Centos – What does EL5 and EL6 means in term of packages

The packages named gpg-pubkey* are fake RPM packages to store and manage the rpm keys. The manpage rpmkeys(8) mention how to list and remove those keys. There is also a YUM addon (package yum-plugin-keys):

$ yum keys
Key owner                                     Key email                Repo        Key ID
CentOS-7 Key (CentOS 7 Official Signing Key)  security@centos.org      installed   f4a80eb5-53a7ff4b
Fedora EPEL (7)                               epel@fedoraproject.org   installed   352c64e5-52ae6884
keys done

Alternatively, you can use RPM to list the keys in a compact view:

$ rpm -qa --scripts  gpg-pubkey* --qf '%{Version}-%{Release}  %{Packager}\n'
4a80eb5-53a7ff4b   CentOS-7 Key (CentOS 7 Official Signing Key) <security@centos.org>
352c64e5-52ae6884  Fedora EPEL (7) <epel@fedoraproject.org>

When a key is imported by the system administrator (using rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7, rpmkeys or yum install) the fake package is created (read where does rpm install custom gpg keys?).

Removing those keys is a good idea, if you purged all packages from that packager/provider/repo, since it will prevent the system from installing or upgrading any package from that repo.

Removing those keys is a bad idea, if you haven't purged all packages from that packager/provider/repo, since it will prevent the system from installing or upgrading any package from that repo.

A drpm stands for delta rpm, which is an addition to an existing rpm, and only contains the different files. Source:

Delta RPM packages contain the difference between an old and a new version of an RPM package. Applying a delta RPM on an old RPM results in the complete new RPM. It is not necessary to have a copy of the old RPM, because a delta RPM can also work with an installed RPM. The delta RPM packages are even smaller in size than patch RPMs, which is an advantage when transferring update packages over the Internet. The drawback is that update operations with delta RPMs involved consume considerably more CPU cycles than plain or patch RPMs.

The README file referred to in the documentation can be found in the GitHub repository. You will see that deltarpm is based on bsdiff.