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

NAME

       sigprocmask, rt_sigprocmask - examine and change blocked signals

SYNOPSIS

       #include <signal.h>

       /* Prototype for the glibc wrapper function */
       int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

       /* Prototype for the underlying system call */
       int rt_sigprocmask(int how, const kernel_sigset_t *set,
			  kernel_sigset_t *oldset, size_t sigsetsize);

       /* Prototype for the legacy system call (deprecated) */
       int sigprocmask(int how, const old_kernel_sigset_t *set,
		       old_kernel_sigset_t *oldset);

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

       sigprocmask(): _POSIX_C_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).

       A set of functions for modifying and inspecting variables of type sigset_t ("signal sets") is described in sigsetops(3).

       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 Either the value specified in how was invalid or the kernel does not support the size passed in sigsetsize.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008.

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.

       Note that it is permissible (although not very useful) to specify both set and oldset as NULL.

   C library/kernel differences
       The  kernel's  definition  of  sigset_t differs in size from that used by the C library.  In this manual page, the former is referred to as
       kernel_sigset_t (it is nevertheless named sigset_t in the kernel sources).

       The glibc wrapper function for sigprocmask() silently ignores attempts to block the two real-time signals that are used internally  by  the
       NPTL threading implementation.  See nptl(7) for details.

       The  original  Linux  system  call  was named sigprocmask().  However, with the addition of real-time signals in Linux 2.2, the fixed-size,
       32-bit sigset_t (referred to as old_kernel_sigset_t in this manual page) type supported by that system call was no longer fit for  purpose.
       Consequently,  a  new system call, rt_sigprocmask(), was added to support an enlarged sigset_t type (referred to as kernel_sigset_t in this
       manual page).  The new system call takes a fourth argument, size_t sigsetsize, which specifies the size in bytes of the signal sets in  set
       and oldset.  This argument is currently required to have a fixed architecture specific value (equal to sizeof(kernel_sigset_t)).

       The glibc sigprocmask() wrapper function hides these details from us, transparently calling rt_sigprocmask() when the kernel provides it.

SEE ALSO

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

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15							    SIGPROCMASK(2)