Yum updates for Oracle Enterprise Linux 5

Oracle Enterprise Linux (variant of Red Hat Enterprise Linux) is one sure choice when it comes to Oracle supported operating systems. Unfortunately the distribution doesn't include all required packages for such elementary software like Database 11g. System tools can be used to fetch updates from Oracle - if you have support contract.
Oracle has published public Yum repository which everybody can configure and use. Anyway Yum is de facto standard of updating RHEL systems and OEL doesn't have any repository configured out of the box so here is what you should do (from http://public-yum.oracle.com):

Fetch Oracle public Yum repository definition file

cd /etc/yum.repos.d
wget http://public-yum.oracle.com/public-yum-el5.repo

Then set enable=1 for your system repositories in the fetched configuration file. Running OEL 5 update 5 they would be entries [el5_u5_base] and [ol5_u5_base].

Update your kernel

yum install kernel

Update Oracle required standard packages

yum install oracle-linux

Reboot your system

reboot

Oracle has also created oracle-validated RPM including common required packages and kernel settings. Oracle Support Note 728346.1 discusses this a bit more. To prepare your environment for Oracle software installations, issue

yum install oracle-validated

Then, if you are still later missing any required packages you can install them with command

yum install [required package]

Yum is superior to plain rpm as it fetches latest available RPMs for your system from the configured repositories, manages dependencies automatically and handles download & install.