Process Control

A running executable is a process to the Unix operating system. When it is run at a command line, a process can be running in the foreground, which suppresses a prompt, or in the background, which returns a prompt to the shell.

To start in the background, add an ampersand & at the end of the command.

$./myexec -o myopt myfile&

Managing Processes

The jobs command lists your running jobs (processes) with their job index.

The key combination control-z (ctrl-z or ^z) suspends the foreground job. To resume the job in the background, type bg.

This can be combined with output from jobs

$bg %1	# place the job number 1 into the background
$fg %4	# place the job number 4 back to the foreground

For more general information about processes, use ps (process status) The -u option limits it to processes owned by user mst3k.

$ps -u mst3k
   PID TTY          TIME CMD
498571 ?        00:00:00 systemd
498575 ?        00:00:00 (sd-pam)
498581 ?        00:00:00 pulseaudio
498582 ?        00:00:00 sshd
498593 pts/3    00:00:00 bash
498665 ?        00:00:00 dbus-daemon
498670 ?        00:00:00 dbus-daemon
498672 ?        00:00:00 dbus-kill-proce
498677 ?        00:00:00 gio
498685 ?        00:00:00 gvfsd
498691 ?        00:00:00 gvfsd-fuse
517189 pts/3    00:00:00 ps

The pid is the process id.

Killing Processes

You have accidentally started a production job on a frontend node. What to do?

You can kill your forground process with Crtl c.

#oops, I was supposed to run this through Slurm
$./myexe  
^c

If you need to kill a background process, you can use jobs to locate and foreground it. You may also have processes that don’t appear with jobs. Use ps to find the PID, then

$kill -9 <pid>

Do not type the angle brackets, just the number. Many processes will ignore the kill command without the -9 option so we routinely include it.

To kill by executable name

$killall -9 <executable name> 

The kill command with -9 immediately kills the process without allowing the process to clean up or save data. The killall command can be used to kill all of the processes that match a specific name or pattern.

If you find yourself in a jam and do not know what is wrong and you must start over,

$kill -9 -1

kills all your processes, including your login.