Difference between revisions of "John's Linux page"

From ProgClub
Jump to: navigation, search
(169 intermediate revisions by the same user not shown)
Line 2: Line 2:
  
 
Note: I have some other disorganised notes on [http://www.jj5.net/sixsigma/UNIX UNIX], which include a few tips for MacOS. I also have some tips for [http://www.jj5.net/sixsigma/OS_X OS X].
 
Note: I have some other disorganised notes on [http://www.jj5.net/sixsigma/UNIX UNIX], which include a few tips for MacOS. I also have some tips for [http://www.jj5.net/sixsigma/OS_X OS X].
 +
 +
Note: the info on this page is probably Ubuntu (and Debian as an outside chance) specific, because I use Ubuntu pretty much everywhere these days.
 +
 +
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.
  
= File searching =
+
To see usage for a specific user run e.g.:
  
== Finding a file with a particular name ==
+
$ top -u jj5
  
$ find -iname "*some-part-of-the-file-name*"
+
To see full command-line press 'c'.
  
Will start searching from the current directory, so maybe
+
When you're in 'top' you can:
  
$ cd /
+
* press '1' (one) to toggle CPU aggregation
 +
* press &lt; and &gt; to change the sort column
  
first. For a case-sensitive search:
+
== Changing memory reporting in 'top' ==
  
$ find -name "*eXaCT CaSE*"
+
To run top:
  
== Finding a file with particular content ==
+
$ top
  
To search in /etc/ for a file with particular content:
+
Press 'E' to switch between top memory units (KiB, MiB, GiB, etc.)
  
$ grep -R "search-string" /etc/*
+
Press 'e' to switch between bottom memory units (KiB, MiB, GiB, etc.)
  
To search the current directory for *.cs files containing the word "Up":
+
Press 'M' to sort by memory utilisation.
  
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
+
Press 'm' to switch between various display modes.
  
== Finding a list of files with particular content ==
+
== Showing full command-line in 'top' ==
  
E.g. to find all the files with the word 'creativity':
+
To see the full command-line for processes run with -c:
  
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
+
  $ top -c
  
== Using the locate command to find files ==
+
== Listing all processes currently running which were started in your current shell session ==
  
  $ locate part-of-filename
+
  $ ps -fl
  
E.g.
+
== Killing specific processes ==
  
  $ locate texvc
+
  # ps aux | grep -e "this\|that" | grep -v grep | tr -s " " | cut -d " " -f 2 | xargs kill -9
  
== Updating locate command's database ==
+
== Run a command for a specified time using timeout ==
  
  # updatedb
+
  $ timeout 3 ping jj5.net
  
= Job control =
+
= Disk management =
  
== Stopping a running process ==
+
== Reporting ext4 file-systems mounted without noatime ==
  
Press Ctrl+Z to stop a running process.
+
$ cat /proc/mounts | grep ext | grep -v noatime | sort
  
== Listing current jobs and their status ==
+
== Creating a partition table ==
  
  $ jobs
+
  # parted /dev/xvdf
  
== Resuming a stopped job in the backgroud ==
+
mktable msdos
  
To resume a stopped process in the background
+
== Creating a partition ==
  
  $ bg %1
+
  # parted /dev/xvdf
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
u MiB
 +
mkpart primary 1 100%
  
== Resuming a stopped job in the foreground ==
+
== Creating an ext4 file-system ==
  
To resume a stopped process in the foreground
+
# mkfs.ext4 /dev/xvdf1
  
$ fg %1
+
== Listing disk drives ==
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
# fdisk -l
  
== Killing a stopped job ==
+
(That's an L for "list")
  
To kill a job
+
== Checking available disk space ==
  
  $ kill %1
+
  $ df -h
  
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
+
== Getting disk information ==
  
== Periodically run a program and watch its output ==
+
# lsblk
  
$ watch /your/command
+
And
  
= Debian/Ubuntu package management =
+
# cat /proc/partitions
  
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
+
Or the Grand Daddy of them all:
  
== configuring debconf ==
+
# lshw -class disk
  
# dpkg-reconfigure debconf
+
(Requires the lshw package.)
  
Set priority to low to get asked detailed questions.
+
== Getting partition UUID and file-system type ==
  
== Showing list of installed packages ==
+
# blkid
  
# dpkg --get-selections
+
== Checking for SSD vs magnetic disk ==
  
== Searching for installed package ==
+
# cat /sys/block/sda/queue/rotational
  
# dpkg --get-selections | grep package-name
+
Will be 0 for SSD and 1 for magnetic.
  
or
+
== Monitoring a ZFS server ==
  
# aptitude search package-name
+
So some commands I run to keep an eye on my new ZFS servers:
  
== Showing which files are installed as part of a package ==
+
# 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
  
# dpkg -L package-name
+
If you have a scrub or resilvering in progress you can report on progress with:
  
== Installing a package ==
+
# watch zpool status -v
  
# apt-get install package-name
+
You can poke about in internals, e.g.:
  
== Uninstalling a package ==
+
# cat /proc/spl/kstat/zfs/arcstats
  
  # apt-get remove package-name
+
  root@orac:/sys/module/zfs/parameters# tail *
  
== Showing system architecture ==
+
You can report on property values with e.g.:
  
  $ dpkg --print-architecture
+
  # zfs get all data
  
== Showing which package a file belongs to ==
+
If you want to get funky:
  
  $ which echo
+
  # cd /tmp
/bin/echo
+
  # perf record -ag #(Ctrl+C after ~15 seconds)
  $ dpkg -S /bin/echo
+
  # perf report --stdio
coreutils: /bin/echo
 
  $ dpkg -l | grep coreutils
 
ii  coreutils                        6.10-6                  The GNU core utilities
 
  
== Showing package information ==
+
You can search for ZFS files like e.g. this:
  
  $ apt-cache showpkg coreutils
+
  root@orac:/# find / -name '*zfs*' -or -name '*zpool*'
  
Or for even more information:
+
You can report history of a zpool:
  
  $ apt-cache show coreutils
+
  # zpool history $poolname
  
== List all installed packages with package version info ==
+
You can get a report on the dedup tables:
  
  dpkg-query -l
+
  # zpool status -D $poolname
 +
 
 +
Or more detailed dedup table info:
 +
 
 +
# zdb -DDD $poolname
 +
 
 +
Note in the output see [https://unix.stackexchange.com/a/405700 here] for details, basically:
  
== Reporting which version of a package is installed ==
+
{|class="wikitable"
 +
! Abbr  !! Description
 +
|-
 +
| LSIZE  || logical size (in memory)
 +
|-
 +
| PSIZE  || physical size
 +
|-
 +
| DSIZE  || size on disk
 +
|-
 +
| refcnt || reference count
 +
|}
  
$ dpkg -l | grep package-name
+
== How to tell if zfs scrub is running ==
  
E.g.:
+
You can get the status from the "scan:" line from:
  
  root@hope:~/letsencrypt# dpkg -l | grep augeas
+
  $ zpool status
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 ==
+
== Measure data throughput ==
  
Try the following:
+
Use the 'pv' command from the 'pv' package, e.g.:
  
  # apt-get update
+
  # cat /dev/sda | pv | cat > /dev/null
# apt-get dist-upgrade
 
# apt-get autoremove
 
# apt-get remove $(deborphan)
 
# update-flashplugin-nonfree --install
 
  
= Networking =
+
Or for ZFS:
  
== net-tools vs iproute2 ==
+
# zfs send data/example | pv | cat > /dev/null
  
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].
+
== Using Smartctl, Smartd and Hddtemp on Debian ==
  
{|class="wikitable"
+
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].
! 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 usage ==
  
For servers:
+
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.
  
# service networking restart
+
== Report hard disk temperatures ==
  
For desktops:
+
E.g.
  
  # service network-manager restart
+
  # hddtemp /dev/sd[a-e]
  
== Pinging with particular packet size ==
+
== Burning an ISO image to USB on Mac ==
  
$ ping -M do -s <packet size in bytes> <host>
+
First insert your USB key and find the appropriate disk with:
  
E.g.
+
# diskutil list
  
$ ping -M do -s 1400 charity.progclub.org
+
Then unmount it with:
  
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
+
# diskutil unmountDisk /dev/disk4
  
# ip route add <host> dev <interface> advmss <packet size>
+
Then copy ISO image with 'dd':
  
E.g.
+
# dd if=ubuntu-18.04.1-desktop-amd64.iso of=/dev/disk4
  
# ip route add 10.0.0.1 dev eth0 advmss 1400
+
You can get dd to report progress by sending it the SIGINFO signal:
  
== Dropping configured MMS for a particular IP address ==
+
# kill -s info 12345
  
# ip route flush <host>
+
== Listing all ext4 file systems ==
  
E.g.
+
To see a list only of the mounted ext4 file systems:
  
  # ip route flush 10.0.0.1
+
  # df -t ext4
  
== Listing open ports and socket information ==
+
== Report hierarchical file system mount points and mount options ==
  
Including which process is listening on which port.
+
$ findmnt
  
# netstat -tulpn
+
== Report the mount point for the current working directory ==
  
Or use the 'ss' command:
+
$ findmnt "$PWD"
  
# ss -s
+
= Monitoring disk I/O =
# ss -l
 
# ss -pl
 
# ss -o state established '( dport = :smtp or sport = :smtp )'
 
  
== Listing open IPv4 connections ==
+
There's an app for that! iotop.
  
# lsof -Pnl +M -i4
+
== Using iotop, top for disks ==
  
You might need to install the lsof package:
+
# iotop -oPa
  
# apt-get install lsof
+
== Monitor disk I/O for performance issues ==
  
== Query for DNS MX record ==
+
# watch iostat
  
$ nslookup
+
Or e.g.
> server 127.0.0.1
 
> set q=mx
 
> mail.blackbrick.com
 
  
== Query for DNS SOA record ==
+
# watch iostat -xd /dev/sd[abc]
  
$ dig @ns2.staticmagic.net -t SOA staticmagic.net
+
Or use groupings like this command for 'tact':
  
== Using nmap to list open ports on remote host ==
+
$ iostat -g system nvme0n1 -g fast sda sdb -g data sdc sdd -d 2
  
To check the 1,000 most common ports:
+
= Monitoring a system =
  
# nmap server.example.com
+
== Simple ZFS monitoring ==
  
Or for a specific port range (e.g. 101 to 102):
+
# watch iostat
 +
# iotop
 +
# zpool iostat -v 5
 +
# watch 'hddtemp /dev/sd[a-e]; echo; zpool list; echo; zfs list'
 +
# nethogs
 +
# top
 +
 
 +
= Monitoring temperature =
  
# nmap -p 101-102 server.example.com
+
See [https://askubuntu.com/a/854029 temperature without third-party apps] for:
  
Or for all ports (1 to 65,535):
+
$ cat /sys/class/thermal/thermal_zone*/temp
  
# nmap -p- server.example.com
+
and:
  
== Links ==
+
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
  
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
+
== Monitoring CPU temperature ==
  
= IPTables =
+
$ watch sensors
  
== Applying firewall rules ==
+
== Monitoring HDD temperature ==
  
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
+
For e.g. SATA drives sda to sdd:
  
  $ sudo vim /etc/iptables.test.rules
+
  # watch hddtemp /dev/sd[a-d]
$ 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 =
+
= ZFS =
  
== Disabling IPSec ==
+
== How can I determine the current size of the ARC in ZFS, and how does the ARC relate to free or cache memory? ==
  
# setkey -FP
+
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?]
  
= OpenSSL =
+
$ cat /proc/spl/kstat/zfs/arcstats
  
== Debugging IMAPS with OpenSSL ==
+
Then:
  
  # openssl s_client -connect localhost:993
+
  c is the target size of the ARC in bytes
  > a1 LOGIN username@host password
+
  c_max is the maximum size of the ARC in bytes
  > a2 LOGOUT
+
  size is the current size of the ARC in bytes
  
== Debugging HTTPS with OpenSSL ==
+
== Stopping a ZFS scrub in progress ==
  
  $ openssl s_client -connect www.example.com:443
+
  # zpool scrub -s $pool
GET /example.html HTTP/1.1
 
host: www.example.com
 
  
== Links ==
+
e.g. for the 'data' pool:
  
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
+
# zpool scrub -s data
  
= Pluggable Authentication Modules (PAM) =
+
= File management =
  
== Links ==
+
== Listing files by size ==
  
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
+
Use capital S for Size:
  
= SSH =
+
$ ls -S
  
== Configuring SSH key login ==
+
== Listing only directories ==
  
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
+
$ ls -l | egrep '^d'
  
$ ssh-keygen -t rsa
+
== Listing only files ==
  
Copy the public key from the client to the server:
+
$ ls -l | egrep -v '^d'
  
$ scp ~/.ssh/id_rsa.pub user@example.org:
+
== Listing hidden files ==
  
Configure the authorized keys on the server:
+
$ ls -al .[!.]*
  
$ ssh user@example.org
+
== Creating a symbolic link ==
$ 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 ==
+
$ ln -s /path/to/target link-name
  
For example, connecting a remote MySQL server to the localhost:
+
== Creating a hard-link ==
  
  $ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
+
  $ ln /path/to/target file-name
  
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
+
== Changing the owner of a file ==
  
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
+
$ chown user:group <files>
  
The -L stanza is localport:remotehost:remoteport where localport is a
+
E.g.
port on your machine, forwarded to remoteport on remotehost.
 
  
== Tunneling over SSH with PuTTY ==
+
$ chown jj5:staff README
 +
$ chown root:root *
  
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
+
To apply recursively into sub-directories use -R,
  
* run putty.exe
+
$ chown -R root:root /etc/*
* Connection -> SSH -> Tunnels
 
** Port forwarding: source port to 3306
 
** destination: 127.0.0.1:3306
 
** check Local
 
** click Add
 
  
== Enabling verbose SSH logging ==
+
== Changing file permissions ==
  
To see what's going on with your ssh connections,
+
{|class="wikitable"
 +
|+ Object codes
 +
! User !! Group !! Other
 +
|-
 +
| u    || g    || o
 +
|}
  
$ ssh -v user@host
+
{|class="wikitable"
 +
|+ Permission codes
 +
! Read !! Write !! Exectue
 +
|-
 +
| r    || w    || x
 +
|-
 +
| 4    || 2    || 1
 +
|}
  
Or
+
{|class="wikitable"
 
+
|+ Numeric codes
$ ssh -vv user@host
+
! 0
 
+
| None
== Unlocking SSH key for session ==
+
|-
 
+
! 1
jj5@orac:~/.config/autostart$ cat ssh-add.desktop
+
| Execute
[Desktop Entry]
+
|-
Type=Application
+
! 2
Name=ssh-add
+
| Write
Comment=Adds my private key to my session.
+
|-
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
+
! 3
 +
| Write, Execute
 +
|-
 +
! 4
 +
| Read
 +
|-
 +
! 5
 +
| Read, Execute
 +
|-
 +
! 6
 +
| Read, Write
 +
|-
 +
! 7
 +
| Read, Write, Execute
 +
|}
  
== Links ==
+
See [http://catcode.com/teachmod/numeric2.html Numeric Mode in Action].
  
* [http://blogs.perl.org/users/smylers/2011/08/ssh-productivity-tips.html SSH Can Do That? Productivity Tips for Working with Remote Servers]
+
$ chmod <user numeric code><group numeric code><other numeric code> <files>
* [http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html PuTTY Download Page]
+
$ chmod <object codes>+|-<permission codes> <files>
  
= Standard IO =
+
E.g.
  
== cat EOF ==
+
$ chmod 600 my-private-file
 +
$ chmod go-rwx my-private-file
 +
$ chmod u+rw my-private-file
 +
$ chmod +x my-script
  
$ cat > output <<EOF
+
== Updating config files ==
> text
 
> EOF
 
  
$ cat output
+
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:
text
 
  
= Script =
+
$ cp old.conf updated.conf
 +
$ merge -A updated.conf new.conf old.conf
  
== Creating a session log with script ==
+
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.
  
$ script -t 2> timing
+
The merge program is a part of the RCS package. If you don't have it:
  
The session log is in the file 'typescript' and the timing data is in 'timing'.
+
$ sudo apt-get install rcs
  
== Replaying a scripted session ==
+
== Listing open files ==
  
  $ scriptreplay timing
+
Use lsof to list open files. E.g.:
 +
 
 +
  # lsof
  
Uses the default file 'typescript' and the 'timing' file as specified.
+
See man lsof for options.
  
= Screen =
+
== List permissions on a whole directory path ==
  
== Creating a new screen or reconnecting to a detached screen ==
+
E.g.:
  
  $ screen -R
+
  $ namei -om /home/jj5/workspace
  
== Detaching a screen ==
+
Outputs:
  
  $ screen -D
+
  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
  
== Reconnecting to screen ==
+
== Counting non-blank lines in a file ==
  
$ screen -D
+
E.g.:
$ screen -R
 
  
I have a script in ~/bin/reconnect like so,
+
$ cat foo.c | sed '/^\s*$/d' | wc -l
  
#!/bin/bash
+
== Cloning one directory to another with rsync ==
screen -D
 
screen -R
 
  
This will detach your last screen, and reconnect it on the current terminal.
+
E.g.:
  
= Vim =
+
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/
  
== First, why Vim? ==
+
== Counting number of files in current directory and all subdirectories ==
  
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
+
$ ls -AlhR . | egrep '^-' | wc -l
  
== Visual modes ==
+
== Counting number of directories in current directory and all subdirectories ==
  
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
+
$ ls -AlhR . | egrep '^d' | wc -l
  
== Configuring spaces instead of tabs ==
+
== Getting the status of a 'dd' process ==
  
I use two spaces instead of tabs. To configure, edit your .vimrc file:
+
First figure out the 'dd' process number, with e.g. 'top' or 'ps aux | grep dd'
  
$ vim ~/.vimrc
+
Then send the dd process the SIGINFO signal, which for dd process 40947 would be:
  
and include the following lines:
+
# kill -s info 40947
  
set tabstop=2
+
The dd process will report its status in the terminal its running in.
set shiftwidth=2
 
set expandtab
 
  
== Configuring syntax highlighting ==
+
== Transferring a large file via FAT32 file system ==
  
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
+
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:
  
Use:
+
$ split -b 4000m input.tgz input.tgz-parts-
  
:syntax on
+
Then copy the small files and reassemble:
  
to turn on syntax highlighting.
+
$ cat input.tgz-parts-* > output.tgz
  
Use:
+
== Find the difference between two directories ==
  
  :syntax off
+
  $ diif -qr $DIR_A $DIR_B
  
to turn off syntax highlighting.
+
= NFS =
  
To always use syntax highlighting:
+
== List NFS shares ==
  
$ vim ~/.vimrc
+
To e.g. show NFS shares on 'love':
  
and add:
+
$ showmount -e love
  
syntax on
+
= Compression =
  
To get a list of supported colour schemes open vim and type:
+
== How to use pigz with tar ==
  
:colorscheme[space][Ctrl+D]
+
See [https://stackoverflow.com/a/39904353 here]:
  
To always use a particular colorscheme edit ~/.vimrc and add (for example):
+
$ tar cf - paths-to-archive | pigz --best -p 8 > archive.tgz
  
colorscheme desert
+
Note: don't use --best unless you're being stingy, running without it will be much faster.
  
== Inserting a TAB character when expandtab is on ==
+
Also from [https://stackoverflow.com/a/50586833 here]:
  
The problem here is that you have configured vim to insert spaces, but for a particular file (e.g. a Makefile) you need to insert a character.
+
Fast pack:
  
Press Ctrl+V TAB to insert a literal tab character.
+
tar -I 'pigz --fast' -cf my.tar.gz whatver
  
Or you can disable tab expansion altogether with:
+
Best pack:
  
  :set expandtab!
+
  tar -I 'pigz --best' -cf my.tar.gz whatver
  
== Changing 2 space indent to 4 space indent (e.g. for python files) ==
+
Fast unpack:
  
  :%s/^\s*/&&/g
+
  tar -I pigz -xf my.tar.gz
  
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ see here].
+
== Best compression with tar ==
  
== Recording and replaying a macro ==
+
From [https://superuser.com/questions/514260/how-to-obtain-maximum-compression-with-tar-gz#544643 here]:
  
To record a macro press 'q' and then a number between 1 and 9. E.g. press "q1". The macro is now recording. When you've finished issuing your commands press 'q' again to finish recording. To replay a macro press '@' followed by the number of the macro. That is, if you pressed "q1" to record the macro, press "@1" to replay the macro. To replay the last macro again press "@@".
+
export GZIP=-9
 +
tar cvzf file.tar.gz /path/to/directory
  
== Deleting to end of line ==
+
or
  
  d$
+
  env GZIP=-9 tar cvzf file.tar.gz /path/to/directory
  
== Deleting to beginning of line ==
+
== Best parallel compression with pigz ==
  
  d^
+
  $ pigz --best
  
== Finding text ==
+
== Best parallel compression with xz ==
  
To search forward for "text":
+
$ xz -9e -T 0
  
/text
+
== Reporting compression ratios with xz ==
  
To search backward for "text":
+
e.g.
  
  ?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
  
To repeat the last search in a forward direction press 'n', or to search again backwards press 'N'.
+
= Symbolic-link management =
  
== Finding and replacing text ==
+
== Data used by sym-linked files:
  
To replace the first instance of "search" on the current line with "destroy":
+
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:
  
  :s/search/destroy/
+
  jj5@tact:/data/backup/unity/latest$ du -hD * | sort -h
  
To replace all instances of "search" on the current line with "destroy":
+
= File searching =
  
:s/search/destroy/g
+
== Finding a file with a particular name ==
  
To replace all instances of "search" on lines 13 to 37 with "destroy":
+
$ find -iname "*some-part-of-the-file-name*"
  
:13,37 s/search/destroy/g
+
Will start searching from the current directory, so maybe
  
To replace all instances of "search" in the entire file with "destroy":
+
$ cd /
  
:%s/search/destroy/g
+
first. For a case-sensitive search:
  
== Changing DOS/Windows line-endings to Unix line-endings ==
+
$ find -name "*eXaCT CaSE*"
  
To set the line-ending to Unix line endings run the command:
+
== Finding a file with particular content ==
  
:setlocal ff=unix
+
To search in /etc/ for a file with particular content:
  
More information on managing file formats [http://vim.wikia.com/wiki/File_format available here].
+
$ grep -R "search-string" /etc/*
  
== Disabling auto-indent etc. to paste from clipboard ==
+
To search the current directory for *.cs files containing the word "Up":
  
To disable smart indenting when you're going to paste in text:
+
$ find . -name '*.cs' -exec grep --color=auto -H Up {} \;
  
:set paste
+
== Finding a list of files with particular content ==
  
To turn it off again:
+
E.g. to find all the files with the word 'creativity':
  
  :set nopaste
+
  $ grep -R creativity . | sed 's/:/ /' | awk '{ print $1 }' | sort | uniq
  
There's more info in this article: [http://vim.wikia.com/wiki/Toggle_auto-indenting_for_code_paste Toggle auto-indenting for code paste]
+
== Using the locate command to find files ==
  
== Positioning windows ==
+
$ locate part-of-filename
  
Use -o for horizontal split, e.g.:
+
E.g.
  
  vim -o a.txt b.txt
+
  $ locate texvc
  
Use -O for vertical split, e.g.:
+
== Updating locate command's database ==
  
  vim -o a.txt b.txt
+
  # updatedb
  
Use ^W to navigate windows then use directional keys h, j, k, l, etc.
+
== Select a random line from a text file ==
  
Use ^W and &lt; or &gt; to resize windows.
+
$ shuf -n 1 input.txt
  
== To indent a block of text in Vim ==
+
== Extra context for grep ==
  
Use the > command. E.g. to indent five lines:
+
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:
  
  5 > >
+
  $ grep -B 3 -A 1 ...
  
Press . (dot) to keep indenting.
+
= Job control =
  
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:
+
== Stopping a running process ==
  
> %
+
Press Ctrl+Z to stop a running process.
  
See [http://stackoverflow.com/questions/235839/indent-multiple-lines-quickly-in-vi#235841 here] for more.
+
== Listing current jobs and their status ==
  
== Open a file in a new window/tab ==
+
$ jobs
  
To open a file on the left hand side:
+
== Resuming a stopped job in the backgroud ==
  
:vert new filename.ext
+
To resume a stopped process in the background
  
Note: ':vnew filename.ext' and ':vsp filename.ext' also work.
+
$ bg %1
  
To open a file at the top:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
:new filename.ext
+
== Resuming a stopped job in the foreground ==
  
See [http://stackoverflow.com/questions/10760310/how-to-open-a-new-file-in-vim-in-a-new-window#10762678 here] for more.
+
To resume a stopped process in the foreground
  
== Explore files in Vim ==
+
$ fg %1
  
Enter:
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
:Explore
+
== Killing a stopped job ==
  
== Switch between Vim tabs ==
+
To kill a job
  
Use gt and gT.
+
$ kill %1
  
== Switch between Vim windows ==
+
where '1' is the job number reported by bash when you pressed Ctrl+Z (or ran 'jobs').
  
To toggle between open windows use:
+
== Periodically run a program and watch its output ==
  
  Ctrl+W W
+
  $ watch /your/command
  
To move in a direction use:
+
= Debian/Ubuntu package management =
  
Ctrl+W h/j/k/l
+
Also see [https://wiki.debian.org/WhereIsIt Where "is" it?] on the Debian Wiki.
  
See [http://superuser.com/questions/280500/how-does-one-switch-between-windows-on-vim#280501 here] for more.
+
== configuring debconf ==
  
 +
# dpkg-reconfigure debconf
  
== Links ==
+
Set priority to low to get asked detailed questions.
  
* [http://www.vim.org/ Vim: the editor]
+
== Showing list of installed packages ==
* [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 =
+
# dpkg --get-selections
  
== Talking to other users on the system ==
+
== Searching for installed package ==
  
'''write''' is a unix command for talking to other users on the system. To use '''write''':
+
# dpkg --get-selections | grep package-name
  
1. SSH to <username>@<hostname> and login with your username and password.
+
or
  
2. Issue the following command to find out who is logged onto the system:
+
# aptitude search package-name
  
$ who
+
== Showing which files are installed as part of a package ==
  
3. Issue the following command to talk to a specific user:
+
# dpkg -L package-name
  
$ write <username>
+
== Installing a package ==
  
4. Enter the message you'd like to send the user, followed by Ctrl+C to send. Press Ctrl+D to cancel.
+
# apt-get install package-name
  
= Date =
+
== Uninstalling a package ==
  
== Reporting the time on the server ==
+
# apt-get remove package-name
  
$ date
+
== Showing system architecture ==
  
== Reporting UTC time ==
+
$ dpkg --print-architecture
  
$ date --utc
+
== Showing which package a file belongs to ==
  
== Getting the date in yyyy-MM-dd-hhmmss format ==
+
$ which echo
 +
/bin/echo
 +
$ dpkg -S /bin/echo
 +
coreutils: /bin/echo
 +
$ dpkg -l | grep coreutils
 +
ii  coreutils                        6.10-6                  The GNU core utilities
  
$ date="`date +%F-%H%M%S`"
+
== Showing package information ==
  
== Getting the year in four digits ==
+
$ apt-cache showpkg coreutils
  
$ year="`date +%Y`"
+
Or for even more information:
  
== Getting the month in two digits ==
+
$ apt-cache show coreutils
  
$ month="`date +%m`"
+
== List all installed packages with package version info ==
  
== Getting the day of the month in two digits ==
+
dpkg-query -l
  
$ day="`date +%d`"
+
== Reporting which version of a package is installed ==
  
== Getting yesterday's date ==
+
$ dpkg -l | grep package-name
  
$ date --date='1 day ago' +%Y-%m-%d
+
E.g.:
  
= MySQL =
+
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
  
== Run mysql without authentication/authorisation ==
+
== Comprehensive upgrade ==
  
# service mysql stop
+
Try the following:
# mysqld_safe --skip-grant-tables &
 
  
Then you can connect without a password, e.g.:
+
# apt-get update
 
+
# apt-get dist-upgrade
  # mysql -u root mysql
+
# apt-get autoremove
 +
# apt-get remove $(deborphan)
 +
  # update-flashplugin-nonfree --install
  
To stop the unauthenticated service:
+
== Searching all available packages ==
  
  # mysqladmin shutdown
+
  $ apt-cache search . | sort -d | less
  
Then restart a normal service:
+
== Reporting unattended upgrades status ==
  
# service mysql start
+
See [https://askubuntu.com/questions/934807/unattended-upgrades-status#934863 here] for more info.
  
== Logging all database queries ==
+
# tail -f /var/log/unattended-upgrades/unattended-upgrades.log
  
# vim /etc/mysql/my.cnf
+
== Searching for Debian packages and versions ==
  
In the [mysqld] section add:
+
* [https://packages.debian.org/search?keywords=dnscrypt-proxy Debian package search]
  
log=/tmp/mysql.log
+
= Networking =
  
Then:
+
== Determining throughput between two hosts ==
  
  # service mysql restart
+
  # apt install iperf3
  
Watch the log with:
+
On the server:
  
  # tail -f /tmp/mysql.log
+
  # iperf3 -s
  
== Dumping a MySQL database ==
+
On the client:
  
You can dump the database into a file using:
+
  # iperf3 -c $SERVER_IP
 
  $ mysqldump -h hostname -u user --password=password databasename > filename
 
  
== Loading a MySQL database from a dump file ==
+
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].
  
You can create a database using:
+
== net-tools vs iproute2 ==
  
$ echo create database databasename | mysql -h hostname -u user -p
+
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].
  
You can restore a database using:
+
{|class="wikitable"
+
! legacy net-tools commands
  $ mysql -h hostname -u user --password=password databasename < filename
+
! 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)
 +
|}
  
== Creating a MySQL user ==
+
== Restart networking ==
  
# mysql -h localhost -u root --password=<password>
+
For servers:
mysql> create user 'username'@'localhost' identified by '<password>';
 
  
== Granting all MySQL user permissions ==
+
# service networking restart
  
# mysql -h localhost -u root --password=<password>
+
For desktops:
mysql> grant all privileges on dbname.* to user@host;
 
  
== Select domain name from email address ==
+
# service network-manager restart
  
SELECT SUBSTR( email, INSTR( email, '@' ) + 1 )
+
== Pinging with particular packet size ==
  
== Check if MySQL connection is encrypted with TLS/SSL ==
+
$ ping -M do -s <packet size in bytes> <host>
  
Check the SSL version in use:
+
E.g.
  
  show status like 'Ssl_version';
+
  $ ping -M do -s 1400 charity.progclub.org
  
Or check the cipher in use:
+
== Setting [http://en.wikipedia.org/wiki/Maximum_segment_size MSS] for a particular IP address on a particular interface ==
  
  show status like 'Ssl_cipher';
+
  # ip route add <host> dev <interface> advmss <packet size>
  
= Apache =
+
E.g.
  
== Maintaining .htaccess passwords ==
+
# ip route add 10.0.0.1 dev eth0 advmss 1400
  
To add or modify the password for a user:
+
== Dropping configured MMS for a particular IP address ==
  
  $ htpasswd /etc/apache2/passwd username
+
  # ip route flush <host>
  
== Configuring PHP session timeout in .htaccess ==
+
E.g.
  
For a session timeout of 9 hours:
+
# ip route flush 10.0.0.1
  
php_value session.cookie_lifetime 32400
+
== Listing open ports and socket information ==
php_value session.gc_maxlifetime 32400
 
  
== Disabling PHP magic quotes in .htaccess ==
+
Including which process is listening on which port.
  
  php_flag magic_quotes_gpc Off
+
  # netstat -tulpn
  
== Requiring HTTP Auth in .htaccess ==
+
Or use the 'ss' command:
  
  AuthType Basic
+
  # ss -s
  AuthName "Speak Friend And Enter"
+
  # ss -l
  AuthUserFile /home/jj5/.htpasswd
+
  # ss -pl
  Require valid-user
+
  # ss -o state established '( dport = :smtp or sport = :smtp )'
  
== Restarting Apache ==
+
== Listing open IPv4 connections ==
  
The hard way
+
# lsof -Pnl +M -i4
  
$ sudo /etc/init.d/apache2 restart
+
You might need to install the lsof package:
  
The graceful way (avoids dropping active connections)
+
# apt-get install lsof
  
$ sudo apache2ctl graceful
+
== Query for DNS MX record ==
  
== Allowing directory browsing ==
+
$ nslookup
 +
> server 127.0.0.1
 +
> set q=mx
 +
> mail.blackbrick.com
  
To show directory index pages, in the apache config file:
+
== Query for DNS SOA record ==
  
  <Directory /var/www/data>
+
  $ dig @ns2.staticmagic.net -t SOA staticmagic.net
  Options Indexes
 
</Directory>
 
  
= C =
+
== Using nmap to list open ports on remote host ==
  
== Locating memset function ==
+
To check the 1,000 most common ports:
  
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]
+
# nmap server.example.com
  
== Links ==
+
Or for a specific port range (e.g. 101 to 102):
  
* [http://www.ibm.com/developerworks/linux/library/l-memory/ Inside memory management]
+
# nmap -p 101-102 server.example.com
  
= PHP =
+
Or for all ports (1 to 65,535):
  
== Including a file relative to the including file ==
+
# nmap -p- server.example.com
  
require_once( dirname( __FILE__ ) . '/relative/path/to.php' );
+
== Network monitoring ==
  
== Enabling error reporting ==
+
See [http://www.binarytides.com/linux-commands-monitor-network/ here] for details. Basically:
  
error_reporting( E_ALL | E_STRICT );
+
# Overall bandwidth: nload, bmon, slurm, bwm-ng, cbm, speedometer, netload
ini_set( 'display_errors', 'On' );
+
# Overall bandwidth (batch style output): vnstat, ifstat, dstat, collectl
 +
# Bandwidth per socket connection: iftop, iptraf, tcptrack, pktstat, netwatch, trafshow
 +
# Bandwidth per process: nethogs
  
== Setting an error handler ==
+
== nload ==
  
set_error_handler( "error_handler", E_ALL | E_STRICT );
+
You can watch network traffic in real-time with nload:
  
  function error_handler( $error_code, $error_message, $error_file, $error_line, $error_context ) {
+
  # nload -u M
  // ...
 
}
 
  
== Disable HTML content in var_dump ==
+
== Reporting network (NIC) speed ==
  
ini_set( 'html_errors', 'off' );
+
From [https://askubuntu.com/questions/431911/how-can-i-verify-the-speed-of-my-nic-in-ubuntu#431912 here]:
  
= BASH scripting =
+
# dmesg | grep eth0
 +
# mii-tool -v eth0
 +
# ethtool eth0
  
For a primer on bash scripting see [http://www.progsoc.org/tfm/tfm03/node37.html TFM: Erotic Fantasy: /bin/sh Programming].
+
Note: use ifconfig to get device name.
  
== Telling a script to run in bash ==
+
== Path MTU discovery ==
  
The first line of the file should be:
+
To do a [https://en.wikipedia.org/wiki/Path_MTU_Discovery Path MTU Discovery], from the iputils-tracepath package:
  
  #!/bin/bash
+
  # tracepath host.example.com
  
== Checking if a command-line argument was passed in ==
+
== Listing available Ethernet devices ==
  
if [ -n "$1" ]; then
+
To see a list of NICs available on the host:
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking if a command-line argument was not passed in ==
+
$ cat /proc/net/dev
  
if [ "$1" = "" ]; then
+
Also
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
Or:
+
$ ip link
  
if [ -z "$1" ]; then
+
== 59 Linux Networking commands and scripts ==
  echo "Missing parameter 1.";
 
  exit 1;
 
fi
 
  
== Checking command exit status ==
+
See [https://haydenjames.io/linux-networking-commands-scripts/ 59 Linux Networking commands and scripts].
  
cd /my/path
+
== Links ==
if [ "$?" -ne "0" ]; then
+
 
  echo "Cannot change dir.";
+
* [http://www.cyberciti.biz/faq/linux-unix-open-ports/ HowTo: UNIX / Linux Open TCP / UDP Ports]
  exit 1;
 
fi
 
  
== Checking if a file does/doesn't exist ==
+
= IPTables =
  
Check if file exists:
+
== Applying firewall rules ==
  
if [ -f "/my/file" ]; then
+
For configuration info see [http://articles.slicehost.com/2008/4/25/ubuntu-hardy-setup-page-1 this article].
  cat /my/file
 
fi
 
  
Check if file doesn't exist:
+
$ 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
  
if [ ! -f "/my/file" ]; then
+
== Blocking an IP address with iptables ==
  touch /my/file
 
fi
 
  
== Checking if a directory does/doesn't exist ==
+
To drop IP address 1.2.3.4:
  
Check if directory exists:
+
# iptables -A INPUT -s 1.2.3.4 -j DROP
  
if [ -d "/my/dir" ]; then
+
= ufw =
  rmdir /my/dir
 
fi
 
  
Check if directory doesn't exist:
+
== Denying hosts with ufw ==
  
if [ ! -d "/my/dir" ]; then
+
See [[Admin_reference#Denying_hosts_with_UFW|denying hosts with ufw]].
  mkdir /my/dir
 
fi
 
  
== Deleting old backups ==
+
= Bind9 =
  
To keep only the latest five backups:
+
== Viewing Bind9 querylog ==
  
  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
+
  $ sudo rndc querylog
 +
$ tail -f /var/log/syslog
  
This script stolen from [http://stackoverflow.com/questions/25785/delete-all-but-the-most-recent-x-files-in-bash stackoverflow].
+
= IPSec =
  
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.
+
== Disabling IPSec ==
  
== Changing into the script's directory ==
+
# setkey -FP
  
cd "`dirname $0`"
+
= OpenSSL =
  
== Getting the absolute path of a relative path ==
+
== Debugging IMAPS with OpenSSL ==
  
  readlink -f ./some/path
+
  # openssl s_client -connect localhost:993
 +
> a1 LOGIN username@host password
 +
> a2 LOGOUT
  
== Creating a temp directory ==
+
== Debugging HTTPS with OpenSSL ==
  
  dir=`mktemp -d` && cd $dir
+
  $ openssl s_client -connect www.example.com:443
 +
GET /example.html HTTP/1.1
 +
host: www.example.com
  
== Reading secret input from stdin ==
+
== Links ==
  
You can read a secret, such as a password, like this:
+
* [http://www.madboa.com/geek/openssl/ OpenSSL Command-Line HOWTO]
  
echo -n "Enter passphrase: "
+
= Pluggable Authentication Modules (PAM) =
stty -echo
 
read passphrase;
 
stty echo
 
echo ""
 
  
After running the above the secret will be in the $passphrase environment variable.
+
== Links ==
  
== String replacements in bash ==
+
* [http://www.centos.org/docs/5/html/Deployment_Guide-en-US/ch-pam.html 42.4. Pluggable Authentication Modules (PAM)]
  
See the [http://www.tldp.org/LDP/abs/html/string-manipulation.html string manipulation] doco. Basically, to replace first occurrence:
+
= SSH =
  
result=${var/find/replace}
+
== Configuring SSH key login ==
  
To replace all occurrences:
+
On the client machine generate a key-pair (if necessary, check for existing ~/.ssh/id_rsa.pub):
  
  result=${var//find/replace}
+
  $ ssh-keygen -t rsa
  
A practical example, get an ISO date and turn it into a path:
+
Copy the public key from the client to the server:
  
  date="$(date +%Y-%m-%d)"
+
  $ scp ~/.ssh/id_rsa.pub user@example.org:
work_dir=${date//-//}
 
  
== Sending a HEREDOC to a file ==
+
Configure the authorized keys on the server:
  
  cat << EOF > /tmp/yourfilehere
+
  $ ssh user@example.org
  These contents will be written to the file.
+
$ mkdir ~/.ssh
        This line is indented.
+
$ chmod go-w .ssh
EOF
+
$ cat ~/id_rsa.pub >> ~/.ssh/authorized_keys
 +
  $ chmod 600 ~/.ssh/authorized_keys
 +
$ rm ~/id_rsa.pub
  
[[Category: Help]]
+
== Tunneling over SSH ==
  
= Sed =
+
For example, connecting a remote MySQL server to the localhost:
  
== Find and replace with sed ==
+
$ ssh -L 3306:localhost:3306 jselliot@ssh.progsoc.org
  
To update the current file use '-i'. E.g.:
+
If the machine you want to connect to is not the localhost of the machine you're ssh'ing to,
  
sed -i 's/search-text/replace-text/' file
+
  $ ssh -L 3306:muspell.progsoc.uts.edu.au:3306 ssh.progsoc.uts.edu.au
  
= Awk =
+
The -L stanza is localport:remotehost:remoteport where localport is a
 +
port on your machine, forwarded to remoteport on remotehost.
  
== Listing IP addresses in an Apache web log ==
+
== Tunneling over SSH with PuTTY ==
  
awk '/GET \/path\/for\/url/ { print $1 }' /var/log/apache2/access.log | sort | uniq
+
See [http://www.anchor.com.au/hosting/support/MySQL/Connecting_to_mysql_remotely Connecting to the MySQL database remotely (via an SSH Tunnel)]
  
== Printing space-separated field ==
+
* run putty.exe
 +
* Connection -> SSH -> Tunnels
 +
** Port forwarding: source port to 3306
 +
** destination: 127.0.0.1:3306
 +
** check Local
 +
** click Add
  
echo 'no no yes no' | awk '{print $3}'
+
== Enabling verbose SSH logging ==
  
== Printing delimited field ==
+
To see what's going on with your ssh connections,
  
  echo 'no:no:yes:no' | awk -F ':' '{print $3}'
+
  $ ssh -v user@host
  
= Subversion =
+
Or
  
== Setting svn:externals from the command-line ==
+
$ ssh -vv user@host
  
See [http://beerpla.net/2009/06/20/how-to-properly-set-svn-svnexternals-property-in-svn-command-line/ here].
+
== Unlocking SSH key for session ==
  
To set an svn:externals from the command-line:
+
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'
  
svn propset svn:externals 'rdfind-php https://www.progclub.org/svn/pcrepo/rdfind.php/branches/0.1' .
+
== Links ==
svn ci -m 'Adding svn:externals for rdfind-php...'
 
svn up
 
  
Or to use a file:
+
* [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]
  
svn propset svn:externals -F svn.externals .
+
= Standard IO =
  
== Setting svn:ignore from the command line ==
+
== cat EOF ==
  
See [http://tedone.typepad.com/blog/2010/03/setting-svnignore-from-the-command-line.html here].
+
$ cat > output <<EOF
 +
> text
 +
> EOF
  
  $ svn propset svn:ignore [file|folder] [path]
+
  $ cat output
 +
text
  
Or use a file and apply recursively:
+
= Script =
  
$ svn propset svn:ignore -RF ./svn-ignore-list.txt .
+
== Creating a session log with script ==
  
= Git =
+
$ script -t 2> timing
  
== Showing status of working copy ==
+
The session log is in the file 'typescript' and the timing data is in 'timing'.
  
git status
+
== Replaying a scripted session ==
  
== Showing repo history ==
+
$ scriptreplay timing
  
git log
+
Uses the default file 'typescript' and the 'timing' file as specified.
  
== Showing remote repositories (including 'origin') ==
+
= Screen =
  
git remote -v
+
== Creating a new screen or reconnecting to a detached screen ==
  
== Handy git aliases ==
+
$ screen -R
  
Save these to your ~/.gitconfig file.
+
== Detaching a screen ==
  
For a nicer view of history than standard 'git log' -- colourful, one-line-per commit, etc:
+
$ screen -D
  
  graph = !git log --all --graph --color --abbrev-commit --pretty=oneline
+
== Reconnecting to screen ==
  
To show only the files that have changed, rather than the full line-by-line content:
+
$ screen -D
 +
$ screen -R
  
  dif  = !git diff --name-status
+
I have a script in ~/bin/reconnect like so,
  
= IRC =
+
#!/bin/bash
 +
screen -D
 +
screen -R
  
== Instructing ChanServ to op an admin ==
+
This will detach your last screen, and reconnect it on the current terminal.
  
/msg ChanServ op #channel user
+
== Scrolling in screen ==
  
E.g.
+
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.
  
/msg ChanServ op #gnurc jj5
+
= tmux =
  
Sub 'op' for 'deop' to remove op privilege.
+
== Live collaboration with tmux ==
 +
 
 +
User A:
 +
 
 +
tmux -S /tmp/collab
 +
chmod 777 /tmp/collab
  
= C++ =
+
User B:
  
== C++ books ==
+
tmux -S /tmp/collab attach
  
=== Books I want ===
+
= Vim =
  
* [http://smile.amazon.com/dp/1785283073 Boost.Asio C++ Network Programming 2ed]
+
== First, why Vim? ==
* [http://smile.amazon.com/dp/1783986549 Boost.Asio C++ Network Programming Cookbook]
 
  
* [http://www.amazon.com/dp/020170353X Accelerated C++] by Andrew Koening
+
Read [http://www.viemu.com/a-why-vi-vim.html Why, oh WHY, do those #?@! nutheads use vi?]
* [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 ===
+
== Visual modes ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 4ed] by Bjarne Stroustrup
+
Use 'v' for visual mode, 'V' for visual line mode and Ctrl+V for visual block mode.
* [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 ===
+
== Configuring spaces instead of tabs ==
  
* [http://www.amazon.com/dp/0321563840 The C++ Programming Language 3ed] by Bjarne Stroustrup &#x2713;
+
I use two spaces instead of tabs. To configure, edit your .vimrc file:
** Note: 3ed is obsolete. Buy 4ed (above).
 
  
=== Books I've read ===
+
$ vim ~/.vimrc
  
* [http://www.amazon.com/dp/0596004966 C++ Pocket Reference] by Kyle Loudon &#x2713;
+
and include the following lines:
  
== C++ blogs/articles ==
+
set tabstop=2
 +
set shiftwidth=2
 +
set expandtab
  
* [http://blogs.msdn.com/b/hsutter/ Herb Sutter's MSDN blog]
+
== Configuring syntax highlighting ==
* [http://herbsutter.com/ Herb Sutter's personal blog]
 
* [http://herbsutter.com/gotw/ Herb Sutter's Guru of the Week (GotW)] updated from [http://gotw.ca/gotw/ gotw.ca]
 
  
== C++ performance tips ==
+
See [http://www.cyberciti.biz/faq/turn-on-or-off-color-syntax-highlighting-in-vi-or-vim/ here].
  
* ++c can be faster than c++.
+
Use:
* 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 =
+
:syntax on
  
[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.
+
to turn on syntax highlighting.
  
== Following a service log ==
+
Use:
  
e.g. for bind9:
+
:syntax off
  
# journalctl -f -u bind9
+
to turn off syntax highlighting.
  
or for everything:
+
To always use syntax highlighting:
  
  # journalctl -f
+
  $ 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) ==
  
== System status ==
+
:%s/^\s*/&&/g
 +
 
 +
For more information [https://www.progclub.org/blog/2013/08/10/vim-reformat-a-python-file-to-have-4-space-indentations/ 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 [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:
 
To see spawned services hierarchy:
  
  # systemctl status
+
  # systemctl status
 
+
 
Or for a specific service e.g.:
+
Or for a specific service e.g.:
 
+
 
  # systemctl status networking
+
  # systemctl status networking
 
+
 
= SaltStack =
+
= SaltStack =
 
+
 
== Running a command on specified minions ==
+
== Running a command on specified minions ==
 
+
 
  salt 'host' cmd.run 'update-locale'
+
From the salt master:
 
+
 
== Running a command on all minions ==
+
  salt 'host' cmd.run 'update-locale'
 
+
 
  salt '*' cmd.run 'update-locale'
+
From the salt minion:
 
+
 
== Listing active jobs ==
+
salt-call cmd.run 'update-locale'
 
+
 
  salt-run jobs.active
+
== Running a command on all minions ==
 
+
 
== Listing available grains ==
+
  salt '*' cmd.run 'update-locale'
 
+
 
  salt 'example' grains.items
+
== Running a specific state file ==
 +
 
 +
From the salt master:
 +
 
 +
salt $MINION_ID state.sls $STATE_FILE
 +
 
 +
From the salt minion:
 +
 
 +
salt-call state.sls $STATE_FILE
 +
 
 +
== Listing active jobs ==
 +
 
 +
  salt-run jobs.active
 +
 
 +
== Listing available grains ==
 +
 
 +
  salt 'example' grains.items
 +
 
 +
== Listing available pillar ==
 +
 
 +
salt 'example' pillar.items
 +
 
 +
== Reporting a grain value ==
 +
 
 +
e.g. for the 'mem_total' grain:
 +
 
 +
salt '*' grains.item mem_total
 +
 
 +
== Passing a variable into a Jinja template from a salt state (SLS) ==
 +
 
 +
e.g.: to pass 'zabbix_deb_{pkg,url}' variables into the source.txt template:
 +
 
 +
<nowiki>/srv/zabbix/release/{{ zabbix_deb_pkg }}.txt:</nowiki>
 +
  file.managed:
 +
    - template: jinja
 +
    - user: root
 +
    - group: root
 +
    - mode: 644
 +
    - source: salt://file/srv/zabbix/release/source.txt
 +
    - require:
 +
      - file: /srv/zabbix/release
 +
    - default:
 +
      <nowiki>zabbix_deb_pkg: {{ zabbix_deb_pkg }}</nowiki>
 +
      <nowiki>zabbix_deb_url: {{ zabbix_deb_url }}</nowiki>
 +
 
 +
= KDE =
 +
 
 +
== Running user login script (X11/XOrg/XWindows) ==
 +
 
 +
A way to run user login scripts which works for KDE Plasma (and apparently other [https://en.wikipedia.org/wiki/X.Org_Server X.Org Server X Window System] environments) is to create a *.desktop file in ~/.config/autostart/. For example I have a ~/.config/autostart/ssh-add.desktop file with the following contents to register my SSH key in the SSH Agent:
 +
 
 +
[Desktop Entry]
 +
Type=Application
 +
Name=ssh-add
 +
Comment=Adds my private key to my session.
 +
Exec=/usr/bin/konsole -e 'ssh-add /home/$USER/.ssh/id_rsa'
 +
 
 +
== Standard KDE shortcut key bindings ==
 +
 
 +
{|class="wikitable"
 +
! Name          !! Shortcut !! Command
 +
|-
 +
| Insert comment || F1      || xdotool type "$(date +%Y-%m-%d ) $USER - "
 +
|-
 +
| Insert sydtime || F4      || xdotool type "$(date +%Y-%m-%d-%H%M%S)"
 +
|-
 +
| Konsole        || Meta+T  || konsole
 +
|-
 +
| Dolphin        || Meta+E  || dolphin
 +
|-
 +
| Kate          || Ctrl+Shift+F12 || kate
 +
|-
 +
| KCalc          || Ctrl+Shift+F11 || kcalc
 +
|-
 +
| Firefox        || Ctrl+Shift+F10 || firefox
 +
|}
 +
 
 +
== 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 =
  
== Listing available pillar ==
+
== How to pretty-print an XML file ==
  
  salt 'example' pillar.items
+
  $ xmllint --format input.xml > output.xml
  
== Reporting a grain value ==
+
= ApacheBench =
  
e.g. for the 'mem_total' grain:
+
== Run a benchmark with ApacheBench ==
  
  salt '*' grains.item mem_total
+
  $ ab -n 1000 -c 100 https://www.example.com/

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/