Package Management

Why Package Management?

Package managers solve the problem of software distribution and dependency tracking at scale:

Without a package manager	With a package manager
Manually download tarballs; build from source	apt install nginx - done
Manually track and update each dependency	Dependencies resolved automatically
No record of what’s installed or why	Full audit: who installed what, when
Remove software by deleting files (hoping you get them all)	apt remove removes exactly the right files
No integrity verification	Checksums and GPG signatures verified on every install

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Package Types

Type	Description
Binary	Pre-compiled; architecture-specific (amd64, arm64). Ready to run; most common.
Source	Code + build instructions; architecture-independent. Reproducible builds.
Architecture-independent	Scripts, docs, configs; no compiled code. Runs on any arch.
Meta-package	No files itself; just dependency declarations. Installs a whole ecosystem (e.g., ubuntu-desktop).

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The Two Package Families

	Debian family	RPM family
Distros	Debian, Ubuntu, Mint, Raspberry Pi OS	RHEL, CentOS, Fedora, SUSE, Rocky, AlmaLinux
Low-level tool	dpkg	rpm
High-level tool	apt (also apt-get, apt-cache)	dnf (also yum on older systems)
Package format	.deb	.rpm
Package DB location	/var/lib/dpkg/	/var/lib/rpm/
Repo config	/etc/apt/sources.list, /etc/apt/sources.list.d/	/etc/yum.repos.d/*.repo

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Debian Family: dpkg and apt

Package File Naming

<name>_<version>-<revision>_<architecture>.deb
logrotate_3.14.0-4_amd64.deb

Note: 64-bit x86 is called amd64 in Debian/Ubuntu (not x86_64).

dpkg - Low-level Debian Package Manager

dpkg installs, removes, and queries .deb files directly. It does not resolve dependencies.

# Install a .deb file
sudo dpkg -i package.deb

# Remove package (keep config files)
sudo dpkg -r package

# Purge package (remove config files too)
sudo dpkg -P package

# List all installed packages
dpkg -l

# Check if a specific package is installed and get version
dpkg -s wget

# List files installed by a package
dpkg -L wget

# Show which package owns a file
dpkg -S /usr/bin/wget

# Inspect a .deb file without installing
dpkg -I package.deb          # package info/metadata
dpkg -c package.deb          # list contents

# Verify integrity of installed packages
dpkg -V
dpkg -V package              # verify one package

apt - High-level Debian Package Manager

apt wraps dpkg with dependency resolution, repository management, and network downloads.

# Update the local package index (before install/upgrade)
sudo apt update

# Install a package (and its dependencies)
sudo apt install nginx

# Install a specific version
sudo apt install nginx=1.18.0-0ubuntu1

# Remove (keep config files)
sudo apt remove nginx

# Purge (remove + config files)
sudo apt purge nginx
# or:
sudo apt remove --purge nginx

# Upgrade all installed packages
sudo apt upgrade

# Upgrade + remove obsolete packages and add new dependencies
sudo apt full-upgrade        # safe, interactive
sudo apt dist-upgrade        # same thing

# Remove auto-installed packages no longer needed
sudo apt autoremove

# Clean downloaded package cache
sudo apt clean               # remove all cached .deb files
sudo apt autoclean           # remove only outdated cached files

# Search for a package
apt search keyword
apt-cache search keyword

# Show package information
apt show nginx
apt-cache show nginx
apt-cache showpkg nginx      # detailed with reverse deps

# List all versions available
apt-cache madison nginx

# Find which package provides a specific file/command
apt-file search /usr/bin/wget   # requires: sudo apt install apt-file; apt-file update

# List direct dependencies of a package
apt-cache depends nginx

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RPM Family: rpm and dnf

Package File Naming

Binary:

<name>-<version>-<release>.<distro>.<arch>.rpm
sed-4.5-2.el8.x86_64.rpm

Source: same format but ends in .src.rpm

rpm - Low-level RPM Package Manager

# Install a package file (verbose + progress bars)
sudo rpm -ivh package.rpm

# Upgrade (install if not present, upgrade if present)
sudo rpm -Uvh package.rpm

# Uninstall (erase) a package
sudo rpm -e package-name     # note: package NAME, not filename

# Test uninstall without doing it
sudo rpm --test -e package-name

# Freshen: upgrade only already-installed packages
sudo rpm -Fvh *.rpm

RPM Queries (-q)

All query options start with -q:

Query	Command
Is this package installed? What version?	rpm -q bash
Which package owns this file?	rpm -qf /bin/bash
What files did this package install?	rpm -ql bash
Package info (description, size, etc.)	rpm -qi bash
Query against a .rpm file (not the DB)	rpm -qip package.rpm
List ALL installed packages	rpm -qa
What does this package require?	rpm -q --requires bash
What package provides this library?	rpm -q --whatprovides libc.so.6

RPM Verification

rpm -V package           # verify one package
rpm -Va                  # verify all packages

# Output key: each character is a field that differs from the installed DB
# S=filesize, M=mode (permissions), 5=MD5 checksum, D=device, L=readLink
# U=user owner, G=group owner, T=mtime
# Example: S.5....T. c /etc/logrotate.conf  (size, md5, mtime differ; it's a config file)

No output = everything OK.

Extracting Files from an RPM (Without Installing)

# Method 1: rpm2cpio (older, classic)
rpm2cpio package.rpm | cpio --extract --make-directories -v

# Extract just one file
rpm2cpio package.rpm | cpio -ivd ./usr/bin/bash

# Method 2: rpm2archive (newer)
rpm2archive package.rpm       # creates package.rpm.tgz
cat package.rpm | rpm2archive - | tar -xvz  # one-liner to extract

# List files in an .rpm before extracting
rpm -qilp package.rpm

dnf - High-level RPM Package Manager

dnf replaced yum as the default on RHEL 8, Fedora. Most yum commands still work with dnf.

Repository Configuration

# View configured repos
sudo dnf repolist

# Repo config files location
ls /etc/yum.repos.d/

# Sample .repo file format
# [repo-name]
# name=My Repository
# baseurl=https://example.com/rpms/
# enabled=1
# gpgcheck=1
# gpgkey=https://example.com/RPM-GPG-KEY

dnf Commands

# Update package index
sudo dnf check-update

# Install
sudo dnf install nginx
sudo dnf localinstall package.rpm    # install from a local file
sudo dnf groupinstall "Development Tools"

# Remove
sudo dnf remove nginx

# Update
sudo dnf update                       # update all packages
sudo dnf update nginx                 # update one package

# Search and info
dnf search keyword
dnf info nginx
dnf list installed
dnf list available
dnf list updates

# Dependency queries
dnf provides /usr/bin/wget            # what package gives this file?
dnf repoquery --requires nginx        # what does nginx require?
dnf repoquery --whatrequires nginx    # what requires nginx?

# Groups
dnf grouplist
dnf groupinfo "Development Tools"
dnf groupinstall "Development Tools"

# History (can undo!)
sudo dnf history
sudo dnf history info 5              # details of transaction #5
sudo dnf history undo 5              # undo transaction #5

# Maintenance
sudo dnf autoremove                  # remove unused dependencies
sudo dnf clean all                   # clean all cached data
sudo dnf clean packages              # remove only cached packages

# Download without installing
sudo dnf install --downloadonly --downloaddir=/tmp nginx

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Kernel Upgrades

On Debian/Ubuntu

# List available kernels
apt search linux-image

# Install a new kernel (apt does NOT remove the old one)
sudo apt install linux-image-6.5.0-18-generic

# Old kernel stays; GRUB shows both; remove when confident
sudo apt remove linux-image-OLD-VERSION
sudo apt autoremove              # also removes related headers/modules
sudo update-grub

On RHEL/Fedora

# Use -i (install), NOT -U (upgrade) for kernels
# -U would remove the old kernel; -i keeps it alongside
sudo rpm -ivh kernel-6.x.x-x.el9.x86_64.rpm
# OR
sudo dnf install kernel-6.x.x  # dnf also keeps old kernel (by policy)

# Remove older kernels
sudo dnf remove --oldinstallonly   # keeps the newest N kernels (set in dnf.conf)

Caution

Never use rpm -Uvh (upgrade) for kernel packages. This removes the running kernel. Use rpm -ivh (install) instead, which lets both kernels coexist so you can boot the old one if the new one fails.

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Quick Reference: Common Tasks

Task	Debian/Ubuntu	RHEL/Fedora
Update repo index	apt update	dnf check-update
Install package	apt install PKG	dnf install PKG
Remove package	apt remove PKG	dnf remove PKG
Purge + config	apt purge PKG	dnf remove PKG (no config)
List installed	dpkg -l	rpm -qa
Search	apt search KW	dnf search KW
Package of file	dpkg -S /path/file	rpm -qf /path/file
Files in package	dpkg -L PKG	rpm -ql PKG
Package info	apt show PKG	dnf info PKG
Update all	apt upgrade	dnf update
Clean cache	apt clean	dnf clean all
Unneeded deps	apt autoremove	dnf autoremove