Type killall -9 viber.
- A
SIGTERM or a signal 15 allows a process to end gracefully.
- A
SIGKILL or a signal 9 kills the process immediately.
By default, kill and killall will send a SIGTERM, so the process should end in a few seconds, but if a process is completely unresponsive, you can specify SIGKILL which will kill the process immediately:
Use SIGKILL only as a last resort.
The -v or --verbose option asks killall to be more elaborate on what it's doing. Hence it says it tried to kill the process with a signal 15, i.e SIGTERM.
Read more about the signals here.