Ubuntu:

Fetch list of available updates:

apt-get update

Strictly upgrade the current packages:

apt-get upgrade

Install updates (new ones):

apt-get dist-upgrade

Red Hat Enterprise Linux 2.1,3,4:

up2date

To update non-interactively:

up2date-nox --update

To install a specific package:

up2date <PACKAGE NAME>

To update a specific package:

up2date -u <PACKAGE NAME>

Red Hat Enterprise Linux 5:

pup

Red Hat Enterprise Linux 6:

yum update

To list a specific installed package: