Bash: Send Sigtstp Signal (Ctrl+Z)

BASH: send SIGTSTP signal (ctrl+z)

Do you want to just start it in the background? For example:

mycommand &

If you want finer grained job control, you can emulate Ctrl-Z and bg. Control-Z sends SIGTSTP ("tty stop") to the program, which suspends it:

kill -TSTP [processid]

And the bg command just sends it a SIGCONT:

kill -CONT [processid]

How to correctly send SIGTSTP signal to a child process?

Your child process is stopped, not exited. If it had exited, WIFSTOPPED(status) would be 0 and WIFEXITED(status) would be nonzero.

To continue the process, when your fg command is executed, send the SIGCONT signal to the child:

kill(child, SIGCONT)

Creating my own shell. Handling Ctrl-Z and then sending SIGCONT closes the process instead of continue it

It seems like the problem is caused because of process groups. I did only create different process groups for background jobs but since you cannot change the process group of a child after it executed exec command, you better do it at the beginning before exec call. Now, the problem is solved thanks to "@that other guy" and "@John Bollinger".

Can successfully trap CTRL-Z, but not SIGTSTP

First you must not trap SIGTSTP for the shell itself (it should ignore it), only for its child. Second if you really want to write a job controller shell, you need to manage children with the help of process group and correctly set the foreground group. Writing a shell that behave correctly with job control is a heavy task. Read POSIX standard about shells, groups, sessions, terminal control.

About your current problem. If your sub process does an exec then each handled signal is reset to its default behavior. This is because exec recovers the old code with the new one, so the previously set handler is no more available. Now you must let the child behave normally against TSTP and just let the parent track its status either with a synchronous call to wait/waitpid or with the asynchronous help of SIGCHLD. When the child stops or terminates, the parent is able to see it in the returned status (WIFEXITED, WIFSIGNALED, WIFSTOPPED).

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