Working with Package Management (RHEL/CentOS)

1. Checking for Updates

Command	Description	Notes
yum check-update	Checks for available updates for all installed packages	Shows only packages with newer versions available
yum check-update <package>	Checks for updates for a specific package	Useful to verify if a particular package has an update available
dnf check-update	Checks for available updates using DNF (newer package manager)	Replaces yum in newer RHEL/CentOS versions (8+)

Example: Checking for updates for a specific package

yum check-update httpd

Note: On systems where yum is not available, use dnf as the command-line tool for package management.

2. Upgrading Packages

Command	Description	Notes
yum update	Updates all installed packages to the latest versions available in repositories.	May upgrade dependencies if needed
yum update <package_name>	Updates a specific package to the latest version.	Useful for targeted updates
yum update --security	Upgrades only packages with security updates.	Recommended for production systems
yum update --bugfix	Upgrades only packages with bug fixes.	Useful for stability improvements

Example: Update a specific package

yum update httpd

Example: Update all packages with security fixes

yum update --security

Note: Before upgrading packages, ensure that the system is backed up or that you have a rollback plan in case of issues.

3. Installing Packages

Command	Description	Example
yum install	Installs one or more packages	`yum install httpd`
yum install <package> <package>	Installs multiple packages	`yum install httpd php mysql`
yum install <package> --assumeno	Checks what would be installed without actually installing	`yum install httpd --assumeno`

Example: Install Apache Web Server

yum install httpd

Note: Ensure the system is up to date before installing packages using yum update.

4. Removing Packages

Command	Description	Notes
yum remove	Removes specified packages and their dependencies	Use with caution as it removes all dependencies that are not required by other packages
yum erase	Alias for `yum remove`	Functionally identical to `yum remove`
dnf remove	Removes packages using DNF package manager (RHEL 8+)	Default package manager in RHEL 8 and newer

Example: Removing a Package with YUM

yum remove httpd

Example: Removing a Package with DNF

dnf remove httpd

Note: Use yum autoremove or dnf autoremove to remove orphaned dependencies after package removal.

Warning: Removing core system packages can lead to system instability or breakage. Always verify package dependencies before removal.

5. Searching for Packages

Command	Description	Example
dnf search	Searches for packages matching a keyword	`dnf search httpd`
dnf search --all	Searches all package metadata for a keyword	`dnf search --all python`
dnf search name:package	Searches for packages by name only	`dnf search name:vim`
dnf search description:package	Searches for packages by description only	`dnf search description:web`

Example: Search for packages containing "node"

dnf search node

Example: Search all package metadata for "mysql"

dnf search --all mysql

Note: The dnf search command searches in the package name, summary, description, and URL fields.

6. Showing Package Information

Command	Description	Example
rpm -qi	Display information about an installed package	`rpm -qi vim`
rpm -ql	List files installed by a package	`rpm -ql vim`
rpm -qf	Find which package owns a file	`rpm -qf /etc/passwd`
rpm -qpi	Display information about a local RPM file	`rpm -qpi /path/to/package.rpm`
rpm -qpl	List files in a local RPM file	`rpm -qpl /path/to/package.rpm`
dnf info	Display detailed information about a package	`dnf info vim`
dnf list installed	List all installed packages	`dnf list installed \| grep vim`
dnf search	Search for packages by name or description	`dnf search vim`

Example: Displaying package information

dnf info vim

Example: Listing files in a package

rpm -ql vim

Example: Finding package owner of a file

rpm -qf /etc/passwd

7. Listing Installed Packages

Command	Description	Example
rpm -qa	List all installed RPM packages	`rpm -qa \| grep -i "httpd"`
rpm -q	Query specific package details	`rpm -q httpd`
yum list installed	List all installed packages using YUM	`yum list installed \| grep -i "httpd"`
dnf list installed	List all installed packages using DNF (RHEL 8+)	`dnf list installed \| grep -i "httpd"`

rpm -qa | grep python

Note: On RHEL 8 and later, dnf is the preferred package manager over yum.

8. Cleaning Package Cache

Use dnf clean to remove cached package data, freeing up disk space and ensuring you're working with the latest package information.

Command	Description	Notes
dnf clean all	Removes all cached data including metadata, packages, and headers.	Useful for a complete cleanup before updating the system.
dnf clean packages	Removes only cached package files (.rpm files).	Keeps metadata and headers for faster updates.
dnf clean metadata	Removes only cached metadata (repomd.xml, primary.xml, etc.).	Keeps downloaded packages, useful for updating without re-downloading packages.
dnf clean expire-cache	Expires the cache and forces metadata refresh on next command.	Does not delete any files, just marks cache as expired.

Example: Cleaning package cache

# Clean all cached data
sudo dnf clean all

# Clean only package files
sudo dnf clean packages

# Clean only metadata
sudo dnf clean metadata

Note: Running dnf clean all will remove all local cache files, including downloaded RPMs and metadata. This can be useful to free up disk space or resolve issues with outdated package information.

9. Managing Repositories

Repository Type	Description	Command	Notes
Base Repository	Primary repository for the OS	`yum install <span class="highlight">base</span>`	Usually included in RHEL/CentOS by default
EPEL	Extra Packages for Enterprise Linux	`yum install <span class="highlight">epel-release</span>`	Provides additional packages not included in base repos
Custom Repository	Manually added repository	`yum-config-manager --add-repo <span class="highlight">URL</span>`	Useful for third-party software or internal packages

Example: Adding a Custom Repository

yum-config-manager --add-repo https://example.com/repo.repo

Note: After adding a repository, run yum clean all to refresh the cache.

Workflow: Enable a Repository

Use yum repolist all to view all repositories
Enable desired repository with yum-config-manager --enable <repo-name>
Verify with yum repolist enabled

Comparison: YUM vs DNF

YUM: Older package manager, still used in CentOS 7 and RHEL 7
DNF: Newer, faster, and more feature-rich package manager in CentOS 8+ and RHEL 8+

10. Installing RPM Packages

Command	Description	Example
yum install	Installs one or more RPM packages	`sudo yum install httpd`
yum install <package> --assumeno	Simulates installation without actually installing	`sudo yum install httpd --assumeno`
yum install <package> --enablerepo=<repo-name>	Installs from a specific enabled repository	`sudo yum install package-name --enablerepo=epel`

Example: Installing a Package

sudo yum install nginx

Note: Ensure you have sufficient privileges (typically root or sudo) to install packages.

Warning: Installing packages may require internet access or local repository configuration.

11. Querying RPM Packages

Command	Description	Example
rpm -q package_name	Query installed packages	`rpm -q httpd`
rpm -ql package_name	List files in a package	`rpm -ql httpd`
rpm -qi package_name	Display package information	`rpm -qi httpd`
rpm -qf file_path	Find which package owns a file	`rpm -qf /etc/httpd/conf/httpd.conf`
rpm -qg group_name	List packages in a group	`rpm -qg "Web Server"`
rpm -qa	List all installed packages	`rpm -qa \| grep httpd`

Example: Find package that owns a file

rpm -qf /etc/passwd
# Output:
# shadow-utils-4.8.1-2.el8.x86_64

Example: List all files in a package

rpm -ql httpd
# Output:
# /etc/httpd/
# /etc/httpd/conf/
# /etc/httpd/conf.d/
# /etc/httpd/conf.modules.d/
# /etc/httpd/conf/httpd.conf
# /etc/httpd/conf/extra/
# /etc/httpd/conf/extra/httpd-ssl.conf
# /etc/httpd/conf/extra/httpd-vhosts.conf
# /etc/httpd/conf/extra/httpd-userdir.conf
# /etc/httpd/conf/extra/httpd-info.conf
# /etc/httpd/conf/extra/httpd-languages.conf
# /etc/httpd/conf/extra/httpd-manual.conf
# /etc/httpd/conf/extra/httpd-mpm.conf
# /etc/httpd/conf/extra/httpd-multilang.conf
# /etc/httpd/conf/extra/httpd-ssl.conf
# /etc/httpd/conf/extra/httpd-userdir.conf
# /etc/httpd/conf/extra/httpd-vhosts.conf
# /etc/httpd/conf/extra/httpd-info.conf
# /etc/httpd/conf/extra/httpd-languages.conf
# /etc/httpd/conf/extra/httpd-manual.conf
# /etc/httpd/conf/extra/httpd-mpm.conf
# /etc/httpd/conf/extra/httpd-multilang.conf

12. Verifying Package Integrity

Command	Description	Example
rpm --verify	Verifies package integrity by checking file checksums and permissions	`rpm --verify httpd`
rpm --checksig	Checks the signature of a package file against the system's GPG keys	`rpm --checksig httpd-2.4.6-80.el7.x86_64.rpm`
rpm -K	Alias for `rpm --checksig`, used to verify package signatures	`rpm -K httpd-2.4.6-80.el7.x86_64.rpm`

Example: Verifying Package Integrity

After installing a package, you can verify its integrity using:

rpm --verify httpd

This command compares installed files with the package's original checksums and reports any discrepancies.

Example: Checking Package Signature

To ensure a package is signed by a trusted source:

rpm --checksig httpd-2.4.6-80.el7.x86_64.rpm

If the signature is valid, it will output something like:

httpd-2.4.6-80.el7.x86_64.rpm: rsa sha1 (md5) pgp md5 OK