Last few month, I’ve been dealing with Linux servers. I had experience with Linux, I even was using Linux distributives as a primary operation system for a few year in the past. But I feel the lack of skill of administration. Here, I’m going to collect all basic commands and command combinations which I use in the day-to-day routine. It’s really difficult to remember all the commands, parameters and keys when you don’t do it every day like a full-time system administrator. This article may be used as a Linux commands cheat sheet.

General shortcuts

  • Ctrl + r commands execution history search.
  • Ctrl + x Ctrl + e opens the current command in editor.
  • Ctrl + a moves cursor to the beginning, Ctrl + e to the end.
  • Alt + moves cursor backward one word.
  • Ctrl + u deletes to the beginning of line.
  • Ctrl + l clears the screen
  • Ctrl + D = exit

General tips

  • cd - - changes directory to the previous one
  • sudo !! - runs previous command with sudo
  • ![command] - runs previous command that starts with [command]
  • [cmd1] ; [cmd2] - executes both commands ignoring result of [cmd1]
  • [cmd1] && [cmd2] executes [cmd2] if [cmd1] is executed without errors
  • [cmd1] || [cmd2] executes [cmd2] if [cmd1] is executed with errors

Output manipulations

  • grep [keyword] - leaves only lines contain keyword, grep -E "[regex]" works with regular expressions
  • awk "{print $1}" - prints the first column of the output
  • awk "{[program]}" - executes Perl-like script
  • sort -bf - sorts output line by line. b - ignore leading blanks, f - ignore case, h - human sort, r - reverse
  • tail [file] - shows the last part of a file. f - monitors a file for updates, -n [N], -[N] - prints last N lines
  • head - opposite to tail

System information

  • lscpu - system specs.
  • lsb_release -a - Ubuntu version information
  • df -h - overall information about filesystems
  • du -hs [path] | sort -hr | head - top 10 biggest directories/files within the path sorted by directory/file size s - displays only total for each directory
  • free -m - current memory usage. m show megabytes, h - human readable.
  • top - displays processes. Sort by: %MEM - Shift + m, %CPU - Shift + p. Shift + e changes units. c toggles between command line and name for processes
  • top -p [PID] - displays information for the specific PID/PIDs
  • ps aux - static version of the top

Archiving

  • tar -zxvf file.tar.gz - extracts tar.gz into current directory. z - gzip, x - extract, v - verbose output, f - work with file (not stdout/stdin)
  • tar -cvzf test.tar.gz ./* - creates tar.gz. c - create a file

SSH

  • ssh-keygen -t rsa - generates key pair
  • cat ~/.ssh/id_rsa.pub | ssh [user@host] "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys" - adds public key to a remote machine. A proper way for linux is ssh-copy-id, but it doesn’t present on MacOS
  • scp [name]@[domain]:[remote path] [local path] or scp [local path] [name]@[domain]:[remote path] - copies file from remote machine to local or vice versa

Network

  • dig [domain] - dns related information
  • nslookup [domain] - translates a domain name to an IP address, nslookup [ip] - vice versa
  • telnet [host] [port] - connects to host:port by TCP
  • iptables -L -n -v - displays status of the firewall. L - list rules, v - verbose, n - shows ip addresses in numeric format
  • nmap -O [host] - shows all open ports on the host

Netstat

Netstat is a command line utility that can show information about network connections in the system.

  • netstat -plunt - show processes that are using ports on the server. u - udp, t - tcp, p - PID and program name, l - only listening, n - numerical addresses
  • netstat -r - shows routing table. See this article to understand the output.
  • netstat -s - statistics

Curl

  • curl -O [url] - downloads file to the current directory
  • curl [url] -F file=@[file path] - uploads file from [file path]
  • curl [url] -X [method] -H [header] -d [data] | python -m json.tool - sends [method] (GET/POST/PUT…) reqest to [url] with headers and [data] body. python -m json.tool formats json (useful tip: alias prettyjson='python -m json.tool')

Misc

Mysql

  • mysqldump -u [uname] -p[pass] [dbname] | gzip -9 > [db.sql.gz] - dumps database to a gzip archive
  • gunzip < db.sql.gz | mysql -u [uname] -p[pass] db - restores database dump from the archive

APT Package management

  • apt-cache search [keyword] - searches package
  • apt-cache show [package name] - retrieves a package description

Docker

  • docker stop $(docker ps -a -q) & docker rm $(docker ps -a -q) - stops and removes all containers, sometimes may require -f to force deletion.
  • docker volume rm $(docker volume ls -qf dangling=true) - removes unused volumes
  • docker rmi $(docker images | grep "^<none>" | awk '{print $3}') - removes untagged images