While taking a Red Hat Training course the instructor showed us a Yum plugin called verify. I've never used any of the Yum plugins before and after a while of playing with Yum Verify, I have decided that I should share this very cool plugin and introduce others to Yum plugins.
What are Yum Plugins
Yum plugins are packages that can be installed to provide extra functionality to the Yellowdog Update Manager or
yum. A plugin my provide an extra command or something for yum to execute in the background like finding the fastest mirror. There are quite a few Yum plugins available, for a comprehensive list you can check out The Yum Wiki.
Enable or Disable yum plugins
You can enable or disable the ability to use yum plugins by editing the
/etc/yum.conf. Within the
[main] section there should be an entry for plugins, To enable the use of plugins we will change this value to
To Enable All Plugins
# vi /etc/yum.conf
If the plugins entry is not already in the
/etc/yum.conf file you can add it anywhere under the
To Disable All Plugins
# vi /etc/yum.conf
Enable or Disable individual yum plugins
In addition to enabling or disabling all yum plugins, you can enable or disable an individual plugin as well. This is helpful if a specific package is interfering with the installation, removal of upgrading of a specific package.
To Disable A Specific Plugin
Each plugin has it's own configuration file in
/etc/yum/pluginconf.d/. By default an installed plugin is enabled, but they can be disabled by changing the
enabled=1 value to
# vi /etc/yum/pluginconf.d/<plugin-name>.conf
To re-enable the plugin you can switch
As a word of advice, if a specific plugin is interfering with the installation of a package I highly recommend disabling that specific package before disabling all plugins.
Yum Plugin: Verify
The verify plugin is the main reason I wanted to write this article. It adds the ability for yum to validate that installed packages are "intact" per the packages specification. As an example if you suspected that the permissions of a configuration file are modified or a binary was removed. You could simply run
yum verify-all to identify if that configuration was modified outside of the packages specifications. This can be extremely useful when troubleshooting a broken server.
To get started with Yum Verify we will first need to install the plugins package.
# yum install yum-plugin-verify
Once the package is installed we can start using it.
Verify a Specific Package
First we will run verify against the grep package that is currently untouched.
# yum verify grep Loaded plugins: fastestmirror, verify verify done
As you can see verify did not detect any abnormalities about the grep package. At least, not yet.
# chmod 0 /bin/grep # yum verify grep Loaded plugins: fastestmirror, verify ==================== Installed Packages ==================== grep.x86_64 : Pattern matching utilities File: /bin/grep Problem: mode does not match Current: user:---, group:---, other:--- Original: user:wrx, group:-rx, other:-rx verify done
After I had changed the permissions on the grep binary, Yum verify was able to detect that the permissions on the grep binary had been changed and reported it back.
Verify all packages
You can also run yum verify against all packages by running
yum verify-all. The
verify-all option works in a similar way to
verify, however it is used to identify all changes to all packages. The
verify-all option can be extremely useful if you are not aware of which package might be causing the issue.
# yum verify-all udev.x86_64 : A userspace implementation of devfs File: /etc/dev.d Tags: ghost Problem: file is missing File: /etc/scsi_id.config Tags: ghost, configuration, missing ok Problem: file is missing File: /etc/udev/devices Tags: ghost Problem: file is missing File: /etc/udev/scripts Tags: ghost Problem: file is missing
As a word of warning, just because a file has been modified outside of the original packages specification does not necessarily mean that it is not working correctly. Configuration files are designed to be modified, so when it comes to config files take the output of yum verify with a grain of salt. Binaries however, are a different story. In general if a binary doesn't match the packages there is either a very good reason or it is potentially a problem. Either way, Yum verify is a great tool for finding inconsistencies within a broken server.
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