Linux Mint via Terminal - Quick Reference

This reference is meant to contain commands and other pieces of info that are hard to keep in mind all the time, but that come in handy every now and then while trying to accomplish tasks in a Linux shell.

If some of the commands mentioned below are not available on your system, you can check my Linux Mint Software Checklist where I have listed all of the packages / software sources I add to a fresh LM installation.

Commands

I assume most Linux users are probably aware of the following commands, and hence I won't be touching on them in this reference: sudo, su, pwd, ls, cd, mkdir, mv, cp, rm, touch, echo, cat, grep, less, view, vim. If you don't know what they do, make sure to check them out before proceeding further (if you need some learning materials, take a look at the links in the end of this document).

Getting Help

• apropos docker - show names / descriptions of man pages matching a keyword
• man bash - show the manual page for a command
• tldr tar - show examples of using a commmand (find out more at tldr.sh)

System Information

• lsb_release -a - print distribution-specific info
• 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)
• ps -p $$ - print out which shell is in use
• uptime - show the time the system was up and the load averages
• date - show the current date and time
• 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.)
• sudo tlp-stat --battery - show the battery charge and capacity

Process / System Management

• ps aux | grep java - show running java processes
• pstree - show running prcesses as a tree
• kill pid - 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 - send the ACPI signal to the system to power down (works great with Alt+F2 in Cinnamon/Gnome)
• halt - terminate all processes and stop all the CPU functions (but leave it powered on)
• shutdown -h now - shut down the system now (similar to poweroff)

Troubleshooting

• dmesg --level err,warn - show errors / warnings 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 tarball in the current directory
• gzip -d source.gz - decompress a gzipped file
• 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 a 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
• finger john - show info about a user

Disks, Partitions, Mounts

• file -s /dev/nvme0n1 - determine file type (especially useful to get info on filesystem types)
• 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
• sync - write all pending writes on all disks (e.g. to make sure dd is finished)
• sync; echo 1 > /proc/sys/vm/drop_caches - clean PageCache (may come in handy when benchmarking)
• 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
• ss -lntup (or sudo netstat -ltup) - list ports that are being listened on & PIDs holding those ports
• lsof -i :8080 - show the process listening on a local port
• 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 packets etc.
• ipcalc 192.168.1.1/24 - calculate details of a given CIDR

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 outlive 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

Special-Purpose Programs

• cal - display a calendar
• bc - start a calculator language interpretor
• startx - initialize an X session (very unlikely that you will ever need to use this command)
• xrandr --output DP-2-2 --same-as eDP-1 - list / manage displays
• update-grub - generate grub config file (delegates to grub-mkconfig)

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

Benchmarking hard drive

• sudo hdparm -Tt /dev/sda - to get the read performance
• ioping -c 10 -s 1M /tmp - to measure latency using 10 requests of 1 megabyte each
• fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=/tmp/random_read_write.fio --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75
• dd if=/dev/zero of=/tmp/output conv=fdatasync bs=384k count=1k; rm -f /tmp/output - to test the write performance

Dotfiles & Configs

NOTE: Before Bash executes the shell-related dot files mentioned below, it also executes commands from /etc/profile or /etc/bash.bashrc (all depending 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
• .xsessionrc - is executed on Debian / Ubuntu / Linux Mint by X startup scripts on a GUI login
• .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)
• .vimrc - configuration for VIM editor (see Example vimrc)

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)
• /etc/fstab - static file system configuration (link to wiki)
• /etc/passwd - a system-wide list of all users, their IDs, home directories etc.
• /etc/group - a system-wide list of all groups (and their members)
• /etc/hostname - contains hostname of the pc
• /etc/hosts - local DNS resolution rules
• /usr/lib/jvm/ - directory where apt / dpkg will install Java
• /var/log - contains logs generated by the OS and other apps

Appendix: Useful Links

A list of links to other similar pages or good reference points for specific topics:

• Bash shortcuts
• Vim shortcuts
• Tmux shotcuts
• Linux Mint Community: Terminal Command Reference
• Linux Commands - A practical reference
• 100 Useful Unit Commands
• Deprecated Linux networking commands
• Advanced Bash-Scripting Guide
• Bash scripting cheatsheet
• Guide to using YubiKey as a SmartCard for GPG and SSH
• Linux DD Command - 15 Examples with All Options