Here, Have a Rails DevOps Cheatsheet
Rubytune has put together a reference sheet of DevOps-y command-line tips dealing with process basics, memory, disk/files, network, and more. Want to get IP/Ethernet info?
Maybe you need to "tail" all queries hitting mysql:
pt-query-digest --processlist h=localhost --print --no-report --user xxxx --password *****
There is, of course, much much more. You can see the rest of the cheatsheet over at Rubytune.