What are your most used troubleshooting commands on Linux servers?

[Rameshsalvi 0]

I'm a NOC guy looking to move up and decided to take on some linux, so I'm curious, what commands or tools do you regularly use to work and troubleshoot linux servers?

[OpenSourcerer 1442]

 

I was trying to compile something useful, but it really depends on what is broken.. you can use a server for pretty much everything.