192 lines
5.6 KiB
Groff
192 lines
5.6 KiB
Groff
.\" $NetBSD: signal.3,v 1.24 2004/06/13 19:17:06 lha Exp $
|
|
.\"
|
|
.\" Copyright (c) 1980, 1991, 1993
|
|
.\" The Regents of the University of California. All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms, with or without
|
|
.\" modification, are permitted provided that the following conditions
|
|
.\" are met:
|
|
.\" 1. Redistributions of source code must retain the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer.
|
|
.\" 2. Redistributions in binary form must reproduce the above copyright
|
|
.\" notice, this list of conditions and the following disclaimer in the
|
|
.\" documentation and/or other materials provided with the distribution.
|
|
.\" 3. Neither the name of the University nor the names of its contributors
|
|
.\" may be used to endorse or promote products derived from this software
|
|
.\" without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
|
|
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
|
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
|
|
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
|
|
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
|
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
|
|
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
|
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
|
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
|
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
|
.\" SUCH DAMAGE.
|
|
.\"
|
|
.\" @(#)signal.3 8.3 (Berkeley) 4/19/94
|
|
.\"
|
|
.Dd June 11, 2004
|
|
.Dt SIGNAL 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm signal
|
|
.Nd simplified software signal facilities
|
|
.Sh LIBRARY
|
|
.Lb libc
|
|
.Sh SYNOPSIS
|
|
.In signal.h
|
|
.\" The following is Quite Ugly, but syntactically correct. Don't try to
|
|
.\" fix it.
|
|
.Ft void \*(lp*
|
|
.Fn signal "int sig" "void \*(lp*func\*(rp\*(lpint\*(rp\*(rp\*(rp\*(lpint"
|
|
.Sh DESCRIPTION
|
|
This
|
|
.Fn signal
|
|
facility
|
|
is a simplified interface to the more general
|
|
.Xr sigaction 2
|
|
facility.
|
|
.Pp
|
|
Signals allow the manipulation of a process from outside its
|
|
domain as well as allowing the process to manipulate itself or
|
|
copies of itself (children).
|
|
There are two general types of signals:
|
|
those that cause termination of a process and those that do not.
|
|
Signals which cause termination of a program might result from
|
|
an irrecoverable error or might be the result of a user at a terminal
|
|
typing the `interrupt' character.
|
|
Signals are used when a process is stopped because it wishes to access
|
|
its control terminal while in the background (see
|
|
.Xr tty 4 ) .
|
|
Signals are optionally generated
|
|
when a process resumes after being stopped,
|
|
when the status of child processes changes,
|
|
or when input is ready at the control terminal.
|
|
Most signals result in the termination of the process receiving them
|
|
if no action
|
|
is taken; some signals instead cause the process receiving them
|
|
to be stopped, or are simply discarded if the process has not
|
|
requested otherwise.
|
|
Except for the
|
|
.Dv SIGKILL
|
|
and
|
|
.Dv SIGSTOP
|
|
signals, the
|
|
.Fn signal
|
|
function allows for a signal to be caught, to be ignored, or to generate
|
|
an interrupt.
|
|
See
|
|
.Xr signal 7
|
|
for comprehensive list of supported signals.
|
|
.Pp
|
|
The
|
|
.Fa func
|
|
procedure allows a user to choose the action upon receipt of a signal.
|
|
To set the default action of the signal to occur as listed above,
|
|
.Fa func
|
|
should be
|
|
.Dv SIG_DFL .
|
|
A
|
|
.Dv SIG_DFL
|
|
resets the default action.
|
|
To ignore the signal
|
|
.Fa func
|
|
should be
|
|
.Dv SIG_IGN .
|
|
This will cause subsequent instances of the signal to be ignored
|
|
and pending instances to be discarded.
|
|
If
|
|
.Dv SIG_IGN
|
|
is not used,
|
|
further occurrences of the signal are
|
|
automatically blocked and
|
|
.Fa func
|
|
is called.
|
|
.Pp
|
|
The handled signal is unblocked when the
|
|
function returns and
|
|
the process continues from where it left off when the signal occurred.
|
|
.Bf -symbolic
|
|
Unlike previous signal facilities, the handler
|
|
func() remains installed after a signal has been delivered.
|
|
.Ef
|
|
.Pp
|
|
For some system calls, if a signal is caught while the call is
|
|
executing and the call is prematurely terminated,
|
|
the call is automatically restarted.
|
|
(The handler is installed using the
|
|
.Dv SA_RESTART
|
|
flag with
|
|
.Xr sigaction 2 ) .
|
|
The affected system calls include
|
|
.Xr read 2 ,
|
|
.Xr write 2 ,
|
|
.Xr sendto 2 ,
|
|
.Xr recvfrom 2 ,
|
|
.Xr sendmsg 2
|
|
and
|
|
.Xr recvmsg 2
|
|
on a communications channel or a low speed device
|
|
and during a
|
|
.Xr ioctl 2
|
|
or
|
|
.Xr wait 2 .
|
|
However, calls that have already committed are not restarted,
|
|
but instead return a partial success (for example, a short read count).
|
|
.Pp
|
|
When a process which has installed signal handlers forks,
|
|
the child process inherits the signals.
|
|
All caught signals may be reset to their default action by a call
|
|
to the
|
|
.Xr execve 2
|
|
function;
|
|
ignored signals remain ignored.
|
|
.Pp
|
|
Only functions that are async-signal-safe can safely be used in signal
|
|
handlers, see
|
|
.Xr signal 7
|
|
for a complete list.
|
|
.Sh RETURN VALUES
|
|
The previous action is returned on a successful call.
|
|
Otherwise,
|
|
.Dv SIG_ERR
|
|
is returned and the global variable
|
|
.Va errno
|
|
is set to indicate the error.
|
|
.Sh ERRORS
|
|
.Fn signal
|
|
will fail and no action will take place if one of the following occur:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EINVAL
|
|
Specified
|
|
.Em sig
|
|
is not a valid signal number.
|
|
.It Bq Er EINVAL
|
|
An attempt is made to ignore or supply a handler for
|
|
.Dv SIGKILL
|
|
or
|
|
.Dv SIGSTOP .
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr kill 1 ,
|
|
.Xr kill 2 ,
|
|
.Xr ptrace 2 ,
|
|
.Xr sigaction 2 ,
|
|
.Xr sigaltstack 2 ,
|
|
.Xr sigprocmask 2 ,
|
|
.Xr sigsuspend 2 ,
|
|
.Xr psignal 3 ,
|
|
.Xr setjmp 3 ,
|
|
.Xr strsignal 3 ,
|
|
.Xr tty 4 ,
|
|
.Xr signal 7
|
|
.Sh HISTORY
|
|
This
|
|
.Fn signal
|
|
facility appeared in
|
|
.Bx 4.0 .
|