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 contains “repodata” directory. Then run “createrepo -g”:
$ 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.
Check the createrepo manpages for more goodness.