How to troubleshoot the issue of not being able to use the “yum” command in Linux?

If you are unable to use the yum command in Linux, it may be due to several reasons:

1. Internet issue: Please check if the network connection is working properly and ensure that you can access the internet.
2. Yum repository configuration issue: it may be caused by incorrect or expired Yum repository settings. You can try changing the Yum repository configuration file, such as /etc/yum.repos.d/CentOS-Base.repo, to modify the default Yum repository to a different available source, or you can use a mirror repository from within the country.
3. Dependency issue: If the system is missing required software packages, it can also cause the yum command to not work. You can try using the rpm command to manually install the missing packages.
4. The yum command has been disabled: It could be due to the system administrator or security policy disabling the yum command. Please contact the system administrator or check the system security policy.

The solution is as follows:

1. Check if the network connection is working properly to ensure access to the internet.
2. Alter the Yum repository configuration file to change the default Yum repository to another available source, or use a domestic mirror source.
3. Create a backup of the CentOS-Base repository file before making any changes by using the command cp /etc/yum.repos.d/CentOS-Base.repo /etc/yum.repos.d/CentOS-Base.repo.bak and then edit the repository file using vi /etc/yum.repos.d/CentOS-Base.repo.
4. Update the baseurl and gpgcheck configuration in the file to point to the available Yum repository, then save and exit.
5. Manually install the missing software package using the rpm command.
6. Install the package.rpm using rpm command
7. The file name package.rpm refers to the software package that needs to be installed.
8. If none of the above methods work, you can try reinstalling the yum command.
9. Reinstall the yum package.

If the issue persists, please consult the relevant documentation or contact the system administrator for further assistance.