Q. How do I apply package updates from the Red Hat Network (RHN)?

A. RHN is subcribtion only network. Once your system is configured properly for RHN, just type the following command at a shell prompt according to your version.
a] (RHEL 4.x/3.x/2.1) - u2pdate : Old tool for installing update and works under RHEL 4.x or older version only.
b] (RHEL 5) - yum : command line tool for installing software updates via yum
c] (RHEL 5) - pup : provides a handsome graphical frontend for installing software updates via yum
To install all updates and patch the system (RHEL version 4.x and older only):
Code:
# up2date -u