How to find the Process ID (PID) of a running terminal program?

Open another terminal and run ps ax | grep foo where foo is the name of the unresponsive program. This should return a line of output that looks something like this:

$ ps ax | grep firefox
2222 ?        S      0:00 /bin/sh /usr/lib/firefox-3.6.9/firefox
2231 ?        Sl   514:36 /usr/lib/firefox-3.6.9/firefox-bin
30290 pts/2    S+     0:00 grep --color=auto firefox

The first field of each line of output is a number which represents the Process ID of the program matched by grep (you can safely ignore the last one, which represents grep itself.

To halt the offending process, do: kill pid where pid is the Process ID of the program. You might have to use your judgment as to which of the matches needs to be killed, or you could use top instead. Using kill by itself sends SIGTERM, which you should try first as it allows the program to properly clean up after itself. If SIGTERM fails, try SIGHUP, which is stonger medicine: kill -HUP pid. If all else fails, send SIGKILL. But, you should only do so as a last resort, because SIGKILL causes the kernel to terminate the process immediately with no possibility for cleanup. This can at times result in data corruption or other problems. So again, only send SIGKILL as a last resort. To do so, do kill -KILL pid or kill -9 pid.

If you are running a graphical interface, of course, you don't have to fool with this crazy command-line stuff to get the job done. Just open "System Monitor", navigate to the Processes tab, choose the process you want to halt (Hm, could it be the one using 90% CPU?) and right-click it. Since the process is already stopped, (that's the problem, right?) choose End Process or Kill Process from the resulting menu.

Credit to koanhead

I don't think there is any need of such long commands when you can accomplish the same commands with pgrep, pkill, pidof etc...

• To get the pid of a Running-Program

pgrep:

   pgrep [options] pattern

DESCRIPTION : pgrep looks through the currently running processes and lists the process IDs which match the selection criteria to stdout. All the criteria have to match. For example,

• To find process named sshd owned by root.

  $ pgrep -u root sshd
  

• List the processes owned by root OR daemon.

  $ pgrep -u root,daemon
  

pidof:

DESCRIPTION:

Pidof finds the process id's (pids) of the named programs. It prints those id's on the standard output.

syntax: pidof program_name

• To kill a program by pid use pkill example:

  pkill pid    
  pkill -f process_name    
  pkill -o process_name    
  pkill -n process_name    
  pkill -l process_name
  

  -f flag: Searches the process_name (see man pkill)
  -o flag: Select only the oldest of the matching processes.
  -n flag: Select only the newest of the matching processes.
  -l flag: List the process name as well as the process ID.

The easiest way to know the pid of a running program is using:

pidof <application name>

For example, if you started vim and want to know its pid:

pidof vim

Remember that you will need to provide the exact program name that has been started.

For example, if you are running vi and execute pidof vim you won't get correct results.

Refer to pidof's manual page for more info.