mirror of https://github.com/mkerrisk/man-pages
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940 lines
24 KiB
Groff
'\" t
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.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
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.\" and Copyright (c) 2002, 2006 by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" and Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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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.\" manual page may be incorrect or out-of-date.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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.\" Modified Sat Jul 24 17:34:08 1993 by Rik Faith (faith@cs.unc.edu)
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.\" Modified Sun Jan 7 01:41:27 1996 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Sun Apr 14 12:02:29 1996 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified Sat Nov 13 16:28:23 1999 by Andries Brouwer (aeb@cwi.nl)
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.\" Modified 10 Apr 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Modified 7 Jun 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Added information on real-time signals
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.\" Modified 13 Jun 2002, by Michael Kerrisk <mtk.manpages@gmail.com>
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.\" Noted that SIGSTKFLT is in fact unused
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.\" 2004-12-03, Modified mtk, added notes on RLIMIT_SIGPENDING
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.\" 2006-04-24, mtk, Added text on changing signal dispositions,
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.\" signal mask, and pending signals.
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.\" 2008-07-04, mtk:
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.\" Added section on system call restarting (SA_RESTART)
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.\" Added section on stop/cont signals interrupting syscalls.
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.\" 2008-10-05, mtk: various additions
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.\"
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.TH SIGNAL 7 2015-03-29 "Linux" "Linux Programmer's Manual"
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.SH NAME
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signal \- overview of signals
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.SH DESCRIPTION
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Linux supports both POSIX reliable signals (hereinafter
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"standard signals") and POSIX real-time signals.
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.SS Signal dispositions
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Each signal has a current
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.IR disposition ,
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which determines how the process behaves when it is delivered
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the signal.
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The entries in the "Action" column of the tables below specify
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the default disposition for each signal, as follows:
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.IP Term
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Default action is to terminate the process.
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.IP Ign
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Default action is to ignore the signal.
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.IP Core
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Default action is to terminate the process and dump core (see
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.BR core (5)).
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.IP Stop
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Default action is to stop the process.
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.IP Cont
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Default action is to continue the process if it is currently stopped.
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.PP
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A process can change the disposition of a signal using
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.BR sigaction (2)
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or
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.BR signal (2).
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(The latter is less portable when establishing a signal handler;
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see
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.BR signal (2)
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for details.)
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Using these system calls, a process can elect one of the
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following behaviors to occur on delivery of the signal:
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perform the default action; ignore the signal;
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or catch the signal with a
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.IR "signal handler" ,
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a programmer-defined function that is automatically invoked
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when the signal is delivered.
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(By default, the signal handler is invoked on the
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normal process stack.
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It is possible to arrange that the signal handler
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uses an alternate stack; see
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.BR sigaltstack (2)
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for a discussion of how to do this and when it might be useful.)
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The signal disposition is a per-process attribute:
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in a multithreaded application, the disposition of a
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particular signal is the same for all threads.
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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 dispositions.
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During an
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.BR execve (2),
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the dispositions of handled signals are reset to the default;
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the dispositions of ignored signals are left unchanged.
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.SS Sending a signal
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The following system calls and library functions allow
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the caller to send a signal:
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.TP 16
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.BR raise (3)
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Sends a signal to the calling thread.
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.TP
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.BR kill (2)
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Sends a signal to a specified process,
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to all members of a specified process group,
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or to all processes on the system.
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.TP
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.BR killpg (2)
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Sends a signal to all of the members of a specified process group.
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.TP
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.BR pthread_kill (3)
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Sends a signal to a specified POSIX thread in the same process as
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the caller.
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.TP
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.BR tgkill (2)
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Sends a signal to a specified thread within a specific process.
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(This is the system call used to implement
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.BR pthread_kill (3).)
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.TP
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.BR sigqueue (3)
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Sends a real-time signal with accompanying data to a specified process.
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.SS Waiting for a signal to be caught
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The following system calls suspend execution of the calling process
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or thread until a signal is caught
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(or an unhandled signal terminates the process):
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.TP 16
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.BR pause (2)
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Suspends execution until any signal is caught.
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.TP
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.BR sigsuspend (2)
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Temporarily changes the signal mask (see below) and suspends
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execution until one of the unmasked signals is caught.
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.SS Synchronously accepting a signal
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Rather than asynchronously catching a signal via a signal handler,
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it is possible to synchronously accept the signal, that is,
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to block execution until the signal is delivered,
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at which point the kernel returns information about the
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signal to the caller.
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There are two general ways to do this:
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.IP * 2
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.BR sigwaitinfo (2),
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.BR sigtimedwait (2),
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and
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.BR sigwait (3)
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suspend execution until one of the signals in a specified
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set is delivered.
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Each of these calls returns information about the delivered signal.
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.IP *
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.BR signalfd (2)
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returns a file descriptor that can be used to read information
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about signals that are delivered to the caller.
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Each
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.BR read (2)
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from this file descriptor blocks until one of the signals
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in the set specified in the
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.BR signalfd (2)
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call is delivered to the caller.
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The buffer returned by
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.BR read (2)
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contains a structure describing the signal.
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.SS Signal mask and pending signals
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A signal may be
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.IR blocked ,
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which means that it will not be delivered until it is later unblocked.
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Between the time when it is generated and when it is delivered
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a signal is said to be
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.IR pending .
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Each thread in a process has an independent
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.IR "signal mask" ,
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which indicates the set of signals that the thread is currently blocking.
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A thread can manipulate its signal mask using
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.BR pthread_sigmask (3).
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In a traditional single-threaded application,
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.BR sigprocmask (2)
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can be used to manipulate the signal mask.
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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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A signal may be generated (and thus pending)
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for a process as a whole (e.g., when sent using
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.BR kill (2))
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or for a specific thread (e.g., certain signals,
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such as
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.B SIGSEGV
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and
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.BR SIGFPE ,
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generated as a
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consequence of executing a specific machine-language instruction
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are thread directed, as are signals targeted at a specific thread using
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.BR pthread_kill (3)).
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A process-directed signal may be delivered to any one of the
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threads that does not currently have the signal blocked.
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If more than one of the threads has the signal unblocked, then the
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kernel chooses an arbitrary thread to which to deliver the signal.
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A thread can obtain the set of signals that it currently has pending
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using
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.BR sigpending (2).
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This set will consist of the union of the set of pending
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process-directed signals and the set of signals pending for
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the calling thread.
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A child created via
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.BR fork (2)
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initially has an empty pending signal set;
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the pending signal set is preserved across an
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.BR execve (2).
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.SS Standard signals
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Linux supports the standard signals listed below.
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Several signal numbers
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are architecture-dependent, as indicated in the "Value" column.
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(Where three values are given, the first one is usually valid for
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alpha and sparc,
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the middle one for x86, arm, and most other architectures,
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and the last one for mips.
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(Values for parisc are
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.I not
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shown; see the Linux kernel source for signal numbering on that architecture.)
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A \- denotes that a signal is absent on the corresponding architecture.)
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First the signals described in the original POSIX.1-1990 standard.
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.TS
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l c c l
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____
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lB c c l.
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Signal Value Action Comment
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SIGHUP \01 Term Hangup detected on controlling terminal
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or death of controlling process
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SIGINT \02 Term Interrupt from keyboard
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SIGQUIT \03 Core Quit from keyboard
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SIGILL \04 Core Illegal Instruction
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SIGABRT \06 Core Abort signal from \fBabort\fP(3)
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SIGFPE \08 Core Floating point exception
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SIGKILL \09 Term Kill signal
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SIGSEGV 11 Core Invalid memory reference
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SIGPIPE 13 Term Broken pipe: write to pipe with no
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readers
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SIGALRM 14 Term Timer signal from \fBalarm\fP(2)
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SIGTERM 15 Term Termination signal
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SIGUSR1 30,10,16 Term User-defined signal 1
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SIGUSR2 31,12,17 Term User-defined signal 2
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SIGCHLD 20,17,18 Ign Child stopped or terminated
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SIGCONT 19,18,25 Cont Continue if stopped
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SIGSTOP 17,19,23 Stop Stop process
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SIGTSTP 18,20,24 Stop Stop typed at terminal
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SIGTTIN 21,21,26 Stop Terminal input for background process
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SIGTTOU 22,22,27 Stop Terminal output for background process
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.TE
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The signals
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.B SIGKILL
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and
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.B SIGSTOP
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cannot be caught, blocked, or ignored.
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Next the signals not in the POSIX.1-1990 standard but described in
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SUSv2 and POSIX.1-2001.
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.TS
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l c c l
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____
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lB c c l.
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Signal Value Action Comment
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SIGBUS 10,7,10 Core Bus error (bad memory access)
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SIGPOLL Term Pollable event (Sys V).
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Synonym for \fBSIGIO\fP
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SIGPROF 27,27,29 Term Profiling timer expired
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SIGSYS 12,31,12 Core Bad argument to routine (SVr4)
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SIGTRAP 5 Core Trace/breakpoint trap
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SIGURG 16,23,21 Ign Urgent condition on socket (4.2BSD)
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SIGVTALRM 26,26,28 Term Virtual alarm clock (4.2BSD)
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SIGXCPU 24,24,30 Core CPU time limit exceeded (4.2BSD)
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SIGXFSZ 25,25,31 Core File size limit exceeded (4.2BSD)
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.TE
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Up to and including Linux 2.2, the default behavior for
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.BR SIGSYS ", " SIGXCPU ", " SIGXFSZ ", "
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and (on architectures other than SPARC and MIPS)
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.B SIGBUS
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was to terminate the process (without a core dump).
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(On some other UNIX systems the default action for
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.BR SIGXCPU " and " SIGXFSZ
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is to terminate the process without a core dump.)
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Linux 2.4 conforms to the POSIX.1-2001 requirements for these signals,
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terminating the process with a core dump.
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Next various other signals.
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.TS
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l c c l
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____
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lB c c l.
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Signal Value Action Comment
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SIGIOT 6 Core IOT trap. A synonym for \fBSIGABRT\fP
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SIGEMT 7,\-,7 Term
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SIGSTKFLT \-,16,\- Term Stack fault on coprocessor (unused)
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SIGIO 23,29,22 Term I/O now possible (4.2BSD)
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SIGCLD \-,\-,18 Ign A synonym for \fBSIGCHLD\fP
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SIGPWR 29,30,19 Term Power failure (System V)
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SIGINFO 29,\-,\- A synonym for \fBSIGPWR\fP
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SIGLOST \-,\-,\- Term File lock lost (unused)
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SIGWINCH 28,28,20 Ign Window resize signal (4.3BSD, Sun)
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SIGUNUSED \-,31,\- Core Synonymous with \fBSIGSYS\fP
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.TE
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(Signal 29 is
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.B SIGINFO
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/
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.B SIGPWR
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on an alpha but
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.B SIGLOST
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on a sparc.)
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.B SIGEMT
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is not specified in POSIX.1-2001, but nevertheless appears
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on most other UNIX systems,
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where its default action is typically to terminate
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the process with a core dump.
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.B SIGPWR
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(which is not specified in POSIX.1-2001) is typically ignored
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by default on those other UNIX systems where it appears.
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.B SIGIO
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(which is not specified in POSIX.1-2001) is ignored by default
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on several other UNIX systems.
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Where defined,
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.B SIGUNUSED
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is synonymous with
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.\" parisc is the only exception: SIGSYS is 12, SIGUNUSED is 31
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.B SIGSYS
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on most architectures.
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.SS Real-time signals
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Starting with version 2.2,
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Linux supports real-time signals as originally defined in the POSIX.1b
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real-time extensions (and now included in POSIX.1-2001).
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The range of supported real-time signals is defined by the macros
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.B SIGRTMIN
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and
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.BR SIGRTMAX .
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POSIX.1-2001 requires that an implementation support at least
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.B _POSIX_RTSIG_MAX
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(8) real-time signals.
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.PP
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The Linux kernel supports a range of 33 different real-time
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signals, numbered 32 to 64.
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However, the glibc POSIX threads implementation internally uses
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two (for NPTL) or three (for LinuxThreads) real-time signals
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(see
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.BR pthreads (7)),
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and adjusts the value of
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.B SIGRTMIN
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suitably (to 34 or 35).
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Because the range of available real-time signals varies according
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to the glibc threading implementation (and this variation can occur
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at run time according to the available kernel and glibc),
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and indeed the range of real-time signals varies across UNIX systems,
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programs should
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.IR "never refer to real-time signals using hard-coded numbers" ,
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but instead should always refer to real-time signals using the notation
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.BR SIGRTMIN +n,
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and include suitable (run-time) checks that
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.BR SIGRTMIN +n
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does not exceed
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.BR SIGRTMAX .
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.PP
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Unlike standard signals, real-time signals have no predefined meanings:
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the entire set of real-time signals can be used for application-defined
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purposes.
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.PP
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The default action for an unhandled real-time signal is to terminate the
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receiving process.
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.PP
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Real-time signals are distinguished by the following:
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.IP 1. 4
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Multiple instances of real-time signals can be queued.
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By contrast, if multiple instances of a standard signal are delivered
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while that signal is currently blocked, then only one instance is queued.
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.IP 2. 4
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If the signal is sent using
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.BR sigqueue (3),
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an accompanying value (either an integer or a pointer) can be sent
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with the signal.
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If the receiving process establishes a handler for this signal using the
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.B SA_SIGINFO
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flag to
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.BR sigaction (2),
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then it can obtain this data via the
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.I si_value
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field of the
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.I siginfo_t
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structure passed as the second argument to the handler.
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Furthermore, the
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.I si_pid
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and
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.I si_uid
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fields of this structure can be used to obtain the PID
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and real user ID of the process sending the signal.
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.IP 3. 4
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Real-time signals are delivered in a guaranteed order.
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Multiple real-time signals of the same type are delivered in the order
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they were sent.
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If different real-time signals are sent to a process, they are delivered
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starting with the lowest-numbered signal.
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(I.e., low-numbered signals have highest priority.)
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By contrast, if multiple standard signals are pending for a process,
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the order in which they are delivered is unspecified.
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.PP
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If both standard and real-time signals are pending for a process,
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POSIX leaves it unspecified which is delivered first.
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Linux, like many other implementations, gives priority
|
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to standard signals in this case.
|
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.PP
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According to POSIX, an implementation should permit at least
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.B _POSIX_SIGQUEUE_MAX
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(32) real-time signals to be queued to
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a process.
|
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However, Linux does things differently.
|
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In kernels up to and including 2.6.7, Linux imposes
|
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a system-wide limit on the number of queued real-time signals
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for all processes.
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This limit can be viewed and (with privilege) changed via the
|
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.I /proc/sys/kernel/rtsig-max
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file.
|
|
A related file,
|
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.IR /proc/sys/kernel/rtsig-nr ,
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can be used to find out how many real-time signals are currently queued.
|
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In Linux 2.6.8, these
|
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.I /proc
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interfaces were replaced by the
|
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.B RLIMIT_SIGPENDING
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resource limit, which specifies a per-user limit for queued
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signals; see
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.BR setrlimit (2)
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|
for further details.
|
|
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The addition or real-time signals required the widening
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of the signal set structure
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.RI ( sigset_t )
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|
from 32 to 64 bits.
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|
Consequently, various system calls were superseded by new system calls
|
|
that supported the larger signal sets.
|
|
The old and new system calls are as follows:
|
|
.TS
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|
lb lb
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|
l l.
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Linux 2.0 and earlier Linux 2.2 and later
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\fBsigaction\fP(2) \fBrt_sigaction\fP(2)
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\fBsigpending\fP(2) \fBrt_sigpending\fP(2)
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\fBsigprocmask\fP(2) \fBrt_sigprocmask\fP(2)
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\fBsigreturn\fP(2) \fBrt_sigreturn\fP(2)
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\fBsigsuspend\fP(2) \fBrt_sigsuspend\fP(2)
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\fBsigtimedwait\fP(2) \fBrt_sigtimedwait\fP(2)
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.TE
|
|
.\"
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.SS Async-signal-safe functions
|
|
.PP
|
|
A signal handler function must be very careful,
|
|
since processing elsewhere may be interrupted
|
|
at some arbitrary point in the execution of the program.
|
|
POSIX has the concept of "safe function".
|
|
If a signal interrupts the execution of an unsafe function, and
|
|
.I handler
|
|
calls an unsafe function, then the behavior of the program is undefined.
|
|
|
|
POSIX.1-2004 (also known as POSIX.1-2001 Technical Corrigendum 2)
|
|
requires an implementation to guarantee that the following
|
|
functions can be safely called inside a signal handler:
|
|
|
|
.in +4
|
|
.nf
|
|
_Exit()
|
|
_exit()
|
|
abort()
|
|
accept()
|
|
access()
|
|
aio_error()
|
|
aio_return()
|
|
aio_suspend()
|
|
alarm()
|
|
bind()
|
|
cfgetispeed()
|
|
cfgetospeed()
|
|
cfsetispeed()
|
|
cfsetospeed()
|
|
chdir()
|
|
chmod()
|
|
chown()
|
|
clock_gettime()
|
|
close()
|
|
connect()
|
|
creat()
|
|
dup()
|
|
dup2()
|
|
execle()
|
|
execve()
|
|
fchmod()
|
|
fchown()
|
|
fcntl()
|
|
fdatasync()
|
|
fork()
|
|
fpathconf()
|
|
fstat()
|
|
fsync()
|
|
ftruncate()
|
|
getegid()
|
|
geteuid()
|
|
getgid()
|
|
getgroups()
|
|
getpeername()
|
|
getpgrp()
|
|
getpid()
|
|
getppid()
|
|
getsockname()
|
|
getsockopt()
|
|
getuid()
|
|
kill()
|
|
link()
|
|
listen()
|
|
lseek()
|
|
lstat()
|
|
mkdir()
|
|
mkfifo()
|
|
open()
|
|
pathconf()
|
|
pause()
|
|
pipe()
|
|
poll()
|
|
posix_trace_event()
|
|
pselect()
|
|
raise()
|
|
read()
|
|
readlink()
|
|
recv()
|
|
recvfrom()
|
|
recvmsg()
|
|
rename()
|
|
rmdir()
|
|
select()
|
|
sem_post()
|
|
send()
|
|
sendmsg()
|
|
sendto()
|
|
setgid()
|
|
setpgid()
|
|
setsid()
|
|
setsockopt()
|
|
setuid()
|
|
shutdown()
|
|
sigaction()
|
|
sigaddset()
|
|
sigdelset()
|
|
sigemptyset()
|
|
sigfillset()
|
|
sigismember()
|
|
signal()
|
|
sigpause()
|
|
sigpending()
|
|
sigprocmask()
|
|
sigqueue()
|
|
sigset()
|
|
sigsuspend()
|
|
sleep()
|
|
sockatmark()
|
|
socket()
|
|
socketpair()
|
|
stat()
|
|
symlink()
|
|
sysconf()
|
|
tcdrain()
|
|
tcflow()
|
|
tcflush()
|
|
tcgetattr()
|
|
tcgetpgrp()
|
|
tcsendbreak()
|
|
tcsetattr()
|
|
tcsetpgrp()
|
|
time()
|
|
timer_getoverrun()
|
|
timer_gettime()
|
|
timer_settime()
|
|
times()
|
|
umask()
|
|
uname()
|
|
unlink()
|
|
utime()
|
|
wait()
|
|
waitpid()
|
|
write()
|
|
.fi
|
|
.in
|
|
.PP
|
|
POSIX.1-2008 removes fpathconf(), pathconf(), and sysconf()
|
|
from the above list, and adds the following functions:
|
|
.PP
|
|
.in +4n
|
|
.nf
|
|
execl()
|
|
execv()
|
|
faccessat()
|
|
fchmodat()
|
|
fchownat()
|
|
fexecve()
|
|
fstatat()
|
|
futimens()
|
|
linkat()
|
|
mkdirat()
|
|
mkfifoat()
|
|
mknod()
|
|
mknodat()
|
|
openat()
|
|
readlinkat()
|
|
renameat()
|
|
symlinkat()
|
|
unlinkat()
|
|
utimensat()
|
|
utimes()
|
|
.fi
|
|
.in
|
|
.SS Interruption of system calls and library functions by signal handlers
|
|
If a signal handler is invoked while a system call or library
|
|
function call is blocked, then either:
|
|
.IP * 2
|
|
the call is automatically restarted after the signal handler returns; or
|
|
.IP *
|
|
the call fails with the error
|
|
.BR EINTR .
|
|
.PP
|
|
Which of these two behaviors occurs depends on the interface and
|
|
whether or not the signal handler was established using the
|
|
.BR SA_RESTART
|
|
flag (see
|
|
.BR sigaction (2)).
|
|
The details vary across UNIX systems;
|
|
below, the details for Linux.
|
|
|
|
If a blocked call to one of the following interfaces is interrupted
|
|
by a signal handler, then the call will be automatically restarted
|
|
after the signal handler returns if the
|
|
.BR SA_RESTART
|
|
flag was used; otherwise the call will fail with the error
|
|
.BR EINTR :
|
|
.\" The following system calls use ERESTARTSYS,
|
|
.\" so that they are restartable
|
|
.RS 4
|
|
.IP * 2
|
|
.BR read (2),
|
|
.BR readv (2),
|
|
.BR write (2),
|
|
.BR writev (2),
|
|
and
|
|
.BR ioctl (2)
|
|
calls on "slow" devices.
|
|
A "slow" device is one where the I/O call may block for an
|
|
indefinite time, for example, a terminal, pipe, or socket.
|
|
(A disk is not a slow device according to this definition.)
|
|
If an I/O call on a slow device has already transferred some
|
|
data by the time it is interrupted by a signal handler,
|
|
then the call will return a success status
|
|
(normally, the number of bytes transferred).
|
|
.IP *
|
|
.BR open (2),
|
|
if it can block (e.g., when opening a FIFO; see
|
|
.BR fifo (7)).
|
|
.IP *
|
|
.BR wait (2),
|
|
.BR wait3 (2),
|
|
.BR wait4 (2),
|
|
.BR waitid (2),
|
|
and
|
|
.BR waitpid (2).
|
|
.IP *
|
|
Socket interfaces:
|
|
.\" If a timeout (setsockopt()) is in effect on the socket, then these
|
|
.\" system calls switch to using EINTR. Consequently, they and are not
|
|
.\" automatically restarted, and they show the stop/cont behavior
|
|
.\" described below. (Verified from 2.6.26 source, and by experiment; mtk)
|
|
.BR accept (2),
|
|
.BR connect (2),
|
|
.BR recv (2),
|
|
.BR recvfrom (2),
|
|
.BR recvmmsg (2),
|
|
.BR recvmsg (2),
|
|
.BR send (2),
|
|
.BR sendto (2),
|
|
and
|
|
.\" FIXME What about sendmmsg()?
|
|
.BR sendmsg (2),
|
|
unless a timeout has been set on the socket (see below).
|
|
.IP *
|
|
File locking interfaces:
|
|
.BR flock (2)
|
|
and
|
|
the
|
|
.BR F_SETLKW
|
|
and
|
|
.BR F_OFD_SETLKW
|
|
operations of
|
|
.BR fcntl (2)
|
|
.IP *
|
|
POSIX message queue interfaces:
|
|
.BR mq_receive (3),
|
|
.BR mq_timedreceive (3),
|
|
.BR mq_send (3),
|
|
and
|
|
.BR mq_timedsend (3).
|
|
.IP *
|
|
.BR futex (2)
|
|
.B FUTEX_WAIT
|
|
(since Linux 2.6.22;
|
|
.\" commit 72c1bbf308c75a136803d2d76d0e18258be14c7a
|
|
beforehand, always failed with
|
|
.BR EINTR ).
|
|
.IP *
|
|
.BR getrandom (2).
|
|
.IP *
|
|
.BR pthread_mutex_lock (3),
|
|
.BR pthread_cond_wait (3),
|
|
and related APIs.
|
|
.IP *
|
|
.BR futex (2)
|
|
.BR FUTEX_WAIT_BITSET .
|
|
.IP *
|
|
POSIX semaphore interfaces:
|
|
.BR sem_wait (3)
|
|
and
|
|
.BR sem_timedwait (3)
|
|
(since Linux 2.6.22;
|
|
.\" as a consequence of the 2.6.22 changes in the futex() implementation
|
|
beforehand, always failed with
|
|
.BR EINTR ).
|
|
.RE
|
|
.PP
|
|
The following interfaces are never restarted after
|
|
being interrupted by a signal handler,
|
|
regardless of the use of
|
|
.BR SA_RESTART ;
|
|
they always fail with the error
|
|
.B EINTR
|
|
when interrupted by a signal handler:
|
|
.\" These are the system calls that give EINTR or ERESTARTNOHAND
|
|
.\" on interruption by a signal handler.
|
|
.RS 4
|
|
.IP * 2
|
|
"Input" socket interfaces, when a timeout
|
|
.RB ( SO_RCVTIMEO )
|
|
has been set on the socket using
|
|
.BR setsockopt (2):
|
|
.BR accept (2),
|
|
.BR recv (2),
|
|
.BR recvfrom (2),
|
|
.BR recvmmsg (2)
|
|
(also with a non-NULL
|
|
.IR timeout
|
|
argument),
|
|
and
|
|
.BR recvmsg (2).
|
|
.IP *
|
|
"Output" socket interfaces, when a timeout
|
|
.RB ( SO_RCVTIMEO )
|
|
has been set on the socket using
|
|
.BR setsockopt (2):
|
|
.BR connect (2),
|
|
.BR send (2),
|
|
.BR sendto (2),
|
|
and
|
|
.\" FIXME What about sendmmsg()?
|
|
.BR sendmsg (2).
|
|
.IP *
|
|
Interfaces used to wait for signals:
|
|
.BR pause (2),
|
|
.BR sigsuspend (2),
|
|
.BR sigtimedwait (2),
|
|
and
|
|
.BR sigwaitinfo (2).
|
|
.IP *
|
|
File descriptor multiplexing interfaces:
|
|
.BR epoll_wait (2),
|
|
.BR epoll_pwait (2),
|
|
.BR poll (2),
|
|
.BR ppoll (2),
|
|
.BR select (2),
|
|
and
|
|
.BR pselect (2).
|
|
.IP *
|
|
System V IPC interfaces:
|
|
.\" On some other systems, SA_RESTART does restart these system calls
|
|
.BR msgrcv (2),
|
|
.BR msgsnd (2),
|
|
.BR semop (2),
|
|
and
|
|
.BR semtimedop (2).
|
|
.IP *
|
|
Sleep interfaces:
|
|
.BR clock_nanosleep (2),
|
|
.BR nanosleep (2),
|
|
and
|
|
.BR usleep (3).
|
|
.IP *
|
|
.BR read (2)
|
|
from an
|
|
.BR inotify (7)
|
|
file descriptor.
|
|
.IP *
|
|
.BR io_getevents (2).
|
|
.RE
|
|
.PP
|
|
The
|
|
.BR sleep (3)
|
|
function is also never restarted if interrupted by a handler,
|
|
but gives a success return: the number of seconds remaining to sleep.
|
|
.SS Interruption of system calls and library functions by stop signals
|
|
On Linux, even in the absence of signal handlers,
|
|
certain blocking interfaces can fail with the error
|
|
.BR EINTR
|
|
after the process is stopped by one of the stop signals
|
|
and then resumed via
|
|
.BR SIGCONT .
|
|
This behavior is not sanctioned by POSIX.1, and doesn't occur
|
|
on other systems.
|
|
|
|
The Linux interfaces that display this behavior are:
|
|
.RS 4
|
|
.IP * 2
|
|
"Input" socket interfaces, when a timeout
|
|
.RB ( SO_RCVTIMEO )
|
|
has been set on the socket using
|
|
.BR setsockopt (2):
|
|
.BR accept (2),
|
|
.BR recv (2),
|
|
.BR recvfrom (2),
|
|
.BR recvmmsg (2)
|
|
(also with a non-NULL
|
|
.IR timeout
|
|
argument),
|
|
and
|
|
.BR recvmsg (2).
|
|
.IP *
|
|
"Output" socket interfaces, when a timeout
|
|
.RB ( SO_RCVTIMEO )
|
|
has been set on the socket using
|
|
.BR setsockopt (2):
|
|
.BR connect (2),
|
|
.BR send (2),
|
|
.BR sendto (2),
|
|
and
|
|
.\" FIXME What about sendmmsg()?
|
|
.BR sendmsg (2),
|
|
if a send timeout
|
|
.RB ( SO_SNDTIMEO )
|
|
has been set.
|
|
.IP * 2
|
|
.BR epoll_wait (2),
|
|
.BR epoll_pwait (2).
|
|
.IP *
|
|
.BR semop (2),
|
|
.BR semtimedop (2).
|
|
.IP *
|
|
.BR sigtimedwait (2),
|
|
.BR sigwaitinfo (2).
|
|
.IP *
|
|
.BR read (2)
|
|
from an
|
|
.BR inotify (7)
|
|
file descriptor.
|
|
.IP *
|
|
Linux 2.6.21 and earlier:
|
|
.BR futex (2)
|
|
.BR FUTEX_WAIT ,
|
|
.BR sem_timedwait (3),
|
|
.BR sem_wait (3).
|
|
.IP *
|
|
Linux 2.6.8 and earlier:
|
|
.BR msgrcv (2),
|
|
.BR msgsnd (2).
|
|
.IP *
|
|
Linux 2.4 and earlier:
|
|
.BR nanosleep (2).
|
|
.RE
|
|
.SH CONFORMING TO
|
|
POSIX.1, except as noted.
|
|
.\" It must be a *very* long time since this was true:
|
|
.\" .SH BUGS
|
|
.\" .B SIGIO
|
|
.\" and
|
|
.\" .B SIGLOST
|
|
.\" have the same value.
|
|
.\" The latter is commented out in the kernel source, but
|
|
.\" the build process of some software still thinks that
|
|
.\" signal 29 is
|
|
.\" .BR SIGLOST .
|
|
.SH SEE ALSO
|
|
.BR kill (1),
|
|
.BR getrlimit (2),
|
|
.BR kill (2),
|
|
.BR killpg (2),
|
|
.BR restart_syscall (2),
|
|
.BR rt_sigqueueinfo (2),
|
|
.BR setitimer (2),
|
|
.BR setrlimit (2),
|
|
.BR sgetmask (2),
|
|
.BR sigaction (2),
|
|
.BR sigaltstack (2),
|
|
.BR signal (2),
|
|
.BR signalfd (2),
|
|
.BR sigpending (2),
|
|
.BR sigprocmask (2),
|
|
.BR sigsuspend (2),
|
|
.BR sigwaitinfo (2),
|
|
.BR abort (3),
|
|
.BR bsd_signal (3),
|
|
.BR longjmp (3),
|
|
.BR raise (3),
|
|
.BR pthread_sigqueue (3),
|
|
.BR sigqueue (3),
|
|
.BR sigset (3),
|
|
.BR sigsetops (3),
|
|
.BR sigvec (3),
|
|
.BR sigwait (3),
|
|
.BR strsignal (3),
|
|
.BR sysv_signal (3),
|
|
.BR core (5),
|
|
.BR proc (5),
|
|
.BR nptl (7),
|
|
.BR pthreads (7),
|
|
.BR sigevent (7)
|