Section: Linux Programmer's Manual (2)
sigprocmask, rt_sigprocmask - examine and change blocked signals
/* 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,
Feature Test Macro Requirements for glibc (see
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
for more details).
The behavior of the call is dependent on the value of
The set of blocked signals is the union of the current set and the
The signals in
are 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
is non-NULL, the previous value of the signal mask is stored in
is NULL, then the signal mask is unchanged (i.e.,
but the current value of the signal mask is nevertheless returned in
(if it is not NULL).
A set of functions for modifying and inspecting variables of type
("signal sets") is described in
The use of
is unspecified in a multithreaded process; see
returns 0 on success and -1 on error.
In the event of an error,
is set to indicate the cause.
argument points outside the process's allocated address space.
Either the value specified in
was invalid or the kernel does not support the size passed in
It is not possible to block
Attempts to do so are silently ignored.
Each of the threads in a process has its own signal mask.
A child created via
inherits a copy of its parent's signal mask;
the signal mask is preserved across
while they are blocked, the result is undefined,
unless the signal was generated by
for details on manipulating signal sets.
Note that it is permissible (although not very useful) to specify both
C library/kernel differences
The kernel's definition of
differs in size from that used
by the C library.
In this manual page, the former is referred to as
(it is nevertheless named
in the kernel sources).
The glibc wrapper function for
silently ignores attempts to block the two real-time signals that
are used internally by the NPTL threading implementation.
The original Linux system call was named
However, with the addition of real-time signals in Linux 2.2,
the fixed-size, 32-bit
(referred to as
in this manual page)
type supported by that system call was no longer fit for purpose.
Consequently, a new system call,
was added to support an enlarged
(referred to as
in this manual page).
The new system call takes a fourth argument,
which specifies the size in bytes of the signal sets in
This argument is currently required to have a fixed architecture specific value
wrapper function hides these details from us, transparently calling
when the kernel provides it.
This page is part of release 5.10 of the Linux
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information about reporting bugs,
and the latest version of this page,
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