top # view top consumers of memory and CPU (press 1 to see per-CPU statistics)
who # Shows who is logged into system
w # Shows which users are logged into system and what they are doing
ps # Shows processes running by user
ps -e # Shows all processes on system; try also '-a' and '-x' arguments
ps aux | grep <user_name> # Shows all processes of one user
ps ax --tree # Shows the child-parent hierarchy of all processes
ps -o %t -p <pid> # Shows how long a particular process was running.
# (E.g. 6-04:30:50 means 6 days 4 hours ...)
Ctrl z <enter> # Suspend (put to sleep) a process
fg # Resume (wake up) a suspended process and brings it into foreground
bg # Resume (wake up) a suspended process but keeps it running
# in the background.
Ctrl c # Kills the process that is currently running in the foreground
kill <process-ID> # Kills a specific process
kill -9 <process-ID> # NOTICE: "kill -9" is a very violent approach.
# It does not give the process any time to perform cleanup procedures.
kill -l # List all of the signals that can be sent to a proccess
kill -s SIGSTOP <process-ID> # Suspend (put to sleep) a specific process
kill -s SIGCONT <process-ID> # Resume (wake up) a specific process
nice -n <nice_value> <cmd> # Run a program with lower priority. Be nice to other headnode users.
# Higher "nice" values mean lower priority. Range 0-20
renice -n <priority_value> <process-ID> # Changes the priority of an existing process.
More on Terminating Processes
DigitalOcean - How To Use ps, kill, and nice to Manage Processes in Linux