11-06-2008
Signals...
(posted this in the scripting forum as well, but figured it should go here) So, what's going on is this:
For our program, we had to create our own shell, and if the user pressed ctrl-c just at the cmdline, then this signal would be ignored, but if there is a foreground process running, let's say, "sleep 10", and ctrl-c was pressed, then this process would be terminated... however, my problem lies within background processes... when I press ctrl-c after running something like "sleep 10 &", where the '&' indicates it's a background process, it uses the correct if branch of my SIGINT_handler, but it terminates the process.... so it's definitely something wrong with either the handler, or the installation of the signal.
What I don't get is... if the ctrl-c at the command line doesn't quit the program, why would it terminate my background process? Is it because the parent process just puts the ctrl-c onto the child processes? If so, is there a way to add something to my SIGINT_handler to make it ignore this signal?
****Let me just say that I have successfully been able to ignore the signal for a background process, but this way doesn't use my SIGINT_handler, which I do want it to use so some text gets printed. The way I'm talking of is just using "signal(SIGINT, SIG_IGN)", but like I said, doesn't use my SIGINT_handler...
This is my SIGINT_handler:
void SIGINT_handler(int sig)
{
if (foreground_pid == 0)
{
fprintf(stderr, "\nSIGINT ignored\n");
}
else
{
kill(foreground_pid, SIGINT);
foreground_pid = 0;
}
}
And then when I install the handler/signal, I use signal(SIGINT, SIGINT_handler) and also set foreground_pid in its respective spot... so if anyone can help, that'd be awesome, and if you need to see more code or some things are unclear, ask. Thanks.
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KILL(2) System Calls Manual KILL(2)
NAME
kill - send signal to a process
SYNOPSIS
kill(pid, sig);
DESCRIPTION
Kill sends the signal sig to the process specified by the process number in r0. See signal(2) for a list of signals.
The sending and receiving processes must have the same effective user ID, otherwise this call is restricted to the super-user.
If the process number is 0, the signal is sent to all other processes in the sender's process group; see tty(4).
If the process number is -1, and the user is the super-user, the signal is broadcast universally except to processes 0 and 1, the scheduler
and initialization processes, see init(8).
Processes may send signals to themselves.
SEE ALSO
signal(2), kill(1)
DIAGNOSTICS
Zero is returned if the process is killed; -1 is returned if the process does not have the same effective user ID and the user is not
super-user, or if the process does not exist.
ASSEMBLER
(kill = 37.)
(process number in r0)
sys kill; sig
KILL(2)