Linux Cheatsheet

Send one command’s output into the next.

• ps aux | grep nginx

  Filter a process list

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• cat access.log | grep 404 | wc -l

  Count matching lines

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• ls -lt | head

  Newest files first

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Write output to a file. > replaces, >> appends.

• echo hello > out.txt

  Overwrite the file

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• echo more >> out.txt

  Append to the file

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• ls > files.txt

  Save a listing

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Capture error output, or merge it with normal output.

• make 2> errors.txt

  Errors only

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• cmd > all.log 2>&1

  Stdout and stderr together

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• cmd &> all.log

  Same, shorter form

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Run the next command only if the previous one succeeded or failed.

• mkdir -p dist && cp app dist/

  Run copy only if mkdir worked

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• grep -q ready status.txt || echo missing

  Print a message if grep found nothing

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• test -f .env && echo found

  Check that a file exists

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Read and set environment variables.

• export PATH="$PATH:/opt/bin"

  Add a directory to PATH

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• echo $HOME

  Print home directory

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• printenv PATH

  Print PATH

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Single quotes keep text literal. Double quotes still expand $VAR.

• echo 'keep $HOME as text'

  No variable expansion

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• echo "user is $USER"

  Expand $USER

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• grep "error 500" app.log

  Pattern with a space

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Match many filenames without typing each one.

• ls *.log

  All .log files

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• rm file-?.txt

  One-character wildcard

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• cp src/*.{js,ts} dist/

  js or ts files

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Print output and save it to a file at the same time.

• make | tee build.log

  See output and save it

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• echo ok | tee -a notes.txt

  Append to a file

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Re-run a previous command.

• history 20

  Last 20 commands

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• !!

  Run the previous command

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• !123

  Run history item 123

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Short name for a command you type often.

• alias ll='ls -lah'

  ll → ls -lah

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• alias

  List aliases

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• unalias ll

  Remove an alias

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Print text. Useful in scripts and redirects.

• echo hello

  Print text

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• echo -n no-newline

  No newline

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• printf "%s\n" "$HOME"

  printf form

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List files in a directory.

• ls

  Names only

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• ls -lah

  Long list, hidden, human sizes

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• ls -lt

  Newest first

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Change the current directory.

• cd

  Go home

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• cd /var/log

  Go to a path

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• cd ..

  Up one level

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• cd -

  Previous directory

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Show the current directory path.

• pwd

  Where am I

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Create a directory. -p also creates parents.

• mkdir logs

  One folder

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• mkdir -p src/app/utils

  Nested folders

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Delete files or directories. Cannot undo.

• rm file.txt

  Delete a file

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• rm -r old-dir/

  Delete a directory

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• rm -rf tmp/

  Force, no promptDestructive

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Copy files or directories.

• cp a.txt b.txt

  Copy a file

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• cp -r src/ backup/

  Copy a directory

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• cp -p file.txt backup.txt

  Keep timestamps

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Move or rename a file.

• mv old.txt new.txt

  Rename

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• mv file.txt /tmp/

  Move to another folder

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Find files by name, time, type, or size.

• find . -name "*.log"

  By filename

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• find /var -mtime -7

  Modified in the last 7 days

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• find . -type f -size +100M

  Files larger than 100MB

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• find . -name "*.tmp" -delete

  Delete matchesDestructive

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Create an empty file, or update its timestamp.

• touch notes.txt

  Create one file

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• touch a.txt b.txt

  Create several

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Create a shortcut (symbolic link) to another path.

• ln -s /opt/app/bin/tool ./tool

  Make a symlink

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• ls -l tool

  Confirm the link

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Print a whole file.

• cat README.md

  Print a file

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• cat a.txt b.txt

  Concatenate two files

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• cat > notes.txt

  Type into a new file (Ctrl+D to end)

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Page through a file. q to quit, / to search.

• less /var/log/syslog

  Open a log

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• dmesg | less

  Page command output

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Show the first lines of a file.

• head file.txt

  First 10 lines

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• head -n 20 file.txt

  First 20 lines

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Show the last lines. -f follows a log as it grows.

• tail file.txt

  Last 10 lines

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• tail -n 50 file.txt

  Last 50 lines

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• tail -f /var/log/nginx/access.log

  Follow a live log

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Count lines, words, or characters.

• wc -l file.txt

  Line count

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• wc file.txt

  Lines, words, bytes

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Show the difference between two files.

• diff a.txt b.txt

  Basic diff

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• diff -u old.txt new.txt

  Unified diff

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Print the current date, time, or Unix timestamp.

• date

  Local date and time

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• date +%Y-%m-%d

  YYYY-MM-DD

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• date +%s

  Unix seconds

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Find lines that match a pattern.

• grep error app.log

  Match in one file

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• grep -i error app.log

  Ignore case

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• grep -n -r "TODO" src/

  Recursive, with line numbers

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• grep -v debug app.log

  Invert: lines that do not match

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Replace text in a file or stream.

• sed 's/foo/bar/g' file.txt

  Print replaced text

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• sed -i 's/foo/bar/g' file.txt

  Edit the file in place

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• sed '/^#/d' file.txt

  Drop comment lines

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Print selected columns, or simple totals.

• awk '{print $1}' file.txt

  First column

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• awk -F, '{print $1,$3}' data.csv

  CSV columns 1 and 3

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• awk '{sum+=$1} END {print sum}' nums.txt

  Sum a column

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Take a column from delimited text.

• cut -d',' -f1 data.csv

  CSV first column

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• cut -d: -f1 /etc/passwd

  Username from passwd

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• cut -c1-10 file.txt

  First 10 characters

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Sort lines. -n sorts numbers.

• sort file.txt

  Alphabetical

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• sort -n nums.txt

  Numeric

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• sort -r file.txt

  Reverse

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Drop duplicate lines. Sort first.

• sort file.txt | uniq

  Unique lines

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• sort file.txt | uniq -c

  Count each line

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• sort file.txt | uniq -d

  Only duplicates

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Turn a list of names into arguments for another command.

• find . -name "*.log" | xargs grep error

  Grep in found files

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• cat urls.txt | xargs curl -O

  Download each URL

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• find . -name "*.tmp" | xargs rm

  Delete found files

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List running processes and PIDs.

• ps aux

  All processes

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• ps aux | grep node

  Find by name

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• ps -ef --forest

  Process tree

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Live CPU and memory view. q to quit.

• top

  Interactive monitor

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• top -p 1234

  One PID

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• htop

  If htop is installed

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Stop a process by PID. Try without -9 first.

• kill 1234

  SIGTERM, polite stop

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• kill -15 1234

  Same as default SIGTERM

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• kill -9 1234

  Force killDestructive

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Stop processes by name instead of PID.

• pkill nginx

  By name

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• killall node

  killall form

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• pgrep -a node

  Show matching processes

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Run a command in the background, or bring it back.

• sleep 60 &

  Start in background

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• jobs

  List jobs

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• fg %1

  Bring to foreground

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• bg %1

  Resume in background

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Keep a command running after you disconnect.

• nohup ./server &

  Survive logout

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• nohup npm start > app.log 2>&1 &

  Save output to a log

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Show RAM and swap. uptime shows load.

• free -h

  Human-readable memory

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• uptime

  Uptime and load

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Show kernel and architecture.

• uname -a

  All kernel info

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• uname -r

  Kernel version

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• lscpu

  CPU details

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Re-run a command every few seconds.

• watch -n 1 df -h

  Refresh every second

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• watch -n 2 'ps aux | grep nginx'

  Watch a filtered process list

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Show addresses and routes. Replaces ifconfig.

• ip addr

  Addresses

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• ip route

  Routes

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• ip link

  Interfaces

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Check whether a host is reachable.

• ping 8.8.8.8

  Until Ctrl+C

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• ping -c 4 example.com

  Four packets then stop

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See listening ports. Replaces netstat.

• ss -tuln

  Listening TCP/UDP ports

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• ss -tulnp

  Include process names

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• ss -tuln | grep :80

  Filter port 80

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Call an HTTP URL. Good for APIs and downloads.

• curl https://example.com

  GET body

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• curl -I https://example.com

  Headers only

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• curl -X POST -H 'Content-Type: application/json' -d '{"ok":true}' https://api.example.com

  JSON POST

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• curl -o file.tgz https://example.com/file.tgz

  Save to a file

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Download a file.

• wget https://example.com/file.tgz

  Download

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• wget -c https://example.com/file.tgz

  Resume a partial download

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Copy a file over SSH.

• scp file.txt user@host:/tmp/

  Local → remote

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• scp user@host:/var/log/app.log .

  Remote → local

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• scp -r dist/ user@host:/var/www/

  Copy a directory

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Sync directories. Copies only what changed.

• rsync -avz ./src/ user@host:/opt/app/

  Sync to a server

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• rsync -avz --progress src/ dest/

  Show progress

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• rsync -avz --delete src/ dest/

  Delete extra files on dest

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Log in to a remote machine.

• ssh user@192.168.1.10

  Password or key login

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• ssh -i ~/.ssh/id_ed25519 user@host

  Choose a key file

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• ssh user@host -p 2222

  Custom port

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See which process is using a port.

• lsof -i :3000

  Who uses port 3000

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• lsof -i TCP:80

  TCP port 80

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• lsof -p 1234

  Files a PID has open

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Pack or unpack .tar.gz. z=gzip, c=create, x=extract, f=file.

• tar -czf backup.tar.gz src/

  Create .tar.gz

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• tar -xzf backup.tar.gz

  Extract here

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• tar -tzf backup.tar.gz

  List contents

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• tar -xzf backup.tar.gz -C /tmp/

  Extract to a folder

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Compress or decompress a single file.

• gzip file.txt

  Creates file.txt.gz

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• gunzip file.txt.gz

  Restore the file

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• gzip -k file.txt

  Keep the original

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Create or extract a .zip archive.

• zip backup.zip a.txt b.txt

  Zip files

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• zip -r backup.zip src/

  Zip a directory

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• unzip backup.zip

  Extract here

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• unzip -l backup.zip

  List contents

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Disk space by filesystem.

• df -h

  All filesystems

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• df -h .

  This directory’s disk

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Which folders are using space.

• du -sh .

  Total for this folder

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• du -h --max-depth=1

  One level of subfolders

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• du -h | sort -hr | head

  Largest first

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Change permission bits. 755 = rwxr-xr-x, 644 = rw-r--r--.

• chmod 755 script.sh

  Owner rwx, others rx (scripts/dirs)

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• chmod +x script.sh

  Make executable

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• chmod 644 file.txt

  Owner rw, others r (normal files)

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• chmod -R 755 dir/

  Recursive

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• chmod 777 file

  World-writable, avoidDestructive

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Change file owner and group.

• chown www-data:www-data app.sock

  One file

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• chown -R deploy:deploy /var/www/

  Recursive

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Run one command as root, or switch user.

• sudo apt update

  One command as root

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• sudo -u www-data command

  Run as another user

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• su -

  Root shell

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• sudo visudo

  Edit sudoers safely

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Show the current user and groups.

• whoami

  Username

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• id

  UID and groups

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• groups

  Group names

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• who

  Logged-in users

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Install packages on Debian and Ubuntu.

• sudo apt update

  Refresh package list

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• sudo apt install curl

  Install

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• apt search nginx

  Search

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• sudo apt remove curl

  Remove

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• apt show curl

  Package info

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Install packages on Fedora, RHEL, and CentOS.

• sudo dnf install curl

  Install (Fedora/RHEL)

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• sudo dnf update

  Update

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• dnf search nginx

  Search

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• sudo yum install curl

  Older yum form

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Start, stop, or enable a service.

• systemctl status nginx

  Is it running?

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• sudo systemctl start nginx

  Start now

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• sudo systemctl restart nginx

  Restart

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• sudo systemctl enable nginx

  Start on boot

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• systemctl --failed

  Failed units

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Read service logs.

• journalctl -u nginx

  This service

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• journalctl -u nginx -f

  Follow live

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• journalctl -p err -n 50

  Recent errors

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• dmesg | tail

  Kernel messages

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