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 =
 +
 +
== Reporting system specifications from the command-line ==
 +
 +
Try any of these:
 +
 +
# neofetch
 +
# inxi
 +
# hwinfo --short
 +
 +
You may need to install the relevant package.
  
 
== Determining which Debian/Ubuntu release your are running ==
 
== Determining which Debian/Ubuntu release your are running ==
Line 13: Line 35:
 
  $ lsb_release
 
  $ lsb_release
  
== Determining which Unix you are running ==
+
== Determining which Linux/Unix you are running ==
  
 
  $ uname
 
  $ uname
 +
 +
Or,
 +
 +
$ uname -mrs
  
 
Or,
 
Or,
  
 
  $ uname -a
 
  $ uname -a
 +
 +
== Determining which Linux kernel you are running ==
 +
 +
$ uname -r
  
 
== Configuring system swappiness ==
 
== Configuring system swappiness ==
Line 36: Line 66:
  
 
  # lshw
 
  # lshw
 
And for CPUs:
 
 
# lscpu
 
  
 
And for PCI devices:
 
And for PCI devices:
Line 48: Line 74:
  
 
  # dmidecode
 
  # dmidecode
 +
 +
Note that the dmidecode command (above) will give you information about your system's motherboard. For motherboard info look for 'System Information' and/or 'Base Board Information'.
  
 
Or the grand daddy of them all:
 
Or the grand daddy of them all:
Line 53: Line 81:
 
  # hwinfo
 
  # hwinfo
  
= Environment =
+
There's also inxi, e.g.:
  
== Configuring vim as your editor ==
+
$ 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
  
Sometimes all you need is:
+
=== Motherboard info ===
  
  $ export EDITOR=/usr/bin/vim
+
  # dmidecode -t 2
  
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
+
=== CPU info ===
  
Other times you need to run
+
# lscpu
  
# update-alternatives --config editor
+
or:
  
And then select vim from the list. This is what you do to configure your visudo editor.
+
# cat /proc/cpuinfo
  
== Configuring your locale ==
+
=== RAM info ===
  
  $ sudo /usr/sbin/locale-gen en_AU.UTF-8
+
  # dmidecode --type memory
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
 
  
= User and group management =
+
=== PCI info ===
  
== Adding a user ==
+
# lspci -v
  
To add a new user on a linux system:
+
=== Drive info ===
  
  # useradd username
+
  # cat /proc/partitions
# passwd username
 
  
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
+
and:
  
  # adduser username
+
  # hdparm -I /dev/sda
  
== Adding a user to a group ==
+
and:
  
To add an existing user to an existing group:
+
# smartctl --info /dev/sda
  
# gpasswd -a username group
+
You can check if a drive is SSD or not with:
  
e.g. to add user 'jj5' to the 'sudo' group:
+
# cat /sys/block/sde/queue/rotational
  
  # gpasswd -a jj5 sudo
+
  0=SSD
 +
1=HDD
  
Alternatively you can use adduser, passing the username and group:
+
== Viewing syslog and other logs with KSystemLog ==
  
# adduser username group
+
Run the 'KSystemLog' program under KDE for a handy log viewer GUI.
  
e.g. to add user 'sclaughl' to the 'staff' group:
+
= CPU =
  
# adduser sclaughl staff
+
== Monitoring CPU clock speed ==
  
== Disabling a user account ==
+
Try something like this:
  
You can disable a user account with:
+
$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'
  
# passwd -l user
+
= Power =
  
Note: that's a lower-case L, not a one.
+
== Reporting on PowerShield DEFENDER UPS status ==
  
== Enabling a disabled user account ==
+
Before running `upsc` ensure service is running:
  
To can re-enable a locked user account with:
+
# upsdrvctl start
  
# passwd -u user
+
To see the status of the [https://powershield.com.au/powersheild_product/defender/ PowerShield DEFENDER] systems on John's LAN:
  
== Finding which user you are logged in as ==
+
$ upsc defender
  
To determine which user you are running as enter the command:
+
E.g.:
  
  $ whoami
+
  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
  
== Finding which groups you are a member of ==
+
== Run commands on PowerShield DEFENDER UPS batteries ==
  
To find which groups you are a member of:
+
You can run "instant commands" using the '''upscmd''' command.
  
$ groups
+
We use the 'beeper.toggle' instant command in our Salt Stack config to disable the beeper, see e.g.:
  
or
+
diligence:/srv/salt/conf/app/defender-1200.sls
  
$ groups username
+
To see "instant commands" supported by the PowerShield DEFENDER:
  
Where 'username' is the username of the user you are querying, e.g.:
+
$ upscmd -l defender
  
$ groups jj5
+
E.g.:
  
== Finding who else is logged in to the system ==
+
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 see who else is logged in,
+
= Service management =
  
$ who
+
== Report running services ==
  
== Running a command as a particular user ==
+
# service --status-all
  
To run "svn update" as the user www-data:
+
= Environment =
  
$ sudo su -c "svn update" www-data
+
== Configuring vim as your editor ==
  
= Memory management =
+
Sometimes all you need is:
  
== Checking available memory ==
+
$ export EDITOR=/usr/bin/vim
  
To report memory statistics in megabytes:
+
Which works for svn, for example. Add it to your ~/.profile file to have it set for all login sessions.
  
$ free -m
+
Other times you need to run
  
= Disk management =
+
# update-alternatives --config editor
  
== Listing disk drives ==
+
And then select vim from the list. This is what you do to configure your visudo editor.
  
# fdisk -l
+
== Configuring your locale ==
  
(That's an L for "list")
+
$ sudo /usr/sbin/locale-gen en_AU.UTF-8
 +
$ sudo /usr/sbin/update-locale LANG=en_AU.UTF-8
  
== Checking available disk space ==
+
= User and group management =
  
$ df -h
+
== Adding a user ==
  
== Getting disk information ==
+
To add a new user on a linux system:
  
  # lsblk
+
  # useradd username
 +
# passwd username
  
And
+
To have the home directory created from '/etc/skel' use the 'adduser' script instead:
  
  # cat /proc/partitions
+
  # adduser username
  
Or the Grand Daddy of them all:
+
== Adding a user to a group ==
  
# lshw -class disk
+
To add an existing user to an existing group:
  
(Requires the lshw package.)
+
# gpasswd -a username group
  
== Getting partition UUID and file-system type ==
+
e.g. to add user 'jj5' to the 'sudo' group:
  
  # blkid
+
  # gpasswd -a jj5 sudo
  
== Checking for SSD vs magnetic disk ==
+
Alternatively you can use adduser, passing the username and group:
  
  # cat /sys/block/sda/queue/rotational
+
  # adduser username group
  
Will be 0 for SSD and 1 for magnetic.
+
e.g. to add user 'sclaughl' to the 'staff' group:
  
= File management =
+
# adduser sclaughl staff
  
== Listing only directories ==
+
== Disabling a user account ==
  
$ ls -l | egrep '^d'
+
You can disable a user account with:
  
== Listing only files ==
+
# passwd -l user
  
$ ls -l | egrep -v '^d'
+
Note: that's a lower-case L, not a one.
  
== Listing hidden files ==
+
== Enabling a disabled user account ==
  
$ ls -al .[!.]*
+
To can re-enable a locked user account with:
  
== Creating a symbolic link ==
+
# passwd -u user
  
$ ln -s /path/to/target link-name
+
== Finding which user you are logged in as ==
  
== Creating a hard-link ==
+
To determine which user you are running as enter the command:
  
  $ ln /path/to/target file-name
+
  $ whoami
  
== Changing the owner of a file ==
+
== Finding which groups you are a member of ==
  
$ chown user:group <files>
+
To find which groups you are a member of:
  
E.g.
+
$ groups
  
$ chown jj5:staff README
+
or
$ chown root:root *
 
  
To apply recursively into sub-directories use -R,
+
$ groups username
  
$ chown -R root:root /etc/*
+
Where 'username' is the username of the user you are querying, e.g.:
  
== Changing file permissions ==
+
$ groups jj5
  
{|class="wikitable"
+
== Finding who else is logged in to the system ==
|+ Object codes
 
! User !! Group !! Other
 
|-
 
| u    || g    || o
 
|}
 
  
{|class="wikitable"
+
To see who else is logged in,
|+ Permission codes
+
 
! Read !! Write !! Exectue
+
$ who
|-
+
 
| r    || w    || x
+
== Running a command as a particular user ==
|-
+
 
| 4    || 2    || 1
+
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
  
{|class="wikitable"
+
= Memory management =
|+ 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].
+
== Checking available memory ==
  
$ chmod <user numeric code><group numeric code><other numeric code> <files>
+
To report memory statistics in megabytes:
$ chmod <object codes>+|-<permission codes> <files>
 
  
E.g.
+
$ free -m
  
$ chmod 600 my-private-file
+
== Check for swap thrashing ==
$ chmod go-rwx my-private-file
 
$ chmod u+rw my-private-file
 
$ chmod +x my-script
 
  
== Updating config files ==
+
Check your virtual memory status with vmstat:
  
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:
+
$ vmstat
  
$ cp old.conf updated.conf
+
== Report memory type ==
$ merge -A updated.conf new.conf old.conf
 
  
Then go through and edit updated.conf resolving all the merge errors, picking and choosing what to update and what to keep. When you're done copy updated.conf to old.conf so it becomes the new config file.
+
Report on RAM DIMMs:
  
The merge program is a part of the RCS package. If you don't have it:
+
# dmidecode --type 17
  
$ sudo apt-get install rcs
+
Report on RAM and CPU cache (including L1, L2, and L3):
  
== Listing open files ==
+
# lshw -short -C memory
  
Use lsof to list open files. E.g.:
+
Or for more detail:
  
  # lsof
+
  # lshw -C memory
  
See man lsof for options.
+
= Video/display management =
  
== List permissions on a whole directory path ==
+
== Viewing EDID data for attached monitor ==
  
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):
  
  $ namei -om /home/jj5/workspace
+
  $ cd /sys/class/drm
 +
$ ls
 +
$ cd card0-HDMI-A-1
 +
$ edid-decode edid
  
Outputs:
+
= Process management =
  
f: /home/jj5/workspace/
+
== Using 'top' for dynamic resource usage reporting ==
  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 ==
+
To run top:
  
E.g.:
+
$ top
  
$ cat foo.c | sed '/^\s*$/d' | wc -l
+
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.
  
== Cloning one directory to another with rsync ==
+
To see usage for a specific user run e.g.:
  
E.g.:
+
$ top -u jj5
  
rsync --stats --human-readable --recursive --del --force --times --links --hard-links --executability --numeric-ids --owner --group --perms --sparse /data/source/ /data/target/
+
To see full command-line press 'c'.
  
= File searching =
+
When you're in 'top' you can:
  
== Finding a file with a particular name ==
+
* press '1' (one) to toggle CPU aggregation
 +
* press &lt; and &gt; to change the sort column
  
$ find -iname "*some-part-of-the-file-name*"
+
== Changing memory reporting in 'top' ==
  
Will start searching from the current directory, so maybe
+
To run top:
  
  $ cd /
+
  $ top
  
first. For a case-sensitive search:
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
$ find -name "*eXaCT CaSE*"
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
== Finding a file with particular content ==
+
Press 'M' to sort by memory utilisation.
  
To search in /etc/ for a file with particular content:
+
Press 'm' to switch between various display modes.
  
$ grep -R "search-string" /etc/*
+
== Showing full command-line in 'top' ==
  
To search the current directory for *.cs files containing the word "Up":
+
To see the full command-line for processes run with -c:
  
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
  $ top -c
  
== Finding a list of files with particular content ==
+
== Listing all processes currently running which were started in your current shell session ==
  
E.g. to find all the files with the word 'creativity':
+
$ ps -fl
  
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
== Killing specific processes ==
  
== Using the locate command to find files ==
+
# ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
$ locate part-of-filename
+
== Run a command for a specified time using timeout ==
  
E.g.
+
$ timeout 3 ping jj5.net
  
$ locate texvc
+
= Disk management =
  
== Updating locate command's database ==
+
== Reporting ext4 file-systems mounted without noatime ==
  
  # updatedb
+
  $ cat /proc/mounts | grep ext | grep -v noatime | sort
  
= Job control =
+
== Creating a partition table ==
  
== Stopping a running process ==
+
# parted /dev/xvdf
  
Press Ctrl+Z to stop a running process.
+
mktable msdos
  
== Listing current jobs and their status ==
+
== Creating a partition ==
  
  $ jobs
+
  # parted /dev/xvdf
  
== Resuming a stopped job in the backgroud ==
+
u MiB
 +
mkpart primary 1 100%
  
To resume a stopped process in the background
+
== Creating an ext4 file-system ==
  
  $ bg %1
+
  # mkfs.ext4 /dev/xvdf1
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Listing disk drives ==
  
== Resuming a stopped job in the foreground ==
+
# fdisk -l
  
To resume a stopped process in the foreground
+
(That's an L for "list")
  
$ fg %1
+
== Checking available disk space ==
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
$ df -h
  
== Killing a stopped job ==
+
== Getting disk information ==
  
To kill a job
+
# lsblk
  
$ kill %1
+
And
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
# cat /proc/partitions
  
== Periodically run a program and watch its output ==
+
Or the Grand Daddy of them all:
  
  $ watch /your/command
+
  # lshw -class disk
  
= Debian/Ubuntu package management =
+
(Requires the lshw package.)
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
== Getting partition UUID and file-system type ==
  
== configuring debconf ==
+
# blkid
  
# dpkg-reconfigure debconf
+
== Checking for SSD vs magnetic disk ==
  
Set priority to low to get asked detailed questions.
+
# cat /sys/block/sda/queue/rotational
  
== Showing list of installed packages ==
+
Will be 0 for SSD and 1 for magnetic.
  
# dpkg --get-selections
+
== Monitoring a ZFS server ==
  
== Searching for installed package ==
+
So some commands I run to keep an eye on my new ZFS servers:
  
  # dpkg --get-selections | grep package-name
+
  # 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
  
or
+
If you have a scrub or resilvering in progress you can report on progress with:
  
  # aptitude search package-name
+
  # watch zpool status -v
  
== Showing which files are installed as part of a package ==
+
You can poke about in internals, e.g.:
  
  # dpkg -L package-name
+
  # cat /proc/spl/kstat/zfs/arcstats
  
== Installing a package ==
+
root@orac:/sys/module/zfs/parameters# tail *
  
# apt-get install package-name
+
You can report on property values with e.g.:
  
== Uninstalling a package ==
+
# zfs get all data
  
# apt-get remove package-name
+
If you want to get funky:
  
== Showing system architecture ==
+
# cd /tmp
 +
# perf record -ag #(Ctrl+C after ~15 seconds)
 +
# perf report --stdio
  
$ dpkg --print-architecture
+
You can search for ZFS files like e.g. this:
  
== Showing which package a file belongs to ==
+
root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
$ which echo
+
You can report history of a zpool:
/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 ==
+
# zpool history $poolname
  
$ apt-cache showpkg coreutils
+
You can get a report on the dedup tables:
  
Or for even more information:
+
# zpool status -D $poolname
  
  $ apt-cache show coreutils
+
Or more detailed dedup table info:
 +
 
 +
  # zdb -DDD $poolname
 +
 
 +
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
== List all installed packages with package version info ==
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
dpkg-query -l
+
== How to tell if zfs scrub is running ==
  
== Reporting which version of a package is installed ==
+
You can get the status from the "scan:" line from:
  
  $ dpkg -l | grep package-name
+
  $ zpool status
  
E.g.:
+
== Measure data throughput ==
  
root@hope:~/letsencrypt# dpkg -l | grep augeas
+
Use the 'pv' command from the 'pv' package, e.g.:
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 ==
+
# cat /dev/sda | pv | cat > /dev/null
  
Try the following:
+
Or for ZFS:
  
  # apt-get update
+
  # zfs send data/example | pv | cat > /dev/null
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
= Networking =
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
== net-tools vs iproute2 ==
+
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].
  
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].
+
== Report hard disk usage ==
  
{|class="wikitable"
+
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.
! 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 ==
+
== Report hard disk temperatures ==
  
For servers:
+
E.g.
  
  # service networking restart
+
  # hddtemp /dev/sd[a-e]
  
For desktops:
+
== Burning an ISO image to USB on Mac ==
  
# service network-manager restart
+
First insert your USB key and find the appropriate disk with:
  
== Pinging with particular packet size ==
+
# diskutil list
  
$ ping -M do -s <packet size in bytes> <host>
+
Then unmount it with:
  
E.g.
+
# diskutil unmountDisk /dev/disk4
  
$ ping -M do -s 1400 charity.progclub.org
+
Then copy ISO image with 'dd':
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
# ip route add <host> dev <interface> advmss <packet size>
+
You can get dd to report progress by sending it the SIGINFO signal:
  
E.g.
+
# kill -s info 12345
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
== Listing all ext4 file systems ==
  
== Dropping configured MMS for a particular IP address ==
+
To see a list only of the mounted ext4 file systems:
  
  # ip route flush <host>
+
  # df -t ext4
  
E.g.
+
== Report hierarchical file system mount points and mount options ==
  
  # ip route flush 10.0.0.1
+
  $ findmnt
  
== Listing open ports and socket information ==
+
== Report the mount point for the current working directory ==
  
Including which process is listening on which port.
+
$ findmnt "$PWD"
  
# netstat -tulpn
+
= Monitoring disk I/O =
  
Or use the 'ss' command:
+
There's an app for that! iotop.
  
# ss -s
+
== Using iotop, top for disks ==
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
# iotop -oPa
  
# lsof -Pnl +M -i4
+
== Monitor disk I/O for performance issues ==
  
You might need to install the lsof package:
+
# watch iostat
  
# apt-get install lsof
+
Or e.g.
  
== Query for DNS MX record ==
+
# watch iostat -xd /dev/sd[abc]
  
$ nslookup
+
Or use groupings like this command for 'tact':
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
= Monitoring a system =
  
== Using nmap to list open ports on remote host ==
+
== Simple ZFS monitoring ==
  
To check the 1,000 most common ports:
+
# watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
  
# nmap server.example.com
+
= Monitoring temperature =
 +
 
 +
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
Or for a specific port range (e.g. 101 to 102):
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
# nmap -p 101-102 server.example.com
+
and:
  
Or for all ports (1 to 65,535):
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
# nmap -p- server.example.com
+
== Monitoring CPU temperature ==
  
== Links ==
+
$ watch sensors
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
== Monitoring HDD temperature ==
  
= IPTables =
+
For e.g. SATA drives sda to sdd:
  
== Applying firewall rules ==
+
# watch hddtemp /dev/sd[a-d]
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
= ZFS =
  
$ sudo vim /etc/iptables.test.rules
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
$ sudo /sbin/iptables -F
 
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
 
$ sudo iptables -L
 
$ sudo -s
 
# iptables-save > /etc/iptables.up.rules
 
# exit
 
  
= IPSec =
+
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?]
  
== Disabling IPSec ==
+
$ cat /proc/spl/kstat/zfs/arcstats
  
# setkey -FP
+
Then:
  
= OpenSSL =
+
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
  
== Debugging IMAPS with OpenSSL ==
+
== Stopping a ZFS scrub in progress ==
  
  # openssl s_client -connect localhost:993
+
  # zpool scrub -s $pool
> a1 LOGIN username@host password
 
> a2 LOGOUT
 
  
== Debugging HTTPS with OpenSSL ==
+
e.g. for the 'data' pool:
  
  $ openssl s_client -connect www.example.com:443
+
  # zpool scrub -s data
GET /example.html HTTP/1.1
+
 
host: www.example.com
+
= File management =
  
== Links ==
+
== Listing files by size ==
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
Use capital S for Size:
  
= Pluggable Authentication Modules (PAM) =
+
$ ls -S
  
== Links ==
+
== Listing only directories ==
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
$ ls -l | egrep '^d'
  
= SSH =
+
== Listing only files ==
  
== Configuring SSH key login ==
+
$ ls -l | egrep -v '^d'
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
== Listing hidden files ==
  
  $ ssh-keygen -t rsa
+
  $ ls -al .[!.]*
  
Copy the public key from the client to the server:
+
== Creating a symbolic link ==
  
  $ scp ~/.ssh/id_rsa.pub user@example.org:
+
  $ ln -s /path/to/target link-name
  
Configure the authorized keys on the server:
+
== Creating a hard-link ==
  
  $ ssh user@example.org
+
  $ ln /path/to/target file-name
$ 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 ==
+
== Changing the owner of a file ==
  
For example, connecting a remote MySQL server to the localhost:
+
$ chown user:group <files>
  
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
E.g.
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
$ chown jj5:staff README
 +
$ chown root:root *
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
To apply recursively into sub-directories use -R,
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
$ chown -R root:root /etc/*
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
== Changing file permissions ==
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
* run putty.exe
+
{|class="wikitable"
* Connection -> SSH -> Tunnels
+
|+ Permission codes
** Port forwarding: source port to 3306
+
! Read !! Write !! Exectue
** destination: 127.0.0.1:3306
+
|-
** check Local
+
| r    || w    || x
** click Add
+
|-
 +
| 4    || 2    || 1
 +
|}
  
== Enabling verbose SSH logging ==
+
{|class="wikitable"
 
+
|+ Numeric codes
To see what's going on with your ssh connections,
+
! 0
 
+
| None
$ ssh -v user@host
+
|-
 
+
! 1
Or
+
| 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].
  
  $ ssh -vv user@host
+
  $ chmod <user numeric code><group numeric code><other numeric code> <files>
 +
$ chmod <object codes>+|-<permission codes> <files>
  
== Unlocking SSH key for session ==
+
E.g.
  
  jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
  $ chmod 600 my-private-file
  [Desktop Entry]
+
  $ chmod go-rwx my-private-file
Type=Application
+
  $ chmod u+rw my-private-file
Name=ssh-add
+
  $ chmod +x my-script
  Comment=Adds my private key to my session.
 
  Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 
  
== Links ==
+
== Updating config files ==
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
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:
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
 
  
= Standard IO =
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
== cat EOF ==
+
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.
  
$ cat > output <<EOF
+
The merge program is a part of the RCS package. If you don't have it:
> text
 
> EOF
 
  
  $ cat output
+
  $ sudo apt-get install rcs
text
 
  
= Script =
+
== Listing open files ==
  
== Creating a session log with script ==
+
Use lsof to list open files. E.g.:
  
  $ script -t 2> timing
+
  # lsof
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
See man lsof for options.
  
== Replaying a scripted session ==
+
== List permissions on a whole directory path ==
  
$ scriptreplay timing
+
E.g.:
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
$ namei -om /home/jj5/workspace
  
= Screen =
+
Outputs:
  
== Creating a new screen or reconnecting to a detached screen ==
+
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
  
$ screen -R
+
== Counting non-blank lines in a file ==
  
== Detaching a screen ==
+
E.g.:
  
  $ screen -D
+
  $ cat foo.c | sed '/^\s*$/d' | wc -l
  
== Reconnecting to screen ==
+
== Cloning one directory to another with rsync ==
  
$ screen -D
+
E.g.:
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
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/
  
#!/bin/bash
+
== Counting number of files in current directory and all subdirectories ==
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
$ ls -AlhR . | egrep '^-' | wc -l
  
= Vim =
+
== Counting number of directories in current directory and all subdirectories ==
  
== First, why Vim? ==
+
$ ls -AlhR . | egrep '^d' | wc -l
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
== Getting the status of a 'dd' process ==
  
== Visual modes ==
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
== Configuring spaces instead of tabs ==
+
# kill -s info 40947
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
The dd process will report its status in the terminal its running in.
  
$ vim ~/.vimrc
+
== Transferring a large file via FAT32 file system ==
  
and include the following lines:
+
So the maximum file size supported by a FAT32 file system (commonly used on USB keys) is 4 GB per file. If you have a file larger than 4 GB you can split it into parts and then reassemble the parts once transferred:
  
  set tabstop=2
+
  $ split -b 4000m input.tgz input.tgz-parts-
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
Then copy the small files and reassemble:
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
$ cat input.tgz-parts-* > output.tgz
  
Use:
+
== Find the difference between two directories ==
  
  :syntax on
+
  $ diif -qr $DIR_A $DIR_B
  
to turn on syntax highlighting.
+
= NFS =
  
Use:
+
== List NFS shares ==
  
:syntax off
+
To e.g. show NFS shares on 'love':
  
to turn off syntax highlighting.
+
$ showmount -e love
  
To always use syntax highlighting:
+
= Compression =
  
$ vim ~/.vimrc
+
== How to use pigz with tar ==
  
and add:
+
See [https://stackoverflow.com/a/39904353 here]:
  
  syntax on
+
  $ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
To get a list of supported colour schemes open vim and type:
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
:colorscheme[space][Ctrl+D]
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
Fast pack:
  
  colorscheme desert
+
  tar -I 'pigz --fast' -cf my.tar.gz whatver
  
== Inserting a TAB character when expandtab is on ==
+
Best pack:
  
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.
+
tar -I 'pigz --best' -cf my.tar.gz whatver
  
Press Ctrl+V TAB to insert a literal tab character.
+
Fast unpack:
  
Or you can disable tab expansion altogether with:
+
tar -I pigz -xf my.tar.gz
  
:set expandtab!
+
== Best compression with tar ==
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
  :%s/^\s*/&&/g
+
  export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
or
  
== Recording and replaying a macro ==
+
env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
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 "@@".
+
== Best parallel compression with pigz ==
  
== Deleting to end of line ==
+
$ pigz --best
  
d$
+
== Best parallel compression with xz ==
  
== Deleting to beginning of line ==
+
$ xz -9e -T 0
  
d^
+
== Reporting compression ratios with xz ==
  
== Finding text ==
+
e.g.
  
To search forward for "text":
+
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
  
/text
+
= Symbolic-link management =
  
To search backward for "text":
+
== Data used by sym-linked files:
  
?text
+
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:
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
== Finding and replacing text ==
+
= File searching =
  
To replace the first instance of "search" on the current line with "destroy":
+
== Finding a file with a particular name ==
  
  :s/search/destroy/
+
  $ find -iname "*some-part-of-the-file-name*"
  
To replace all instances of "search" on the current line with "destroy":
+
Will start searching from the current directory, so maybe
  
  :s/search/destroy/g
+
  $ cd /
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
first. For a case-sensitive search:
  
  :13,37 s/search/destroy/g
+
  $ find -name "*eXaCT CaSE*"
  
To replace all instances of "search" in the entire file with "destroy":
+
== Finding a file with particular content ==
  
:%s/search/destroy/g
+
To search in /etc/ for a file with particular content:
  
== Changing DOS/Windows line-endings (CRLF) to Unix line-endings ==
+
$ grep -R "search-string" /etc/*
  
To set the line-ending to Unix line endings run the command:
+
To search the current directory for *.cs files containing the word "Up":
  
  :setlocal ff=unix
+
  $ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
== Finding a list of files with particular content ==
  
== Disabling auto-indent etc. to paste from clipboard ==
+
E.g. to find all the files with the word 'creativity':
  
To disable smart indenting when you're going to paste in text:
+
$ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
:set paste
+
== Using the locate command to find files ==
  
To turn it off again:
+
$ locate part-of-filename
  
:set nopaste
+
E.g.
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
$ locate texvc
  
== Positioning windows ==
+
== Updating locate command's database ==
  
Use -o for horizontal split, e.g.:
+
# updatedb
  
vim -o a.txt b.txt
+
== Select a random line from a text file ==
  
Use -O for vertical split, e.g.:
+
$ shuf -n 1 input.txt
  
vim -o a.txt b.txt
+
== Extra context for grep ==
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
If you need to show extra lines before or after your grep results use -B NUM to set how many lines before the match and -A NUM for the number of lines after the match:
  
Use ^W and &lt; or &gt; to resize windows.
+
$ grep -B 3 -A 1 ...
  
== To indent a block of text in Vim ==
+
= Job control =
  
Use the > command. E.g. to indent five lines:
+
== Stopping a running process ==
  
5 > >
+
Press Ctrl+Z to stop a running process.
  
Press . (dot) to keep indenting.
+
== Listing current jobs and their status ==
  
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:
+
$ jobs
  
> %
+
== Resuming a stopped job in the backgroud ==
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
To resume a stopped process in the background
  
== Open a file in a new window/tab ==
+
$ bg %1
  
To open a file on the left hand side:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
:vert new filename.ext
+
== Resuming a stopped job in the foreground ==
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
To resume a stopped process in the foreground
  
To open a file at the top:
+
$ fg %1
  
:new filename.ext
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
== Killing a stopped job ==
  
== Explore files in Vim ==
+
To kill a job
  
Enter:
+
$ kill %1
  
:Explore
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
== Switch between Vim tabs ==
+
== Periodically run a program and watch its output ==
  
Use gt and gT.
+
$ watch /your/command
  
== Switch between Vim windows ==
+
= Debian/Ubuntu package management =
  
To toggle between open windows use:
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
Ctrl+W W
+
== configuring debconf ==
  
To move in a direction use:
+
# dpkg-reconfigure debconf
  
Ctrl+W h/j/k/l
+
Set priority to low to get asked detailed questions.
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
== Showing list of installed packages ==
  
 +
# dpkg --get-selections
  
== Links ==
+
== Searching for installed package ==
  
* [http://www.vim.org/ Vim: the editor]
+
# dpkg --get-selections | grep package-name
* [http://yannesposito.com/Scratch/en/blog/Learn-Vim-Progressively/ Learn Vim Progressively]
 
* [http://michael.peopleofhonoronly.com/vim/ Vim cheat sheet for programmers]
 
* [http://stackoverflow.com/questions/4781070/how-to-insert-tab-character-when-expandtab-option-is-on-in-vim How to insert Tab character when expandtab option is ON in VIM]
 
* [https://www.linux.com/learn/tutorials/8255-vim-tips-the-basics-of-search-and-replace Vim tips: the basics of search and replace]
 
* [http://vim.wikia.com/wiki/File_format File format]
 
* [http://www.viemu.com/a_vi_vim_graphical_cheat_sheet_tutorial.html Graphical vi-vim Cheat Sheet and Tutorial]
 
* [http://www.angelwatt.com/coding/notes/vim-commands.html Vim Commands Cheat Sheet]
 
  
= Write =
+
or
  
== Talking to other users on the system ==
+
# aptitude search package-name
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
== Showing which files are installed as part of a package ==
  
1. SSH to <username>@<hostname> and login with your username and password.
+
# dpkg -L package-name
  
2. Issue the following command to find out who is logged onto the system:
+
== Installing a package ==
  
  $ who
+
  # apt-get install package-name
  
3. Issue the following command to talk to a specific user:
+
== Uninstalling a package ==
  
  $ write <username>
+
  # apt-get remove package-name
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
== Showing system architecture ==
  
= Date =
+
$ dpkg --print-architecture
  
== Reporting the time on the server ==
+
== Showing which package a file belongs to ==
  
  $ date
+
  $ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
== Reporting UTC time ==
+
== Showing package information ==
  
  $ date --utc
+
  $ apt-cache showpkg coreutils
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
Or for even more information:
  
  $ date="`date +%F-%H%M%S`"
+
  $ apt-cache show coreutils
  
== Getting the year in four digits ==
+
== List all installed packages with package version info ==
  
  $ year="`date +%Y`"
+
  dpkg-query -l
  
== Getting the month in two digits ==
+
== Reporting which version of a package is installed ==
  
  $ month="`date +%m`"
+
  $ dpkg -l | grep package-name
  
== Getting the day of the month in two digits ==
+
E.g.:
  
  $ day="`date +%d`"
+
  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
  
== Getting yesterday's date ==
+
== Comprehensive upgrade ==
  
$ date --date='1 day ago' +%Y-%m-%d
+
Try the following:
  
== Running timedatectl from systemd ==
+
# apt-get update
 
+
# apt-get dist-upgrade
There's a new command bundled with systmed:
+
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
# update-flashplugin-nonfree --install
  
# timedatectl
+
== Searching all available packages ==
 
 
It reports on (and controls) how the system time is configured.
 
  
= MySQL =
+
$ apt-cache search . | sort -d | less
  
== Run mysql without authentication/authorisation ==
+
== Reporting unattended upgrades status ==
  
# service mysql stop
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
# mysql -u root mysql
+
== Searching for Debian packages and versions ==
  
To stop the unauthenticated service:
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
# mysqladmin shutdown
+
= Networking =
  
Then restart a normal service:
+
== Determining throughput between two hosts ==
  
  # service mysql start
+
  # apt install iperf3
  
== Logging all database queries ==
+
On the server:
  
  # vim /etc/mysql/my.cnf
+
  # iperf3 -s
  
In the [mysqld] section add:
+
On the client:
  
  log=/tmp/mysql.log
+
  # iperf3 -c $SERVER_IP
  
Then:
+
For more info see: [https://www.cyberciti.biz/faq/how-to-test-the-network-speedthroughput-between-two-linux-servers/ How to test the network speed/throughput between two Linux servers].
  
# service mysql restart
+
== net-tools vs iproute2 ==
  
Watch the log with:
+
The older 'net-tools' package has been replaced with 'iproute2' e.g. in [https://www.debian.org/releases/stretch/amd64/release-notes/ch-information.en.html#iproute2 stretch].
  
  # tail -f /tmp/mysql.log
+
{|class="wikitable"
 +
! legacy net-tools commands
 +
! iproute2 replacement commands
 +
|-
 +
| arp      || ip n (ip neighbor)
 +
|-
 +
| ifconfig || ip a (ip addr), ip link, ip -s (ip -stats)
 +
|-
 +
| iptunnel || ip tunnel
 +
|-
 +
| iwconfig || iw
 +
|-
 +
| nameif  || ip link, ifrename
 +
|-
 +
| netstat || ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
 +
|-
 +
| route    || ip r (ip route)
 +
|}
  
== Dumping a MySQL database ==
+
== Restart networking ==
  
You can dump the database into a file using:  
+
For servers:
 
$ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
# service networking restart
  
You can create a database using:
+
For desktops:
  
  $ echo create database databasename | mysql -h hostname -u user -p
+
  # service network-manager restart
  
You can restore a database using:
+
== Pinging with particular packet size ==
 
$ mysql -h hostname -u user --password=password databasename < filename
 
  
== Creating a MySQL user ==
+
$ ping -M do -s <packet size in bytes> <host>
  
# mysql -h localhost -u root --password=<password>
+
E.g.
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
$ ping -M do -s 1400 charity.progclub.org
  
# mysql -h localhost -u root --password=<password>
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
# ip route add <host> dev <interface> advmss <packet size>
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
E.g.
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
Check the SSL version in use:
+
== Dropping configured MMS for a particular IP address ==
  
  show status like 'Ssl_version';
+
  # ip route flush <host>
  
Or check the cipher in use:
+
E.g.
  
  show status like 'Ssl_cipher';
+
  # ip route flush 10.0.0.1
  
= Apache =
+
== Listing open ports and socket information ==
  
== Maintaining .htaccess passwords ==
+
Including which process is listening on which port.
  
To add or modify the password for a user:
+
# netstat -tulpn
  
$ htpasswd /etc/apache2/passwd username
+
Or use the 'ss' command:
  
== Configuring PHP session timeout in .htaccess ==
+
# ss -s
 +
# ss -l
 +
# ss -pl
 +
# ss -o state established '( dport = :smtp or sport = :smtp )'
  
For a session timeout of 9 hours:
+
== Listing open IPv4 connections ==
  
  php_value session.cookie_lifetime 32400
+
  # lsof -Pnl +M -i4
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
You might need to install the lsof package:
  
  php_flag magic_quotes_gpc Off
+
  # apt-get install lsof
  
== Requiring HTTP Auth in .htaccess ==
+
== Query for DNS MX record ==
  
  AuthType Basic
+
  $ nslookup
  AuthName "Speak Friend And Enter"
+
  > server 127.0.0.1
  AuthUserFile /home/jj5/.htpasswd
+
  > set q=mx
  Require valid-user
+
  > mail.blackbrick.com
  
== Restarting Apache ==
+
== Query for DNS SOA record ==
  
The hard way
+
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
  
$ sudo /etc/init.d/apache2 restart
+
== Using nmap to list open ports on remote host ==
  
The graceful way (avoids dropping active connections)
+
To check the 1,000 most common ports:
  
  $ sudo apache2ctl graceful
+
  # nmap server.example.com
  
== Allowing directory browsing ==
+
Or for a specific port range (e.g. 101 to 102):
  
To show directory index pages, in the apache config file:
+
# nmap -p 101-102 server.example.com
  
<Directory /var/www/data>
+
Or for all ports (1 to 65,535):
  Options Indexes
 
</Directory>
 
  
= C =
+
# nmap -p- server.example.com
  
== Locating memset function ==
+
== Network monitoring ==
  
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]
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
== Links ==
+
# 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
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
== nload ==
  
= PHP =
+
You can watch network traffic in real-time with nload:
  
== Including a file relative to the including file ==
+
# nload -u M
  
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
== Reporting network (NIC) speed ==
  
== Enabling error reporting ==
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
  error_reporting( E_ALL | E_STRICT );
+
  # dmesg | grep eth0
  ini_set( 'display_errors', 'On' );
+
  # mii-tool -v eth0
 +
# ethtool eth0
  
== Setting an error handler ==
+
Note: use ifconfig to get device name.
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
== Path MTU discovery ==
  
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
# tracepath host.example.com
  
ini_set( 'html_errors', 'off' );
+
== Listing available Ethernet devices ==
  
= BASH scripting =
+
To see a list of NICs available on the host:
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
$ cat /proc/net/dev
  
== Telling a script to run in bash ==
+
Also
  
The first line of the file should be:
+
$ ip link
  
#!/bin/bash
+
== 59 Linux Networking commands and scripts ==
  
== Checking if a command-line argument was passed in ==
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
if [ -n "$1" ]; then
+
== Links ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  
if [ "$1" = "" ]; then
+
= IPTables =
  echo "Missing parameter 1.";
+
 
  exit 1;
+
== Applying firewall rules ==
fi
 
  
Or:
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  
  if [ -z "$1" ]; then
+
  $ sudo vim /etc/iptables.test.rules
  echo "Missing parameter 1.";
+
$ sudo /sbin/iptables -F
  exit 1;
+
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
fi
+
$ sudo iptables -L
 +
$ sudo -s
 +
# iptables-save > /etc/iptables.up.rules
 +
# exit
  
== Checking command exit status ==
+
== Blocking an IP address with iptables ==
  
cd /my/path
+
To drop IP address 1.2.3.4:
if [ "$?" -ne "0" ]; then
 
  echo "Cannot change dir.";
 
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
Check if file exists:
+
= ufw =
  
if [ -f "/my/file" ]; then
+
== Denying hosts with ufw ==
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  
if [ ! -f "/my/file" ]; then
+
= Bind9 =
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
== Viewing Bind9 querylog ==
  
Check if directory exists:
+
$ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
if [ -d "/my/dir" ]; then
+
= IPSec =
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
== Disabling IPSec ==
  
  if [ ! -d "/my/dir" ]; then
+
  # setkey -FP
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
= OpenSSL =
  
To keep only the latest five backups:
+
== Debugging IMAPS with OpenSSL ==
  
  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
+
  # openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
== Debugging HTTPS with OpenSSL ==
  
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.
+
$ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
== Changing into the script's directory ==
+
== Links ==
  
cd "`dirname $0`"
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
== Getting the absolute path of a relative path ==
+
= Pluggable Authentication Modules (PAM) =
  
readlink -f ./some/path
+
== Links ==
  
== Creating a temp directory ==
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
dir=`mktemp -d` && cd $dir
+
= SSH =
  
== Reading secret input from stdin ==
+
== Configuring SSH key login ==
  
You can read a secret, such as a password, like this:
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
  echo -n "Enter passphrase: "
+
  $ ssh-keygen -t rsa
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
Copy the public key from the client to the server:
  
== String replacements in bash ==
+
$ scp ~/.ssh/id_rsa.pub user@example.org:
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
Configure the authorized keys on the server:
  
  result=${var/find/replace}
+
  $ ssh user@example.org
 +
$ mkdir ~/.ssh
 +
$ chmod go-w .ssh
 +
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
$ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
To replace all occurrences:
+
== Tunneling over SSH ==
  
result=${var//find/replace}
+
For example, connecting a remote MySQL server to the localhost:
  
A practical example, get an ISO date and turn it into a path:
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
date="$(date +%Y-%m-%d)"
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
cat << EOF > /tmp/yourfilehere
+
The -L stanza is localport:remotehost:remoteport where localport is a
These contents will be written to the file.
+
port on your machine, forwarded to remoteport on remotehost.
        This line is indented.
 
EOF
 
  
[[Category: Help]]
+
== Tunneling over SSH with PuTTY ==
  
== Bash case/switch statement ==
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
See [http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_03.html using case statements], e.g.:
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
case $space in
+
== Enabling verbose SSH logging ==
[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 see what's going on with your ssh connections,
  
To enable dot-file matching in globs, set the dotglob shell option:
+
$ ssh -v user@host
  
$ shopt -s dotglob
+
Or
  
= Sed =
+
$ ssh -vv user@host
  
== Find and replace with sed ==
+
== Unlocking SSH key for session ==
  
To update the current file use '-i'. E.g.:
+
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'
  
sed -i 's/search-text/replace-text/' file
+
== Links ==
  
= Awk =
+
* [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]
  
== Listing IP addresses in an Apache web log ==
+
= Standard IO =
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
== cat EOF ==
  
== Printing space-separated field ==
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  echo 'no no yes no' | awk '{print $3}'
+
  $ cat output
 +
text
  
== Printing delimited field ==
+
= Script =
  
echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
== Creating a session log with script ==
  
= Subversion =
+
$ script -t 2> timing
  
== Setting svn:externals from the command-line ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
== Replaying a scripted session ==
  
To set an svn:externals from the command-line:
+
$ scriptreplay timing
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
Uses the default file 'typescript' and the 'timing' file as specified.
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
= Screen =
  
svn propset svn:externals -F svn.externals .
+
== Creating a new screen or reconnecting to a detached screen ==
  
== Setting svn:ignore from the command line ==
+
$ screen -R
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
== Detaching a screen ==
  
  $ svn propset svn:ignore [file|folder] [path]
+
  $ screen -D
  
Or use a file and apply recursively:
+
== Reconnecting to screen ==
  
  $ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
  $ screen -D
 +
$ screen -R
  
= Git =
+
I have a script in ~/bin/reconnect like so,
  
== Showing status of working copy ==
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
git status
+
This will detach your last screen, and reconnect it on the current terminal.
  
== Showing repo history ==
+
== Scrolling in screen ==
  
git 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.
  
== Showing remote repositories (including 'origin') ==
+
= tmux =
  
git remote -v
+
== Live collaboration with tmux ==
  
== Handy git aliases ==
+
User A:
  
Save these to your ~/.gitconfig file.
+
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
User B:
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
tmux -S /tmp/collab attach
  
To show only the files that have changed, rather than the full line-by-line content:
+
= Vim =
  
  dif  = !git diff --name-status
+
== First, why Vim? ==
  
= IRC =
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
 +
 
 +
== Visual modes ==
  
== Instructing ChanServ to op an admin ==
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
  
/msg ChanServ op #channel user
+
== Configuring spaces instead of tabs ==
  
E.g.
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
  
  /msg ChanServ op #gnurc jj5
+
  $ vim ~/.vimrc
  
Sub 'op' for 'deop' to remove op privilege.
+
and include the following lines:
  
= C++ =
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
== C++ books ==
+
== Configuring syntax highlighting ==
  
=== Books I want ===
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
Use:
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
:syntax on
* [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 ===
+
to turn on syntax highlighting.
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
Use:
* [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 ===
+
:syntax off
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
to turn off syntax highlighting.
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
To always use syntax highlighting:
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
$ vim ~/.vimrc
  
== C++ blogs/articles ==
+
and add:
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
syntax on
* [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 ==
+
To get a list of supported colour schemes open vim and type:
  
* ++c can be faster than c++.
+
:colorscheme[space][Ctrl+D]
* use const for everything that you possibly can.
 
* use 'inline' when you need to define a function in a header. Typically only do that if it's small and the increase in code size from inlining is worth the cost to avoid the cost of a function call. For anything except trivially small functions you'll probably need to profile to know if it's worth it.
 
* don't use registers.
 
* const [http://www.gotw.ca/gotw/081.htm rarely affects performance].
 
* debunking a number of [http://www.open-std.org/jtc1/sc22/wg21/docs/TR18015.pdf C++ myths that won't die].
 
* std::sort<> is typically faster than qsort() because it can avoid indirection at runtime.
 
* if you've got parallelisation going on, you may be able to just replace a std::for_each with a parallel equivalent.
 
* read about [http://stackoverflow.com/questions/579887/how-expensive-is-rtti performance cost of RTTI] (Run Time Type Information) and [http://stackoverflow.com/questions/4486609/when-can-compiling-c-without-rtti-cause-problems how to disable it]
 
* don't use dynamic_cast because it is slow (typeid is faster but still relies on RTTI)
 
* prefer unique_ptr to shared_ptr when possible. unique_ptr has less overhead.
 
* [http://sunsite.uakom.sk/sunworldonline/swol-02-1996/swol-02-perf.html Which is better, static or dynamic linking?]
 
* [http://stackoverflow.com/questions/2550281/floating-point-vs-integer-calculations-on-modern-hardware Integer vs Floating-Point performance]
 
  
= systemd =
+
To always use a particular colorscheme edit ~/.vimrc and add (for example):
  
[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.
+
colorscheme desert
  
== Following a service log ==
+
== Inserting a TAB character when expandtab is on ==
  
e.g. for bind9:
+
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.
  
# journalctl -f -u bind9
+
Press Ctrl+V TAB to insert a literal tab character.
  
or for everything:
+
Or you can disable tab expansion altogether with:
  
  # journalctl -f
+
  :set expandtab!
  
== System status ==
+
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
  
To see spawned services hierarchy:
+
:%s/^\s*/&&/g
  
# systemctl status
+
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
  
Or for a specific service e.g.:
+
== Recording and replaying a macro ==
  
# systemctl status networking
+
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 "@@".
  
= SaltStack =
+
== Deleting to end of line ==
  
== Running a command on specified minions ==
+
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 [http://vim.wikia.com/wiki/File_format 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: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste 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 &lt; or &gt; 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 [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 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 [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 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 [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
 +
 
 +
== Insert block comment in Vim ==
 +
 
 +
See [https://stackoverflow.com/a/253391/868138 here] for line-commenting.
 +
 
 +
So it's:
 +
 
 +
# Ctrl+V (Note: not Shift+V!)
 +
# Up/Down to select rows
 +
# Shift+I
 +
# Enter your text, e.g. '#' or '//'
 +
# 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 [https://www.quora.com/How-do-you-auto-format-HTML-in-Vim here].
 +
 
 +
# 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=
 +
 
 +
== Links ==
 +
 
 +
* [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]
 +
 
 +
== Create PDF from text using Vim ==
 +
 
 +
Generate PDF from input.txt with:
 +
 
 +
$ vim input.txt -c "hardcopy > doc.ps | q" && ps2pdf doc.ps
 +
 
 +
Examine output with:
 +
 
 +
$ okular doc.pdf
 +
 
 +
= Write =
 +
 
 +
== Talking to other users on the system ==
 +
 
 +
'''write''' is a unix command for talking to other users on the system. To use '''write''':
 +
 
 +
1. SSH to <username>@<hostname> and login with your username and password.
 +
 
 +
2. Issue the following command to find out who is logged onto the system:
 +
 
 +
$ who
 +
 
 +
3. Issue the following command to talk to a specific user:
 +
 
 +
$ write <username>
 +
 
 +
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
 +
 
 +
= Date =
 +
 
 +
== Reporting the time on the server ==
 +
 
 +
$ date
 +
 
 +
== Reporting UTC time ==
 +
 
 +
$ date --utc
 +
 
 +
== Getting the date in yyyy-MM-dd-hhmmss format ==
 +
 
 +
$ date="`date +%F-%H%M%S`"
 +
 
 +
== Getting the year in four digits ==
 +
 
 +
$ year="`date +%Y`"
 +
 
 +
== Getting the month in two digits ==
 +
 
 +
$ month="`date +%m`"
 +
 
 +
== Getting the day of the month in two digits ==
 +
 
 +
$ day="`date +%d`"
 +
 
 +
== Getting yesterday's date ==
 +
 
 +
$ date --date='1 day ago' +%Y-%m-%d
 +
 
 +
== Converting Unix time (seconds since epoch) ==
 +
 
 +
For timestamp '1501370200':
 +
 
 +
$ date -d @1501370200 +%F-%H%M%S
 +
 
 +
== Running timedatectl from systemd ==
 +
 
 +
There's a new command bundled with systmed:
 +
 
 +
# timedatectl
 +
 
 +
It reports on (and controls) how the system time is configured.
 +
 
 +
= MySQL (and MariaDB) =
 +
 
 +
== Run mysql without authentication/authorisation ==
 +
 
 +
# service mysql stop
 +
# mysqld_safe --skip-grant-tables &
 +
 
 +
Then you can connect without a password, e.g.:
 +
 
 +
# mysql -u root mysql
 +
 
 +
To stop the unauthenticated service:
 +
 
 +
# mysqladmin shutdown
 +
 
 +
Then restart a normal service:
 +
 
 +
# service mysql start
 +
 
 +
== Logging all database queries ==
 +
 
 +
# vim /etc/mysql/my.cnf
 +
 
 +
In the [mysqld] section add:
 +
 
 +
log=/tmp/mysql.log
 +
 
 +
Then:
 +
 
 +
# service mysql restart
 +
 
 +
Watch the log with:
 +
 
 +
# tail -f /tmp/mysql.log
 +
 
 +
Or:
 +
 
 +
SET GLOBAL log_output = 'FILE';
 +
SET GLOBAL general_log_file = 'my_logs.txt';
 +
SET GLOBAL general_log = 'ON';
 +
 
 +
my_logs.txt will be in /var/lib/mysql
 +
 
 +
== Dumping a MySQL database ==
 +
 
 +
You can dump the database into a file using:
 +
 +
$ mysqldump -h hostname -u user --password=password databasename > filename
 +
 
 +
== Loading a MySQL database from a dump file ==
 +
 
 +
You can create a database using:
 +
 
 +
$ echo create database databasename | mysql -h hostname -u user -p
 +
 
 +
You can restore a database using:
 +
 +
$ mysql -h hostname -u user --password=password databasename < filename
 +
 
 +
== Creating a MySQL user ==
 +
 
 +
# mysql -h localhost -u root --password=<password>
 +
mysql> create user 'username'@'localhost' identified by '<password>';
 +
 
 +
== Granting all MySQL user permissions ==
 +
 
 +
# mysql -h localhost -u root --password=<password>
 +
mysql> grant all privileges on dbname.* to user@host;
 +
 
 +
== Select domain name from email address ==
 +
 
 +
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
 +
 
 +
== Check if MySQL connection is encrypted with TLS/SSL ==
 +
 
 +
Check the SSL version in use:
 +
 
 +
show status like 'Ssl_version';
 +
 
 +
Or check the cipher in use:
 +
 
 +
show status like 'Ssl_cipher';
 +
 
 +
== Report on server config ==
 +
 
 +
See [https://dev.mysql.com/doc/refman/5.7/en/show.html SHOW Statements] for the full list, but check out:
 +
 
 +
SHOW VARIABLES
 +
 
 +
and
 +
 
 +
SHOW STATUS
 +
 
 +
and
 +
 
 +
SHOW PROCESSLIST
 +
 
 +
== Monitor MySQL activity ==
 +
 
 +
$ watch "mysql -t -e 'show processlist'"
 +
 
 +
= Apache =
 +
 
 +
== Reporting loaded Apache modules ==
 +
 
 +
# apache2ctl -M
 +
 
 +
== Maintaining .htaccess passwords ==
 +
 
 +
To add or modify the password for a user:
 +
 
 +
$ htpasswd /etc/apache2/passwd username
 +
 
 +
== Configuring PHP session timeout in .htaccess ==
 +
 
 +
For a session timeout of 9 hours:
 +
 
 +
php_value session.cookie_lifetime 32400
 +
php_value session.gc_maxlifetime 32400
 +
 
 +
== Disabling PHP magic quotes in .htaccess ==
 +
 
 +
php_flag magic_quotes_gpc Off
 +
 
 +
== Requiring HTTP Auth in .htaccess ==
 +
 
 +
AuthType Basic
 +
AuthName "Speak Friend And Enter"
 +
AuthUserFile /home/jj5/.htpasswd
 +
Require valid-user
 +
 
 +
== Restarting Apache ==
 +
 
 +
The hard way
 +
 
 +
$ sudo /etc/init.d/apache2 restart
 +
 
 +
The graceful way (avoids dropping active connections)
 +
 
 +
$ sudo apache2ctl graceful
 +
 
 +
== Allowing directory browsing ==
 +
 
 +
To show directory index pages, in the apache config file:
 +
 
 +
<Directory /var/www/data>
 +
  Options Indexes
 +
</Directory>
 +
 
 +
= C =
 +
 
 +
== Locating memset function ==
 +
 
 +
The memset function is in &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'
 
  salt 'host' cmd.run 'update-locale'
  
== Running a command on all minions ==
+
From the salt minion:
 
+
 
  salt '*' cmd.run 'update-locale'
+
salt-call cmd.run 'update-locale'
 
+
 
== Listing active jobs ==
+
== Running a command on all minions ==
 
+
 
  salt-run jobs.active
+
  salt '*' cmd.run 'update-locale'
 
+
 
== Listing available grains ==
+
== Running a specific state file ==
 
+
 
  salt 'example' grains.items
+
From the salt master:
 
+
 
== Listing available pillar ==
+
salt $MINION_ID state.sls $STATE_FILE
 
+
 
  salt 'example' pillar.items
+
From the salt minion:
 
+
 
== Reporting a grain value ==
+
salt-call state.sls $STATE_FILE
 +
 
 +
== Listing active jobs ==
 +
 
 +
  salt-run jobs.active
 +
 
 +
== Listing available grains ==
 +
 
 +
  salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
  salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 +
|-
 +
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 +
|-
 +
| Konsole        || Meta+T  || konsole
 +
|-
 +
| Dolphin        || Meta+E  || dolphin
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|-
 +
| Firefox        || Ctrl+Shift+F10 || firefox
 +
|}
 +
 
 +
== Shutting down KDE/Plasma ==
 +
 
 +
# /etc/init.d/sddm stop
 +
 
 +
= VirtualBox =
 +
 
 +
== Mounting a VirtualBox VDI file ==
 +
 
 +
Note: instead of doing this consider booting with a live CD.
 +
 
 +
See [https://askubuntu.com/questions/19430/mount-a-virtualbox-drive-image-vdi/50290#50290 here]:
 +
 
 +
Install qemu if necessary:
 +
 
 +
# apt install qemu
 +
 
 +
Then you'll need to load the network block device module:
 +
 
 +
# rmmod nbd
 +
# modprobe nbd max_part=16
 +
 
 +
Attach the .vdi image to one of the nbd you just created:
 +
 
 +
# qemu-nbd -c /dev/nbd0 drive.vdi
 +
 
 +
Now you will get a /dev/nbd0 block device, along with several /dev/nbd0p* partition device nodes.
 +
 
 +
# mount /dev/nbd0p1 /mnt
 +
 
 +
Once you are done, unmount everything and disconnect the device:
 +
 
 +
# qemu-nbd -d /dev/nbd0
 +
 
 +
= Elasticsearch =
 +
 
 +
== Report on health of your Elasticsearch cluster ==
 +
 
 +
$ curl http://localhost:9200/_cluster/health?pretty
 +
 
 +
= Zabbix =
 +
 
 +
== Zabbix Agent on Mac OS X ==
 +
 
 +
Download and install agent.
 +
 
 +
Config file is here: /usr/local/etc/zabbix/zabbix_agentd.conf
 +
 
 +
Unload agent with:
 +
 
 +
# launchctl unload /Library/LaunchDaemons/com.zabbix.zabbix_agentd.plist
 +
 
 +
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
 +
|}
 +
 
 +
= XML =
  
e.g. for the 'mem_total' grain:
+
== How to pretty-print an XML file ==
  
  salt '*' grains.item mem_total
+
  $ xmllint --format input.xml > output.xml
 
 
= KDE =
 
  
== Running user login script (X11/XOrg/XWindows) ==
+
= ApacheBench =
  
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:
+
== Run a benchmark with ApacheBench ==
  
  [Desktop Entry]
+
  $ ab -n 1000 -c 100 https://www.example.com/
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'
 

Revision as of 17:53, 25 November 2022

Hi there, I'm John. I just wanted a page where I could document various Linux things that I bump into. This is that page. Thank you ProgClub. :)

Note: I have some other disorganised notes on UNIX, which include a few tips for MacOS. I also have some tips for OS X.

Note: the info on this page is probably Ubuntu (and Debian as an outside chance) specific, because I use Ubuntu pretty much everywhere these days.

You might also be interested in John's hacks.

Quick jump to: NetBeans.

References

Command-line

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

System

Reporting system specifications from the command-line

Try any of these:

# neofetch
# inxi
# hwinfo --short

You may need to install the relevant package.

Determining which Debian/Ubuntu release your are running

$ lsb_release -r

Or for more information:

$ lsb_release

Determining which Linux/Unix you are running

$ uname

Or,

$ uname -mrs

Or,

$ uname -a

Determining which Linux kernel you are running

$ uname -r

Configuring system swappiness

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

vm.swappiness = 0

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

echo 0 > /proc/sys/vm/swappiness

Hardware information

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

# lshw

And for PCI devices:

# lspci

And for DMI info:

# dmidecode

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

Or the grand daddy of them all:

# hwinfo

There's also inxi, e.g.:

$ inxi -b

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

Motherboard info

# dmidecode -t 2

CPU info

# lscpu

or:

# cat /proc/cpuinfo

RAM info

# dmidecode --type memory

PCI info

# lspci -v

Drive info

# cat /proc/partitions

and:

# hdparm -I /dev/sda

and:

# smartctl --info /dev/sda

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

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

Viewing syslog and other logs with KSystemLog

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

CPU

Monitoring CPU clock speed

Try something like this:

$ watch 'grep MHz /proc/cpuinfo | awk "{ print \$4 }" | sort -n'

Power

Reporting on PowerShield DEFENDER UPS status

Before running `upsc` ensure service is running:

# upsdrvctl start

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

$ upsc defender

E.g.:

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

Run commands on PowerShield DEFENDER UPS batteries

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

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

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

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

$ upscmd -l defender

E.g.:

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

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

Service management

Report running services

# service --status-all

Environment

Configuring vim as your editor

Sometimes all you need is:

$ export EDITOR=/usr/bin/vim

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

Other times you need to run

# update-alternatives --config editor

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

Configuring your locale

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

User and group management

Adding a user

To add a new user on a linux system:

# useradd username
# passwd username

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

# adduser username

Adding a user to a group

To add an existing user to an existing group:

# gpasswd -a username group

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

# gpasswd -a jj5 sudo

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

# adduser username group

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

# adduser sclaughl staff

Disabling a user account

You can disable a user account with:

# passwd -l user

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

Enabling a disabled user account

To can re-enable a locked user account with:

# passwd -u user

Finding which user you are logged in as

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

$ whoami

Finding which groups you are a member of

To find which groups you are a member of:

$ groups

or

$ groups username

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

$ groups jj5

Finding who else is logged in to the system

To see who else is logged in,

$ who

Running a command as a particular user

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

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

Reporting user and group info for the current user

$ id

Memory management

Checking available memory

To report memory statistics in megabytes:

$ free -m

Check for swap thrashing

Check your virtual memory status with vmstat:

$ vmstat

Report memory type

Report on RAM DIMMs:

# dmidecode --type 17

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

# lshw -short -C memory

Or for more detail:

# lshw -C memory

Video/display management

Viewing EDID data for attached monitor

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

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

Process management

Using 'top' for dynamic resource usage reporting

To run top:

$ top

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

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

$ top -u jj5

To see full command-line press 'c'.

When you're in 'top' you can:

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

Changing memory reporting in 'top'

To run top:

$ top

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

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

Press 'M' to sort by memory utilisation.

Press 'm' to switch between various display modes.

Showing full command-line in 'top'

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

$ top -c

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

$ ps -fl

Killing specific processes

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

Run a command for a specified time using timeout

$ timeout 3 ping jj5.net

Disk management

Reporting ext4 file-systems mounted without noatime

$ cat /proc/mounts | grep ext | grep -v noatime | sort

Creating a partition table

# parted /dev/xvdf
mktable msdos

Creating a partition

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

Creating an ext4 file-system

# mkfs.ext4 /dev/xvdf1

Listing disk drives

# fdisk -l

(That's an L for "list")

Checking available disk space

$ df -h

Getting disk information

# lsblk

And

# cat /proc/partitions

Or the Grand Daddy of them all:

# lshw -class disk

(Requires the lshw package.)

Getting partition UUID and file-system type

# blkid

Checking for SSD vs magnetic disk

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

Will be 0 for SSD and 1 for magnetic.

Monitoring a ZFS server

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

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

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

# watch zpool status -v

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

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

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

# zfs get all data

If you want to get funky:

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

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

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

You can report history of a zpool:

# zpool history $poolname

You can get a report on the dedup tables:

# zpool status -D $poolname

Or more detailed dedup table info:

# zdb -DDD $poolname

Note in the output see here for details, basically:

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

How to tell if zfs scrub is running

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

$ zpool status

Measure data throughput

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

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

Or for ZFS:

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

Using Smartctl, Smartd and Hddtemp on Debian

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

Report hard disk usage

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

Report hard disk temperatures

E.g.

# hddtemp /dev/sd[a-e]

Burning an ISO image to USB on Mac

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

# diskutil list

Then unmount it with:

# diskutil unmountDisk /dev/disk4

Then copy ISO image with 'dd':

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

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

# kill -s info 12345

Listing all ext4 file systems

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

# df -t ext4

Report hierarchical file system mount points and mount options

$ findmnt

Report the mount point for the current working directory

$ findmnt "$PWD"

Monitoring disk I/O

There's an app for that! iotop.

Using iotop, top for disks

# iotop -oPa

Monitor disk I/O for performance issues

# watch iostat

Or e.g.

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

Or use groupings like this command for 'tact':

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

Monitoring a system

Simple ZFS monitoring

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

Monitoring temperature

See temperature without third-party apps for:

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

and:

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

Monitoring CPU temperature

$ watch sensors

Monitoring HDD temperature

For e.g. SATA drives sda to sdd:

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

ZFS

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

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

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

Then:

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

Stopping a ZFS scrub in progress

# zpool scrub -s $pool

e.g. for the 'data' pool:

# zpool scrub -s data

File management

Listing files by size

Use capital S for Size:

$ ls -S

Listing only directories

$ ls -l | egrep '^d'

Listing only files

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

Listing hidden files

$ ls -al .[!.]*

Creating a symbolic link

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

Creating a hard-link

$ ln /path/to/target file-name

Changing the owner of a file

$ chown user:group <files>

E.g.

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

To apply recursively into sub-directories use -R,

$ chown -R root:root /etc/*

Changing file permissions

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

See Numeric Mode in Action.

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

E.g.

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

Updating config files

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

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

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

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

$ sudo apt-get install rcs

Listing open files

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

# lsof

See man lsof for options.

List permissions on a whole directory path

E.g.:

$ namei -om /home/jj5/workspace

Outputs:

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

Counting non-blank lines in a file

E.g.:

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

Cloning one directory to another with rsync

E.g.:

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

Counting number of files in current directory and all subdirectories

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

Counting number of directories in current directory and all subdirectories

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

Getting the status of a 'dd' process

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

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

# kill -s info 40947

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

Transferring a large file via FAT32 file system

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

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

Then copy the small files and reassemble:

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

Find the difference between two directories

$ diif -qr $DIR_A $DIR_B

NFS

List NFS shares

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

$ showmount -e love

Compression

How to use pigz with tar

See here:

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

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

Also from here:

Fast pack:

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

Best pack:

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

Fast unpack:

tar -I pigz -xf my.tar.gz

Best compression with tar

From here:

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

or

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

Best parallel compression with pigz

$ pigz --best

Best parallel compression with xz

$ xz -9e -T 0

Reporting compression ratios with xz

e.g.

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

Symbolic-link management

== Data used by sym-linked files:

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

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

File searching

Finding a file with a particular name

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

Will start searching from the current directory, so maybe

$ cd /

first. For a case-sensitive search:

$ find -name "*eXaCT CaSE*"

Finding a file with particular content

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

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

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

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

Finding a list of files with particular content

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

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

Using the locate command to find files

$ locate part-of-filename

E.g.

$ locate texvc

Updating locate command's database

# updatedb

Select a random line from a text file

$ shuf -n 1 input.txt

Extra context for grep

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

$ grep -B 3 -A 1 ...

Job control

Stopping a running process

Press Ctrl+Z to stop a running process.

Listing current jobs and their status

$ jobs

Resuming a stopped job in the backgroud

To resume a stopped process in the background

$ bg %1

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

Resuming a stopped job in the foreground

To resume a stopped process in the foreground

$ fg %1

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

Killing a stopped job

To kill a job

$ kill %1

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

Periodically run a program and watch its output

$ watch /your/command

Debian/Ubuntu package management

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

configuring debconf

# dpkg-reconfigure debconf 

Set priority to low to get asked detailed questions.

Showing list of installed packages

# dpkg --get-selections

Searching for installed package

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

or

# aptitude search package-name

Showing which files are installed as part of a package

# dpkg -L package-name

Installing a package

# apt-get install package-name

Uninstalling a package

# apt-get remove package-name

Showing system architecture

$ dpkg --print-architecture

Showing which package a file belongs to

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

Showing package information

$ apt-cache showpkg coreutils

Or for even more information:

$ apt-cache show coreutils

List all installed packages with package version info

dpkg-query -l

Reporting which version of a package is installed

$ dpkg -l | grep package-name

E.g.:

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

Comprehensive upgrade

Try the following:

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

Searching all available packages

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

Reporting unattended upgrades status

See here for more info.

# tail -f /var/log/unattended-upgrades/unattended-upgrades.log

Searching for Debian packages and versions

Networking

Determining throughput between two hosts

# apt install iperf3

On the server:

# iperf3 -s

On the client:

# iperf3 -c $SERVER_IP

For more info see: How to test the network speed/throughput between two Linux servers.

net-tools vs iproute2

The older 'net-tools' package has been replaced with 'iproute2' e.g. in stretch.

legacy net-tools commands iproute2 replacement commands
arp ip n (ip neighbor)
ifconfig ip a (ip addr), ip link, ip -s (ip -stats)
iptunnel ip tunnel
iwconfig iw
nameif ip link, ifrename
netstat ss, ip route (for netstat-r), ip -s link (for netstat -i), ip maddr (for netstat-g)
route ip r (ip route)

Restart networking

For servers:

# service networking restart

For desktops:

# service network-manager restart

Pinging with particular packet size

$ ping -M do -s <packet size in bytes> <host>

E.g.

$ ping -M do -s 1400 charity.progclub.org

Setting MSS for a particular IP address on a particular interface

# ip route add <host> dev <interface> advmss <packet size>

E.g.

# ip route add 10.0.0.1 dev eth0 advmss 1400

Dropping configured MMS for a particular IP address

# ip route flush <host>

E.g.

# ip route flush 10.0.0.1

Listing open ports and socket information

Including which process is listening on which port.

# netstat -tulpn

Or use the 'ss' command:

# ss -s
# ss -l
# ss -pl
# ss -o state established '( dport = :smtp or sport = :smtp )'

Listing open IPv4 connections

# lsof -Pnl +M -i4

You might need to install the lsof package:

# apt-get install lsof

Query for DNS MX record

$ nslookup
> server 127.0.0.1
> set q=mx
> mail.blackbrick.com

Query for DNS SOA record

$ dig @ns2.staticmagic.net -t SOA staticmagic.net

Using nmap to list open ports on remote host

To check the 1,000 most common ports:

# nmap server.example.com

Or for a specific port range (e.g. 101 to 102):

# nmap -p 101-102 server.example.com

Or for all ports (1 to 65,535):

# nmap -p- server.example.com

Network monitoring

See here for details. Basically:

  1. Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
  2. Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
  3. Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
  4. Bandwidth per process: nethogs

nload

You can watch network traffic in real-time with nload:

# nload -u M

Reporting network (NIC) speed

From here:

# dmesg | grep eth0
# mii-tool -v eth0
# ethtool eth0

Note: use ifconfig to get device name.

Path MTU discovery

To do a Path MTU Discovery, from the iputils-tracepath package:

# tracepath host.example.com

Listing available Ethernet devices

To see a list of NICs available on the host:

$ cat /proc/net/dev

Also

$ ip link

59 Linux Networking commands and scripts

See 59 Linux Networking commands and scripts.

Links

IPTables

Applying firewall rules

For configuration info see this article.

$ sudo vim /etc/iptables.test.rules
$ sudo /sbin/iptables -F
$ sudo /sbin/iptables-restore < /etc/iptables.test.rules
$ sudo iptables -L
$ sudo -s
# iptables-save > /etc/iptables.up.rules
# exit

Blocking an IP address with iptables

To drop IP address 1.2.3.4:

# iptables -A INPUT -s 1.2.3.4 -j DROP

ufw

Denying hosts with ufw

See denying hosts with ufw.

Bind9

Viewing Bind9 querylog

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

IPSec

Disabling IPSec

# setkey -FP

OpenSSL

Debugging IMAPS with OpenSSL

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

Debugging HTTPS with OpenSSL

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

Links

Pluggable Authentication Modules (PAM)

Links

SSH

Configuring SSH key login

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

$ ssh-keygen -t rsa

Copy the public key from the client to the server:

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

Configure the authorized keys on the server:

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

Tunneling over SSH

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

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

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

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

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

Tunneling over SSH with PuTTY

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

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

Enabling verbose SSH logging

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

$ ssh -v user@host

Or

$ ssh -vv user@host

Unlocking SSH key for session

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

Links

Standard IO

cat EOF

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

Script

Creating a session log with script

$ script -t 2> timing

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

Replaying a scripted session

$ scriptreplay timing

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

Screen

Creating a new screen or reconnecting to a detached screen

$ screen -R

Detaching a screen

$ screen -D

Reconnecting to screen

$ screen -D
$ screen -R

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

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

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

Scrolling in screen

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

tmux

Live collaboration with tmux

User A:

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

User B:

tmux -S /tmp/collab attach

Vim

First, why Vim?

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

Visual modes

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

Configuring spaces instead of tabs

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

$ vim ~/.vimrc

and include the following lines:

set tabstop=2
set shiftwidth=2
set expandtab

Configuring syntax highlighting

See here.

Use:

:syntax on

to turn on syntax highlighting.

Use:

:syntax off

to turn off syntax highlighting.

To always use syntax highlighting:

$ vim ~/.vimrc

and add:

syntax on

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

:colorscheme[space][Ctrl+D]

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

colorscheme desert

Inserting a TAB character when expandtab is on

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

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

Or you can disable tab expansion altogether with:

:set expandtab!

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

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

For more information see here.

Recording and replaying a macro

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

Deleting to end of line

d$

Deleting to beginning of line

d^

Finding text

To search forward for "text":

/text

To search backward for "text":

?text

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

Finding and replacing text

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

:s/search/destroy/

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

:s/search/destroy/g

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

:13,37 s/search/destroy/g

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

:%s/search/destroy/g

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

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

:setlocal ff=unix

More information on managing file formats available here.

Disabling auto-indent etc. to paste from clipboard

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

:set paste

To turn it off again:

:set nopaste

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

Positioning windows

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

vim -o a.txt b.txt

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

vim -o a.txt b.txt

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

Use ^W and < or > to resize windows.

To indent a block of text in Vim

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

5 > >

Press . (dot) to keep indenting.

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

> %

See here for more.

Open a file in a new window/tab

To open a file on the left hand side:

:vert new filename.ext

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

To open a file at the top:

:new filename.ext

See here for more.

Explore files in Vim

Enter:

:Explore

Switch between Vim tabs

Use gt and gT.

Switch between Vim windows

To toggle between open windows use:

Ctrl+W W

To move in a direction use:

Ctrl+W h/j/k/l

See here for more.

Insert block comment in Vim

See here for line-commenting.

So it's:

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

Navigate to matching tag

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

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

Auto-format HTML tags

Stolen from here.

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

Links

Create PDF from text using Vim

Generate PDF from input.txt with:

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

Examine output with:

$ okular doc.pdf

Write

Talking to other users on the system

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

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

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

$ who

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

$ write <username>

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

Date

Reporting the time on the server

$ date

Reporting UTC time

$ date --utc

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

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

Getting the year in four digits

$ year="`date +%Y`"

Getting the month in two digits

$ month="`date +%m`"

Getting the day of the month in two digits

$ day="`date +%d`"

Getting yesterday's date

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

Converting Unix time (seconds since epoch)

For timestamp '1501370200':

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

Running timedatectl from systemd

There's a new command bundled with systmed:

# timedatectl

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

MySQL (and MariaDB)

Run mysql without authentication/authorisation

# service mysql stop
# mysqld_safe --skip-grant-tables &

Then you can connect without a password, e.g.:

# mysql -u root mysql

To stop the unauthenticated service:

# mysqladmin shutdown

Then restart a normal service:

# service mysql start

Logging all database queries

# vim /etc/mysql/my.cnf

In the [mysqld] section add:

log=/tmp/mysql.log

Then:

# service mysql restart

Watch the log with:

# tail -f /tmp/mysql.log

Or:

SET GLOBAL log_output = 'FILE';
SET GLOBAL general_log_file = 'my_logs.txt';
SET GLOBAL general_log = 'ON';

my_logs.txt will be in /var/lib/mysql

Dumping a MySQL database

You can dump the database into a file using:

$ mysqldump -h hostname -u user --password=password databasename > filename

Loading a MySQL database from a dump file

You can create a database using:

$ echo create database databasename | mysql -h hostname -u user -p

You can restore a database using:

$ mysql -h hostname -u user --password=password databasename < filename

Creating a MySQL user

# mysql -h localhost -u root --password=<password>
mysql> create user 'username'@'localhost' identified by '<password>';

Granting all MySQL user permissions

# mysql -h localhost -u root --password=<password>
mysql> grant all privileges on dbname.* to user@host;

Select domain name from email address

SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )

Check if MySQL connection is encrypted with TLS/SSL

Check the SSL version in use:

show status like 'Ssl_version';

Or check the cipher in use:

show status like 'Ssl_cipher';

Report on server config

See SHOW Statements for the full list, but check out:

SHOW VARIABLES

and

SHOW STATUS

and

SHOW PROCESSLIST

Monitor MySQL activity

$ watch "mysql -t -e 'show processlist'"

Apache

Reporting loaded Apache modules

# apache2ctl -M

Maintaining .htaccess passwords

To add or modify the password for a user:

$ htpasswd /etc/apache2/passwd username

Configuring PHP session timeout in .htaccess

For a session timeout of 9 hours:

php_value session.cookie_lifetime 32400
php_value session.gc_maxlifetime 32400

Disabling PHP magic quotes in .htaccess

php_flag magic_quotes_gpc Off

Requiring HTTP Auth in .htaccess

AuthType Basic
AuthName "Speak Friend And Enter"
AuthUserFile /home/jj5/.htpasswd
Require valid-user

Restarting Apache

The hard way

$ sudo /etc/init.d/apache2 restart

The graceful way (avoids dropping active connections)

$ sudo apache2ctl graceful

Allowing directory browsing

To show directory index pages, in the apache config file:

<Directory /var/www/data>
  Options Indexes
</Directory>

C

Locating memset function

The memset function is in <string.h> as described in this article Using memset(), memcpy(), and memmove() in C

Links

PHP

Including a file relative to the including file

require_once( dirname( __FILE__ ) . '/relative/path/to.php' );

Enabling error reporting

error_reporting( E_ALL | E_STRICT );
ini_set( 'display_errors', 'On' );

Setting an error handler

set_error_handler( "error_handler", E_ALL | E_STRICT );
function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
  // ...
}

Disable HTML content in var_dump

ini_set( 'html_errors', 'off' );

Report PHP modules

$ php -m

PHP Security Best Practices For Sys Admins

See Linux 25 PHP Security Best Practices For Sys Admins.

BASH scripting

For a primer on bash scripting see TFM: Erotic Fantasy: /bin/sh Programming.

Telling a script to run in bash

The first line of the file should be:

#!/bin/bash

Checking if a command-line argument was passed in

if [ -n "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking if a command-line argument was not passed in

if [ "$1" = "" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Or:

if [ -z "$1" ]; then
  echo "Missing parameter 1.";
  exit 1;
fi

Checking command exit status

cd /my/path
if [ "$?" -ne "0" ]; then
  echo "Cannot change dir.";
  exit 1;
fi

Checking if a file does/doesn't exist

Check if file exists:

if [ -f "/my/file" ]; then
  cat /my/file
fi

Check if file doesn't exist:

if [ ! -f "/my/file" ]; then
  touch /my/file
fi

Checking if a directory does/doesn't exist

Check if directory exists:

if [ -d "/my/dir" ]; then
  rmdir /my/dir
fi

Check if directory doesn't exist:

if [ ! -d "/my/dir" ]; then
  mkdir /my/dir
fi

Deleting old backups

To keep only the latest five backups:

find . -maxdepth 1 -type f -printf '%T@ %p\0' | sort -r -z -n | awk 'BEGIN { RS="\0"; ORS="\0"; FS="" } NR > 5 { sub("^[0-9]*(.[0-9]*)? ", ""); print }' | xargs -0 rm -f

This script stolen from stackoverflow.

Requires GNU find for -printf, GNU sort for -z, GNU awk for "\0" and GNU xargs for -0, but handles files with embedded newlines or spaces.

Changing into the script's directory

cd "`dirname $0`"

Getting the absolute path of a relative path

readlink -f ./some/path

Creating a temp directory

dir=`mktemp -d` && cd $dir

Reading secret input from stdin

You can read a secret, such as a password, like this:

echo -n "Enter passphrase: "
stty -echo
read passphrase;
stty echo
echo ""

After running the above the secret will be in the $passphrase environment variable.

String replacements in bash

See the string manipulation doco. Basically, to replace first occurrence:

result=${var/find/replace}

To replace all occurrences:

result=${var//find/replace}

A practical example, get an ISO date and turn it into a path:

date="$(date +%Y-%m-%d)"
work_dir=${date//-//}

Sending a HEREDOC to a file

cat << EOF > /tmp/yourfilehere
These contents will be written to the file.
        This line is indented.
EOF

Bash case/switch statement

See using case statements, e.g.:

case $space in
[1-6]*)
  Message="All is quiet."
  ;;
[7-8]*)
  Message="Start thinking about cleaning out some stuff.  There's a partition that is $space % full."
  ;;
9[1-8])
  Message="Better hurry with that new disk...  One partition is $space % full."
  ;;
99)
  Message="I'm drowning here!  There's a partition at $space %!"
  ;;
*)
  Message="I seem to be running with an nonexistent amount of disk space..."
  ;;
esac

Using dotglob shopt to match dot-files

To enable dot-file matching in globs, set the dotglob shell option:

$ shopt -s dotglob

Stopping a script from running if it previously exited due to error

persistentDataDir=/var/lib/something
alarm() {
  touch $persistentDataDir/alarm
}
trap alarm ERR
[ -f $persistentDataDir/alarm ] && exit 1

Make sure only one instance of a script is running at a time

ephemeralDataDir=/var/run/something
unlock() {
  rmdir $ephemeralDataDir/lock
}
mkdir $ephemeralDataDir/lock || exit 1;
trap unlock EXIT

BASH programming advice

See Anybody can write good bash (with a little effort).

Run a command using arguments that come from an array

See here:

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

Display a CSV in columnar or tabular format

$ column -t -s , data.csv

Maximum command line length

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

$ getconf ARG_MAX    # Get argument limit in bytes/chars

Sed

Find and replace with sed

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

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

Awk

Listing IP addresses in an Apache web log

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

Printing space-separated field

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

Printing delimited field

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

Subversion

Setting svn:externals from the command-line

See here.

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

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

Or to use a file:

svn propset svn:externals -F svn.externals .

Setting svn:ignore from the command line

See here.

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

Or use a file and apply recursively:

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

Git

Showing status of working copy

git status

Showing repo history

git log

Showing remote repositories (including 'origin')

git remote -v

Handy git aliases

Save these to your ~/.gitconfig file.

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

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

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

 dif   = !git diff --name-status

Show git remote URL

git config --get remote.origin.url

IRC

Instructing ChanServ to op an admin

/msg ChanServ op #channel user

E.g.

/msg ChanServ op #gnurc jj5

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

C++

C++ books

Books I want

Books I own

Books I'm not reading

Books I've read

C++ blogs/articles

C++ performance tips

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

systemd

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

Following a service log

e.g. for bind9:

# journalctl -f -u bind9

or for everything:

# journalctl -f

System status

To see spawned services hierarchy:

# systemctl status

Or for a specific service e.g.:

# systemctl status networking

SaltStack

Running a command on specified minions

From the salt master:

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

From the salt minion:

salt-call cmd.run 'update-locale'

Running a command on all minions

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

Running a specific state file

From the salt master:

salt $MINION_ID state.sls $STATE_FILE

From the salt minion:

salt-call state.sls $STATE_FILE

Listing active jobs

salt-run jobs.active

Listing available grains

salt 'example' grains.items

Listing available pillar

salt 'example' pillar.items

Reporting a grain value

e.g. for the 'mem_total' grain:

salt '*' grains.item mem_total

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

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

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

KDE

Running user login script (X11/XOrg/XWindows)

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

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

Standard KDE shortcut key bindings

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

Shutting down KDE/Plasma

# /etc/init.d/sddm stop

VirtualBox

Mounting a VirtualBox VDI file

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

See here:

Install qemu if necessary:

# apt install qemu

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

# rmmod nbd
# modprobe nbd max_part=16

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

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

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

# mount /dev/nbd0p1 /mnt

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

# qemu-nbd -d /dev/nbd0

Elasticsearch

Report on health of your Elasticsearch cluster

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

Zabbix

Zabbix Agent on Mac OS X

Download and install agent.

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

Unload agent with:

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

Load agent with:

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

To add a 'pki' group:

# dseditgroup -o create pki

To monitor syslog on Mac OS X:

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

Installing Zabbix Agent from source on Mac OS X

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

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

NetBeans

NetBeans shortcut keys

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

XML

How to pretty-print an XML file

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

ApacheBench

Run a benchmark with ApacheBench

$ ab -n 1000 -c 100 https://www.example.com/