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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.

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
       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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