Debian Cheat Sheet

Common commands for Debian Server Administration.

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Getting Help

Command / Resource	Description
man page or man bash	Read the help page for every command and many configuration files. Also available online: https://www.manpages.debian.org/
command [--help, -h]	Brief help for most commands.
/usr/share/doc/package-name/	Find all documentation here; the optional file README.Debian contains Debian-specific notes.
Web documentation	Reference, manuals, FAQs, HOWTOs, etc.
Mailing lists	The community is always helpful; search for users. Or use other channels like IRC: https://www.debian.org/support/
The Wiki	Contains all kinds of useful information.
⭐ man -k keyword / apropos keyword	Search man pages by keyword.
⭐ info command	Read GNU info documentation.
⭐ whatis command	One-line description of a command.
⭐ type command / which command	Show how a command resolves / where it lives.
⭐ tldr command	Simplified community examples (needs tldr package).

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Installation

Resource	Description
Installer	All information about the installer.
CD images	Download installation images.
boot: expert	E.g. to set up the network without DHCP or to adapt the bootloader installation.
Live image	Contains the user-friendly Calamares installer.
⭐ sha256sum -c SHA256SUMS	Verify the integrity of a downloaded ISO.
⭐ sudo dd if=debian.iso of=/dev/sdX bs=4M status=progress conv=fsync	Write an ISO to a USB drive (double-check /dev/sdX!).

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Configuration

Command / Path	Description
/etc/	All system configuration files are under this directory.
editor files	Default text editor. May be nano, emacs, vi, joe.
CUPS	Browser interface to the printing system (http://hostname:631).
dpkg-reconfigure package-name	Reconfigure a package, e.g. keyboard-configuration (keyboard), locales (localization).
update-alternatives options	Manage command alternatives.
update-grub	Run after changing /etc/default/grub.
⭐ sudo update-alternatives --config editor	Interactively choose the default editor.
⭐ sudo visudo	Safely edit /etc/sudoers.
⭐ sudo timedatectl set-timezone America/Santiago	Set the system time zone.
⭐ timedatectl	Show date, time, and NTP sync status.
⭐ sudo hostnamectl set-hostname NAME	Set the machine hostname.
⭐ sudo dpkg-reconfigure tzdata	Reconfigure time zone interactively.
⭐ locale / sudo dpkg-reconfigure locales	Show / configure system locales.
⭐ /etc/apt/sources.list and /etc/apt/sources.list.d/	APT repository definitions (Trixie also supports deb822 .sources files).
⭐ /etc/fstab	Filesystems mounted at boot.
⭐ /etc/hosts	Static hostname-to-IP mappings.

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Daemons and System

Command / Path	Description
systemctl restart name.service	Restart a service / system daemon.
systemctl stop name.service	Stop a service / system daemon.
systemctl start name.service	Start a service / system daemon.
systemctl halt	Halts the system.
systemctl reboot	Reboots the system.
systemctl poweroff	Shuts down the system.
systemctl suspend	Suspends the system.
systemctl hibernate	Hibernates the system.
/var/log/	All log files are under this directory.
/etc/default/	Default values for many daemons and services.
⭐ systemctl status name.service	Show service status and recent log lines.
⭐ systemctl enable name.service	Start a service at boot.
⭐ systemctl enable --now name.service	Enable at boot and start immediately.
⭐ systemctl disable name.service	Do not start a service at boot.
⭐ systemctl reload name.service	Reload configuration without full restart.
⭐ systemctl is-active name.service	Check if a service is running.
⭐ systemctl list-units --type=service	List loaded services.
⭐ systemctl list-unit-files --state=enabled	List services enabled at boot.
⭐ systemctl --failed	List failed units.
⭐ systemctl daemon-reload	Reload systemd after editing unit files.
⭐ systemctl edit name.service	Create a drop-in override for a unit.
⭐ journalctl -u name.service -f	Follow logs for a service.
⭐ journalctl -xe	Show recent logs with explanations.
⭐ journalctl -b	Logs since the current boot.
⭐ journalctl -p err -b	Only errors since boot.
⭐ journalctl --vacuum-time=7d	Trim journal logs older than 7 days.
⭐ systemd-analyze blame	Show which units slow down boot.
⭐ uptime / uname -a / hostnamectl	System uptime / kernel info / host info.
⭐ lsb_release -a / cat /etc/os-release	Show Debian version.
⭐ crontab -e / crontab -l	Edit / list the user’s cron jobs.
⭐ systemctl list-timers	List systemd timers.

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Important Shell Commands

Files and directories

Command	Description
cat files	Print files to screen.
cd directory	Change to directory.
cp files dest	Copy files and directories.
echo string	Echo string to screen.
gzip, bzip2, xz [-d] files	Compress, uncompress files.
pager files	Show contents of files.
ls [files]	List files.
mkdir directory-names	Create directories.
mv file1 file2	Move, rename files.
rm files	Remove files.
rmdir dirs	Remove empty directories.
tar [c][x][t][z][j][J] -f file.tar [files]	Create (c), extract (x), list table of (t) archive file; z for .gz, j for .bz2, J for .xz.
find directories expressions	Find files, like -name name or -size +1000, etc.
grep search-string files	Find search-string in files.
ln -s file link	Create a symbolic link to a file.

Processes and users

Command	Description
ps [options]	Show current processes.
kill [-9] PID	Send signal to a process (e.g. terminate it). Use ps for the PID.
su - [username]	Become another user, e.g. root.
sudo command	Execute a command as root as a normal user, see /etc/sudoers.

Redirection and pipes

Command	Description
command > file	Overwrite file with output of command.
command >> file	Append output of command to file.
cmd1 | cmd2	Use output of command 1 as input of command 2.
command < file	Use file as input for command.

⭐ Additional shell commands

Command	Description
ls -lah	Long listing, hidden files, human-readable sizes.
tree -L 2	Directory tree, 2 levels deep (needs tree).
cp -a src dest	Copy preserving permissions, timestamps, links.
rm -rf dir	Remove a directory recursively (dangerous, no undo).
touch file	Create an empty file / update timestamp.
head -n 20 file / tail -n 20 file	First / last lines of a file.
tail -f file	Follow a file as it grows (logs).
less file	Scroll through a file (q to quit, / to search).
wc -l file	Count lines.
sort file | uniq -c	Sort and count duplicates.
cut -d: -f1 /etc/passwd	Extract a column by delimiter.
sed -i 's/old/new/g' file	In-place search and replace.
awk '{print $1}' file	Print first column.
grep -rin "text" .	Recursive, case-insensitive search with line numbers.
find . -name "*.log" -mtime +7	Find .log files older than 7 days.
find . -type f -size +100M	Find files larger than 100 MB.
xargs	Build commands from stdin, e.g. find . -name "*.tmp" | xargs rm.
tar -czvf out.tar.gz dir/	Create a gzip-compressed archive.
tar -xzvf in.tar.gz -C /dest	Extract a gzip archive to a destination.
zip -r out.zip dir/ / unzip file.zip	Create / extract zip files.
chmod 755 file / chmod +x script.sh	Change permissions.
chown user:group file	Change owner and group.
chown -R user:group dir	Change ownership recursively.
umask	Show default permission mask.
stat file	Detailed file information.
file name	Detect file type.
diff -u a b	Compare two files.
alias ll='ls -lah'	Create a shell alias (persist in ~/.bashrc).
history / Ctrl+R	Command history / reverse search.
!!	Repeat last command (e.g. sudo !!).
source ~/.bashrc	Reload shell configuration.
export VAR=value	Set an environment variable.
env / printenv	List environment variables.
watch -n 2 command	Re-run a command every 2 seconds.
time command	Measure how long a command takes.
tmux / screen	Persistent terminal sessions (need packages).

⭐ Users and groups

Command	Description
whoami / id	Current user / UID, GID, and groups.
sudo adduser name	Create a user (interactive, Debian-friendly).
sudo usermod -aG sudo name	Add a user to the sudo group.
sudo deluser --remove-home name	Delete a user and their home directory.
sudo passwd name	Change a user’s password.
groups name	Show a user’s groups.
last	Show recent logins.
w / who	Who is logged in and what they are doing.

⭐ Processes and resources

Command	Description
top / htop	Interactive process viewer (htop needs package).
ps aux	List all processes.
ps aux | grep name	Find a process by name.
pgrep -a name	Find PIDs by name.
pkill name	Kill processes by name.
killall name	Kill all processes with that name.
nice -n 10 cmd / renice -n 5 -p PID	Start with / change priority.
bg / fg / jobs	Manage background jobs.
command &	Run a command in background.
nohup command &	Keep running after logout.
free -h	Memory usage.
vmstat 1	Live virtual memory/CPU stats.
lsof -i :80	Which process uses port 80.
dmesg -T | tail	Recent kernel messages with human-readable time.

⭐ Disk and filesystems

Command	Description
df -h	Free disk space per filesystem.
du -sh *	Size of each item in the current directory.
du -h --max-depth=1 / | sort -h	Largest top-level directories.
ncdu	Interactive disk usage browser (needs package).
lsblk	List block devices.
lsblk -f	List block devices with filesystems and UUIDs.
blkid	Show UUIDs and filesystem types.
sudo fdisk -l	List disk partitions.
sudo mount /dev/sdX1 /mnt / sudo umount /mnt	Mount / unmount a partition.
sudo mount -a	Mount everything in /etc/fstab (test your edits).
sudo fsck /dev/sdX1	Check a filesystem (unmounted!).
sudo mkfs.ext4 /dev/sdX1	Format as ext4 (destroys data).
sudo smartctl -a /dev/sda	Disk SMART health (needs smartmontools).

⭐ Hardware info

Command	Description
lscpu	CPU information.
lspci / lsusb	PCI / USB devices.
sudo lshw -short	Hardware summary.
sudo dmidecode -t system	BIOS/system information.
sensors	Temperatures (needs lm-sensors).
nvidia-smi	NVIDIA GPU status (with proprietary drivers).

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APT

Command	Description
apt update	Update package listings from repositories listed in /etc/apt/sources.list. Required whenever that file or the contents of the repositories change.
apt search search-string	Search packages and descriptions for the string.
apt list -a package-name	Show versions and archive areas of available packages.
apt show -a package-name	Show package information including description.
apt install package-names	Install packages from repositories with all dependencies.
apt upgrade	Install newest versions of all packages currently installed.
apt full-upgrade	Like apt upgrade, but with advanced conflict resolution.
apt remove package-names	Remove packages.
apt autoremove	Remove packages that no other packages depend on.
apt depends package-name	List all packages needed by the one given.
apt rdepends package-name	List all packages that need the one given.
apt-file update	Update content listings from package repositories, see apt update.
apt-file search file-name	Search packages for a file.
apt-file list package-name	List contents of a package.
aptitude	Console interface to APT (needs aptitude).
synaptic	GUI interface to APT (needs synaptic).

⭐ Additional APT commands

Command	Description
sudo apt update && sudo apt upgrade -y	Typical full refresh and upgrade.
sudo apt full-upgrade	Upgrade handling changed dependencies.
sudo apt purge package	Remove a package and its configuration files.
sudo apt autoremove --purge	Remove unused packages and their configs.
sudo apt clean	Delete all cached .deb files.
sudo apt autoclean	Delete only obsolete cached .deb files.
sudo apt install ./file.deb	Install a local .deb resolving dependencies.
sudo apt install --reinstall package	Reinstall a package.
sudo apt install package=version	Install a specific version.
sudo apt install -t trixie-backports package	Install from backports.
sudo apt --fix-broken install	Repair broken dependencies.
apt list --installed	List installed packages.
apt list --upgradable	List packages with updates available.
apt policy package	Show candidate version and pinning/priorities.
apt-mark hold package / apt-mark unhold package	Prevent / allow upgrades of a package.
apt-mark showhold	List held packages.
apt-mark showmanual	List manually installed packages.
sudo apt build-dep package	Install build dependencies (needs deb-src).
apt source package	Download package source.
sudo apt modernize-sources	Convert legacy sources.list to deb822 format.
sudo apt-get dist-upgrade	Legacy equivalent of full-upgrade.
needrestart	Show services/processes needing restart after upgrades (needs package).
sudo unattended-upgrades --dry-run	Test automatic security upgrades (needs unattended-upgrades).
sudo add-apt-repository	Not shipped by default on Debian; edit /etc/apt/sources.list.d/ instead.

⭐ Third-party repository (modern way, with keyrings)

sudo install -d -m 0755 /etc/apt/keyrings
curl -fsSL https://example.com/key.gpg | sudo gpg --dearmor -o /etc/apt/keyrings/example.gpg
echo "deb [signed-by=/etc/apt/keyrings/example.gpg] https://example.com/apt stable main" \
  | sudo tee /etc/apt/sources.list.d/example.list
sudo apt update

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Dpkg

Command	Description
dpkg -l [names]	List packages.
dpkg -I pkg.deb	Show package information.
dpkg -c pkg.deb	List contents of a package file.
dpkg -S filename	Show which package a file belongs to.
dpkg -i pkg.deb	Install package files.
dpkg -V [package-names]	Audit checksums of installed packages.
dpkg-divert [options] file	Override a package’s version of a file.
dpkg --compare-versions v1 gt v2	Compare version numbers; view results with echo $?.
dpkg-query -W --showformat=format	Query installed packages, format e.g. '${Package} ${Version} ${Installed-Size}\n'
dpkg --get-selections > file	Write package selections to file.
dpkg --set-selections < file	Set package selections from file.

⭐ Additional dpkg commands

Command	Description
dpkg -L package	List files installed by a package.
dpkg -s package	Show status of an installed package.
dpkg -r package	Remove a package (keep config).
dpkg -P package	Purge a package (remove config too).
sudo dpkg --configure -a	Finish configuring interrupted installations.
dpkg --print-architecture	Show the native architecture.
dpkg --print-foreign-architectures	Show enabled foreign architectures.
sudo dpkg --add-architecture i386	Enable multiarch (e.g. i386).
dpkg -l | grep ^ii	Only fully installed packages.
dpkg -l | grep ^rc	Removed packages with leftover config.
sudo dpkg -P $(dpkg -l | awk '/^rc/{print $2}')	Purge leftover configs of removed packages.

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The Network

Command / Path	Description
/etc/network/interfaces	Interface configuration (if not controlled via NetworkManager).
if[up][down] device	Start, stop network interfaces according to the file above.
ip	Show and manipulate network interfaces and routing (needs iproute2).
ssh -X user@host	Login at another machine (with X11 forwarding).
scp files user@host:path	Copy files to another machine (and vice versa).

⭐ Additional networking commands

Command	Description
ip a / ip addr	Show IP addresses.
ip -br a	Brief address overview.
ip link	Show network interfaces and state.
sudo ip link set eth0 up / down	Bring an interface up / down.
ip route	Show routing table.
ip route get 1.1.1.1	Show which route/interface reaches a host.
ss -tulpn	Listening TCP/UDP sockets with owning processes.
ss -tn	Established TCP connections.
ping -c 4 host	Test connectivity.
traceroute host / mtr host	Trace the route to a host (need packages).
dig domain / nslookup domain	DNS lookups (need dnsutils/bind9-dnsutils).
dig +short domain	Only the answer.
host domain	Simple DNS lookup.
resolvectl status	DNS resolver status (systemd-resolved).
curl -I https://example.com	Fetch HTTP headers only.
curl -fsSL URL -o file	Download a file quietly, failing on errors.
wget URL / wget -c URL	Download / resume download.
nmcli device status	NetworkManager device status.
nmcli connection show	List NetworkManager connections.
nmcli device wifi list / nmcli device wifi connect SSID password PASS	List / connect to Wi-Fi.
nmtui	Text UI for NetworkManager.
sudo systemctl restart networking	Restart ifupdown networking.
sudo systemctl restart NetworkManager	Restart NetworkManager.
hostname -I	Show all local IP addresses.
curl ifconfig.me	Show public IP address.
nc -zv host 22	Test whether a TCP port is open (needs netcat).
nmap host	Port scan (needs nmap; only scan hosts you own/are authorized to).
sudo tcpdump -i eth0 port 80	Capture packets (needs tcpdump).

⭐ SSH and file transfer

Command	Description
ssh user@host	Connect to a remote machine.
ssh -p 2222 user@host	Connect using a non-default port.
ssh -i ~/.ssh/key user@host	Connect with a specific key.
ssh-keygen -t ed25519 -C "comment"	Generate an Ed25519 key pair.
ssh-copy-id user@host	Install your public key on a remote host.
ssh -L 8080:localhost:80 user@host	Local port forwarding (tunnel).
ssh -D 1080 user@host	SOCKS proxy through SSH.
ssh -J jump@host user@target	Connect through a jump host.
scp -r dir user@host:/path	Copy a directory recursively.
scp -P 2222 file user@host:/path	Copy using a non-default port.
rsync -avzP src/ user@host:/dest/	Efficient sync with progress and resume.
rsync -avz --delete src/ dest/	Mirror, deleting extra files at the destination.
sftp user@host	Interactive file transfer.
~/.ssh/config	Per-host SSH settings (Host, HostName, User, Port, IdentityFile).

⭐ Firewall

Command	Description
sudo ufw status verbose	Show firewall status (needs ufw).
sudo ufw allow 22/tcp	Allow SSH.
sudo ufw allow from 192.168.1.0/24 to any port 5432	Allow a subnet to a port.
sudo ufw allow from 192.168.1.0 to any port 5432	Allow a specific ip to a port.
sudo ufw allow from 192.168.1.0 to any port 5432 proto tcp	Allow a specific ip to a port with only tcp protocol.
sudo ufw deny 23	Block a port.
sudo ufw enable / disable	Enable / disable the firewall.
sudo ufw delete allow 22/tcp	Remove a rule.
sudo nft list ruleset	Show nftables rules (Debian default backend).
sudo systemctl status fail2ban	Check brute-force protection (needs fail2ban).

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Kernel and boot

Command	Description
uname -r	Running kernel version.
dpkg -l 'linux-image*' | grep ^ii	Installed kernels.
sudo update-initramfs -u	Rebuild the initramfs.
sudo update-grub	Regenerate GRUB configuration.
lsmod	Loaded kernel modules.
sudo modprobe module	Load a kernel module.
sudo sysctl -a | grep keyword	Search kernel parameters.
sudo sysctl -p	Reload /etc/sysctl.conf.

Upgrading Debian to a new release (e.g. 12 → 13)

# 1. Fully update the current system first
sudo apt update && sudo apt full-upgrade
# 2. Back up, then change codenames in /etc/apt/sources.list(.d/)
sudo sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
# 3. Upgrade in two steps
sudo apt update
sudo apt upgrade --without-new-pkgs
sudo apt full-upgrade
# 4. Clean up and reboot
sudo apt autoremove --purge
sudo reboot

Always read the official release notes before a major upgrade: https://www.debian.org/releases/stable/releasenotes

Handy one-liners

# Show the 10 biggest files/directories under the current path
du -ah . 2>/dev/null | sort -rh | head -n 10

# Show the 10 processes using the most memory
ps aux --sort=-%mem | head -n 11

# Find which process is using a port
sudo ss -tulpn | grep :8080

# Count files in a directory recursively
find . -type f | wc -l

# Update everything and clean up in one go
sudo apt update && sudo apt full-upgrade -y && sudo apt autoremove --purge -y && sudo apt clean