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+.\" Copyright (c) 2005 Michael Kerrisk
+.\" based on earlier work by faith@cs.unc.edu and
+.\" Mike Battersby <mib@deakin.edu.au>
+.\"
+.\" SPDX-License-Identifier: Linux-man-pages-copyleft
+.\"
+.\" 2005-09-15, mtk, Created new page by splitting off from sigaction.2
+.\"
+.TH sigprocmask 2 (date) "Linux man-pages (unreleased)"
+.SH NAME
+sigprocmask, rt_sigprocmask \- examine and change blocked signals
+.SH LIBRARY
+Standard C library
+.RI ( libc ", " \-lc )
+.SH SYNOPSIS
+.B #include <signal.h>
+.P
+.nf
+/* Prototype for the glibc wrapper function */
+.BI "int sigprocmask(int " how ", const sigset_t *_Nullable restrict " set ,
+.BI "                           sigset_t *_Nullable restrict " oldset );
+.P
+.BR "#include <signal.h>" "           /* Definition of " SIG_* " constants */"
+.BR "#include <sys/syscall.h>" "      /* Definition of " SYS_* " constants */"
+.B #include <unistd.h>
+.P
+/* Prototype for the underlying system call */
+.BI "int syscall(SYS_rt_sigprocmask, int " how ,
+.BI "                           const kernel_sigset_t *_Nullable " set ,
+.BI "                           kernel_sigset_t *_Nullable " oldset ,
+.BI "                           size_t " sigsetsize );
+.P
+/* Prototype for the legacy system call */
+.BI "[[deprecated]] int syscall(SYS_sigprocmask, int " how ,
+.BI "                           const old_kernel_sigset_t *_Nullable " set ,
+.BI "                           old_kernel_sigset_t *_Nullable " oldset );
+.fi
+.P
+.RS -4
+Feature Test Macro Requirements for glibc (see
+.BR feature_test_macros (7)):
+.RE
+.P
+.BR sigprocmask ():
+.nf
+    _POSIX_C_SOURCE
+.fi
+.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).
+.P
+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 .
+.P
+If
+.I oldset
+is non-NULL, the previous value of the signal mask is stored in
+.IR oldset .
+.P
+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).
+.P
+A set of functions for modifying and inspecting variables of type
+.I sigset_t
+("signal sets") is described in
+.BR sigsetops (3).
+.P
+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.
+On failure, \-1 is returned and
+.I errno
+is set to indicate the error.
+.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 VERSIONS
+.SS C library/kernel differences
+The kernel's definition of
+.I 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).
+.P
+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.
+.P
+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
+.I sigset_t
+(referred to as
+.I 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
+.I sigset_t
+type
+(referred to as
+.I 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
+.I 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.
+.P
+The glibc
+.BR sigprocmask ()
+wrapper function hides these details from us, transparently calling
+.BR rt_sigprocmask ()
+when the kernel provides it.
+.\"
+.SH STANDARDS
+POSIX.1-2008.
+.SH HISTORY
+POSIX.1-2001.
+.SH NOTES
+It is not possible to block
+.BR SIGKILL " or " SIGSTOP .
+Attempts to do so are silently ignored.
+.P
+Each of the threads in a process has its own signal mask.
+.P
+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).
+.P
+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).
+.P
+See
+.BR sigsetops (3)
+for details on manipulating signal sets.
+.P
+Note that it is permissible (although not very useful) to specify both
+.I set
+and
+.I oldset
+as NULL.
+.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)