The dnf Command

• introduced in RHEL 8
• can use interchangeably with yum in RHEL
  • yum is a soft link to the dnf utility.
• requires the system to have access to either:
  • a local or remote software repository
  • a local installable package file.

Subscription Management* (RHSM) service

• available in the Red Hat Customer Portal

• offers access to official Red Hat software repositories.

• Other web-based repositories that host packages are available

• You can also set up a local, custom repository on your system and add packages of your choice to it.

Primary benefit of using dnf over rpm:

• Resolve dependencies automatically

  • by identifying and installing any additional required packages

• With multiple repositories set up, dnf extracts the software from wherever it finds it.

• Perform abundant software administration tasks.

• Invokes the rpm utility in the background

• Can perform a number of operations on individual packages, package groups, and modules:

  • listing
  • querying
  • installing
  • removing
  • enabling and disabling specific module streams.

Software handling tasks that dnf can perform on packages:

• clean and repolist are specific to repositories.
• Refer to the manual pages of dnf for additional subcommands, operators, options, examples, and other details.

dnf subcommands that are intended for operations on package groups and modules:

For labs, you’ll need to create a definition file and configure access to the two repositories available on the RHEL 8 ISO image.

Lab: Configure Access to Pre-Built Repositories

Set up access to the two dnf repositories that are available on RHEL 9 image. (You should have already configured an automatic mounting of RHEL 9 image on /mnt.) Create a definition file for the repositories and confirm.

1. Verify that the image is currently mounted:

df -h | grep mnt

2. Create a definition file called local.repo in /etc/yum.repos.d/ using the vim editor and define the following data for both repositories in it:

[BaseOS] 
name=BaseOS 
baseurl=file:///mnt/BaseOS 
gpgcheck=0 

[AppStream] 
name=AppStream 
baseurl=file:///mnt/AppStream 
gpgcheck=0

3. Confirm access to the repositories:

sudo dnf repolist

• Ignore lines 1-4 in the output that are related to subscription and system registration.
• Lines 5 and 6 show the rate at which the command read the repo data.
• Line 7 displays the timestamp of the last metadata check.
• last two lines show the repo IDs, repo names, and a count of packages they hold.
• AppStream repo consists of 4,672 packages
• BaseOS repo contains 1,658 packages.
• Both repos are enabled by default and are ready for use.

dnf yum Repository

dnf repository (yum repository or a repo)

• Digital library for storing software packages

• Repository is accessed for package retrieval, query, update, and installation

• The two repositories

  • BaseOS and AppStream
    • come preconfigured with the RHEL 9 ISO image.

• Number of other repositories available on the Internet that are maintained by software publishers such as Red Hat and CentOS.

• Can build private custom repositories for internal IT use for stocking and delivering software.

  • Good practice for an organization with a large Linux server base, as it manages dependencies automatically and aids in maintaining software consistency across the board.

• Can also be used to store in-house developed packages.

• It is important to obtain software packages from authentic and reliable sources such as Red Hat to prevent potential damage to your system and to circumvent possible software corruption.

• There is a process to create repositories and to access preconfigured repositories.

• There are two pre-set repositories available on the RHEL 9 image. You will configure access to them via a definition file to support the exercises and lab environment.

Repository Definition File

• Repo definition files are located in /etc/yum.repos.d/
• Can create local.repo file in this directory to specify local repos
• See dnf.conf man page

Sample repo definition file and key directives:

[BaseOS_RHEL_9]
name= RHEL 9 base operating system components
baseurl=file://*mnt*BaseOS
enabled=1
gpgcheck=0

EXAM TIP:

• Knowing how to configure a dnf/yum repository using a URL plays an important role in completing some of the RHCSA exam tasks successfully.
• Use two forward slash characters (//) with the baseurl directive for an FTP, HTTP, or HTTPS source.

Five lines from a sample repo file: Line 1 defines an exclusive ID within the square brackets. Line 2 is a brief description of the repo with the “name” directive. Line 3 is the location of the repodata directory with the “baseurl” directive. Line 4 shows whether this repository is active. Line 5 shows if packages are to be GPGchecked for authenticity.

• Each repository definition file must have:

  • Unique ID
  • Description
  • Baseurl directive defined
  • Other directives are set as required.

• The baseurl directive for a local directory path is defined as file:///local_path

  • The first two forward slash characters represent the URL convention, and the third forward slash is for the absolute path to the destination directory)
  • FTP and
    • \ftp://hostname/network_path
  • HTTP(S)
    • http(s)://hostname/network_path
  • network path must include a resolvable hostname or an IP address.

Software Management with dnf

• Tools are available to work with individual packages as well as package groups and modules.
• rpm command is limited to managing one package at a time.
• dnf has an associated configuration file that can define settings to control its behavior.

dnf Configuration File

• Key configuration file: /etc/dnf/dnf.conf
• “main” section - sets directives that have a global effect on dnf operations.
• Can define separate sections for each custom repository that you plan to set up on the system.
• Preferred location to store configuration for each custom repository in their own definition files is in /etc/yum.repos.d
  • default location created for this purpose.

Default content of this configuration file:

cat /etc/dnf/dnf.conf

[main]
gpgcheck=1
installonly_limit=3
clean_requirements_on_remove=True
best=True
skip_if_unavailable=False

The above and a few other directives that you may define in the file:

For other directives: man 5 dnf.conf