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745b20f712
already found in the sigaction(2) manual. As discussed with the committer of that delta, cross-reference the list in sigaction(2) instead of duplicating the list of functions that are safe for use within signal handlers.
244 lines
8.3 KiB
Groff
244 lines
8.3 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)signal.3 8.3 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd April 19, 1994
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.Dt SIGNAL 3
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.Os
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.Sh NAME
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.Nm signal
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.Nd simplified software signal facilities
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.Fd #include <signal.h>
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.\" The following is Quite Ugly, but syntactically correct. Don't try to
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.\" fix it.
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.Ft void \*(lp*
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.Fn signal "int sig" "void \*(lp*func\*(rp\*(lpint\*(rp\*(rp\*(rp\*(lpint"
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.Pp
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or in
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.Fx Ns 's
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equivalent but easier to read typedef'd version:
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.Ft typedef "void \*(lp*sig_t\*(rp \*(lpint\*(rp"
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.Ft sig_t
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.Fn signal "int sig" "sig_t func"
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.Sh DESCRIPTION
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This
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.Fn signal
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facility
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is a simplified interface to the more general
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.Xr sigaction 2
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facility.
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.Pp
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Signals allow the manipulation of a process from outside its
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domain as well as allowing the process to manipulate itself or
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copies of itself (children). There are two general types of signals:
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those that cause termination of a process and those that do not.
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Signals which cause termination of a program might result from
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an irrecoverable error or might be the result of a user at a terminal
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typing the `interrupt' character.
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Signals are used when a process is stopped because it wishes to access
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its control terminal while in the background (see
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.Xr tty 4 ) .
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Signals are optionally generated
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when a process resumes after being stopped,
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when the status of child processes changes,
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or when input is ready at the control terminal.
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Most signals result in the termination of the process receiving them
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if no action
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is taken; some signals instead cause the process receiving them
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to be stopped, or are simply discarded if the process has not
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requested otherwise.
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Except for the
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.Dv SIGKILL
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and
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.Dv SIGSTOP
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signals, the
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.Fn signal
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function allows for a signal to be caught, to be ignored, or to generate
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an interrupt.
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These signals are defined in the file
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.Aq Pa signal.h :
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.Bl -column SIGVTALARMXX "create core imagexxx"
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.It Sy "Name Default Action Description"
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.It Dv SIGHUP Ta "terminate process" Ta "terminal line hangup"
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.It Dv SIGINT Ta "terminate process" Ta "interrupt program"
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.It Dv SIGQUIT Ta "create core image" Ta "quit program"
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.It Dv SIGILL Ta "create core image" Ta "illegal instruction"
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.It Dv SIGTRAP Ta "create core image" Ta "trace trap"
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.It Dv SIGABRT Ta "create core image" Ta "abort program"
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(formerly
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.Dv SIGIOT )
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.It Dv SIGEMT Ta "create core image" Ta "emulate instruction executed"
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.It Dv SIGFPE Ta "create core image" Ta "floating-point exception"
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.It Dv SIGKILL Ta "terminate process" Ta "kill program"
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.It Dv SIGBUS Ta "create core image" Ta "bus error"
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.It Dv SIGSEGV Ta "create core image" Ta "segmentation violation"
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.It Dv SIGSYS Ta "create core image" Ta "non-existent system call invoked"
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.It Dv SIGPIPE Ta "terminate process" Ta "write on a pipe with no reader"
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.It Dv SIGALRM Ta "terminate process" Ta "real-time timer expired"
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.It Dv SIGTERM Ta "terminate process" Ta "software termination signal"
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.It Dv SIGURG Ta "discard signal" Ta "urgent condition present on socket"
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.It Dv SIGSTOP Ta "stop process" Ta "stop (cannot be caught or ignored)"
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.It Dv SIGTSTP Ta "stop process" Ta "stop signal generated from keyboard"
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.It Dv SIGCONT Ta "discard signal" Ta "continue after stop"
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.It Dv SIGCHLD Ta "discard signal" Ta "child status has changed"
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.It Dv SIGTTIN Ta "stop process" Ta "background read attempted from control terminal"
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.It Dv SIGTTOU Ta "stop process" Ta "background write attempted to control terminal"
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.It Dv SIGIO Ta "discard signal" Ta Tn "I/O"
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is possible on a descriptor (see
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.Xr fcntl 2 )
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.It Dv SIGXCPU Ta "terminate process" Ta "cpu time limit exceeded (see"
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.Xr setrlimit 2 )
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.It Dv SIGXFSZ Ta "terminate process" Ta "file size limit exceeded (see"
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.Xr setrlimit 2 )
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.It Dv SIGVTALRM Ta "terminate process" Ta "virtual time alarm (see"
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.Xr setitimer 2 )
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.It Dv SIGPROF Ta "terminate process" Ta "profiling timer alarm (see"
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.Xr setitimer 2 )
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.It Dv SIGWINCH Ta "discard signal" Ta "Window size change"
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.It Dv SIGINFO Ta "discard signal" Ta "status request from keyboard"
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.It Dv SIGUSR1 Ta "terminate process" Ta "User defined signal 1"
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.It Dv SIGUSR2 Ta "terminate process" Ta "User defined signal 2"
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.El
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.Pp
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The
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.Fa sig
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parameter specifies which signal was received.
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The
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.Fa func
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procedure allows a user to choose the action upon receipt of a signal.
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To set the default action of the signal to occur as listed above,
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.Fa func
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should be
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.Dv SIG_DFL .
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A
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.Dv SIG_DFL
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resets the default action.
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To ignore the signal
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.Fa func
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should be
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.Dv SIG_IGN .
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This will cause subsequent instances of the signal to be ignored
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and pending instances to be discarded.
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If
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.Dv SIG_IGN
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is not used,
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further occurrences of the signal are
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automatically blocked and
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.Fa func
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is called.
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.Pp
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The handled signal is unblocked when the
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function returns and
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the process continues from where it left off when the signal occurred.
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.Bf -symbolic
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Unlike previous signal facilities, the handler
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func() remains installed after a signal has been delivered.
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.Ef
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.Pp
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For some system calls, if a signal is caught while the call is
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executing and the call is prematurely terminated,
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the call is automatically restarted.
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(The handler is installed using the
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.Dv SA_RESTART
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flag with
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.Xr sigaction 2 . )
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The affected system calls include
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.Xr read 2 ,
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.Xr write 2 ,
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.Xr sendto 2 ,
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.Xr recvfrom 2 ,
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.Xr sendmsg 2
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and
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.Xr recvmsg 2
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on a communications channel or a low speed device
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and during a
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.Xr ioctl 2
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or
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.Xr wait 2 .
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However, calls that have already committed are not restarted,
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but instead return a partial success (for example, a short read count).
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This semantics could be changed with
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.Xr siginterrupt 3 .
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.Pp
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When a process which has installed signal handlers forks,
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the child process inherits the signals.
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All caught signals may be reset to their default action by a call
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to the
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.Xr execve 2
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function;
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ignored signals remain ignored.
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.Pp
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See
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.Xr sigaction 2
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for a list of functions
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that are considered safe for use in signal handler.
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.Sh RETURN VALUES
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The previous action is returned on a successful call.
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Otherwise, SIG_ERR is returned and the global variable
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn Signal
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will fail and no action will take place if one of the
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following occur:
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.Bl -tag -width Er
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.It Bq Er EINVAL
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.Em Sig
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is not a valid signal number.
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.It Bq Er EINVAL
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An attempt is made to ignore or supply a handler for
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.Dv SIGKILL
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or
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.Ev SIGSTOP .
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.El
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.Sh SEE ALSO
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.Xr kill 1 ,
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.Xr kill 2 ,
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.Xr ptrace 2 ,
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.Xr sigaction 2 ,
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.Xr sigaltstack 2 ,
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.Xr sigprocmask 2 ,
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.Xr sigsuspend 2 ,
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.Xr fpsetmask 3 ,
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.Xr setjmp 3 ,
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.Xr siginterrupt 3 ,
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.Xr tty 4
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.Sh HISTORY
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This
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.Fn signal
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facility appeared in
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.Bx 4.0 .
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