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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