Understanding how to manage software packages is a fundamental skill for administering Linux servers. On Red Hat-based distributions, such as AlmaLinux and Rocky Linux, the primary tools for this are the package managers Yum and its successor, DNF.

It’s important to note that while you may be familiar with Yum, it has been replaced by DNF in Red Hat 8 and its derivatives. Fortunately, DNF is essentially the same thing as Yum, and the commands you use with Yum will also work with DNF.

For a quick reference, a helpful Yum cheat sheet is available from Red Hat.

https://access.redhat.com/articles/yum-cheat-sheet

Key configuration files

The main configuration file for the package manager (Yum/DNF) is located at: /etc/yum.conf

Understanding repositories

Software packages (specifically, RPM files) are obtained from repositories, often shortened to “repos”. These repositories are configured using files found in the following directory: /etc/yum.repos.d/

Any file in this directory ending in .repo will be read and processed by the package manager.

Within a .repo file, several settings are crucial for defining a repository:

**name=**: Specifies a human-readable name for the repository.
**baseurl=**: Defines the URL where the packages for this repository are stored.
**enabled=**: Controls whether the repository is active (1) or inactive (0).

Essential commands

Here are some common commands for managing packages:

To view information about installed or available packages, including versions and architectures:

yum list $package

To search specifically for available packages matching a pattern or a string:

yum list available ea*php70* yum search $string

To install a new software package onto your system:

yum install $package

To update a specific package to its latest available version:

yum update $package

To update all installed packages on your system to their latest versions:

yum update

To remove a package from your system. Please be aware that yum remove removes dependencies by default. Using this command carelessly could potentially damage the operating system. The command will ask for confirmation before proceeding. If you see a long list of packages scheduled for removal, it is strongly recommended to say ‘no’ and seek an alternative method to achieve your goal.

yum remove $package

More advanced operations

Beyond basic installation and removal, Yum and DNF offer more powerful tools:

To determine which package a specific file belongs to:

yum provides <path_to_file>

For example, to find the package for the less command:

yum provides ``which less``

If you know a filename but not its full path, you can use wildcards:

yum provides *filename*

For example, to find packages containing libm.so.6:

yum provides *libm.so.6

To clear the package manager’s local cache of repository metadata and packages:

yum clean all

To view the list of dependencies required by a particular package:

yum deplist $package

To install an older version of a package that is currently installed:

yum downgrade $package

To display detailed information about a package, such as description, version, release, size, and repository:

yum info $package

To install a package file that you have downloaded to your server locally:

yum localinstall $package

To reinstall a package that is already installed. Note that this command only works if your system is currently up to date.

yum reinstall $package

To see a list of all repositories currently configured and enabled on your system:

yum repolist

To manage past package manager actions using the history feature. First, you can list previous transactions to find the one you want to affect:

yum history list

Then, you can attempt to undo a specific transaction using its number. Be extremely careful to select the correct transaction number, as selecting the wrong one can potentially cause further system issues.

yum history undo $transaction_number

Using these commands and understanding the repository configuration will help you effectively manage software on your Red Hat-based systems using either Yum or DNF.

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