.\" Copyright (c) 2005 Michael Kerrisk .\" based on earlier work by faith@cs.unc.edu and .\" Mike Battersby .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .\" 2005-09-15, mtk, Created new page by splitting off from sigaction.2 .\" .TH SIGPROCMASK 2 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME sigprocmask, rt_sigprocmask \- examine and change blocked signals .SH SYNOPSIS .B #include .PP .nf /* Prototype for the glibc wrapper function */ .BI "int sigprocmask(int " how ", const sigset_t *" set ", sigset_t *" oldset ); .PP /* Prototype for the underlying system call */ .BI "int rt_sigprocmask(int " how ", const kernel_sigset_t *" set , .BI " kernel_sigset_t *" oldset ", size_t " sigsetsize ); .PP /* Prototype for the legacy system call (deprecated) */ .BI "int sigprocmask(int " how ", const old_kernel_sigset_t *" set , .BI " old_kernel_sigset_t *" oldset ); .fi .PP .RS -4 Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .RE .PP .ad l .BR sigprocmask (): _POSIX_C_SOURCE .ad b .SH DESCRIPTION .BR 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 .BR signal (7) for more details). .PP The behavior of the call is dependent on the value of .IR how , as follows. .TP .B SIG_BLOCK The set of blocked signals is the union of the current set and the .I set argument. .TP .B SIG_UNBLOCK The signals in .I set are removed from the current set of blocked signals. It is permissible to attempt to unblock a signal which is not blocked. .TP .B SIG_SETMASK The set of blocked signals is set to the argument .IR set . .PP If .I oldset is non-NULL, the previous value of the signal mask is stored in .IR oldset . .PP If .I set is NULL, then the signal mask is unchanged (i.e., .I how is ignored), but the current value of the signal mask is nevertheless returned in .I oldset (if it is not NULL). .PP A set of functions for modifying and inspecting variables of type .I sigset_t ("signal sets") is described in .BR sigsetops (3). .PP The use of .BR sigprocmask () is unspecified in a multithreaded process; see .BR pthread_sigmask (3). .SH RETURN VALUE .BR sigprocmask () returns 0 on success and \-1 on error. In the event of an error, .I errno is set to indicate the cause. .SH ERRORS .TP .B EFAULT The .I set or .I oldset argument points outside the process's allocated address space. .TP .B EINVAL Either the value specified in .I how was invalid or the kernel does not support the size passed in .I sigsetsize. .SH CONFORMING TO POSIX.1-2001, POSIX.1-2008. .SH NOTES It is not possible to block .BR SIGKILL " or " SIGSTOP . Attempts to do so are silently ignored. .PP Each of the threads in a process has its own signal mask. .PP A child created via .BR fork (2) inherits a copy of its parent's signal mask; the signal mask is preserved across .BR execve (2). .PP If .BR SIGBUS , .BR SIGFPE , .BR SIGILL , or .B SIGSEGV are generated while they are blocked, the result is undefined, unless the signal was generated by .BR kill (2), .BR sigqueue (3), or .BR raise (3). .PP See .BR sigsetops (3) for details on manipulating signal sets. .PP Note that it is permissible (although not very useful) to specify both .I set and .I oldset as NULL. .\" .SS C library/kernel differences The kernel's definition of .IR sigset_t differs in size from that used by the C library. In this manual page, the former is referred to as .I kernel_sigset_t (it is nevertheless named .I sigset_t in the kernel sources). .PP The glibc wrapper function for .BR sigprocmask () silently ignores attempts to block the two real-time signals that are used internally by the NPTL threading implementation. See .BR nptl (7) for details. .PP The original Linux system call was named .BR sigprocmask (). However, with the addition of real-time signals in Linux 2.2, the fixed-size, 32-bit .IR sigset_t (referred to as .IR 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, .BR rt_sigprocmask (), was added to support an enlarged .IR sigset_t type (referred to as .IR kernel_sigset_t in this manual page). The new system call takes a fourth argument, .IR "size_t sigsetsize" , which specifies the size in bytes of the signal sets in .IR set and .IR oldset . This argument is currently required to have a fixed architecture specific value (equal to .IR sizeof(kernel_sigset_t) ). .\" sizeof(kernel_sigset_t) == _NSIG / 8, .\" which equals to 8 on most architectures, but e.g. on MIPS it's 16. .PP The glibc .BR sigprocmask () wrapper function hides these details from us, transparently calling .BR rt_sigprocmask () when the kernel provides it. .\" .SH SEE ALSO .BR kill (2), .BR pause (2), .BR sigaction (2), .BR signal (2), .BR sigpending (2), .BR sigsuspend (2), .BR pthread_sigmask (3), .BR sigqueue (3), .BR sigsetops (3), .BR signal (7) .SH COLOPHON This page is part of release 5.10 of the Linux .I 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/.