What is the difference between SIGSTOP and SIGTSTP?

Question

Just wondering about the difference between SIGSTOP and SIGTSTP signals.

Answer 1

Both signals are designed to suspend a process which will be eventually resumed with SIGCONT. The main differences between them are:

• SIGSTOP is a signal sent programmatically (eg: kill -STOP pid ) while SIGTSTP (for signal - terminal stop) may also be sent through the tty driver by a user typing on a keyboard, usually Control-Z.

• SIGSTOP cannot be ignored. SIGTSTP might be.

Answer 2

SIGSTOP can't be ignored by the targetted process.

A good example of that is the video player mpv, it can ignore SIGTSTP but not SIGSTOP.

You can test with a video running :

kill -SIGTSTP $(pidof mpv) and kill -SIGSTOP $(pidof mpv)

Of course kill -SIGCONT $(pidof mpv) to resume playing.

Answer 3

/usr/include/x86_64-linux-gnu/bits/signum.h

#define SIGSTOP     19  /* Stop, unblockable (POSIX).  */
#define SIGTSTP     20  /* Keyboard stop (POSIX).  */