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YUM-Configure-Offline.md

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YUM Configuration on CentOS 9

YUM (Yellowdog Updater, Modified) is a powerful package management tool used in RPM-based Linux distributions like CentOS, RHEL, and Fedora. It simplifies the process of installing, updating, and managing software packages by handling dependencies and accessing remote repositories.

Key Features of YUM

  • Automatic Dependency Resolution: Automatically installs required dependencies for packages.
  • Remote Repository Support: Downloads and installs packages from configured repositories.
  • Group Package Management: Installs related packages grouped together (e.g., Development Tools).
  • Rollback Feature: Allows undoing updates and reverting to previous package versions (in some versions).

Note: In modern Linux distributions, YUM has been replaced by DNF (Dandified YUM), which offers improved performance and better dependency handling. However, YUM is still widely used and understood.

Configuring YUM with a Local Repository

In environments without internet access or with limited bandwidth, configuring YUM to use a local repository from a CentOS 9 ISO image is invaluable. This setup allows you to install and manage packages offline.

Step 1: Mount the CentOS 9 ISO

Mount the CentOS 9 ISO image to access its contents. Assuming the ISO is available as a device (e.g., /dev/sr0):

mount /dev/sr0 /mnt/

Step 2: Verify the Mount and Available Space

Check that the ISO is mounted correctly and verify available disk space:

df -h

Step 3: Copy ISO Contents to a Directory

Create a directory to hold the ISO contents and copy them:

mkdir /centos9

cp -vr /mnt/* /centos9/
  • cp -vr:
    • -v: Verbose output, shows files being copied.
    • -r: Recursively copy all files and directories.

Step 4: Unmount the ISO

After copying the contents, unmount the ISO:

umount /mnt/

Understanding the Repository Contents

Inside /centos9, you'll find several directories. Notably:

  • AppStream: Contains additional software packages and modules not part of the minimal base OS but available for installation.
  • BaseOS: Contains core packages required for the base operating system.

To see the number of packages in the AppStream/Packages directory:

ls -l /centos9/AppStream/Packages | wc -l

Creating Repository Metadata with createrepo

YUM requires metadata to understand the packages available in a repository. We use createrepo to generate this metadata.

Step 1: Install createrepo

Since we are working offline, we'll install createrepo from the packages we copied.

Find the createrepo_c packages:

ls /centos9/AppStream/Packages | grep createrepo_c

You should see:

createrepo_c-0.20.1-2.el9.x86_64.rpm
createrepo_c-libs-0.20.1-2.el9.x86_64.rpm

Install createrepo_c and its dependency createrepo_c-libs using rpm:

rpm -ivh /centos9/AppStream/Packages/createrepo_c-libs-0.20.1-2.el9.x86_64.rpm

rpm -ivh /centos9/AppStream/Packages/createrepo_c-0.20.1-2.el9.x86_64.rpm
  • rpm -ivh:
    • -i: Install package.
    • -v: Verbose output.
    • -h: Display hash marks to show progress.

Step 2: Verify createrepo Installation

Check the version of createrepo to verify it's installed:

createrepo -V

Step 3: Generate Repository Metadata

Create the repository metadata for the packages in AppStream/Packages:

createrepo -vd /centos9/AppStream/Packages
  • Options:
    • -v: Verbose output.
    • -d or --database: Create SQLite database files (used by YUM).

This command generates a repodata directory inside /centos9/AppStream/Packages, containing metadata files like repomd.xml, which YUM uses to resolve dependencies.

Configuring YUM to Use the Local Repository

Step 1: Backup Existing YUM Repository Files

Navigate to the YUM repository directory:

cd /etc/yum.repos.d

Create a backup directory and move existing repository files:

mkdir /backuprepo

mv /etc/yum.repos.d/* /backuprepo/

Reason: This prevents YUM from attempting to access online repositories, which is important for offline setups.

Step 2: Verify No Repositories Are Enabled

Check the current list of repositories:

yum repolist all

You should see that no repositories are enabled.

Step 3: Create a New YUM Repository Configuration File

Create a new repository file:

vim /etc/yum.repos.d/my-centos9.repo

Insert the following content:

[centos9]
name=CentOS 9 Local Repository
baseurl=file:///centos9/AppStream/Packages
enabled=1
gpgcheck=0
  • Explanation:
    • [centos9]: Unique repository ID.
    • name: Descriptive name of the repository.
    • baseurl: Path to the local repository (note the three slashes).
    • enabled=1: Enables the repository.
    • gpgcheck=0: Disables GPG signature checking (since packages are from a trusted source).

Optional: Add the BaseOS repository:

[centos9-baseos]
name=CentOS 9 BaseOS Local Repository
baseurl=file:///centos9/BaseOS/Packages
enabled=1
gpgcheck=0

Step 4: Clean YUM Cache and Rebuild Metadata

Clean all YUM caches:

yum clean all

Rebuild YUM cache:

yum makecache

Step 5: Verify the New Repository

List all repositories to confirm your local repository is recognized:

yum repolist all

You should see entries for centos9 and centos9-baseos.

Step 6: List Available Packages

List all available packages from the repository:

yum list all

Or list only available (not installed) packages:

yum list available

Installing Packages from the Local Repository

Step 1: Search for a Package

To search for a specific package, use yum search:

yum search firefox

Step 2: Install a Package

Install a package using yum install followed by the package name:

yum install firefox

YUM will resolve dependencies and install firefox along with any required packages from your local repository.

Important Notes

  • Dependency Resolution: By creating the repository metadata with createrepo, YUM can handle dependencies automatically, even in an offline environment.
  • GPG Check: Setting gpgcheck=0 disables GPG signature verification. Since you are using packages directly from the CentOS ISO (a trusted source), this is acceptable. In production environments with internet access, it's recommended to enable GPG checks.
  • Consistency: Ensure that both AppStream and BaseOS repositories are configured if you want full access to all packages available on the CentOS 9 ISO.

Troubleshooting Tips

  • Missing Packages: If a package is not found, verify that it exists in your repository by listing contents:

    ls /centos9/AppStream/Packages | grep package-name

  • Dependency Errors: If you encounter dependency issues, make sure that the repository metadata is up to date and that all necessary packages are available in your repository directories.

  • YUM Cache Issues: If packages aren't being found or repositories aren't recognized, clean the YUM cache:

    yum clean all

    And rebuild the cache:

    yum makecache