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Question about system command in C

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# 8  
Old 03-17-2011
minor typo:
Code:
sigprocmask(SIG_SETMASK,&old, NULL);

I think that means any other children which quit while system() was waiting for its own wouldn't interrupt it. Once you unblock the signals again they should come through.

You forgot to return the signals to the way they were again before you return. Do sigprocmask(SIG_SETMASK,&old, NULL); again right before return().
# 9  
Old 03-17-2011
ok so if SIG_BLOCK blocks the signal, is there such thing as SIG_IGNORE ?
edit: i think its SIG_IGN

so to ignore SIGINT and SIGQUIT, I need something like
sigprocmask(SIG_IGN, &new, &old);
Last edited by omega666; 03-17-2011 at 06:38 PM..
# 10  
Old 03-17-2011
No. sigprocmask only blocks or unblocks signals. See man sigprocmask.

SIG_IGN is used by sigaction(). I think you use it like
Code:
struct sigaction act;

act.sa_handler=SIG_IGN;
act.sa_flags=0;

sigaction(SIGINT, &act, NULL);

# 11  
Old 03-17-2011
so i have to be using
Code:
sigset_t new, old;      
sigemptyset (&new);      
sigaddset(&new, SIGINT, SIGQUIT);  

sigaction(SIGINT, &new, %old);
sigaction(SIGQUIT, &new, %old);

Last edited by Scott; 03-17-2011 at 05:40 PM.. Reason: Code tags
# 12  
Old 03-17-2011
No, sigaction has nothing to do with sigprocmask. See man sigprocmask and man sigaction. These manual pages will be very, very helpful to you.

I don't know what %old is supposed to do. That doesn't look like valid C.

I edited in an example while you were answering I think.
# 13  
Old 03-17-2011
OK then i should be using
Code:
struct sigaction act1, act2; 
act1.sa_handler=SIG_IGN; act1.sa_flags=0;
act2.sa_handler=SIG_QUIT; act2.sa_flags=0;
sigaction(SIGINT, &act1, NULL);
sigaction(SIGQUIT, &act2, NULL);

Last edited by Scott; 03-17-2011 at 05:48 PM..
# 14  
Old 03-17-2011
Close.
Code:
act2.sa_handler=SIG_IGN; act2.sa_flags=0;

And actually, it just occurred to me that you should be putting back the old actions once you're done.

Code:
struct sigaction act1, oldact1;

act1.sa_handler=SIG_IGN; act1.sa_flags=0;
// Set a new action for SIGINT and save the old one for later
sigaction(SIGINT, &act1, &oldact1);

...

// Put it back after
sigaction(SIGINT, &oldact1, NULL);

I'm not sure if you should undo it in the child before exec or not.
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