Linux Administration Cookbook

How it works...

When you run the preceding package manager commands, what you are doing is querying whichever upstream servers they're configured to talk to, and asking if there are any newer versions of the installed packages available.

Configured repositories are in /etc/yum.repos.d/ on CentOS and /etc/apt/sources.list.d (or sources.list.conf).

If there are newer versions of your software available, you have the option to install or download for later. Generally, it's a good idea to ensure that all your software is kept up to date, but this is especially true for public-facing services, such as web servers and SSH daemons.