ps - report a snapshot of the current processes.
Show all processes:
ps -aux
ps -ef
Show processes based on username:
ps -f -u joe
Show processes based on command name:
ps -f -C find
Show processes based on pid (process id):
ps -f -p 25009
Show processes in a hierarchy (like pstree command):
ps -e --forest
Show processes threads:
ps -C apache -L