Essential apt-get and System Commands for Debian and Ubuntu

Essential apt-get Commands for Debian/Ubuntu

The apt-get command is the core package management tool for Debian-based systems like Ubuntu. Here are the most commonly used commands.

Package Installation & Removal

• apt-get install package: Install a package.
• apt-get install package --reinstall: Reinstall a package.
• apt-get -f install: Fix broken dependencies (-f is short for --fix-missing).
• apt-get remove package: Remove a package but keep its configuration files.
• apt-get remove package --purge: Remove a package and delete its configuration files.

Package Updates & Upgrades

• apt-get update: Refresh the local package index from repositories.
• apt-get upgrade: Upgrade all installed packages to their latest versions (does not handle dependency changes).
• apt-get dist-upgrade: Perform a distribution upgrade, intelligently handling dependency changes (may add or remove packages).
• apt-get dselect-upgrade: Upgrade packages based on selections made with the dselect tool.

Source Code & Build Environment

• apt-get build-dep package: Install all dependencies required to build a specific package from source.
• apt-get source package: Download the source code for a package.

System Cleanup

• apt-get clean: Remove all downloaded package files (.deb) from /var/cache/apt/archives/.
• apt-get autoclean: Remove only outdated package files from the cache.
• apt-get autoremove: Automatically remove packages that were installed as dependencies but are no longer needed.
• apt-get check: Verify the system for broken dependencies.

apt-cache Query Commands

The apt-cache command queries the APT package cache for information without installing or removing anything.

• apt-cache show package: Display detailed information about a package.
• apt-cache search keyword: Search for packages matching a keyword.
• apt-cache showpkg package: Show package details, focusing on dependencies.
• apt-cache policy package: Show the installation status, candidate version, and repository priority for a package.
• apt-cache depends package: List dependencies for a package.
• apt-cache rdepends package: List reverse dependencies (packages that depend on the specified package).

Essential dpkg Operations

• dpkg -L package: List all files installed by a package.
• dpkg -S filename: Find which installed package owns a specific file.
• dpkg --get-selections > list.txt: Backup the list of currently selected packages.
• dpkg --set-selections < list.txt followed by apt-get dselect-upgrade: Restore package selections from a backup file.

System Information & Maintenance

System Information

• Kernel version: uname -a
• Distribution info: cat /etc/os-release
• CPU info: cat /proc/cpuinfo
• Memory usage: free -h
• Disk space: df -h
• Directory size: du -sh directory_name

Process Management

• View processes: ps aux or top
• Terminate process: kill PID or killall process_name
• Force kill: kill -9 PID

Network Commands

• IP address: ip addr show (preferred) or ifconfig
• Routing table: ip route show or route -n
• Test connectivity: ping host
• Network connections: ss -tuln (preferred) or netstat -tuln
• Transfer files via SSH:

  scp -r local_file user@remote_host:/path/  # Upload
  scp -r user@remote_host:/path/file local_destination  # Download

File & Directory Operations

• Find files: find /path -name "filename"
• Search content: grep -r "pattern" /path
• Tail log file: tail -f /var/log/syslog (follow in real-time)
• Archive & compress:
  • Extract .tar.gz: tar -xzf file.tar.gz
  • Extract .tar.bz2: tar -xjf file.tar.bz2
  • Create archive: tar -czf archive.tar.gz dir1 dir2

Other Useful Commands

• Time sync: sudo timedatectl set-ntp true (systemd) or sudo ntpdate pool.ntp.org
• Command manual: man command or command --help
• Search commands: apropos keyword

Note: Most commands listed require superuser privileges. Prepend sudo if you are a regular user. Some commands may vary based on system version or configuration; consult the manual (man) for the most current information.