mirror of https://github.com/mkerrisk/man-pages
237 lines
6.2 KiB
Groff
237 lines
6.2 KiB
Groff
.\" Copyright (c) 2005 Michael Kerrisk
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.\" based on earlier work by faith@cs.unc.edu and
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.\" Mike Battersby <mib@deakin.edu.au>
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\" %%%LICENSE_END
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.\"
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.\" 2005-09-15, mtk, Created new page by splitting off from sigaction.2
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.\"
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.TH SIGPROCMASK 2 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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sigprocmask, rt_sigprocmask \- examine and change blocked signals
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.SH SYNOPSIS
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.B #include <signal.h>
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.PP
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.nf
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/* Prototype for the glibc wrapper function */
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.BI "int sigprocmask(int " how ", const sigset_t *restrict " set ,
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.BI " sigset_t *restrict " oldset );
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.PP
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.BR "#include <signal.h>" " /* Definition of " SIG_* " constants */"
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.BR "#include <sys/syscall.h>" " /* Definition of " SYS_* " constants */"
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.B #include <unistd.h>
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.PP
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/* Prototype for the underlying system call */
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.BI "int syscall(SYS_rt_sigprocmask, int " how ", const kernel_sigset_t *" set ,
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.BI " kernel_sigset_t *" oldset ", size_t " sigsetsize );
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.PP
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/* Prototype for the legacy system call (deprecated) */
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.BI "int syscall(SYS_sigprocmask, int " how ", const old_kernel_sigset_t *" set ,
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.BI " old_kernel_sigset_t *" oldset );
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.fi
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.PP
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.RS -4
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.RE
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.PP
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.BR sigprocmask ():
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.nf
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_POSIX_C_SOURCE
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.fi
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.SH DESCRIPTION
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.BR sigprocmask ()
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is used to fetch and/or change the signal mask of the calling thread.
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The signal mask is the set of signals whose delivery is currently
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blocked for the caller
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(see also
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.BR signal (7)
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for more details).
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.PP
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The behavior of the call is dependent on the value of
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.IR how ,
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as follows.
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.TP
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.B SIG_BLOCK
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The set of blocked signals is the union of the current set and the
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.I set
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argument.
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.TP
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.B SIG_UNBLOCK
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The signals in
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.I set
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are removed from the current set of blocked signals.
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It is permissible to attempt to unblock a signal which is not blocked.
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.TP
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.B SIG_SETMASK
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The set of blocked signals is set to the argument
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.IR set .
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.PP
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If
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.I oldset
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is non-NULL, the previous value of the signal mask is stored in
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.IR oldset .
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.PP
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If
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.I set
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is NULL, then the signal mask is unchanged (i.e.,
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.I how
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is ignored),
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but the current value of the signal mask is nevertheless returned in
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.I oldset
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(if it is not NULL).
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.PP
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A set of functions for modifying and inspecting variables of type
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.I sigset_t
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("signal sets") is described in
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.BR sigsetops (3).
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.PP
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The use of
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.BR sigprocmask ()
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is unspecified in a multithreaded process; see
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.BR pthread_sigmask (3).
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.SH RETURN VALUE
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.BR sigprocmask ()
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returns 0 on success.
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On failure, \-1 is returned and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.TP
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.B EFAULT
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The
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.I set
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or
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.I oldset
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argument points outside the process's allocated address space.
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.TP
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.B EINVAL
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Either the value specified in
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.I how
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was invalid or the kernel does not support the size passed in
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.I sigsetsize.
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.SH CONFORMING TO
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POSIX.1-2001, POSIX.1-2008.
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.SH NOTES
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It is not possible to block
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.BR SIGKILL " or " SIGSTOP .
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Attempts to do so are silently ignored.
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.PP
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Each of the threads in a process has its own signal mask.
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.PP
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A child created via
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.BR fork (2)
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inherits a copy of its parent's signal mask;
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the signal mask is preserved across
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.BR execve (2).
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.PP
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If
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.BR SIGBUS ,
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.BR SIGFPE ,
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.BR SIGILL ,
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or
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.B SIGSEGV
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are generated
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while they are blocked, the result is undefined,
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unless the signal was generated by
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.BR kill (2),
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.BR sigqueue (3),
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or
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.BR raise (3).
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.PP
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See
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.BR sigsetops (3)
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for details on manipulating signal sets.
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.PP
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Note that it is permissible (although not very useful) to specify both
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.I set
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and
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.I oldset
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as NULL.
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.\"
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.SS C library/kernel differences
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The kernel's definition of
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.IR sigset_t
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differs in size from that used
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by the C library.
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In this manual page, the former is referred to as
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.I kernel_sigset_t
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(it is nevertheless named
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.I sigset_t
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in the kernel sources).
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.PP
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The glibc wrapper function for
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.BR sigprocmask ()
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silently ignores attempts to block the two real-time signals that
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are used internally by the NPTL threading implementation.
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See
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.BR nptl (7)
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for details.
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.PP
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The original Linux system call was named
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.BR sigprocmask ().
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However, with the addition of real-time signals in Linux 2.2,
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the fixed-size, 32-bit
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.IR sigset_t
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(referred to as
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.IR old_kernel_sigset_t
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in this manual page)
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type supported by that system call was no longer fit for purpose.
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Consequently, a new system call,
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.BR rt_sigprocmask (),
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was added to support an enlarged
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.IR sigset_t
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type
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(referred to as
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.IR kernel_sigset_t
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in this manual page).
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The new system call takes a fourth argument,
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.IR "size_t sigsetsize" ,
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which specifies the size in bytes of the signal sets in
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.IR set
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and
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.IR oldset .
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This argument is currently required to have a fixed architecture specific value
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(equal to
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.IR sizeof(kernel_sigset_t) ).
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.\" sizeof(kernel_sigset_t) == _NSIG / 8,
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.\" which equals to 8 on most architectures, but e.g. on MIPS it's 16.
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.PP
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The glibc
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.BR sigprocmask ()
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wrapper function hides these details from us, transparently calling
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.BR rt_sigprocmask ()
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when the kernel provides it.
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.\"
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.SH SEE ALSO
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.BR kill (2),
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.BR pause (2),
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.BR sigaction (2),
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.BR signal (2),
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.BR sigpending (2),
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.BR sigsuspend (2),
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.BR pthread_sigmask (3),
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.BR sigqueue (3),
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.BR sigsetops (3),
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.BR signal (7)
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