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NAME

       sigprocmask - examine and change blocked signals

SYNOPSIS

       #include <signal.h>

       int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

DESCRIPTION

       sigprocmask()  is  used to change the signal mask, the set of currently
       blocked signals.  The behavior of the call is dependent on the value of
       how, as follows.

       SIG_BLOCK
              The  set  of blocked signals is the union of the current set and
              the set argument.

       SIG_UNBLOCK
              The signals in set are removed from the current set  of  blocked
              signals.   It  is  legal to attempt to unblock a signal which is
              not blocked.

       SIG_SETMASK
              The set of blocked signals is set to the argument set.

       If oldset is non-null, the previous value of the signal mask is  stored
       in oldset.

       If  set  is  NULL,  then  the  signal  mask  is unchanged (i.e., how is
       ignored), but the current value of  the  signal  mask  is  nevertheless
       returned in oldset (it is not NULL).

       The use of sigprocmask() is unspecified in a multithreaded process; see
       pthread_sigmask(3).

RETURN VALUE

       sigprocmask() returns 0 on success and -1 on error.

ERRORS

       EINVAL The value specified in how was invalid.

CONFORMING TO

       POSIX.1-2001.

NOTES

       It is not possible to block SIGKILL or SIGSTOP.  Attempts to do so  are
       silently ignored.

       If  SIGBUS,  SIGFPE,  SIGILL,  or  SIGSEGV are generated while they are
       blocked, the result is undefined, unless the signal  was  generated  by
       the kill(2), sigqueue(2), or raise(3).

       See sigsetops(3) for details on manipulating signal sets.

SEE ALSO

       kill(2), pause(2), sigaction(2), signal(2), sigpending(2), sigqueue(2),
       sigsuspend(2), pthread_sigmask(3), sigsetops(3), signal(7)

COLOPHON

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