Section (2) sigprocmask
sigprocmask, rt_sigprocmask — examine and change blocked signals
#include <signal.h> /* Prototype for the glibc wrapper function */
|const sigset_t *set,|
/* Prototype for the underlying system call */
|const kernel_sigset_t *set,|
/* Prototype for the legacy system call (deprecated) */
|const old_kernel_sigset_t *set,|
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
The behavior of the call is dependent on the value of
how, as follows.
The set of blocked signals is the union of the current set and the
The signals in
setare removed from the current set of blocked signals. It is permissible to attempt to unblock a signal which is not blocked.
The set of blocked signals is set to the argument
non-NULL, the previous value of the signal mask is stored in
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
A set of functions for modifying and inspecting variables of type sigset_t (signal sets) is described in sigsetops(3).
The use of
unspecified in a multithreaded process; see pthread_sigmask(3).
sigprocmask() returns 0 on
success and −1 on error. In the event of an error,
errno is set to indicate the
oldsetargument points outside the process_zsingle_quotesz_s allocated address space.
Either the value specified in
howwas invalid or the kernel does not support the size passed in
It is not possible to block
SIGSTOP. Attempts to do so are silently
Each of the threads in a process has its own signal mask.
See sigsetops(3) for details on manipulating signal sets.
Note that it is permissible (although not very useful) to
oldset as NULL.
C library/kernel differences
The kernel_zsingle_quotesz_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
oldset. This argument is
currently required to have a fixed architecture specific
value (equal to
wrapper function hides these details from us, transparently
the kernel provides it.
This page is part of release 4.16 of the Linux
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description of the project, information about reporting bugs,
and the latest version of this page, can be found at
Copyright (c) 2005 Michael Kerrisk
based on earlier work by faithcs.unc.edu and
Mike Battersby <mibdeakin.edu.au>
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2005-09-15, mtk, Created new page by splitting off from sigaction.2