When using package managers like Yum and DNF on a Linux system, it is important to have control over package updates to prevent unexpected changes to the system. There may be instances where you want to disable or lock package updates to maintain system stability or to prevent specific packages from being updated. Here are four ways to accomplish this:

1. Exclude Packages from Updates:
   One way to prevent packages from being updated in Yum and DNF is to exclude them from the update process. This can be done by creating a configuration file that lists the packages to exclude. For Yum, create a file named /etc/yum.conf and add the following lines:

exclude=package1 package2 package3

For DNF, create a file named /etc/dnf/dnf.conf and add the following lines:

exclude=package1 package2 package3

Replace package1, package2, and package3 with the names of the packages you want to exclude from updates.

1. Lock Packages:
   Another way to disable package updates in Yum and DNF is to lock specific packages to a certain version. This can be done by using the yum versionlock or dnf versionlock command. To lock a package in Yum, use the following command:

yum versionlock add package1

To lock a package in DNF, use the following command:

dnf versionlock add package1

This will prevent the specified package from being updated to a newer version.

1. Set Package Preferences:
   You can also disable package updates by setting preferences for specific packages in Yum and DNF. This can be done by creating a configuration file that specifies the package preferences. For Yum, create a file named /etc/yum.repos.d/example.repo and add the following lines:

[example]
name=Example Repository
baseurl=http://example.com/repo
enabled=1
gpgcheck=1
priority=1

For DNF, create a file named /etc/yum.repos.d/example.repo and add the same lines as above.

1. Disable Yum or DNF Repository:
   If you want to completely disable updates for all packages in Yum or DNF, you can disable the repository that contains the packages. This can be done by editing the repository configuration file and setting the enabled option to 0. For example, to disable the updates repository in Yum, edit the file /etc/yum.repos.d/CentOS-Base.repo and set the following line:

enabled=0

For DNF, edit the /etc/yum.repos.d/CentOS-Base.repo file and set the same line as above.

In conclusion, by using these four methods, you can effectively disable or lock package updates in Yum and DNF to maintain system stability and prevent unwanted changes to your Linux system. Just remember to always be careful when making changes to your package manager configuration to avoid any unintended consequences.