sigprocmask, rt_sigprocmask — examine and change blocked signals
|const 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
set 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
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
points outside the process's allocated address
The value specified in
how was invalid.
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.
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 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. 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 the value
sizeof(sigset_t) (or the
error EINVAL results). The
function hides these details from us, transparently calling
rt_sigprocmask() when the
kernel provides it.
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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