Sometimes on your RHEL-like system you may encounter the following error:
$ sudo yum grouplist Loaded plugins: rhnplugin, security This system is not registered with ULN. You can use up2date --register to register. ULN support will be disabled. Setting up Group Process Error: No group data available for configured repositories
This may happen when you're hosting your own YUM package repository and the group metadata in the repository is missing. This error is easily fixable on the YUM repo with createrepo command.
Log onto your repository server and go to your repo directory that
repodata directory. Then run
$ cd /repo/CentOS/6/os/x86_64 $ createrepo -g repodata/comps.xml .
This will create the groups listing for your repository.
If you do not have the
repodata/comps.xml file, try looking at the
mirror that you're mirroring from. It should have this file. Sometimes
it may not be copied correctly, especially if you use reposync command
to sync your repos.
createrepo manpages for more goodness.