UNIX one-liner to kill a hanging Firefox process

Here's a useful one-liner that uses awk (and grep, sort and sed too), to kill a Firefox process that has hung.

Firefox hung just now on my machine - so I ran this command:

# kill -HUP ` ps -aef | grep -i firefox | sort -k 2 -r | sed 1d | awk ' { print $2 } ' `


NOTE: That's sed space one d in the line above, i.e. the digit "one", not the letter "ell".

The command does all of the following:

- Uses the ps command to get a list of all running processes; the list is written to standard output.

- Pipes that to grep -i firefox to identify all Firefox-related processes (this is needed because, on Ubuntu Linux, there is more than one such process (even for a single running Firefox instance), because the firefox command you run is a shell script which calls another script which finally calls the real firefox binary).

- Pipes that to sort -k 2 -r to sort the output in descending order by the process-id (2nd field of the ps output).

- Pipes that to sed 1d to delete the line of output that refers to the grep in the pipeline itself - otherwise I'd end up killing the grep as well (because grep -i firefox matches the line for the grep process as well as the actual Firefox-related processes).

NOTE: This part (using sed 1d to kill the grep) is based on knowing that the grep process is the process that currently has the highest-numbered process id (due to the preceding sort command), of all the processes that match the grep pattern. So it'll be the first line of output, so sed 1d deletes it (and passes all the other lines untouched, to the next command in the pipeline).

- Pipes that to awk ' { print $2 } ' to extract only the 2nd field, the process-id, from each line.

- And, since the entire part of the command after the HUP is enclosed in backward quotes (also called backticks or grave accents), what happens is that the final output of the commands between the backticks replaces the backticks and everything between them, so what the shell finally sees before it runs the kill command, is something like this:

kill -HUP 8849 8845 8833

- which results in automagically killing all (and only) the processes related to the single instance of Firefox that was running (but hung) on my machine.

WARNING: Don't try this command (exactly as shown) if you're on a Linux system with multiple users, since it would end up deleting all their running Firefox processes as well - and don't run it even if you yourself are running multiple instances of Firefox and only want to kill one of them.

NOTE: The sort command uses the -r option to list the processes in reverse numeric order by process-id, so that we kill each child before its parent, to avoid creating orphan processes.

Vasudev Ram.