Files/Directories

• rm [file/dir] — remove a file or a dir
  • -r — delete recursively, also to delete directories
  • -f — force-delete
• cp [source] [target] — copy files/directories
  • -r — copy recursively
  • -i — show notification on conflicts
  • -n — don’t overwrite
• mv [source] [destination] — move files/directories
• scp -P [port] [user]@[hostname]:[source] [target] — copy files/directories
• rsync -a --stats [source] [target] — copy files/directories with ability to resume and mirror
• rsync -a --stats --delete -P [source] [target] — copy files/directories with ability to resume and delete files in destination that are not in the source.
• rsync --rsync-path="sudo rsync" [source] [target] — copy files/directories with sudo
• tar -cvzf [archive.tar.gz] [file/dir] — archive a file/dir

Directories

• ls — list current directory contents
  • -h — show file size in Kb/Mb
  • -l — show extended information
  • -a — show hidden files
  • -t — sort by date
  • -S — sort by size
• ls [dir] — list dir contents
• cd [dir] — switch to dir
• mkdir [dir] — create dir
• pwd — show current directory
• du -sh [dir] — show dir size
• du -hsx * | sort -rh | head -10 — show 10 biggest files/directories in the current directory
• ncdu — show the size of directories and files graphically

Files

• ln -s [file] [link-file] — create a symbolic link (need to use full paths)
• cat [file] — print file contents
• cat > [file] — create file. After entering the command, enter the file content and press [Ctrl + D].
• more [file] — show file contents with ability to browse through the file
• head [file] — get the file header
  • -n [x] — show x number of lines
• tail [file] — get the file tail
  • -n [x] — show x number of lines
  • -f — auto-update
• touch [file] — create an empty file
• sed -i 's/[old-text]/[new-text]/g' [file] — replace text in a file
• sed -i '/^$/d' [file] — remove empty lines in a file
• grep -v [text] [file] > [file2] — remove lines containing text in a file and save to file2
• truncate -s 0 [file] — truncate a file to 0 bytes

Text

• echo [text] — print text
• echo [text] | awk '{ print $1 }' — print first column of text

Processes

• ps — show running processes
  • ps aux — show running processes in more detail. See What does aux mean in “ps aux”? for more details
• kill [PID] — kill process with PID (soft)
  • -9 — kill process with PID (hard)

Access Rights

For all of the chrgrp and chown commands below: -r — recursive change.

• chgrp [group] [file/dir] — change group for a file/dir
• chown [user]:[group] [file/dir] — change file/dir’s group and owner
• chown [user] [file/dir] — change file/dir’s owner
• chmod [ABC] [file/dir] — change file/dir’s mode bits to ABC (example — 644)
• find [path] -type d -exec chmod [ABC] {} \; — set ABC permissions for all directories in path recursively
• find [path] -type f -exec chmod [ABC] {} \; — set ABC permissions for all files in path recursively

Search

• grep [text] [file/dir] — search for text
  • -r — recursive search
  • -i — case insensitive search
  • -I — ignore binary files
• Search files using locate
  • locate [file] — locate a file
  • sudo updatedb — update the search index
• find [dir] -name "[mask]" -type f — list files in a dir recursively. mask can be *.* for example
  • -delete — remove the found files
• find . -type f -exec cat {} + — output contents of all files in the current directory recursively

Device Mounting

• mount [device] [dir] — mount a device to a dir
• umount [device] — unmount a device
• umount [dir] — unmount a dir

Network

• netstat -peanut — show open ports
• netstat -peanut | grep ":[port]" — find process which uses port
• nc -zv [host] [port] — check connection to a host:port

Administration

• sudo [program] — run program with root privileges
  • sudo su — switch to user root
  • sudo su [user] — switch to the user
• sudo shutdown now/sudo init 0 — shutdown
• sudo reboot — reboot
• df -h — show disk space
• free -h — show RAM utilization
• uname -a — show information about the installed version of Linux
• sudo hostname your-new-name — change the hostname. Permanent value is in /etc/hostname
• journalctl -S [date-time1] -U [date-time2] — show journal records from date-time1 until date-time2. Where date-time format is like this: 2022-01-0100:00:00

User Administration

• sudo useradd [user] -m — create a user and a home directory
• sudo userdel [user] — delete a user
• sudo passwd [user] — change user’s password

Package Management (Debian)

• sudo dpkg -i [package] — install a package
• sudo apt — package manager
  • install [package] — install a package
  • remove --purge [package] — remove a package
  • update — update the list of available packages
  • upgrade — upgrade installed packages
  • autoremove — remove unused packages
• sudo add-apt-repository ppa:[user]/[name] — add apt sources.list entries
• sudo add-apt-repository ppa:[user]/[name] --remove — remove apt sources.list entries

Fedora

• sudo systemctl restart chronyd — sync date & time
• sudo rpm -i [file] — install rpm package

Ubuntu/Debian

• lsb_release -a — show Ubuntu information
• sudo /usr/sbin/ntpdate ntp.ubuntu.com — synchronize date and time

Variables

• VAR="123" — define a variable
• export VAR — export a variable
• unset VAR — unset a variable

HTTP

• curl [url] — send a GET request
  • -d — send data
  • -H — add header
  • -I — get headers only
  • -X POST — send a POST request
  • --resolve [domain]:[port]:[ip] [scheme]://[domain] — send a request with specified domain resolution

Patches

• diff [old-file] [new-file] > [patch] — create a patch
• patch [old-file] [patch] — apply a patch

Conversion

• yq eval -j [file-yaml] > [file-json] — convert a YAML file file-yaml to a JSON file file-json.
• cat [file-json] | yq e -P - > [file-yaml] — convert a JSON file file-json to a YAML file file-yaml.

Miscellaneous

• wget [file-url] — download a file
• watch [command] — watch changes of the command continuously
  • watch '[command1] | [command2]' — watch changes of the command continuously when using pipes
• man [program] — get program’s manual
• date — show current date and time
  • date [format] — show date in a specified format. Format can be +%d-%m-%Y for example
  • date -d "yesterday" — get yesterday’s day
• time [program] — show how long a program is running
• sleep [x] — wait for x seconds
• pwgen -ys 15 1 — generate password
• screen — screen manager
  • -r — restore screen
• ssh [user]@[ip] — connect to an ip with user through SSH
  • -i [key] — connect with key
• timedatectl — find the current time sync status
• [command] 2>[file] — redirect error output to file. Example - file = /dev/null