Troubleshooting a "server down" or a "filesystem full"

Server myserver down:
ping myserver
ssh myuser@myserver

check if Hyperic monitoring agent is running:
ps -eaf|grep agent|grep java|grep -v grep

For a file system full or about to be full:

df –k
cd filesystemName
du 2> /dev/null | sort -nr | cut -f2- | xargs du -hs 2> /dev/null | more

(see http://serverfault.com/questions/62411/how-can-i-sort-du-h-output-by-size)