Linux Commands Cheatsheet

# structure:
# command  -flag  argument

# 𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖
# list files in a folder
ls -l /home

# command = ls
# flag    = -l  (long format)
# argument= /home  (the folder)

# 𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖𝄖
# copy a file
cp -r myfolder/ backup/

# command  = cp
# flag     = -r  (recursive)
# arguments= myfolder/  backup/

# short help — fits on one screen
ls --help

# full manual page
# press q to quit
man ls

# search inside man page
# press / then type your search word
man grep

# if you only remember part of a command name
apropos "copy file"
# shows all commands related to that topic

# where am I right now?
pwd
# output: /home/alice

# what's in the current folder?
ls

# show hidden files too (files starting with .)
ls -a

# show details: size, permissions, date
ls -l

# combine flags
ls -la

# move into a folder
cd Documents

# move into a nested folder
cd Documents/projects

# absolute path — starts from root /
cd /home/alice/Documents

# relative path — starts from where you are
cd Documents

# go up one folder
cd ..

# go up two folders
cd ../..

# go to your home folder (fastest way)
cd ~
# or just:
cd

# go back to the previous folder
cd -

# combine shortcuts
cd ~/Documents/projects

# see the whole tree from root
ls /

# your personal folder
ls /home/alice

# system config files
ls /etc

# system logs (needs sudo sometimes)
ls /var/log

# where programs are installed
ls /usr/bin

# temporary files (cleared on reboot)
ls /tmp

# create an empty file
touch notes.txt

# create multiple files at once
touch file1.txt file2.txt file3.txt

# create a folder
mkdir projects

# create nested folders in one step
# -p creates parent folders if they don't exist
mkdir -p projects/2024/january

# create a folder and go into it
mkdir my-app && cd my-app

# copy a file
cp notes.txt backup.txt

# copy to a different folder
cp notes.txt ~/Documents/

# copy a folder and everything inside it
# -r means recursive
cp -r projects/ projects-backup/

# move a file to a folder
mv notes.txt ~/Documents/

# rename a file
mv old-name.txt new-name.txt

# move and rename at the same time
mv notes.txt ~/Documents/my-notes.txt

# delete a file
rm notes.txt

# delete multiple files
rm file1.txt file2.txt

# delete a folder and everything inside
rm -r projects/

# ask for confirmation before each delete
rm -ri projects/

# delete an empty folder only
rmdir empty-folder/

# safe habit: check what you're deleting first
ls projects/
# then delete
rm -r projects/

# install first if needed
sudo apt install tree

# show folder structure
tree

# limit to 2 levels deep
tree -L 2

# show hidden files too
tree -a

# show only folders, no files
tree -d

# show a specific folder
tree ~/Documents

# print the whole file
cat notes.txt

# show line numbers
cat -n notes.txt

# scroll through a long file
# press q to quit, / to search
less /var/log/syslog

# first 10 lines
head notes.txt

# first 20 lines
head -n 20 notes.txt

# last 10 lines
tail notes.txt

# watch a log file update live
# Ctrl+C to stop
tail -f /var/log/syslog

# print text to the terminal
echo "Hello, Linux"

# write to a file (overwrites)
echo "Hello" > greetings.txt

# append to a file (keeps existing content)
echo "World" >> greetings.txt

# write multiple lines
echo "line one" > notes.txt
echo "line two" >> notes.txt

# write command output to a file
ls -l > file-list.txt

# append command output to a file
ls -la >> file-list.txt

# open or create a file
nano notes.txt

# nano shows shortcuts at the bottom
# ^ means Ctrl key

# Ctrl+O  → save
# Ctrl+X  → exit
# Ctrl+W  → search
# Ctrl+K  → cut line
# Ctrl+U  → paste line
# Ctrl+G  → help

# open a file and jump to a line
nano +42 notes.txt

# count lines, words, characters
wc notes.txt
# output: 12  45  230  notes.txt
#         lines words chars

# count lines only
wc -l notes.txt

# sort lines alphabetically
sort names.txt

# sort in reverse order
sort -r names.txt

# sort numerically
sort -n numbers.txt

# remove duplicate lines (input must be sorted)
sort names.txt | uniq

# count how many times each line appears
sort names.txt | uniq -c

# find a file by name (case sensitive)
find /home -name "notes.txt"

# case insensitive name search
find /home -iname "notes.txt"

# find all .txt files
find /home -name "*.txt"

# find only folders
find /home -type d -name "projects"

# find only files
find /home -type f -name "*.log"

# find files larger than 100MB
find / -size +100M

# find files changed in the last 7 days
find /home -mtime -7

# find and delete matching files
find /tmp -name "*.tmp" -delete

# search for a word in a file
grep "error" logs.txt

# case insensitive
grep -i "error" logs.txt

# show line numbers
grep -n "error" logs.txt

# search all files in a folder
grep -r "TODO" ~/projects/

# case insensitive + recursive
grep -ri "password" ~/projects/

# show only filenames that match
grep -rl "TODO" ~/projects/

# show lines that do NOT match
grep -v "debug" logs.txt

# search for an exact whole word
grep -w "cat" animals.txt
# won't match "catch" or "scatter"

# count how many lines contain 'error'
grep -i "error" logs.txt | wc -l

# find .txt files then count them
find /home -name "*.txt" | wc -l

# list processes and search for one
ps aux | grep "nginx"

# list files, sort them, show top 5
ls -l | sort -k5 -n | tail -5

# search logs, remove duplicates
grep "ERROR" logs.txt | sort | uniq

# find large files and sort by size
du -h /var/log/* | sort -rh | head -10

# show permissions for all files
ls -l

# example output:
# -rw-r--r-- 1 alice users  420 Jan 5 notes.txt
# drwxr-xr-x 2 alice users 4096 Jan 5 projects/

# breakdown of: -rw-r--r--
# -         = it's a file (d = directory)
# rw-       = owner can read + write
# r--       = group can only read
# r--       = others can only read

# breakdown of: drwxr-xr-x
# d         = it's a directory
# rwx       = owner can read, write, enter
# r-x       = group can read and enter
# r-x       = others can read and enter

# symbolic method
# u=owner, g=group, o=others, a=all
# +=add, -=remove, ==set exactly

# add execute for owner
chmod u+x script.sh

# remove write for group
chmod g-w notes.txt

# set read-only for everyone
chmod a=r notes.txt

# numeric method (most common)
# 7 = rwx (4+2+1)
# 6 = rw- (4+2)
# 5 = r-x (4+1)
# 4 = r-- (4)

# owner=rwx, group=r-x, others=r-x
chmod 755 script.sh

# owner=rw-, group=r--, others=r--
chmod 644 notes.txt

# apply to a whole folder recursively
chmod -R 755 projects/

# change owner of a file
sudo chown alice notes.txt

# change owner and group
sudo chown alice:developers notes.txt

# change only the group
sudo chgrp developers notes.txt

# change owner recursively for a folder
sudo chown -R alice:developers projects/

# check who owns a file
ls -l notes.txt
# output: -rw-r--r-- 1 alice developers ...
#                      ^^^^^  ^^^^^^^^^^
#                      owner  group

# who am I logged in as?
whoami

# full user info: ID, groups
id

# run one command as admin
sudo apt update

# switch to another user
su alice

# switch to root (use carefully)
sudo su

# see who is currently logged in
who

# see login history
last

# create a new user (Ubuntu/Debian)
# asks for password and info interactively
sudo adduser alice

# create user (manual, less friendly)
sudo useradd -m alice

# set or change a password
sudo passwd alice

# delete a user (keeps home folder)
sudo deluser alice

# delete user and their home folder
sudo deluser --remove-home alice

# add user to a group (e.g. sudo group)
sudo usermod -aG sudo alice

# lock a user account
sudo usermod -L alice

# unlock a user account
sudo usermod -U alice

# see which groups you belong to
groups

# see groups for another user
groups alice

# create a new group
sudo groupadd developers

# add a user to a group
sudo usermod -aG developers alice

# remove a user from a group
sudo gpasswd -d alice developers

# delete a group
sudo groupdel developers

# list all groups on the system
cat /etc/group

# snapshot of all running processes
ps aux

# columns: USER  PID  %CPU  %MEM  COMMAND

# find a specific process
ps aux | grep nginx

# live view of processes
# press q to quit
top

# friendlier live view (install if needed)
sudo apt install htop
htop

# show process tree (parent → children)
pstree

# find the PID first
ps aux | grep firefox

# polite stop (process can clean up)
kill 1234

# force stop (immediate, no cleanup)
kill -9 1234

# stop all processes with a name
killall firefox

# stop by name (more flexible)
pkill firefox

# stop by name, force kill
pkill -9 firefox

# run a command in the background
sleep 60 &
# prints: [1] 1234  (job number, PID)

# see all background jobs
jobs

# bring job 1 back to foreground
fg %1

# send current foreground job to background
# first pause it:
# Ctrl+Z
# then resume in background:
bg %1

# run a command that survives logout
nohup long-script.sh &

# check if it's still running
ps aux | grep long-script.sh

# disk space left on all partitions
df -h

# example output:
# Filesystem  Size  Used  Avail  Use%  Mounted on
# /dev/sda1   50G   22G   26G    46%   /

# size of a folder
du -h ~/Documents

# size of every item in a folder
du -h ~/Documents/*

# total size only
du -sh ~/Documents

# find the 10 biggest folders
du -h /var/* | sort -rh | head -10

# RAM usage
free -h
# output: total  used  free  available

# kernel and OS info
uname -a
# shows: kernel version, hostname, architecture

# just the kernel version
uname -r

# how long the system has been running
uptime
# output: 14:32  up 3 days, 2:15, 2 users

# your machine's hostname
hostname

# full system info summary
uname -a

# OS name and version
cat /etc/os-release

# list all storage devices and partitions
lsblk

# example output:
# NAME   SIZE  TYPE  MOUNTPOINT
# sda    500G  disk
# ├─sda1 499G  part  /
# └─sda2   1G  part  [SWAP]
# sdb     32G  disk
# └─sdb1  32G  part  /media/usb

# see currently mounted devices
mount | grep "^/dev"

# mount a USB drive
sudo mount /dev/sdb1 /mnt/usb

# unmount safely before unplugging
sudo umount /mnt/usb

# test if a server is reachable
ping google.com
# Ctrl+C to stop

# ping exactly 4 times
ping -c 4 google.com

# show your IP addresses
ip addr show

# shorter version
ip a

# older command (may need installing)
ifconfig

# download a file
curl -O https://example.com/file.zip

# see response headers only
curl -I https://example.com

# download with wget
wget https://example.com/file.zip

# connect to a remote server
ssh alice@192.168.1.100

# connect with a custom port
ssh -p 2222 alice@192.168.1.100

# connect using an SSH key file
ssh -i ~/.ssh/mykey.pem alice@server.com

# generate an SSH key pair
ssh-keygen -t ed25519 -C "[email protected]"

# copy your public key to a server
# (lets you log in without a password)
ssh-copy-id alice@192.168.1.100

# run one command on remote server
ssh alice@server.com "ls /var/www"

# copy file TO a remote server
scp notes.txt alice@server.com:/home/alice/

# copy file FROM a remote server
scp alice@server.com:/home/alice/notes.txt .

# copy a whole folder
scp -r projects/ alice@server.com:/home/alice/

# rsync — smarter: only copies what changed
rsync -av projects/ alice@server.com:/home/alice/projects/

# rsync flags:
# -a = archive (preserves permissions, dates)
# -v = verbose (show what's being copied)
# -z = compress during transfer
# --delete = remove files on destination
#            that no longer exist on source

# show all listening ports (modern)
ss -tuln

# columns: protocol, local address, port

# show with process names
ss -tulnp

# older command (same purpose)
netstat -tuln

# check if a specific port is in use
ss -tuln | grep :80

# show established connections
ss -tn state established

# refresh the package list
sudo apt update

# install available upgrades
sudo apt upgrade

# install a package
sudo apt install nginx

# install multiple packages
sudo apt install git curl wget

# remove a package
sudo apt remove nginx

# remove package + its config files
sudo apt purge nginx

# remove unused dependencies
sudo apt autoremove

# search for a package
apt search nginx

# show package details
apt show nginx

# install a package (Fedora/RHEL/CentOS)
sudo dnf install nginx

# update all packages
sudo dnf update

# remove a package
sudo dnf remove nginx

# search for a package
dnf search nginx

# show package info
dnf info nginx

# list installed packages
dnf list installed

# older systems: replace dnf with yum
sudo yum install nginx
sudo yum update
sudo yum remove nginx

# snap — works on most distros
# install a snap package
sudo snap install code --classic

# list installed snaps
snap list

# update all snaps
sudo snap refresh

# remove a snap
sudo snap remove code

# flatpak — another universal format
# install flatpak support first
sudo apt install flatpak

# add the main app store
flatpak remote-add --if-not-exists flathub \
  https://flathub.org/repo/flathub.flatpakrepo

# install an app
flatpak install flathub org.gimp.GIMP

# run a flatpak app
flatpak run org.gimp.GIMP

# create a compressed archive
tar -czf backup.tar.gz projects/

# extract an archive
tar -xzf backup.tar.gz

# extract to a specific folder
tar -xzf backup.tar.gz -C /home/alice/

# list contents without extracting
tar -tvf backup.tar.gz

# create archive without compression
tar -cf backup.tar projects/

# extract .tar.bz2 (uses bzip2 instead)
tar -xjf backup.tar.bz2

# gzip: compress a single file
# (original file is replaced by .gz)
gzip notes.txt
# creates: notes.txt.gz

# decompress
gunzip notes.txt.gz

# gzip without removing original
gzip -k notes.txt

# zip: create a .zip archive
zip archive.zip file1.txt file2.txt

# zip a whole folder
zip -r archive.zip projects/

# unzip
unzip archive.zip

# unzip to a specific folder
unzip archive.zip -d /home/alice/

# list contents of a zip
unzip -l archive.zip

# create a variable (local to this shell)
NAME="Alice"

# use it with $
echo $NAME

# export: available to child processes
export NAME="Alice"

# see all environment variables
env

# see one specific variable
echo $HOME
echo $PATH
printenv HOME

# add a folder to PATH
# (so you can run programs in that folder)
export PATH=$PATH:/home/alice/scripts

# see your current shell
echo $SHELL

# open your shell config
nano ~/.bashrc

# add aliases (shortcuts)
alias ll='ls -la'
alias ..='cd ..'
alias gs='git status'

# add a permanent export
export EDITOR=nano
export PATH=$PATH:/home/alice/scripts

# apply changes without restarting terminal
source ~/.bashrc
# or shorter:
. ~/.bashrc

# for Zsh users
nano ~/.zshrc
source ~/.zshrc

# show all past commands
history

# show last 20 commands
history 20

# search history interactively
# Ctrl+R then type to search
# Ctrl+R again for next match
# Enter to run, Esc to cancel

# run the last command again
!!

# run command number 42 from history
!42

# run the last command starting with 'git'
!git

# clear history
history -c

# autocomplete
# type part of a name, then press Tab
ls Doc<Tab>
# completes to: ls Documents/

# press Tab twice to see all matches
ls D<Tab><Tab>
# shows: Desktop/  Documents/  Downloads/

# cancel current command
# Ctrl+C

# clear the screen
# Ctrl+L

# jump to start / end of line
# Ctrl+A  /  Ctrl+E

# delete from cursor to start of line
# Ctrl+U

# delete from cursor to end of line
# Ctrl+K

# paste what you just deleted
# Ctrl+Y

# close the terminal / exit shell
# Ctrl+D

# check what a wildcard matches BEFORE deleting
echo *.log
# shows: error.log  access.log  debug.log

# then delete confidently
rm *.log

# ask for confirmation on each file
rm -i *.log

# preview a find + delete without actually deleting
find /tmp -name "*.tmp" -print
# check the output, then delete:
find /tmp -name "*.tmp" -delete

# before removing a folder
ls -la projects/old-stuff/
# satisfied? then:
rm -r projects/old-stuff/

# ❌ NEVER run these

# deletes everything on the system
rm -rf /

# deletes your entire home folder
rm -rf ~/

# crashes system with infinite processes
# (fork bomb)
:(){ :|:& };:

# overwrites entire hard drive
dd if=/dev/random of=/dev/sda

# these need sudo
sudo apt install nginx
sudo systemctl restart nginx
sudo nano /etc/nginx/nginx.conf
sudo chown root:root /etc/config

# these do NOT need sudo
ls ~/Documents
cd /var/log
grep "error" ~/app/logs/app.log
cp myfile.txt ~/backup/

# check if a command failed because of permissions
# look for: Permission denied
ls /root
# output: ls: cannot open '/root': Permission denied
# then use sudo:
sudo ls /root

# && — second runs only if first succeeds
mkdir my-app && cd my-app

# useful: update then upgrade, only if update worked
sudo apt update && sudo apt upgrade

# || — second runs only if first fails
cd projects || mkdir projects

# ; — always run both (success or fail)
echo "Starting..."; npm install; echo "Done"

# combine all three
sudo apt update && sudo apt upgrade -y || echo "Update failed"

# find where a program is installed
which nginx
which python3

# see all active aliases
alias

# current date and time
date

# calendar for this month
cal

# how long a command takes to run
time npm install

# repeat a command every 2 seconds
# (like a live dashboard)
watch -n 2 df -h

# see the last 10 commands with timestamps
HISTTIMEFORMAT="%F %T " history 10

# quickly make a backup copy of a file
cp nginx.conf nginx.conf.bak

# download and run a script in one line
# (only from sources you trust)
curl -fsSL https://example.com/install.sh | bash