How to Troubleshoot YUM Repository Issues on CentOS 7 and CentOS 8 VMs

If you're working with CentOS 7 and CentOS 8 virtual machines and facing issues with YUM repositories despite having EPEL enabled, you're not alone. Common YUM repository issues on CentOS can stem from database errors, DNS issues, or misconfigured repository settings. Here’s a step-by-step guide on how to troubleshoot and resolve these problems.

Scenario

You have two VMs:

• CentOS 7 VM:
  • Release: CentOS Linux release 7.8.2003 (Core)
  • Repository Status: yum repolist shows repositories with a total of 25,055 packages.
• CentOS 8 VM:
  • Release: CentOS Linux release 8.2.2004 (Core)

You've ensured that:

• DNS works for all servers listed in /etc/yum.repos.d/*.repo.
• The fastestmirror plugin is disabled by setting enabled=0 in /etc/yum/pluginconf.d/fastestmirror.conf.

Despite these checks, YUM commands still hang or fail. Here’s how you can fix it.

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Step 1: Check DNS Configuration

Start by confirming DNS configuration is functioning correctly, as any DNS issues can lead to YUM command delays. Here’s how to verify:

1. Use ping or nslookup to check connectivity:

   
   ping google.com
   nslookup google.com
   

2. Ensure that /etc/resolv.conf has a valid DNS server configured. A commonly used DNS server is 8.8.8.8 (Google's DNS).

Step 2: Clear YUM Cache

Sometimes, YUM cache issues can lead to problems. Try cleaning YUM cache files:

yum clean all

This will remove cached files and force YUM to re-download repository data.

Step 3: Rebuild the RPM Database

If YUM still encounters issues, it could be due to a corrupted RPM database. Rebuilding the RPM database can often fix these types of errors. Here’s how:

1. Remove Temporary RPM Database Files:

   
   rm -f /var/lib/rpm/__*
   

2. Rebuild the RPM Database:

   
   rpm --rebuilddb -v -v
   

3. Retry the YUM Command: Now, rerun the YUM command that was causing issues. You may see a slight delay with “Determining fastest mirrors,” but it should eventually complete without errors.

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Step 4: Review the Fastest Mirror Configuration

Even though you’ve disabled the fastestmirror plugin, double-check its configuration to ensure it's fully disabled. The file to edit is:

vi /etc/yum/pluginconf.d/fastestmirror.conf

Make sure enabled=0 is set correctly. This stops YUM from spending time determining the fastest mirrors, which may reduce delays if there are network latency issues.

Step 5: Check Repository Files

Finally, verify each repository file in /etc/yum.repos.d for correctness:

1. Open each .repo file and check the baseurl and mirrorlist lines to ensure they point to valid URLs.
2. Test each URL by using curl or wget to confirm that they’re accessible from your system.

For example:

curl -I <repo_url>

Replace <repo_url> with the actual URL from your .repo files.

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Summary

To resolve YUM repository issues on CentOS, ensure DNS is configured correctly, clear the YUM cache, rebuild the RPM database, and check each repository’s configuration. The steps above should help you diagnose and solve common repository problems on CentOS 7 and CentOS 8.

Additional Note: If the problem persists, consider updating CentOS to the latest supported version, as outdated versions may have unsupported repositories or dependencies that can cause issues with YUM.