Ubuntu Terminal Commands

Introduction

The terminal is a text window into a shell — a program (on Ubuntu, usually bash) that reads the commands you type, runs them, and prints the result. Everything below is a command you type at the prompt and press Enter.
A few conventions used on this page:

<placeholder> means "replace this with your own value", e.g. <file> → notes.txt.
Commands are grouped from beginner (navigation, files) to advanced (services, scheduling, SSH keys). You don't need to read it in order — jump to the section you need from the top or the right-hand outline.
Most commands here work on any Linux distribution; a few (like apt) are specific to Ubuntu/Debian.

man <command> || opens the manual page for <command> — the single most useful command on this page when you forget a flag | 'in1'

<command> --help || prints a short usage summary for most commands, without opening the full manual | 'in2'

clear || clears the terminal screen (or ctrl+l) | 'in3'

Navigation

pwd || prints the full path of the current directory (print working directory) | 'nav1'

ls || lists files and directories in the current directory | 'nav2'

ls -la || lists all files (including hidden dotfiles) in long format: permissions, owner, size, date | 'nav3'

ls -lh || long format with human-readable sizes (KB/MB/GB instead of bytes) | 'nav4'

cd <directory> || changes into <directory> | 'nav5'

cd .. || moves one directory up | 'nav6'

cd - || jumps back to the previous directory you were in | 'nav7'

cd || jumps to your home directory (same as cd ~) | 'nav8'

tree || shows the directory structure as a tree (install with sudo apt install tree) | 'nav9'

pushd <directory> / popd || pushes the current directory on a stack and jumps to <directory>, then pops back later — handy for bouncing between two directories | 'nav10'

Files & directories

touch <file> || creates an empty file, or updates its modified time if it already exists | 'file1'

mkdir <dir> || creates a new directory | 'file2'

mkdir -p <a/b/c> || creates nested directories in one go, without erroring if some already exist | 'file3'

cp <source> <dest> || copies a file | 'file4'

cp -r <source_dir> <dest_dir> || copies a directory recursively | 'file5'

mv <source> <dest> || moves or renames a file or directory | 'file6'

rm <file> || deletes a file (no trash bin — this is permanent) | 'file7'

rm -r <dir> || deletes a directory and everything in it, recursively | 'file8'

rm -rf <dir> || same as -r, but never prompts and ignores missing files — the classic "measure twice" command | 'file9'

rmdir <dir> || removes a directory, but only if it's empty | 'file10'

ln -s <target> <link_name> || creates a symbolic link (a pointer to another file/dir, like a shortcut) | 'file11'

cat <file1> <file2> > <merged> || concatenates files together into a new file | 'file12'

Viewing & searching text

cat <file> || prints the whole file to the terminal | 'view1'

less <file> || opens the file for scrollable, searchable reading (q to quit, / to search) | 'view2'

head <file> || prints the first 10 lines of a file | 'view3'

tail <file> || prints the last 10 lines of a file | 'view4'

tail -f <file> || follows a file live as new lines are appended — the standard way to watch a log file | 'view5'

grep <pattern> <file> || prints lines in <file> matching <pattern> | 'view6'

grep -r <pattern> <dir> || searches for <pattern> recursively through every file in <dir> | 'view7'

grep -ri <pattern> <dir> || same as above, case-insensitive | 'view8'

wc -l <file> || counts the number of lines in a file | 'view9'

sort <file> || sorts the lines of a file alphabetically | 'view10'

sort -n <file> || sorts lines numerically instead of alphabetically | 'view11'

uniq || removes consecutive duplicate lines (usually piped after sort) | 'view12'

diff <file1> <file2> || shows the line-by-line differences between two files | 'view13'

sed 's/<old>/<new>/g' <file> || stream-edits a file, replacing every <old> with <new> | 'view14'

awk '{print $1}' <file> || prints the first whitespace-separated column of each line — awk is a full text-processing language, this is its most common use | 'view15'

Pipes, redirection & search

The terminal's real power comes from chaining small commands together instead of memorizing big ones.

<cmd1> | <cmd2>

pipes the output of <cmd1> into the input of <cmd2>, e.g. ls -la | grep .conf

<cmd> > <file> || redirects <cmd>'s output into <file>, overwriting it | 'pipe2'

<cmd> >> <file> || redirects <cmd>'s output into <file>, appending instead of overwriting | 'pipe3'

<cmd> < <file> || feeds <file> in as <cmd>'s input | 'pipe4'

<cmd1> && <cmd2> || runs <cmd2> only if <cmd1> succeeded | 'pipe5'

<cmd1> ; <cmd2> || runs <cmd2> regardless of whether <cmd1> succeeded | 'pipe6'

find <dir> -name "<pattern>" || finds files/directories under <dir> matching <pattern>, e.g. find . -name "*.py" | 'pipe7'

find <dir> -type f -mtime -1 || finds files under <dir> modified in the last day | 'pipe8'

which <command> || shows the full path of the executable that would run for <command> | 'pipe9'

xargs

builds and runs a command from piped-in input, e.g. find . -name "*.log" | xargs rm

Permissions & ownership

Every file has an owner, a group, and three permission sets (owner/group/others), each with read (r), write (w), and execute (x). ls -l shows them as a string like -rwxr-xr--.

chmod +x <file> || makes <file> executable for everyone | 'perm1'

chmod 755 <file> || sets permissions using octal notation: owner=rwx(7), group=rx(5), others=rx(5) | 'perm2'

chmod 644 <file> || common file permission: owner=rw(6), group=r(4), others=r(4) — no execute | 'perm3'

chown <user>:<group> <file> || changes the owner and group of a file | 'perm4'

chown -R <user>:<group> <dir> || changes ownership recursively for a whole directory | 'perm5'

sudo <command> || runs <command> with administrator (root) privileges | 'perm6'

sudo -i || opens a root shell (use with care) | 'perm7'

Package management (apt)

sudo apt update || refreshes the local list of available packages and versions (run this before installing anything) | 'pkg1'

sudo apt upgrade || upgrades all installed packages to their latest available version | 'pkg2'

sudo apt install <package> || installs a package | 'pkg3'

sudo apt remove <package> || uninstalls a package, keeping its configuration files | 'pkg4'

sudo apt purge <package> || uninstalls a package and its configuration files | 'pkg5'

sudo apt autoremove || removes packages that were installed as dependencies and are no longer needed | 'pkg6'

apt search <term> || searches package names and descriptions for <term> | 'pkg7'

apt show <package> || shows details about a package: version, size, dependencies | 'pkg8'

dpkg -l || lists all packages currently installed on the system | 'pkg9'

Processes & jobs

ps aux || lists all running processes on the system, with owner, CPU, and memory usage | 'proc1'

top || live, auto-refreshing view of running processes sorted by resource usage (q to quit) | 'proc2'

htop || a friendlier, colorized version of top (install with sudo apt install htop) | 'proc3'

kill <pid> || asks the process with ID <pid> to terminate gracefully | 'proc4'

kill -9 <pid> || force-kills a process immediately, no cleanup — last resort | 'proc5'

pkill <name> || kills all processes whose name matches <name>, without needing the PID | 'proc6'

<command> & || runs <command> in the background, freeing up the terminal | 'proc7'

jobs || lists background jobs started in the current terminal session | 'proc8'

fg / bg || brings a background job to the foreground, or resumes a stopped job in the background | 'proc9'

nohup <command> & || runs <command> in the background so it keeps running after you log out (output goes to nohup.out) | 'proc10'

ctrl+c || interrupts (stops) the currently running foreground command | 'proc11'

ctrl+z || suspends the currently running foreground command (resume with fg) | 'proc12'

System & disk info

uname -a || prints kernel name, version, and architecture | 'sys1'

lsb_release -a || prints the Ubuntu release name and version | 'sys2'

df -h || shows disk space usage for all mounted filesystems, in human-readable form | 'sys3'

du -sh <dir> || shows the total size of <dir>, human-readable | 'sys4'

du -sh * | sort -h

shows the size of every item in the current directory, sorted smallest to largest

free -h || shows RAM and swap usage, human-readable | 'sys6'

lsblk || lists block devices (disks and partitions) as a tree | 'sys7'

uptime || shows how long the system has been running and the load average | 'sys8'

whoami || prints the current username | 'sys9'

id || prints the current user's UID, GID, and group memberships | 'sys10'

Networking

ip a || lists network interfaces and their IP addresses (modern replacement for ifconfig) | 'net1'

ping <host> || sends repeated packets to <host> to test connectivity/latency (ctrl+c to stop) | 'net2'

curl <url> || fetches a URL and prints the response body to the terminal | 'net3'

curl -O <url> || downloads the URL's content to a local file with the same name | 'net4'

wget <url> || downloads a file from <url> to the current directory | 'net5'

ssh <user>@<host> || opens a secure shell session on a remote machine | 'net6'

scp <file> <user>@<host>:<path> || copies <file> to <path> on a remote machine over SSH | 'net7'

rsync -avz <source> <dest> || syncs files/directories, only transferring what changed — the robust way to copy large trees, local or remote | 'net8'

ss -tulpn || lists listening network ports and the process using each one (modern replacement for netstat) | 'net9'

Archives & compression

tar -czvf <archive.tar.gz> <dir> || creates a compressed tarball from <dir> | 'arc1'

tar -xzvf <archive.tar.gz> || extracts a .tar.gz archive into the current directory | 'arc2'

tar -tvf <archive.tar> || lists the contents of a tar archive without extracting it | 'arc3'

zip -r <archive.zip> <dir> || creates a .zip archive from <dir> | 'arc4'

unzip <archive.zip> || extracts a .zip archive into the current directory | 'arc5'

Environment, shell config & aliases

bash reads ~/.bashrc every time you open a new terminal — it's the place to put aliases, environment variables, and prompt customizations you want to persist.

echo $<VAR> || prints the value of environment variable <VAR>, e.g. echo $PATH | 'env1'

export <VAR>=<value> || sets an environment variable for the current shell session (and anything launched from it) | 'env2'

env || lists all environment variables currently set | 'env3'

alias <name>='<command>' || creates a shortcut <name> for a longer <command>, e.g. alias ll='ls -la' | 'env4'

source ~/.bashrc || reloads your shell config file without opening a new terminal | 'env5'

history || lists previously run commands, numbered | 'env6'

!<n> || re-runs command number <n> from history | 'env7'

ctrl+r || searches command history interactively as you type | 'env8'

!! || re-runs the last command (common pattern: sudo !!) | 'env9'

Users & system administration

sudo adduser <username> || creates a new user account, interactively | 'user1'

sudo passwd <username> || sets or changes a user's password | 'user2'

sudo usermod -aG <group> <username> || adds <username> to <group> (e.g. sudo, docker) without removing existing groups | 'user3'

su - <username> || switches to another user's shell and environment | 'user4'

groups || lists the groups the current user belongs to | 'user5'

Advanced: services, scheduling & SSH keys

systemctl status <service> | https://www.freedesktop.org/software/systemd/man/systemctl.html | shows whether a system service is running, and its recent log lines | 'adv1'

sudo systemctl start <service> || starts a system service | 'adv2'

sudo systemctl enable <service> || makes a service start automatically on boot | 'adv3'

journalctl -u <service> -f || follows the live logs for a systemd service | 'adv4'

crontab -e || opens your personal cron table for editing, to schedule recurring commands | 'adv5'

crontab -l || lists your currently scheduled cron jobs | 'adv6'

A crontab line has five time fields (minute hour day month weekday) followed by the command, e.g. 0 3 * * * /home/me/backup.sh runs backup.sh every day at 3 AM.

ssh-keygen -t ed25519 -C "<email>" | https://www.ssh.com/academy/ssh/keygen | generates a new SSH key pair for passwordless login | 'adv7'

ssh-copy-id <user>@<host> || copies your public SSH key to a remote host's authorized_keys, enabling passwordless login | 'adv8'

watch -n <seconds> <command> || re-runs <command> every <seconds> and shows the output live, e.g. watch -n 2 df -h | 'adv9'

strace -f -e trace=open,openat <command> || traces the system calls a command makes — useful for debugging "why can't it find this file" | 'adv10'

lsof -i :<port> || shows which process is listening on <port> | 'adv11'

screen -S <name>

starts a named terminal-multiplexer session that survives disconnects (see the tmux page for the more modern alternative)

reference

Ubuntu: Command line for beginners
GNU Bash Reference Manual
explainshell.com — paste a command to see every part explained