I'm using Mac OS X Terminal. And I use Ctrl+Z or Ctrl+C to stop some programs. But I realized that I don't know what they're exactly doing. What are they and what's the difference between them?
Control+Z is used for suspending a process by sending it the signal
SIGSTOP, which cannot be intercepted by the program. While Control+C is used to kill a process with the signal
SIGINT, and can be intercepted by a program so it can clean its self up before exiting, or not exit at all.
If you suspend a process, this will show up in the shell to tell you it has been suspended:
+ Stopped yes
However, if you kill one, you won't see any confirmation other than being dropped back to a shell prompt. When you suspend a process, you can do fancy things with it, too. For instance, running this:
With a program suspended will bring it back to the foreground.
And running the command
With a program suspended will allow it to run in the background (the program's output will still go to the TTY, though).
If you want to kill a suspended program, you don't have to bring it back with
fg first, you can simply do the command:
If you have multiple suspended commands, running
will list them, like this:
- Stopped pianobar + Stopped yes
# is the job number (the one in square brackets from the
jobs output) with
kill, can be used to do the action on that job.
Ctrl+Z suspends the process with SIGTSTP, you can resume it later. Ctrl+C kills the process with SIGINT, which terminates the process unless it is handled/ignored by the target, so you can't resume it. There's also a SIGSTOP which can be sent by
kill() and which the process can't intercept. SIGCONT is the counterpart to both SIGSTOP and SIGTSTP that un-suspends the process.
CTRL+Z stops (pauses) a job
CTRL+C terminates a job
with CTRL+C you cannot resume the process but with CTRL+Z the job can be resumed by just entering at the command promt:
if you have multiple processes paused then you should do
to see the output and select the appropriate number to resume e.g.
resumes the third job in the list. You can also have jobs running in the background with
where n is the job number.