Advanced package management (RPM, YUM, DNF)

Advanced Package Management in RHEL: RPM, YUM, and DNF
Red Hat Enterprise Linux (RHEL) uses a robust package management system to install, update, and manage software. Below is a detailed breakdown of the core tools—RPM, YUM, and DNF—and their advanced use cases for experienced administrators:

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1. RPM (Red Hat Package Manager)

Basics:

• Low-level tool for installing, querying, and managing individual .rpm packages.
• Does not resolve dependencies automatically (unlike YUM/DNF).

Advanced Use Cases:

• Querying Packages:

  rpm -qa                        # List all installed packages
  rpm -qi <package>              # Show package info
  rpm -ql <package>              # List files installed by a package
  rpm -qf /path/to/file          # Find which package owns a file

• Verify Package Integrity:

  rpm -V <package>               # Check for changes to package files
  rpm --checksig <package.rpm>   # Verify GPG signature

• Install/Remove Packages Manually:

  rpm -ivh <package.rpm>         # Install with verbose output
  rpm -e <package>               # Remove a package (if no dependencies)

• Extract Files from RPM Without Installing:

  rpm2cpio <package.rpm> | cpio -idmv

Key Notes:

• Use RPM for direct control over specific packages (e.g., air-gapped systems).
• Dependency resolution must be handled manually.

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2. YUM (Yellowdog Updater Modified)

Basics:

• High-level tool that automates dependency resolution using RPM under the hood.
• Default in RHEL 7, deprecated in RHEL 8/9 in favor of DNF (but still aliased as yum).

Advanced Use Cases:

• Manage Repositories:

  yum repolist                   # List enabled repositories
  yum-config-manager --add-repo=http://repo.url
  yum-config-manager --disable <repo-id>

• Clean Up:

  yum clean all                  # Remove cached metadata and packages
  yum autoremove                 # Remove unused dependencies

• Downgrade Packages:

  yum history list               # View transaction history
  yum history undo <transaction-id>  # Roll back a specific update

• Version Locking:

  yum install yum-plugin-versionlock
  yum versionlock <package>      # Prevent updates to a package

• Security Updates:

  yum updateinfo list security   # List available security patches
  yum update --security          # Apply only security updates

Key Notes:

• Slower than DNF due to Python 2 dependency (in older versions).
• Still useful for legacy scripts, but DNF is preferred in RHEL 8/9.

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3. DNF (Dandified YUM)

Basics:

• Modern replacement for YUM in RHEL 8/9.
• Written in Python 3 with faster dependency resolution and improved performance.

Advanced Use Cases:

• Modularity (RHEL 8/9 AppStream):

  dnf module list                 # List available modules
  dnf module install nodejs:14    # Install a specific module stream
  dnf module reset nodejs         # Reset to default module

• Advanced Queries:

  dnf repoquery <pattern>         # Search packages in repositories (even if not installed)
  dnf provides /path/to/file      # Find which package provides a file

• Transaction History:

  dnf history                     # View all transactions
  dnf history undo <ID>           # Roll back a transaction
  dnf history rollback            # Revert to a previous state

• Groups and Environments:

  dnf group list                  # List package groups (e.g., "Development Tools")
  dnf group install "Development Tools"

• Parallel Downloads & Delta RPMs:

  # Enable delta RPMs in /etc/dnf/dnf.conf:
  deltarpm=1

• Automate with Scripts:

  dnf install -y --nogpgcheck <package>   # Skip GPG checks (use cautiously)
  dnf update --downloadonly               # Download updates without installing

Key Differences from YUM:

• Faster dependency resolution with libsolv library.
• Better support for modular packages and parallel operations.
• Cleaner command syntax and improved plugins.

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Best Practices for Advanced Admins

1. Use DNF as Default:

• In RHEL 8/9, yum is an alias for dnf, but use dnf for scripting to avoid future compatibility issues.

1. Secure Repositories:

• Always enable GPG checks for repositories.
• Use rpm --import <key> to add trusted GPG keys.

1. Automate with Ansible:

• Use the dnf Ansible module for idempotent package management: “`yaml
  • name: Install Apache
    dnf:
    name: httpd
    state: latest
    “`

1. Resolve Dependency Hell:

• Use dnf repoquery --deplist <package> to analyze dependencies.
• Remove conflicting packages with dnf remove --duplicates.

1. Create Local Repositories:

• Use createrepo to build a local mirror for air-gapped systems.

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Comparison Table

Feature	RPM	YUM	DNF
Dependency Resolution	❌ No	✔️ Yes	✔️ Yes (faster)
Modularity Support	❌ No	❌ Limited	✔️ Full
Transaction History	❌ No	✔️ Basic	✔️ Advanced
Performance	Fast (per-pkg)	Slow	Very Fast
RHEL Version	All	RHEL 7 (legacy)	RHEL 8/9

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Troubleshooting Tips

• Broken Dependencies:

  dnf clean all && dnf autoremove
  dnf distro-sync                # Resync packages with repository

• Corrupted RPM Database:

  rm -f /var/lib/rpm/__db.*       # Remove corrupted DB files
  rpm --rebuilddb                # Rebuild RPM database

• Debug Package Issues:

  dnf --verbose install <package>  # Show detailed installation logs

By mastering these tools, you’ll streamline deployments, ensure system consistency, and troubleshoot complex package issues efficiently.