Linux

Files and Directories

Command	Action
ls -lah	detailed list with sizes
ls -lAtr	sorted by mtime, oldest first
cd -	previous directory
pwd	print working directory
cp -a SRC DST	archive copy (preserves metadata, links)
mv OLD NEW	move / rename
rm -rf path	recursive delete
mkdir -p a/b/c	create with parents
ln -s TARGET LINK	symbolic link
stat path	metadata
readlink -f path	resolve symlinks
find . -name '*.log'	search by name
find . -mtime -7	modified in last 7 days
find . -size +100M	larger than 100 MB
find . -name '*.tmp' -delete delete matches
find . -type f -exec cmd {} \; run cmd per file
tree -L 2	show tree (depth 2)

Disk Usage

Command	Action
df -h	free space per filesystem
du -sh dir	total size of dir
du -h --max-depth=1	sizes of immediate children
ncdu /	interactive du
lsblk	block devices
mount	show mounts
findmnt	tree view of mounts

Processes

Command	Action
ps aux	all processes
ps -ef	System V style
ps -o pid,user,cmd --sort=-%mem | head	top memory
top / htop	interactive
btop	prettier interactive
pgrep -af nginx	find by name
pidof sshd
pkill -f pattern	kill by pattern
kill -9 PID	SIGKILL
nohup CMD &	background, survives logout
disown %1	detach job from shell
jobs	list shell jobs

Permissions and Users

Command	Action
id	current user / groups
whoami
groups USER
chmod 644 path	set numeric mode
chmod u+x path	add execute for owner
chown user:group path	change ownership
sudo -i	interactive root shell
sudo -u user CMD	run as user
passwd	change password
getent passwd USER	user record
getent group GROUP	group record
usermod -aG group USER	add to group

Text Processing

Command	Action
cat / less / head -20 / tail -20 / tail -f
grep -RIn 'TODO' src/	recursive grep
rg PATTERN	ripgrep (faster)
rg --files-with-matches PATTERN
sed 's/old/new/g' file	substitute
sed -i 's/old/new/g' file	in place (GNU)
awk '{ print $2 }'	column 2
awk '$3 > 100 { sum += $3 } END { print sum }'
cut -d: -f1 /etc/passwd	field 1 of colon-separated
sort | uniq -c | sort -rn	frequency counts
tr -d '\r'	remove CR
wc -l file	line count
column -t	tabularize
jq '.field'	JSON
yq '.field'	YAML

Compression and Archives

Command	Action
tar -czf out.tgz dir/	gzip archive
tar -cJf out.txz dir/	xz archive
tar -xzf in.tgz	extract gzip
tar -tf in.tgz	list contents
zip -r out.zip dir/
unzip out.zip
gzip / gunzip
zstd / unzstd

Packages

Debian / Ubuntu (apt):

Command	Action
sudo apt update && sudo apt upgrade	update and upgrade
sudo apt install PKG	install
sudo apt remove PKG	remove
apt search QUERY	search
apt show PKG	info
dpkg -l | grep PKG	installed packages
dpkg -L PKG	files in package
dpkg -S /path	owner of file

Fedora / RHEL (dnf):

Command	Action
sudo dnf install PKG
sudo dnf upgrade
rpm -qa | grep PKG
rpm -ql PKG
rpm -qf /path

Arch (pacman):

Command	Action
sudo pacman -Syu	sync + upgrade
sudo pacman -S PKG	install
sudo pacman -Rs PKG	remove with deps
pacman -Ss QUERY
pacman -Qi PKG
pacman -Ql PKG

Alpine (apk):

Command	Action
sudo apk update && sudo apk upgrade
sudo apk add PKG
sudo apk del PKG
apk info -L PKG

systemd

Command	Action
systemctl status SVC	service status
sudo systemctl start SVC
sudo systemctl stop SVC
sudo systemctl restart SVC
sudo systemctl reload SVC
sudo systemctl enable --now SVC enable + start
sudo systemctl disable SVC
systemctl list-units --type=service
systemctl list-timers
journalctl -u SVC -f	follow logs
journalctl --since '1 hour ago'
journalctl -p err	priority error

Inspecting

Command	Action
uname -a	kernel info
hostnamectl	hostname / OS / kernel
cat /etc/os-release	distro
lscpu	CPU details
free -h	memory
vmstat 1	CPU / memory / IO
iostat -xz 1	disk IO (sysstat)
lsof -i :PORT	who has port open
ss -tulpn	listening sockets
ip addr	interfaces
ip route	routes
dmesg | tail	kernel messages