Debian Command Cheat Sheet: apt-get, dpkg, and File Operations

Working on Debian and its derivatives (Ubuntu et al.), a few command groups come up every day: apt-get and dpkg for installing software, ls for viewing files, cd and pwd for moving between directories, cp and mv for copying and moving. This post organizes them into a cheat sheet by function — flip through it when setting up a new machine or switching environments. All output in this post was tested in a debian:12 container (Debian 12.15, apt 2.6.1, dpkg 1.21.23).

apt-get: Repository Package Management

apt-get is the package-management CLI of the Debian family, handling package installation, upgrades, and removal with automatic dependency resolution.

Command	What it does	Example
`apt-get update`	Refresh the repository index	`sudo apt-get update`
`apt-get upgrade`	Upgrade all installed packages	`sudo apt-get upgrade`
`apt-get install <pkg>`	Install a package	`sudo apt-get install nginx`
`apt-get remove <pkg>`	Remove a package (keeps config)	`sudo apt-get remove nginx`
`apt-get purge <pkg>`	Remove a package and delete its config	`sudo apt-get purge nginx`
`apt-get autoremove`	Clean up dependencies no longer needed	`sudo apt-get autoremove`
`apt-get install -s <pkg>`	Simulate an install — inspect dependencies without touching the system	`sudo apt-get install -s wget`
`apt-cache search <word>`	Search package names in the repositories	`apt-cache search ^wget$`

Common options:

Option	What it does
`-y`	Auto-answer yes to all interactive prompts — always add it in scripts
`-s` / `--dry-run`	Simulate execution, only printing what would change
`-q`	Quiet mode, less progress output
`--no-install-recommends`	Skip recommended packages, install hard dependencies only

Live verification (installing a package on a fresh container without refreshing the index errors out; after update, a -s simulated install of wget):

Trap: update and upgrade are two different things — update only refreshes the repository index and upgrades nothing; upgrade is what actually upgrades. Running update without upgrade changes not a single package on the system.

dpkg: Local .deb Package Operations

dpkg is also a Debian-family package management tool, used to install, build, remove, and manage .deb packages. Division of labor with apt-get: apt-get works through repositories and resolves dependencies automatically, while dpkg only operates on the package files in your hand and does not resolve dependencies — when installing a .deb with missing dependencies, apt-get still has to fill the gap (sudo apt-get install -f).

Command	What it does	Example
`dpkg -i <file>.deb`	Install a local .deb package	`sudo dpkg -i app_1.0_amd64.deb`
`dpkg -l`	List all installed packages	`dpkg -l`, `dpkg -l curl`
`dpkg -s <pkg>`	Query a package’s detailed info	`dpkg -s curl`
`dpkg -L <pkg>`	List every file the package installed	`dpkg -L curl`
`dpkg -r <pkg>`	Remove a package, keeping config files	`sudo dpkg -r curl`
`dpkg -P <pkg>`	Remove a package and purge config	`sudo dpkg -P curl`

Live verification (querying the installed curl):

Trap: in dpkg -l, the first-column status code ii means properly installed, while rc means removed with config residue left behind (only purge clears it); after removing with -r and reinstalling, the old config is still there — use -P for a clean uninstall.

ls: List Directories

ls lists directory contents — one of the most-used commands.

Command	What it does
`ls`	List the files and directories in the current directory
`ls -l`	Details: permissions, owner, size, modification time
`ls -a`	Include hidden files (dot-prefixed)
`ls -la`	Both combined: full info including hidden files
`ls -h`	Sizes in human-readable K/M/G format
`ls -d <dir>`	Show the directory itself, not its contents

Each ls -l line has seven columns: permissions, link count, owner, group, size, modification time, filename. The first column, e.g. -rw-r--r--: the leading - marks a regular file (d for a directory), and the remaining nine characters split into three groups — the read/write/execute permissions of owner, group, and others.

cd and pwd: Navigating and Locating

cd (change directory) switches directories; pwd (print working directory) shows the full path of the current working directory.

Command	What it does
`cd /home`	Switch to the absolute path /home
`cd dir1`	Switch to dir1 under a relative path
`cd ..`	Go up one level
`cd -`	Return to the previous directory
`cd` / `cd ~`	Return to the current user’s home directory
`pwd`	Show the current path

cp and mv: Copying and Moving

cp copies files or directories; mv moves or renames them.

Command	What it does
`cp source.txt dest.txt`	Copy a file
`cp -r srcdir/ destdir/`	Copy a directory (`-r` for recursion is mandatory)
`mv source.txt /some/dest/`	Move a file to the given directory
`mv old.txt new.txt`	Rename (a move within the same directory)
`mv -i <file> <target>`	Ask before overwriting, guarding against accidental clobbering

Live verification (copy, move, confirm with ls):

Trap: cp without -r errors out outright on directories; mv overwrites existing files silently by default — use mv -i or back things up yourself before touching important data.

Caveats

apt-get and dpkg divide the labor differently: apt-get works through repositories and resolves dependencies automatically, while dpkg only handles local .deb files — prefer apt-get day to day.
apt-get update and apt-get upgrade are two separate steps; running update without upgrade upgrades nothing.
dpkg’s -r removes a package while keeping its config files, so the old config persists on reinstall; use -P (purge) to clear the config along with the package.
ls’s -l and -a combine (ls -la), which makes reading full info on hidden files easier.
In production, run remove/purge/autoremove with -s first to preview the list of packages about to change, then execute for real.