SIGPROCMASK(2)						     Linux Programmer's Manual						    SIGPROCMASK(2)

NAME

       sigprocmask - examine and change blocked signals

SYNOPSIS

       #include <signal.h>

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       sigprocmask(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE

DESCRIPTION

       sigprocmask()  is  used to fetch and/or change the signal mask of the calling thread.  The signal mask is the set of signals whose delivery
       is currently blocked for the caller (see also signal(7) for more details).

       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 permissible 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 (if 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.

       Each of the threads in a process has its own signal mask.

       A child created via fork(2) inherits a copy of its parent's signal mask; the signal mask is preserved across execve(2).

       If SIGBUS, SIGFPE, SIGILL, or SIGSEGV are generated while they are blocked, the result is undefined, unless the	signal	was  generated	by
       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

       This  page is part of release 3.25 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2008-10-17							    SIGPROCMASK(2)