Package Management Commands

Two Major Families

flowchart LR subgraph Debian-based APT["apt / apt-get"] --> DPKG["dpkg (.deb files)"] end subgraph "Red Hat-based" DNF["dnf / yum"] --> RPM["rpm (.rpm files)"] end

apt/dnf are high-level tools that resolve dependencies automatically and fetch from remote repositories. dpkg/rpm are low-level tools that install a single package file directly — you handle dependencies yourself.

Debian / Ubuntu: apt

sudo apt update                    # refresh the package index (does NOT install/upgrade anything)
sudo apt upgrade                     # upgrade all installed packages to latest versions
sudo apt install nginx                 # install a package (+ dependencies)
sudo apt remove nginx                    # remove a package, keep its config files
sudo apt purge nginx                       # remove a package AND its config files
sudo apt autoremove                          # remove orphaned dependencies no longer needed

apt search nginx                                # search available packages
apt show nginx                                    # detailed info about a package
apt list --installed | grep nginx                   # check if/which version is installed

dpkg -i package.deb            # install a local .deb file directly
dpkg -L nginx                    # list files installed by a package
dpkg -S /etc/nginx/nginx.conf      # which package owns this file?

RHEL / CentOS / Amazon Linux / Fedora: dnf (or yum)

sudo dnf update                     # update all packages (yum equivalent: yum update)
sudo dnf install nginx                # install a package
sudo dnf remove nginx                   # remove a package
sudo dnf search nginx                     # search available packages
sudo dnf info nginx                         # detailed package info
sudo dnf list installed | grep nginx          # check installed version
sudo dnf history                                # log of past transactions
sudo dnf history undo <id>                        # roll back a specific transaction

rpm -qa | grep nginx           # query all installed packages, filter by name
rpm -ql nginx                    # list files installed by a package
rpm -qf /etc/nginx/nginx.conf      # which package owns this file?
rpm -ivh package.rpm                 # install a local .rpm file directly

Repository Management

# Debian/Ubuntu
cat /etc/apt/sources.list
ls /etc/apt/sources.list.d/
sudo add-apt-repository ppa:some/ppa

# RHEL/CentOS
ls /etc/yum.repos.d/
sudo dnf config-manager --add-repo <url>

Checking for Available Updates (Without Installing)

apt list --upgradable            # Debian/Ubuntu: what WOULD be upgraded
sudo dnf check-update               # RHEL/Fedora: same idea

Production Considerations

Always run apt update before apt install/apt upgrade on a fresh session — an install can otherwise fail silently against a stale package index.
dnf history undo is a genuine safety net after a bad update on RHEL-family systems — there’s no exact equivalent in apt, making pre-upgrade snapshots more important on Debian-family hosts.
Pin critical package versions (apt-mark hold <pkg> / dnf versionlock) for production systems where an unplanned major-version bump (e.g., a database engine) could break compatibility.

Quick Interview Answer

“Debian-based distros use apt (high-level, dependency-resolving) on top of dpkg (low-level, single-package installs); Red Hat-based distros use dnf/yum on top of rpm the same way. apt update refreshes the package index, apt upgrade actually upgrades packages — they’re often confused but do very different things. dnf history undo gives RHEL-family systems a built-in rollback that apt doesn’t have natively.”

Common Mistakes

Confusing apt update (refresh index) with apt upgrade (actually upgrade packages) — a very common beginner mix-up.
Installing a .deb/.rpm directly with dpkg -i/rpm -ivh and then being surprised dependencies aren’t resolved automatically.
Not pinning/holding critical package versions before a routine apt upgrade/dnf update on a production server.