Package Management Basics: Getting Started with apt and yum

2026-05-13 Reading time: About 14 min Difficulty: Intermediate

What You'll Learn

• A side-by-side map of apt and yum/dnf commands
• A reliable workflow for searching, installing, updating, and removing packages
• When to use yum vs dnf, and the difference between update and upgrade
• How to diagnose common errors like Unable to locate package and NO_PUBKEY

1. apt vs yum/dnf Command Map

The single most useful table you can keep handy.

2. apt: Minimum Viable Workflow

2-1. Refresh → Install

$ sudo apt update
$ sudo apt install nginx

2-2. Search (when you only remember part of the name)

$ apt search nginx
$ apt show nginx

apt search does full-text search across descriptions, which is why "search for nginx" returns dozens of results. To narrow down to actual names, use a glob:

$ apt list 'nginx*'
$ apt list --installed 2>/dev/null | grep nginx

2-3. Upgrade

$ sudo apt update
$ sudo apt upgrade           # Bump installed packages
$ sudo apt full-upgrade      # Allow removals to resolve deps (kernels, etc.)

2-4. Remove

$ sudo apt remove nginx      # Binary gone; /etc/ configs remain
$ sudo apt purge nginx       # Configs deleted too
$ sudo apt autoremove        # Drop orphaned dependencies

3. yum / dnf: Minimum Viable Workflow

3-1. yum vs dnf — Which One Do I Use?

• CentOS 7 / RHEL 7: yum is native
• CentOS 8+ / Rocky 8+ / AlmaLinux 8+ / RHEL 8+ / Fedora: dnf is native; the yum command is a compatibility wrapper around dnf

3-2. Core Operations

$ sudo dnf check-update            # Show available updates
$ sudo dnf install nginx
$ sudo dnf upgrade                 # Upgrade all
$ sudo dnf remove nginx
$ dnf search nginx
$ dnf info nginx
$ dnf list installed | grep nginx

3-3. Group Install (a dnf strength)

Install a bundle of related packages in one step.

$ dnf grouplist
$ sudo dnf groupinstall "Development Tools"

Debian-family achieves the same outcome through meta-packages instead:

$ sudo apt install build-essential

4. Searching in Practice

"I forgot the exact package name" is the most common stumbling block. These three patterns cover almost every case.

4-1. Narrow by Name Pattern

# Debian
$ apt list 'php*' 2>/dev/null

# RHEL
$ dnf list 'php*'

4-2. Reverse Lookup from a Binary or File

When you know the command name but not the package, use apt-file / dnf provides.

# Debian (apt-file is not installed by default)
$ sudo apt install apt-file
$ sudo apt-file update
$ apt-file search /usr/bin/htop

# RHEL (built in)
$ dnf provides /usr/bin/htop
$ dnf provides '*/sshd_config'

4-3. Verify You Have the Right Package

$ apt show nginx
$ dnf info nginx

Check Version, Source, and Homepage to distinguish the package you want from a same-named impostor.

5. Repository Inspection

5-1. List Active Repositories

# Debian
$ apt policy                              # Per-package source priorities
$ ls /etc/apt/sources.list.d/             # Extra repo definitions
$ cat /etc/apt/sources.list

# RHEL
$ dnf repolist                            # Enabled repos
$ dnf repolist --all                      # Include disabled
$ ls /etc/yum.repos.d/

5-2. Adding a Third-Party Repository — Caveats

5-3. Modern Repo-Add Pattern (Debian-family)

Ubuntu 22.04+ deprecates apt-key. The recommended pattern is to place GPG keys under /etc/apt/keyrings/ and reference them from each source list with signed-by=.

# Stage the key (follow vendor instructions)
$ sudo install -d -m 0755 /etc/apt/keyrings
$ curl -fsSL https://download.example.com/key.gpg \
    | sudo tee /etc/apt/keyrings/example.gpg > /dev/null

# Repo definition
$ echo "deb [signed-by=/etc/apt/keyrings/example.gpg] https://download.example.com/apt stable main" \
    | sudo tee /etc/apt/sources.list.d/example.list
$ sudo apt update

6. Troubleshooting the Common Errors

6-1. Unable to locate package <pkg> (apt)

Diagnose in this order:

1. You skipped apt update
2. The package name is wrong (python vs python3, etc.)
3. The right repository component is disabled (e.g. universe / multiverse)

$ sudo apt update
$ apt search <approximate-keyword>
$ apt-cache policy <pkg>

6-2. No match for argument (dnf)

Same diagnosis. Frequently fixed by rebuilding metadata:

$ sudo dnf clean all
$ sudo dnf makecache
$ dnf search <approximate-keyword>

6-3. Could not get lock /var/lib/dpkg/lock

Another apt process is running, or a previous run crashed. Confirm first, then recover.

$ ps -ef | grep -E 'apt|dpkg' | grep -v grep
# Only if no live process exists:
$ sudo rm /var/lib/apt/lists/lock
$ sudo rm /var/lib/dpkg/lock-frontend
$ sudo dpkg --configure -a

6-4. GPG Errors (NO_PUBKEY / Signature couldn't be verified)

A third-party repo's signing key expired or was rotated.

$ sudo apt update
# -> NO_PUBKEY ABCD1234...

Fix by fetching the vendor's current key and placing it under /etc/apt/keyrings/. Avoid --allow-unauthenticated and never blindly run apt-key del.

6-5. Install Fails Due to Disk Space

$ df -h /var /usr
$ sudo apt clean        # Drop downloaded .deb files
$ sudo dnf clean all    # Same for dnf cache

/var/cache/apt/archives/ and /var/cache/dnf/ are the usual suspects.

7. Production Rules That Save Pain

$ dnf history list
$ sudo dnf history undo <ID>

8. Copy-Paste Templates

# First-time setup
sudo apt update && sudo apt upgrade -y

# Search -> inspect -> install
apt list 'nginx*'
apt show nginx
sudo apt install nginx

# Preview upgrades before applying
apt list --upgradable
sudo apt upgrade

# Remove including configs
sudo apt purge nginx && sudo apt autoremove

# First-time setup
sudo dnf upgrade -y

# Search -> inspect -> install
dnf search nginx
dnf info nginx
sudo dnf install nginx

# Preview updates
dnf check-update

# Roll back a transaction
dnf history list
sudo dnf history undo <ID>