:set nopaste
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
# 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
  
== Positioning windows ==
+
== nload ==
  
Use -o for horizontal split, e.g.:
+
You can watch network traffic in real-time with nload:
  
  vim -o a.txt b.txt
+
  # nload -u M
  
Use -O for vertical split, e.g.:
+
== Reporting network (NIC) speed ==
  
vim -o a.txt b.txt
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
Use ^W and &lt; or &gt; to resize windows.
+
Note: use ifconfig to get device name.
  
== To indent a block of text in Vim ==
+
== Path MTU discovery ==
  
Use the > command. E.g. to indent five lines:
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
  5 > >
+
  # tracepath host.example.com
  
Press . (dot) to keep indenting.
+
== Listing available Ethernet devices ==
  
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:
+
To see a list of NICs available on the host:
  
  > %
+
  $ cat /proc/net/dev
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
Also
  
== Open a file in a new window/tab ==
+
$ ip link
 
 
To open a file on the left hand side:
 
  
:vert new filename.ext
+
== 59 Linux Networking commands and scripts ==
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
To open a file at the top:
+
== Links ==
  
:new filename.ext
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
= IPTables =
  
== Explore files in Vim ==
+
== Applying firewall rules ==
  
Enter:
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
  :Explore
+
  $ sudo vim /etc/iptables.test.rules
 +
$ sudo /sbin/iptables -F
 +
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 +
$ sudo iptables -L
 +
$ sudo -s
 +
# iptables-save > /etc/iptables.up.rules
 +
# exit
 +
 
 +
== Blocking an IP address with iptables ==
  
== Switch between Vim tabs ==
+
To drop IP address 1.2.3.4:
  
Use gt and gT.
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
== Switch between Vim windows ==
+
= ufw =
  
To toggle between open windows use:
+
== Denying hosts with ufw ==
  
Ctrl+W W
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
To move in a direction use:
+
= Bind9 =
  
Ctrl+W h/j/k/l
+
== Viewing Bind9 querylog ==
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
$ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
== Insert block comment in Vim ==
+
= IPSec =
  
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
+
== Disabling IPSec ==
  
So it's:
+
# setkey -FP
  
# Ctrl+V (Note: not Shift+V!)
+
= OpenSSL =
# Up/Down to select rows
+
 
# Shift+I
+
== Debugging IMAPS with OpenSSL ==
# Enter your text, e.g. '#' or '//'
 
# Ctrl+[ (or 'Esc')
 
  
== Navigate to matching tag ==
+
# openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
To navigate to the matching beginning or end tag use '%'.
+
== Debugging HTTPS with OpenSSL ==
  
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
== Auto-format HTML tags ==
+
== Links ==
  
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
# first join all the lines - ggVGgJ
+
= Pluggable Authentication Modules (PAM) =
# 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 ==
 
== Links ==
  
* [http://www.vim.org/ Vim: the editor]
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
+
 
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
+
= SSH =
* [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 =
+
== Configuring SSH key login ==
  
== Talking to other users on the system ==
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
$ ssh-keygen -t rsa
  
1. SSH to <username>@<hostname> and login with your username and password.
+
Copy the public key from the client to the server:
  
2. Issue the following command to find out who is logged onto the system:
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
$ who
+
Configure the authorized keys on the server:
  
3. Issue the following command to talk to a specific user:
+
$ 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
  
$ write <username>
+
== Tunneling over SSH ==
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
For example, connecting a remote MySQL server to the localhost:
  
= Date =
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
== Reporting the time on the server ==
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
$ date
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
== Reporting UTC time ==
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
$ date --utc
+
== Tunneling over SSH with PuTTY ==
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
$ date="`date +%F-%H%M%S`"
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
== Getting the year in four digits ==
+
== Enabling verbose SSH logging ==
  
$ year="`date +%Y`"
+
To see what's going on with your ssh connections,
  
== Getting the month in two digits ==
+
$ ssh -v user@host
  
$ month="`date +%m`"
+
Or
  
== Getting the day of the month in two digits ==
+
$ ssh -vv user@host
  
$ day="`date +%d`"
+
== Unlocking SSH key for session ==
  
== Getting yesterday's date ==
+
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'
  
$ date --date='1 day ago' +%Y-%m-%d
+
== Links ==
  
== Converting Unix time (seconds since epoch) ==
+
* [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]
  
For timestamp '1501370200':
+
= Standard IO =
  
$ date -d @1501370200 +%F-%H%M%S
+
== cat EOF ==
  
== Running timedatectl from systemd ==
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
There's a new command bundled with systmed:
+
$ cat output
 +
text
  
# timedatectl
+
= Script =
  
It reports on (and controls) how the system time is configured.
+
== Creating a session log with script ==
  
= MySQL =
+
$ script -t 2> timing
  
== Run mysql without authentication/authorisation ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
# service mysql stop
+
== Replaying a scripted session ==
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
$ scriptreplay timing
  
# mysql -u root mysql
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
To stop the unauthenticated service:
+
= Screen =
  
# mysqladmin shutdown
+
== Creating a new screen or reconnecting to a detached screen ==
  
Then restart a normal service:
+
$ screen -R
  
# service mysql start
+
== Detaching a screen ==
  
== Logging all database queries ==
+
$ screen -D
  
# vim /etc/mysql/my.cnf
+
== Reconnecting to screen ==
  
In the [mysqld] section add:
+
$ screen -D
 +
$ screen -R
  
log=/tmp/mysql.log
+
I have a script in ~/bin/reconnect like so,
  
Then:
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
# service mysql restart
+
This will detach your last screen, and reconnect it on the current terminal.
  
Watch the log with:
+
== Scrolling in screen ==
  
# tail -f /tmp/mysql.log
+
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.
  
== Dumping a MySQL database ==
+
= tmux =
  
You can dump the database into a file using:
+
== Live collaboration with tmux ==
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
User A:
  
You can create a database using:
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
$ echo create database databasename | mysql -h hostname -u user -p
+
User B:
  
You can restore a database using:
+
  tmux -S /tmp/collab attach
   
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
= Vim =
  
# mysql -h localhost -u root --password=<password>
+
== First, why Vim? ==
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
  
# mysql -h localhost -u root --password=<password>
+
== Visual modes ==
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
== Configuring spaces instead of tabs ==
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
Check the SSL version in use:
+
$ vim ~/.vimrc
  
show status like 'Ssl_version';
+
and include the following lines:
  
Or check the cipher in use:
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
show status like 'Ssl_cipher';
+
== Configuring syntax highlighting ==
  
= Apache =
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
== Maintaining .htaccess passwords ==
+
Use:
  
To add or modify the password for a user:
+
:syntax on
  
$ htpasswd /etc/apache2/passwd username
+
to turn on syntax highlighting.
  
== Configuring PHP session timeout in .htaccess ==
+
Use:
  
For a session timeout of 9 hours:
+
:syntax off
  
php_value session.cookie_lifetime 32400
+
to turn off syntax highlighting.
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
To always use syntax highlighting:
  
  php_flag magic_quotes_gpc Off
+
  $ vim ~/.vimrc
  
== Requiring HTTP Auth in .htaccess ==
+
and add:
  
  AuthType Basic
+
  syntax on
AuthName "Speak Friend And Enter"
 
AuthUserFile /home/jj5/.htpasswd
 
Require valid-user
 
  
== Restarting Apache ==
+
To get a list of supported colour schemes open vim and type:
  
The hard way
+
:colorscheme[space][Ctrl+D]
  
$ sudo /etc/init.d/apache2 restart
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
The graceful way (avoids dropping active connections)
+
colorscheme desert
  
$ sudo apache2ctl graceful
+
== Inserting a TAB character when expandtab is on ==
  
== Allowing directory browsing ==
+
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.
  
To show directory index pages, in the apache config file:
+
Press Ctrl+V TAB to insert a literal tab character.
  
<Directory /var/www/data>
+
Or you can disable tab expansion altogether with:
  Options Indexes
 
</Directory>
 
  
= C =
+
:set expandtab!
  
== Locating memset function ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
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]
+
:%s/^\s*/&&/g
  
== Links ==
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
== Recording and replaying a macro ==
  
= PHP =
+
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 "@@".
  
== Including a file relative to the including file ==
+
== Deleting to end of line ==
  
  require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
  d$
  
== Enabling error reporting ==
+
== Deleting to beginning of line ==
  
  error_reporting( E_ALL | E_STRICT );
+
  d^
ini_set( 'display_errors', 'On' );
 
  
== Setting an error handler ==
+
== Finding text ==
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
To search forward for "text":
  
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
  /text
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
To search backward for "text":
  
  ini_set( 'html_errors', 'off' );
+
  ?text
  
= BASH scripting =
+
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
== Finding and replacing text ==
  
== Telling a script to run in bash ==
+
To replace the first instance of "search" on the current line with "destroy":
  
The first line of the file should be:
+
:s/search/destroy/
  
#!/bin/bash
+
To replace all instances of "search" on the current line with "destroy":
  
== Checking if a command-line argument was passed in ==
+
:s/search/destroy/g
  
if [ -n "$1" ]; then
+
To replace all instances of "search" on lines 13 to 37 with "destroy":
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
:13,37 s/search/destroy/g
  
if [ "$1" = "" ]; then
+
To replace all instances of "search" in the entire file with "destroy":
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
:%s/search/destroy/g
  
if [ -z "$1" ]; then
+
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
To set the line-ending to Unix line endings run the command:
  
  cd /my/path
+
  :setlocal ff=unix
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
  
Check if file exists:
+
== Disabling auto-indent etc. to paste from clipboard ==
  
if [ -f "/my/file" ]; then
+
To disable smart indenting when you're going to paste in text:
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
:set paste
  
if [ ! -f "/my/file" ]; then
+
To turn it off again:
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
:set nopaste
  
Check if directory exists:
+
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
  
if [ -d "/my/dir" ]; then
+
== Positioning windows ==
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
Use -o for horizontal split, e.g.:
  
  if [ ! -d "/my/dir" ]; then
+
  vim -o a.txt b.txt
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
Use -O for vertical split, e.g.:
  
To keep only the latest five backups:
+
vim -o a.txt b.txt
  
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
+
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
Use ^W and &lt; or &gt; to resize windows.
  
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.
+
== To indent a block of text in Vim ==
  
== Changing into the script's directory ==
+
Use the > command. E.g. to indent five lines:
  
  cd "`dirname $0`"
+
  5 > >
  
== Getting the absolute path of a relative path ==
+
Press . (dot) to keep indenting.
  
readlink -f ./some/path
+
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:
  
== Creating a temp directory ==
+
> %
  
dir=`mktemp -d` && cd $dir
+
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
  
== Reading secret input from stdin ==
+
== Open a file in a new window/tab ==
  
You can read a secret, such as a password, like this:
+
To open a file on the left hand side:
 +
 
 +
:vert new filename.ext
  
echo -n "Enter passphrase: "
+
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
To open a file at the top:
  
== String replacements in bash ==
+
:new filename.ext
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
  
result=${var/find/replace}
+
== Explore files in Vim ==
  
To replace all occurrences:
+
Enter:
  
  result=${var//find/replace}
+
  :Explore
  
A practical example, get an ISO date and turn it into a path:
+
== Switch between Vim tabs ==
  
date="$(date +%Y-%m-%d)"
+
Use gt and gT.
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
== Switch between Vim windows ==
  
cat << EOF > /tmp/yourfilehere
+
To toggle between open windows use:
These contents will be written to the file.
 
        This line is indented.
 
EOF
 
  
== Bash case/switch statement ==
+
Ctrl+W W
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
To move in a direction use:
  
  case $space in
+
  Ctrl+W h/j/k/l
[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 ==
+
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
  
To enable dot-file matching in globs, set the dotglob shell option:
+
== Insert block comment in Vim ==
  
$ shopt -s dotglob
+
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
  
== Stopping a script from running if it previously exited due to error ==
+
So it's:
  
persistentDataDir=/var/lib/something
+
# Ctrl+V (Note: not Shift+V!)
alarm() {
+
# Up/Down to select rows
  touch $persistentDataDir/alarm
+
# Shift+I
}
+
# Enter your text, e.g. '#' or '//'
trap alarm ERR
+
# Ctrl+[ (or 'Esc')
[ -f $persistentDataDir/alarm ] && exit 1
 
  
== Make sure only one instance of a script is running at a time ==
+
== Navigate to matching tag ==
  
ephemeralDataDir=/var/run/something
+
To navigate to the matching beginning or end tag use '%'.
unlock() {
 
  rmdir $ephemeralDataDir/lock
 
}
 
mkdir $ephemeralDataDir/lock || exit 1;
 
trap unlock EXIT
 
  
= Sed =
+
You can also use e.g. '[{' to match the previous '{', or e.g. '])' to match the next ')'.
  
== Find and replace with sed ==
+
== Auto-format HTML tags ==
  
To update the current file use '-i'. E.g.:
+
Stolen from [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
  
sed -i 's/search-text/replace-text/' file
+
# first join all the lines - ggVGgJ
 +
# Now break tags to new lines - :%s/>\s*</>\r</g
 +
# Now set filetype - :set ft=html (you can do this before too)
 +
# Now Indent - ggVG=
  
= Awk =
+
== Links ==
  
== Listing IP addresses in an Apache web log ==
+
* [http://www.vim.org/ Vim: the editor]
 +
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 +
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 +
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 +
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 +
* [http://vim.wikia.com/wiki/File_format File format]
 +
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 +
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
== Create PDF from text using Vim ==
  
== Printing space-separated field ==
+
Generate PDF from input.txt with:
  
  echo 'no no yes no' | awk '{print $3}'
+
  $ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
  
== Printing delimited field ==
+
Examine output with:
  
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
  $ okular doc.pdf
  
= Subversion =
+
= Write =
  
== Setting svn:externals from the command-line ==
+
== Talking to other users on the system ==
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
'''write''' is a unix command for talking to other users on the system. To use '''write''':
  
To set an svn:externals from the command-line:
+
1. SSH to <username>@<hostname> and login with your username and password.
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
2. Issue the following command to find out who is logged onto the system:
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
$ who
  
svn propset svn:externals -F svn.externals .
+
3. Issue the following command to talk to a specific user:
  
== Setting svn:ignore from the command line ==
+
$ write <username>
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
  
$ svn propset svn:ignore [file|folder] [path]
+
= Date =
  
Or use a file and apply recursively:
+
== Reporting the time on the server ==
  
  $ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
  $ date
  
= Git =
+
== Reporting UTC time ==
  
== Showing status of working copy ==
+
$ date --utc
  
git status
+
== Getting the date in yyyy-MM-dd-hhmmss format ==
  
== Showing repo history ==
+
$ date="`date +%F-%H%M%S`"
  
git log
+
== Getting the year in four digits ==
  
== Showing remote repositories (including 'origin') ==
+
$ year="`date +%Y`"
  
git remote -v
+
== Getting the month in two digits ==
  
== Handy git aliases ==
+
$ month="`date +%m`"
  
Save these to your ~/.gitconfig file.
+
== Getting the day of the month in two digits ==
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
$ day="`date +%d`"
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
== Getting yesterday's date ==
  
To show only the files that have changed, rather than the full line-by-line content:
+
$ date --date='1 day ago' +%Y-%m-%d
  
  dif  = !git diff --name-status
+
== Converting Unix time (seconds since epoch) ==
  
= IRC =
+
For timestamp '1501370200':
  
== Instructing ChanServ to op an admin ==
+
$ date -d @1501370200 +%F-%H%M%S
  
/msg ChanServ op #channel user
+
== Running timedatectl from systemd ==
  
E.g.
+
There's a new command bundled with systmed:
  
  /msg ChanServ op #gnurc jj5
+
  # timedatectl
  
Sub 'op' for 'deop' to remove op privilege.
+
It reports on (and controls) how the system time is configured.
  
= C++ =
+
= MySQL =
  
== C++ books ==
+
== Run mysql without authentication/authorisation ==
  
=== Books I want ===
+
# 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:
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
# mysqladmin shutdown
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
Then restart a normal service:
* [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 ===
+
# service mysql start
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
== Logging all database queries ==
* [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]
+
# vim /etc/mysql/my.cnf
* [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 ===
+
In the [mysqld] section add:
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
log=/tmp/mysql.log
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
Then:
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
# service mysql restart
  
== C++ blogs/articles ==
+
Watch the log with:
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
# tail -f /tmp/mysql.log
* [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 ==
+
== Dumping a MySQL database ==
  
* ++c can be faster than c++.
+
You can dump the database into a file using:  
* 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.
+
$ mysqldump -h hostname -u user --password=password databasename > filename
* 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 =
+
== Loading a MySQL database from a dump file ==
  
[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.
+
You can create a database using:
  
== Following a service log ==
+
$ echo create database databasename | mysql -h hostname -u user -p
  
e.g. for bind9:
+
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
  
# journalctl -f -u bind9
+
== Creating a MySQL user ==
  
or for everything:
+
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
  
  # journalctl -f
+
== 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:
  
== System status ==
+
show status like 'Ssl_cipher';
  
To see spawned services hierarchy:
+
= Apache =
  
# systemctl status
+
== Reporting loaded Apache modules ==
  
Or for a specific service e.g.:
+
# apache2ctl -M
  
# systemctl status networking
+
== Maintaining .htaccess passwords ==
  
= SaltStack =
+
To add or modify the password for a user:
  
== Running a command on specified minions ==
+
$ htpasswd /etc/apache2/passwd username
  
salt 'host' cmd.run 'update-locale'
+
== Configuring PHP session timeout in .htaccess ==
  
== Running a command on all minions ==
+
For a session timeout of 9 hours:
 
+
 
  salt '*' cmd.run 'update-locale'
+
php_value session.cookie_lifetime 32400
 
+
php_value session.gc_maxlifetime 32400
== Listing active jobs ==
+
 
 
+
== Disabling PHP magic quotes in .htaccess ==
  salt-run jobs.active
+
 
 
+
php_flag magic_quotes_gpc Off
== Listing available grains ==
+
 
 
+
== Requiring HTTP Auth in .htaccess ==
  salt 'example' grains.items
+
 
 
+
AuthType Basic
== Listing available pillar ==
+
AuthName "Speak Friend And Enter"
 
+
AuthUserFile /home/jj5/.htpasswd
  salt 'example' pillar.items
+
Require valid-user
 
+
 
== Reporting a grain value ==
+
== Restarting Apache ==
 
+
 
e.g. for the 'mem_total' grain:
+
The hard way
 
+
 
  salt '*' grains.item mem_total
+
$ 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 &lt;string.h> as described in this article [http://www.java-samples.com/showtutorial.php?tutorialid=591 Using memset(), memcpy(), and memmove() in C]
 +
 
 +
== Links ==
 +
 
 +
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
 +
 
 +
= 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 [https://www.cyberciti.biz/tips/php-security-best-practices-tutorial.html Linux 25 PHP Security Best Practices For Sys Admins].
 +
 
 +
= BASH scripting =
 +
 
 +
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html 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 [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
 +
 
 +
== Maximum command line length ==
 +
 
 +
Technically this is an operating system limit, not a BASH limit.
 +
 
 +
$ getconf ARG_MAX    # Get argument limit in bytes/chars
 +
 
 +
= Sed =
 +
 
 +
== Find and replace with sed ==
 +
 
 +
To update the current file use '-i'. E.g.:
 +
 
 +
sed -i 's/search-text/replace-text/' file
 +
 
 +
= Awk =
 +
 
 +
== Listing IP addresses in an Apache web log ==
 +
 
 +
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
 +
 
 +
== Printing space-separated field ==
 +
 
 +
echo 'no no yes no' | awk '{print $3}'
 +
 
 +
== Printing delimited field ==
 +
 
 +
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
 +
 
 +
= Subversion =
 +
 
 +
== Setting svn:externals from the command-line ==
 +
 
 +
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
 +
 
 +
To set an svn:externals from the command-line:
 +
 
 +
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
 +
svn ci -m 'Adding svn:externals for rdfind-php...'
 +
svn up
 +
 
 +
Or to use a file:
 +
 
 +
svn propset svn:externals -F svn.externals .
 +
 
 +
== Setting svn:ignore from the command line ==
 +
 
 +
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
 +
 
 +
$ svn propset svn:ignore [file|folder] [path]
 +
 
 +
Or use a file and apply recursively:
 +
 
 +
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
 +
 
 +
= Git =
 +
 
 +
== Showing status of working copy ==
 +
 
 +
git status
 +
 
 +
== Showing repo history ==
 +
 
 +
git log
 +
 
 +
== Showing remote repositories (including 'origin') ==
 +
 
 +
git remote -v
 +
 
 +
== Handy git aliases ==
 +
 
 +
Save these to your ~/.gitconfig file.
 +
 
 +
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
 +
 
 +
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
 +
 
 +
To show only the files that have changed, rather than the full line-by-line content:
 +
 
 +
  dif  = !git diff --name-status
 +
 
 +
== Show git remote URL ==
 +
 
 +
git config --get remote.origin.url
 +
 
 +
= IRC =
 +
 
 +
== Instructing ChanServ to op an admin ==
 +
 
 +
/msg ChanServ op #channel user
 +
 
 +
E.g.
 +
 
 +
/msg ChanServ op #gnurc jj5
 +
 
 +
Sub 'op' for 'deop' to remove op privilege.
 +
 
 +
= C++ =
 +
 
 +
== C++ books ==
 +
 
 +
=== Books I want ===
 +
 
 +
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
 +
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 +
 
 +
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
 +
* [http://www.amazon.com/dp/0321334876 Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/1491903996 Effective Modern C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/020163371X More Effective C++] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201749629 Effective STL] by Scott Meyers
 +
* [http://www.amazon.com/dp/0201615622 Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/020170434X More Exceptional C++] by Herb Sutter
 +
* [http://www.amazon.com/dp/0201760428 Exceptional C++ Style] by Herb Sutter
 +
* [http://www.amazon.com/dp/0321227255 C++ Template Metaprogramming] by David Abrahams
 +
* [http://www.amazon.com/dp/059652269X 97 Things Every Software Architect Should Know] by Richard Monson-Haefel
 +
* [http://www.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries] by Robert Demming
 +
 
 +
=== Books I own ===
 +
 
 +
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
 +
* [http://smile.amazon.com/dp/9491028022 Introduction to the Boost C++ Libraries; Volume II - Advanced Libraries]
 +
* [http://smile.amazon.com/dp/1849514887 Boost C++ Application Development Cookbook]
 +
* [http://smile.amazon.com/dp/1782163263 Boost.Asio C++ Network Programming]
 +
* [http://www.amazon.com/dp/0321113586 C++ Coding Standards] by Herb Sutter &#x2713;
 +
* [http://www.amazon.com/dp/0201704315 Modern C++ Design] by Andrei Alexandrescu &#x2713;
 +
* [http://www.amazon.com/dp/0596809484 97 Things Every Programmer Should Know] by Kevlin Henney &#x2713;
 +
* [http://www.amazon.com/dp/0321133544 Beyond the C++ Standard Library] by Björn Karlsson &#x2713;
 +
* [http://www.amazon.com/dp/9491028014 Introduction to the Boost C++ Libraries; Volume I - Foundations] by Robert Demming &#x2713;
 +
* [http://www.amazon.com/dp/0123850037 API Design for C++] by Martin Reddy &#x2713;
 +
* [http://www.amazon.com/dp/B00CB23URA Advanced C++ Metaprogramming] by Davide Di Gennaro &#x2713;
 +
** Note: the next version of this book is: [http://www.amazon.com/dp/1484210115 Advanced Metaprogramming in Classic C++]
 +
* [http://www.amazon.com/dp/1933988770 C++ Concurrency in Action: Practical Multithreading] by Anthony Williams &#x2713;
 +
 
 +
=== Books I'm not reading ===
 +
 
 +
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
 +
** Note: 3ed is obsolete. Buy 4ed (above).
 +
 
 +
=== Books I've read ===
 +
 
 +
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
 +
 
 +
== C++ blogs/articles ==
 +
 
 +
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
 +
* [http://herbsutter.com/ Herb Sutter's personal blog]
 +
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
 +
 
 +
== C++ performance tips ==
 +
 
 +
* ++c can be faster than c++.
 +
* use const for everything that you possibly can.
 +
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
 +
* don't use registers.
 +
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 +
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 +
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 +
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 +
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 +
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 +
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 +
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 +
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 +
 
 +
= systemd =
 +
 
 +
[https://en.wikipedia.org/wiki/Systemd systemd] is an init system used in most Linux distributions to bootstrap the user space and manage all processes subsequently.
 +
 
 +
== Following a service log ==
 +
 
 +
e.g. for bind9:
 +
 
 +
# journalctl -f -u bind9
 +
 
 +
or for everything:
 +
 
 +
# journalctl -f
 +
 
 +
== System status ==
 +
 
 +
To see spawned services hierarchy:
 +
 
 +
# systemctl status
 +
 
 +
Or for a specific service e.g.:
 +
 
 +
# systemctl status networking
 +
 
 +
= SaltStack =
 +
 
 +
== Running a command on specified minions ==
 +
 
 +
From the salt master:
 +
 
 +
salt 'host' cmd.run 'update-locale'
 +
 
 +
From the salt minion:
 +
 
 +
salt-call cmd.run 'update-locale'
 +
 
 +
== Running a command on all minions ==
 +
 
 +
  salt '*' cmd.run 'update-locale'
 +
 
 +
== Running a specific state file ==
 +
 
 +
From the salt master:
 +
 
 +
salt $MINION_ID state.sls $STATE_FILE
 +
 
 +
From the salt minion:
 +
 
 +
salt-call state.sls $STATE_FILE
 +
 
 +
== Listing active jobs ==
 +
 
 +
  salt-run jobs.active
 +
 
 +
== Listing available grains ==
 +
 
 +
  salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
  salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
  salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| 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
 +
|}
  
= KDE =
+
= XML =
  
== Running user login script (X11/XOrg/XWindows) ==
+
== How to pretty-print an XML file ==
  
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:
+
$ xmllint --format input.xml > output.xml
 
 
[Desktop Entry]
 
Type=Application
 
Name=ssh-add
 
Comment=Adds my private key to my session.
 
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 

Latest revision as of 20:54, 4 October 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

References

Command-line

See Shell Commands I Wish I Knew Earlier for some interesting options.

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 PCI devices:

# lspci

And for DMI info:

# dmidecode

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

Or the grand daddy of them all:

# hwinfo

There's also inxi, e.g.:

$ inxi -b

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

Motherboard info

# dmidecode -t 2

CPU info

# lscpu

or:

# cat /proc/cpuinfo

RAM info

# dmidecode --type memory

PCI info

# lspci -v

Drive info

# cat /proc/partitions

and:

# hdparm -I /dev/sda

and:

# smartctl --info /dev/sda

You can check if a drive is SSD or not with:

# cat /sys/block/sde/queue/rotational
0=SSD
1=HDD

Viewing syslog and other logs with KSystemLog

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

Power

Reporting on PowerShield DEFENDER UPS status

Before running `upsc` ensure service is running:

# upsdrvctl start

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

$ upsc defender

E.g.:

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

Run commands on PowerShield DEFENDER UPS batteries

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

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

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

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

$ upscmd -l defender

E.g.:

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

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

Environment

Configuring vim as your editor

Sometimes all you need is:

$ export EDITOR=/usr/bin/vim

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

Other times you need to run

# update-alternatives --config editor

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

Configuring your locale

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

User and group management

Adding a user

To add a new user on a linux system:

# useradd username
# passwd username

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

# adduser username

Adding a user to a group

To add an existing user to an existing group:

# gpasswd -a username group

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

# gpasswd -a jj5 sudo

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

# adduser username group

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

# adduser sclaughl staff

Disabling a user account

You can disable a user account with:

# passwd -l user

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

Enabling a disabled user account

To can re-enable a locked user account with:

# passwd -u user

Finding which user you are logged in as

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

$ whoami

Finding which groups you are a member of

To find which groups you are a member of:

$ groups

or

$ groups username

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

$ groups jj5

Finding who else is logged in to the system

To see who else is logged in,

$ who

Running a command as a particular user

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

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

Reporting user and group info for the current user

$ id

Memory management

Checking available memory

To report memory statistics in megabytes:

$ free -m

Check for swap thrashing

Check your virtual memory status with vmstat:

$ vmstat

Report memory type

Report on RAM DIMMs:

# dmidecode --type 17

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

# lshw -short -C memory

Or for more detail:

# lshw -C memory

Video/display management

Viewing EDID data for attached monitor

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

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

Process management

Using 'top' for dynamic resource usage reporting

To run top:

$ top

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

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

$ top -u jj5

To see full command-line press 'c'.

When you're in 'top' you can:

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

Changing memory reporting in 'top'

To run top:

$ top

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

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

Press 'M' to sort by memory utilisation.

Press 'm' to switch between various display modes.

Showing full command-line in 'top'

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

$ top -c

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

$ ps -fl

Killing specific processes

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

Run a command for a specified time using timeout

$ timeout 3 ping jj5.net

Disk management

Creating a partition table

# parted /dev/xvdf
mktable msdos

Creating a partition

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

Creating an ext4 file-system

# mkfs.ext4 /dev/xvdf1

Listing disk drives

# fdisk -l

(That's an L for "list")

Checking available disk space

$ df -h

Getting disk information

# lsblk

And

# cat /proc/partitions

Or the Grand Daddy of them all:

# lshw -class disk

(Requires the lshw package.)

Getting partition UUID and file-system type

# blkid

Checking for SSD vs magnetic disk

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

Will be 0 for SSD and 1 for magnetic.

Monitoring a ZFS server

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

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

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

# watch zpool status -v

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

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

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

# zfs get all data

If you want to get funky:

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

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

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

You can report history of a zpool:

# zpool history $poolname

You can get a report on the dedup tables:

# zpool status -D $poolname

Or more detailed dedup table info:

# zdb -DDD $poolname

Note in the output see here for details, basically:

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

How to tell if zfs scrub is running

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

$ zpool status

Measure data throughput

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

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

Or for ZFS:

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

Using Smartctl, Smartd and Hddtemp on Debian

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

Report hard disk usage

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

Report hard disk temperatures

E.g.

# hddtemp /dev/sd[a-e]

Burning an ISO image to USB on Mac

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

# diskutil list

Then unmount it with:

# diskutil unmountDisk /dev/disk4

Then copy ISO image with 'dd':

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

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

# kill -s info 12345

Listing all ext4 file systems

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

# df -t ext4

Report hierarchical file system mount points and mount options

$ findmnt

Report the mount point for the current working directory

$ findmnt "$PWD"

Monitoring disk I/O

There's an app for that! iotop.

Using iotop, top for disks

# iotop -oPa

Monitor disk I/O for performance issues

# watch iostat

Or e.g.

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

Or use groupings like this command for 'tact':

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

Monitoring a system

Simple ZFS monitoring

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

Monitoring temperature

See temperature without third-party apps for:

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

and:

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

Monitoring CPU temperature

$ watch sensors

Monitoring HDD temperature

For e.g. SATA drives sda to sdd:

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

ZFS

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

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

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

Then:

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

Stopping a ZFS scrub in progress

# zpool scrub -s $pool

e.g. for the 'data' pool:

# zpool scrub -s data

File management

Listing files by size

Use capital S for Size:

$ ls -S

Listing only directories

$ ls -l | egrep '^d'

Listing only files

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

Listing hidden files

$ ls -al .[!.]*

Creating a symbolic link

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

Creating a hard-link

$ ln /path/to/target file-name

Changing the owner of a file

$ chown user:group <files>

E.g.

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

To apply recursively into sub-directories use -R,

$ chown -R root:root /etc/*

Changing file permissions

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

See Numeric Mode in Action.

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

E.g.

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

Updating config files

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

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

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

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

$ sudo apt-get install rcs

Listing open files

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

# lsof

See man lsof for options.

List permissions on a whole directory path

E.g.:

$ namei -om /home/jj5/workspace

Outputs:

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

Counting non-blank lines in a file

E.g.:

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

Cloning one directory to another with rsync

E.g.:

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

Counting number of files in current directory and all subdirectories

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

Counting number of directories in current directory and all subdirectories

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

Getting the status of a 'dd' process

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

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

# kill -s info 40947

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

Transferring a large file via FAT32 file system

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

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

Then copy the small files and reassemble:

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

Find the difference between two directories

$ diif -qr $DIR_A $DIR_B

NFS

List NFS shares

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

$ showmount -e love

Compression

How to use pigz with tar

See here:

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

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

Also from here:

Fast pack:

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

Best pack:

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

Fast unpack:

tar -I pigz -xf my.tar.gz

Best compression with tar

From here:

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

or

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

Best parallel compression with pigz

$ pigz --best

Best parallel compression with xz

$ xz -9e -T 0

Reporting compression ratios with xz

e.g.

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

Symbolic-link management

== Data used by sym-linked files:

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

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

File searching

Finding a file with a particular name

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

Will start searching from the current directory, so maybe

$ cd /

first. For a case-sensitive search:

$ find -name "*eXaCT CaSE*"

Finding a file with particular content

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

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

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

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

Finding a list of files with particular content

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

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

Using the locate command to find files

$ locate part-of-filename

E.g.

$ locate texvc

Updating locate command's database

# updatedb

Select a random line from a text file

$ shuf -n 1 input.txt

Extra context for grep

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

$ grep -B 3 -A 1 ...

Job control

Stopping a running process

Press Ctrl+Z to stop a running process.

Listing current jobs and their status

$ jobs

Resuming a stopped job in the backgroud

To resume a stopped process in the background

$ bg %1

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

Resuming a stopped job in the foreground

To resume a stopped process in the foreground

$ fg %1

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

Killing a stopped job

To kill a job

$ kill %1

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

Periodically run a program and watch its output

$ watch /your/command

Debian/Ubuntu package management

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

configuring debconf

# dpkg-reconfigure debconf 

Set priority to low to get asked detailed questions.

Showing list of installed packages

# dpkg --get-selections

Searching for installed package

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

or

# aptitude search package-name

Showing which files are installed as part of a package

# dpkg -L package-name

Installing a package

# apt-get install package-name

Uninstalling a package

# apt-get remove package-name

Showing system architecture

$ dpkg --print-architecture

Showing which package a file belongs to

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

Showing package information

$ apt-cache showpkg coreutils

Or for even more information:

$ apt-cache show coreutils

List all installed packages with package version info

dpkg-query -l

Reporting which version of a package is installed

$ dpkg -l | grep package-name

E.g.:

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

Comprehensive upgrade

Try the following:

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

Searching all available packages

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

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

Blocking an IP address with iptables

To drop IP address 1.2.3.4:

# iptables -A INPUT -s 1.2.3.4 -j DROP

ufw

Denying hosts with ufw

See denying hosts with ufw.

Bind9

Viewing Bind9 querylog

$ sudo rndc querylog
$ tail -f /var/log/syslog

IPSec

Disabling IPSec

# setkey -FP

OpenSSL

Debugging IMAPS with OpenSSL

# openssl s_client -connect localhost:993
> a1 LOGIN username@host password
> a2 LOGOUT

Debugging HTTPS with OpenSSL

$ openssl s_client -connect www.example.com:443
GET /example.html HTTP/1.1
host: www.example.com

Links

Pluggable Authentication Modules (PAM)

Links

SSH

Configuring SSH key login

On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):

$ ssh-keygen -t rsa

Copy the public key from the client to the server:

$ scp ~/.ssh/id_rsa.pub user@example.org:

Configure the authorized keys on the server:

$ ssh user@example.org
$ mkdir ~/.ssh
$ chmod go-w .ssh
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
$ chmod 600 ~/.ssh/authorized_keys
$ rm ~/id_rsa.pub

Tunneling over SSH

For example, connecting a remote MySQL server to the localhost:

$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org

If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,

 $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au

The -L stanza is localport:remotehost:remoteport where localport is a port on your machine, forwarded to remoteport on remotehost.

Tunneling over SSH with PuTTY

See Connecting to the MySQL database remotely (via an SSH Tunnel)

  • run putty.exe
  • Connection -> SSH -> Tunnels
    • Port forwarding: source port to 3306
    • destination: 127.0.0.1:3306
    • check Local
    • click Add

Enabling verbose SSH logging

To see what's going on with your ssh connections,

$ ssh -v user@host

Or

$ ssh -vv user@host

Unlocking SSH key for session

jj5@orac:~/.config/autostart$ cat ssh-add.desktop 
[Desktop Entry]
Type=Application
Name=ssh-add
Comment=Adds my private key to my session.
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'

Links

Standard IO

cat EOF

$ cat > output <<EOF
> text
> EOF
$ cat output
text

Script

Creating a session log with script

$ script -t 2> timing

The session log is in the file 'typescript' and the timing data is in 'timing'.

Replaying a scripted session

$ scriptreplay timing

Uses the default file 'typescript' and the 'timing' file as specified.

Screen

Creating a new screen or reconnecting to a detached screen

$ screen -R

Detaching a screen

$ screen -D

Reconnecting to screen

$ screen -D
$ screen -R

I have a script in ~/bin/reconnect like so,

#!/bin/bash
screen -D
screen -R

This will detach your last screen, and reconnect it on the current terminal.

Scrolling in screen

See How to scroll in GNU Screen. Basically press Ctrl+A ESC then use Page Up and Page Down. Press ESC again to exit copy mode. As usual you can use Ctrl+[ in place of ESC.

tmux

Live collaboration with tmux

User A:

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

User B:

tmux -S /tmp/collab attach

Vim

First, why Vim?

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

Visual modes

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

Configuring spaces instead of tabs

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

$ vim ~/.vimrc

and include the following lines:

set tabstop=2
set shiftwidth=2
set expandtab

Configuring syntax highlighting

See here.

Use:

:syntax on

to turn on syntax highlighting.

Use:

:syntax off

to turn off syntax highlighting.

To always use syntax highlighting:

$ vim ~/.vimrc

and add:

syntax on

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

:colorscheme[space][Ctrl+D]

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

colorscheme desert

Inserting a TAB character when expandtab is on

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

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

Or you can disable tab expansion altogether with:

:set expandtab!

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

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

For more information see here.

Recording and replaying a macro

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

Deleting to end of line

d$

Deleting to beginning of line

d^

Finding text

To search forward for "text":

/text

To search backward for "text":

?text

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

Finding and replacing text

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

:s/search/destroy/

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

:s/search/destroy/g

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

:13,37 s/search/destroy/g

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

:%s/search/destroy/g

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

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

:setlocal ff=unix

More information on managing file formats available here.

Disabling auto-indent etc. to paste from clipboard

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

:set paste

To turn it off again:

:set nopaste

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

Positioning windows

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

vim -o a.txt b.txt

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

vim -o a.txt b.txt

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

Use ^W and < or > to resize windows.

To indent a block of text in Vim

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

5 > >

Press . (dot) to keep indenting.

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

> %

See here for more.

Open a file in a new window/tab

To open a file on the left hand side:

:vert new filename.ext

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

To open a file at the top:

:new filename.ext

See here for more.

Explore files in Vim

Enter:

:Explore

Switch between Vim tabs

Use gt and gT.

Switch between Vim windows

To toggle between open windows use:

Ctrl+W W

To move in a direction use:

Ctrl+W h/j/k/l

See here for more.

Insert block comment in Vim

See here for line-commenting.

So it's:

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

Navigate to matching tag

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

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

Auto-format HTML tags

Stolen from here.

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

Links

Create PDF from text using Vim

Generate PDF from input.txt with:

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

Examine output with:

$ okular doc.pdf

Write

Talking to other users on the system

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

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

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

$ who

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

$ write <username>

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

Date

Reporting the time on the server

$ date

Reporting UTC time

$ date --utc

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

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

Getting the year in four digits

$ year="`date +%Y`"

Getting the month in two digits

$ month="`date +%m`"

Getting the day of the month in two digits

$ day="`date +%d`"

Getting yesterday's date

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

Converting Unix time (seconds since epoch)

For timestamp '1501370200':

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

Running timedatectl from systemd

There's a new command bundled with systmed:

# timedatectl

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

MySQL

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

Maximum command line length

Technically this is an operating system limit, not a BASH limit.

$ getconf ARG_MAX    # Get argument limit in bytes/chars

Sed

Find and replace with sed

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

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

Awk

Listing IP addresses in an Apache web log

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

Printing space-separated field

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

Printing delimited field

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

Subversion

Setting svn:externals from the command-line

See here.

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

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

Or to use a file:

svn propset svn:externals -F svn.externals .

Setting svn:ignore from the command line

See here.

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

Or use a file and apply recursively:

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

Git

Showing status of working copy

git status

Showing repo history

git log

Showing remote repositories (including 'origin')

git remote -v

Handy git aliases

Save these to your ~/.gitconfig file.

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

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

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

 dif   = !git diff --name-status

Show git remote URL

git config --get remote.origin.url

IRC

Instructing ChanServ to op an admin

/msg ChanServ op #channel user

E.g.

/msg ChanServ op #gnurc jj5

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

C++

C++ books

Books I want

Books I own

Books I'm not reading

Books I've read

C++ blogs/articles

C++ performance tips

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

systemd

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

Following a service log

e.g. for bind9:

# journalctl -f -u bind9

or for everything:

# journalctl -f

System status

To see spawned services hierarchy:

# systemctl status

Or for a specific service e.g.:

# systemctl status networking

SaltStack

Running a command on specified minions

From the salt master:

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

From the salt minion:

salt-call cmd.run 'update-locale'

Running a command on all minions

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

Running a specific state file

From the salt master:

salt $MINION_ID state.sls $STATE_FILE

From the salt minion:

salt-call state.sls $STATE_FILE

Listing active jobs

salt-run jobs.active

Listing available grains

salt 'example' grains.items

Listing available pillar

salt 'example' pillar.items

Reporting a grain value

e.g. for the 'mem_total' grain:

salt '*' grains.item mem_total

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

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

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

KDE

Running user login script (X11/XOrg/XWindows)

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

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

Standard KDE shortcut key bindings

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

VirtualBox

Mounting a VirtualBox VDI file

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

See here:

Install qemu if necessary:

# apt install qemu

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

# rmmod nbd
# modprobe nbd max_part=16

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

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

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

# mount /dev/nbd0p1 /mnt

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

# qemu-nbd -d /dev/nbd0

Elasticsearch

Report on health of your Elasticsearch cluster

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

Zabbix

Zabbix Agent on Mac OS X

Download and install agent.

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

Unload agent with:

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

Load agent with:

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

To add a 'pki' group:

# dseditgroup -o create pki

To monitor syslog on Mac OS X:

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

Installing Zabbix Agent from source on Mac OS X

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

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

NetBeans

NetBeans shortcut keys

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

XML

How to pretty-print an XML file

$ xmllint --format input.xml > output.xml