Yum configuration files located in the directory /etc/yum.repos.d on CentOS 7 systems are crucial for package and repository management. These files define the sources from which yum can download and install software. Accidentally deleting these files can lead to issues with software installation and updates. This article provides a detailed guide on how to restore such files and ensure proper functionality of the yum package manager.

Preparation for Restoration

1. Backup Existing Configurations: Before making any changes, it's crucial to back up existing configuration files. If any files are still present in /etc/yum.repos.d, back them up using the command:

   sudo cp -a /etc/yum.repos.d /etc/yum.repos.d.backup
   ​

2. Identify Missing Files: To identify which repository files should be present, you can use another CentOS 7 system as a reference or search online.

Restoring Standard CentOS Repositories

1. Creating a New Repository File: If essential repositories like CentOS-Base.repo are missing, you can restore them by manually creating a new file in an editor:

   sudo nano /etc/yum.repos.d/CentOS-Base.repo
   

   Then, insert the basic repository configuration into this file, which can be found on the official CentOS website or in the documentation.

2. Using Rescue Mode or Live CD: If you're unable to boot the system due to missing configuration files, you can use rescue mode or a CentOS Live CD. Once you gain access to the file system, you can create or restore configuration files as outlined in the previous step.

Restoring Custom or Third-Party Repositories

1. Finding Repository Configurations: Configurations for custom or third-party repositories may be available online on official project websites or in documentation. Locate these configurations and manually add them to files in /etc/yum.repos.d.

Final Steps

1. Cleaning Yum Cache: After restoring configuration files, it's essential to clean the yum cache to prevent conflicts. This can be done with the command:

   sudo yum clean all
   ​

2. Verifying Configuration: Finally, verify the configuration's correctness and repository availability using the command:

   sudo yum repolist
   ​

This command will display a list of all configured repositories and help verify that the restoration was successful.

Conclusion

Restoring deleted yum configuration files from /etc/yum.repos.d on CentOS 7 requires careful steps, including manually creating or restoring files and subsequent verification. This process is crucial to ensuring that the system can properly manage software again. By following the steps outlined and handling configuration files with care, the system can be quickly restored to full functionality.