Software list for CentOS

This is a rough procedure I use to determine what software is installed on my system, and what has changed.

1. Create a text file with the list of currently installed software. This is usually best done on a fresh system. This code will also date the file so you can insert it into your scripts:
   
   sudo rpm -qa > ~/`hostname -s`-software-`date +%Y%m%d`.txt


2. We can now send ourselves an email of what has been installed on this system (in case the system is compromised):
   
   mail -s "`hostname -s` Software `date +%Y%m%d`" john@example.com.au < ~/host-software-20111026.txt


3. We can also compare files to see how our system has changed (for instance, on an update):
   
   diff host-software-20111026.txt host-software-20111027.txt