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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);

   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.  In the event of an  error,  errno  is
       set to indicate the cause.


ERRORS
       EFAULT the set or oldset argument points outside the process's allocated address space.

       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(3), or raise(3).

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


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


COLOPHON
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       http://www.kernel.org/doc/man-pages/.