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An index of useful linux commands to refer back to when you forget
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linux_command_index.md

Customization

Keyboard

Change the layout to suit. List available layouts and options:

more /usr/share/X11/xkb/rules/base.lst

Set the layout:

setxkbmap -layout 'us,us' -option 'ctrl:swap_lalt_lctl'

Prevent gnome from clobbering the changes:

sudo gsettings set org.gnome.settings-daemon.plugins.keyboard active false

Organization

stow will generate symlinks for a given directory tree, thus making it easy to keep files backed-up, managed, etc. https://www.gnu.org/software/stow/

Programming

Create quick and easy GUI widgets from the command line, and use the return to further do other actions...

zenity Is simply awesome! Example - display a prompt with text input, and use the input to populate the clipboard...

zenity --entry | xsel --clipboard
Getting Help
  • man bash - show the manual page for a command
  • tldr tar - show examples of using a commmand
System Information
  • inxi -F - print the detailed system / hardware info
  • whoami - return the current user name
  • uname -a - print out some basic system info (e.g. Kernel version)
  • uptime - show the time the system was up and the load averages
  • lshw - list hardware
  • lsusb - list USB devices
  • lspci - list PCI devices
  • lsblk - list block devices (e.g. disk partitions and loopback devices)
System Monitoring
  • top - show linux processes, cpu utilization, memory usage etc
  • htop - an "improved" version of top
  • glances - an alternative to htop, includes disk and network stats
  • vmstat 1 - print out (every second) the resource utilization in a tabular format
  • free - display the amount of free and used memory
  • iostat 1 - report (every second) read/write and other statistics for devices and partitions
  • s-tui - show graphs of frequency, utilization and temprature of CPU, as well as the power usage
  • sudo powertop - power consumption / power management tool
  • stress -c 4 - run 4 CPU-loading workers (can also stress-test memory, io etc.)
Process / System Management
  • ps aux | grep java - show running java processes
  • pstree - show running prcesses as a tree
  • kill process_id - send a signal for the process to terminate (or kill -9 pid to forcefully terminate the process)
  • crontab -l - list (edit) cron jobs of the current user
  • reboot - signal system to reboot
  • poweroff - signal system to shutdown (works great with Alt+F2 in Cinnamon/Gnome)
Troubleshooting
  • dmesg --level err,warn - show errors/warning in the kernel ring buffer
  • sudo systemctl start|stop|restart|reload docker - start/stop/restart/reload a systemd unit (e.g. docker daemon)
  • sudo service --status-all - show status of all services (can also start/stop/restart/reload individual services)
  • journalctl -b - show all journald messages from this boot
  • strace -f script.py - trace system calls
  • man 2 open - shows a manual for a system call
Package Management
  • dpkg -l - lists all installed packages
  • dpkg -S /usr/bin/ab - shows the package owning a file
  • apt search linux-image-* - searches repos for a package
  • apt policy linux-image-4.13.0-45 - shows repositories that contain the package
Files
  • whereis ls - locate the binary, source, man page for a command
  • ln -s file symlink - create a symbolic link to a file / folder
  • md5sum file.tar.gz - calculate MD5 checksum
  • find ~/Document -name *.sh - find files under the given directory
  • tar xzf source.tar.gz - extract a gzipped archive in the current directory
  • zip -r my.zip ~/Documents - package and compress a directory as a zip file
  • sed -i -e 's/find/replace/g' filename - replaces a string in a file
  • perl -p -i -e 's/find/replace/g' filenames - replaces a string in one or more files
Users & Groups
  • id - print current user and group IDs
  • sudo useradd john - create a new user
  • sudo passwd john - change password of the user (or just passwd for the current user)
  • sudo userdel -r john - remove the user and their home directory
  • sudo groupadd visitor - create a new group (groupdel to delete group)
  • sudo adduser john visitor - add the user to the group
  • w and who - show who is logged in and their activity
  • chmod u+x script.py - make a file executable by the user owning it
  • chown ubuntu:ubuntu ~/Applications - change ownership of a file / directory

Bonus...apply the new group to the user without needing to logout

  • newgrp <groupname>
Disks, Partitions, Mounts
  • df -h - report disk space usage
  • du -sh ~/Documents - estimate file / directory space usage
  • dd if=file.iso of=/dev/usb_drive status=progress - make a bootable usb drive from an isohybrid file
  • findmnt - list (or search in) all mounted file systems
  • mount /dev/sdb2 /media/myusername/usb/ - mount a file system (e.g. usb drive)
  • umount /dev/sdb* - unmount a file system (e.g. usb drive)
  • mkfs.ext4 /dev/sdb2 (and bunch of other mkfs.*) - create a filesystem in a disk partition
  • sudo fdisk -l - list / manipulate disk partitions (using MBR, hence only for <2TB disks)
  • gdisk - GPT fdisk (supports disks >2TB)
  • sudo parted -l - an alternative to fdisk / gdisk
  • rsync - sync files to / from a remote host
SSH & HTTP
  • ssh -L 9999:remote-postgres:5432 bastion-host - connect remotely to servers / create tunnels to access resources from a different network
  • scp myapp.jar remote-server:/tmp/myapp-1.0.jar - copy file(s) securely over SSH
  • wget http://example.com/backup.zip - non-interactive download of files over HTTP(S) and FTP
  • curl -XGET http://example.com/api/v1/user/123 - transfer data over HTTP, FTP and other protocols
  • ab -n 100 url - Apache HTTP server benchmarking tool (WARNING! don't DDoS servers you don't own)
Networking
  • nmcli - a cli tool for controlling NetworkManager
  • ping 8.8.8.8 - test connectity between host and provided IP
  • traceroute 8.8.8.8 or tracepath 8.8.8.8 - trace packets route to a host
  • dig example.com or nslookup example.com - tools for "interrogating" DNS name servers
  • ip address (or now deprecated ifconfig) - show / manipulate network interfaces
  • ip route (or now deprecated route) - show / manipulate the IP routing table
  • ip link set eth0 up/down (ifup/ifdown) - enable / disable a network interface
  • ss -a (or now deprecated netstat) - list open sockets
  • iw (or now deprecated ifconfig) - show / manipulate wireless devices
  • tcpdump -i eth0 port 80 - capture traffic off a network interface
  • tcpflow -c -i eth0 port 80 - capture and save traffic for analysis / debugging
  • nmap - network exploration tool / port scanner
  • nc (or more versatile socat) - listen on / connect to ports, forward data etc.
Shell Tools
  • env - print all environment variables
  • history - print the history of executed commands
  • which - locate a command in $PATH
  • cat args.txt | xargs command - turn each line of input into an argument for a command
  • alias l='ls -l' - create an alias for the command
  • sleep 30 > output.log 2>&1 & - run a command in the background, redirecting its output to a file
  • jobs - list processes started by the current shell (e.g. with & or by pressing Ctrl+Z)
  • fg - run a previously suspended (or started in backgroud) process (spawed by the current shell) in the foreground
  • bg - run a previously suspended process in the background
  • nohup sleep 30 & - allow the process to outline the shell that it was started from (by ignoring HUP signal)
  • time sleep 1 - measure time the command takes to execute
  • watch - run a command repeatedly, monitoring the output
  • cat my.txt | head -n 10 - limit output to first n lines
  • tail -n 10 -f output.log - show last n lines and then keep reading from (following) the file
  • echo "hello" | tee trace.txt - read from std in and write to std out cloning output to a file / another command
  • cat output.log | grep keyword | wc -l - count the number of (lines or words), here only those containing a keyword due to grep
  • vmstat 1 | awk '{print $1}' - use AWK programming language (here used to extract 1st column of a tabular output)
  • cat file.json | jq . - prettify / process JSON

Recipies

Creating a bootable USB stick from .iso file

  • umount /dev/sdb*
  • sudo fdisk -l and figure out how the USB drive is called (e.g. /dev/sdb)
  • sudo mkfs.vfat /dev/sdb -I
  • dd if=~/Documents/ISOs/linuxmint-19-cinnamon-64bit-beta.iso of=/dev/sdb status=progress

Dotfiles & Configs

NOTE: Before Bash executes the dot files mentioned below, it also executes commands from /etc/profile or /etc/bash.bashrc (depends on the type of the shell). You can find more info on this topic in man bash.

  • .bash_profile - is executed (by Bash) for interactive login shells (in my case it simply sources .bashrc)
  • .bashrc - is executed (by Bash) for interactive non-login shells (e.g. the ones started by Tmux, Guake or any other GUI Terminal)
  • .bash_aliases - (at least in my case) is sourced directly by .bashrc, and contains various command aliases / functions
  • .profile - is executed (by Sh, or other shell types if their config is missing) for interactive login shells
  • .inputrc - configuration of GNU readline (I only use it to make Bash auto-completion ignore case)
  • .selected_editor - allows setting the default text editor, which, for example, is opened by crontab -e
  • .gitconfig - global configuration for Git (the version control tools)
  • .npmrc - configuration for npm, NodeJS package manager
  • .tmux.conf - configration for Tmux
  • .ssh/config - configuration for SSH client (allows defining aliases for hosts, keys to be used for each server etc.)
  • .gnupg/gpg.conf - gpg/gpg2 configuration
  • .gnupg/gpg-agent.conf - gpg agent configuration (if you are using gpg-agent instead of ssh-agent)

Filesystem

  • ~/.xsession-errors - error log produced by X server (look here if you have troubles logging into the system)

  • ~/.local/share/applications/ - stores user-specific desktop files (place your custom desktop files here)

  • /usr/lib/jvm/ - directory where apt / dpkg will install Java

  • /var/log - contains logs generated by the OS and other apps

Appendix A: Repos / PPAs

In order to be able to install and/or get the latest version of the following software, add the repos mentioned below:

  • TLP
sudo add-apt-repository ppa:linrunner/tlp
  • Yubikey Tools
sudo add-apt-repository ppa:yubico/stable
  • Vivaldi
echo "deb http://repo.vivaldi.com/stable/deb/ stable main" | sudo tee /etc/apt/sources.list.d/vivaldi.list > /dev/null
wget -q -O - http://repo.vivaldi.com/stable/linux_signing_key.pub | sudo apt-key add -
  • Chrome
echo "deb [arch=amd64] http://dl.google.com/linux/chrome/deb/ stable main" | sudo tee /etc/apt/sources.list.d/google-chrome.list > /dev/null
wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -

Depending on your Linux distro, you might also want to add more repos to be able to use the latest versions of the following: Docker, NodeJS, Postgres etc.

Appendix B: Software Checklist

  • apt install guake - Guake - a dropdown terminal that can be shown / hidden with a shortcut

  • apt install tmux - Tmux, a terminal multiplexer, e.g. allows splitting your terminal into panes

  • apt install vim-gnome - Vim, a version of Vim that allows yanking/pasting to/from the clipboard ("+y/"+p)

  • apt install direnv - Direnv, unclutter your .bashrc by moving environment vars to individual .envrc files

  • apt install docker.io - Docker, software for running containers i.e. the lightweight VMs

  • apt install vivaldi-stable - Vivaldi, a browser that supports grouping multiple web pages in a single tab

  • apt install google-chrome-stable - Google Chrome, a free web browser from Google, IMO a bit more stable than Chromium

  • apt install tlp tlp-rdw - TLP, a Linux power management tool, must-have on laptops

  • apt install nodejs - Node.js, a javascript runtime, brings npm on board

  • apt install snapd - Snappy, a cross-distro package manager developed by Canonical

  • apt install yubioath-desktop yubikey-neo-manager yubikey-personalization-gui - Yubikey Authenticator, Yubikey Neo Manager, Yubikey Personalization Tool, all needed, one way or another, in case if you are using Yubikeys

  • apt install virtualbox virtualbox-qt - VirtualBox, software for running VMs

  • apt install vagrant - Vagrant, a tool for managing development environments, requires VirtualBox or an alternative

  • apt install wireshark-qt - Wireshark, a GUI for wireshark packet analyzer

  • snap install skype - Skype, a text/voice/video chat app pwned owned by Microsoft

  • snap install slack - Slack, a team colaboration tool, i.e. a text chat on steroids

  • snap install spotify - Spotify, a music streaming app by Spotify

  • snap install intellij-idea-ultimate- Intellij IDEA, possibly the best IDE for developing any app that is JVM-based, there is also a free community edition with less features

  • snap install bitwarden - BitWarden, an open source password manager done right (at least from the user perspective)

  • pip install --user s-tui - S-TUI, a cli tool that graps cpu freq, utilization and temperature over time

  • npm install -g tldr - TLDR, a great collection of simplified man pages, first stop for help on any terminal command

To use some of the commands from this reference, you will need to install the following packages: apt install htop powertop glances jq apache2-utils

TODO Check if there are more packages I need to include. Also, try using flatpak instead of snapd, at least for deps that can be installed from flathub.

TODO Add to the list: docker-compose, kubectl, aws cli, sdkman

Appendix C: Useful Links

After I had almost finished compiling my list of commands, I actually discovered at least a couple of vastly overlapping Terminal references, which you might also want to check out (see the links below).

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