Troubleshooting commands

dmesg
strace -p pid
/var/log/messages

kill commands

kill -3 process-id (Will not kill the process. Will create a threaddump useful for java troubleshooting)
kill -9 process-id  (Kill the process)
kill -11 process-id (Grace kill the process)
kill -15 process-id

Mail commands

To view the mailq in linux
#mailq

Check file /var/spool/mail/username