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238 lines
7.5 KiB
Groff
238 lines
7.5 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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.\"
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.TH SIGNAL 3 "19 January 1997" GNO "System Calls"
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.SH NAME
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.BR signal
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\- simplified software signal facilities
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.SH SYNOPSIS
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.br
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#include <signal.h>
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.sp 1
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void (*\fBsignal\fR (int \fIsig\fR, void (*\fIfunc\fR)(int, int)))(int, int);
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.sp 1
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or in GNO's equivalent but easier to read typedef'd version:
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.sp 1
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typedef void (*sig_t) (int, int)
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.sp 1
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sig_t
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\fBsignal\fR(int \fIsig\fR, sig_t \fIfunc\fR);
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.SH DESCRIPTION
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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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.BR 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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.LP
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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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The
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.BR 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, except for
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.BR SIGCONT
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(which cannot be blocked), and
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.BR SIGKILL
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and
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.BR SIGSTOP
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(which cannot be caught, blocked, or ignored).
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.LP
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These signals are defined in the file <signal.h>:
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.RS
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.nf
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Name Default Action Description
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SIGHUP termination terminal line hangup
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SIGINT termination interrupt program
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SIGQUIT termination quit program
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SIGILL termination illegal instruction
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SIGTRAP termination trace trap
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SIGABRT termination abort (generated by \fBabort\fR(3))
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SIGEMT termination emulator trap
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SIGFPE termination arithmetic exception
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SIGKILL termination kill program
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SIGBUS termination bus error
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SIGSEGV termination segmentation fault
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SIGSYS termination bad argument to system call
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SIGPIPE termination write on a socket with no readers
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SIGALRM termination real-time timer expired
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SIGTERM termination software termination
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SIGURG discarded urgent condition present on socket
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SIGSTOP stop stop
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SIGTSTP stop stop signal from keyboard
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SIGCONT discarded continue after stop
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SIGCHLD discarded child status has changed
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SIGCLD discarded SYSV name for SIGCHLD
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SIGTTIN stop background read attempted
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SIGTTOU stop background write attempted
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SIGIO discarded input/output possible on a file descriptor
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SIGPOLL discarded SYSV name for SIGIO
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SIGXCPU termination exceeded CPU time limit
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SIGUSR1 termination user defined signal 1
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SIGUSR2 termination user defined signal 2
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.fi
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.RE
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.LP
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The
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.I 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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.I func
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should be
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.BR SIG_DFL .
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A
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.BR SIG_DFL
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resets the default action.
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To ignore the signal
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.I func
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should be
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.BR 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. If
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.BR 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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.I func
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is called.
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.LP
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The handled signal is unblocked with 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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\fIUnlike previous Unix signal facilities, the handler
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func() remains installed after a signal has been delivered.\fR
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This behavior remains unchanged from GNO v2.0.4.
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.LP
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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 affected system calls include
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.BR read (2),
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.BR write (2),
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.BR sendto (2),
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.BR recvfrom (2),
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.BR sendmsg (2)
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and
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.BR 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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.BR ioctl (2)
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or
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.BR 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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.LP
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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 will be reset to their default action by a call
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to one of the
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.BR execve (2)
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family of functions;
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ignored signals remain ignored.
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.SH NOTES
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As can be surmised from the prototype above,
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.IR func
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should be defined as follows:
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.RS
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.sp 1
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void \fIfunc\fR(int \fIsig\fR, int \fIcode\fR)
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.sp 1
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.RE
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.I sig
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is the signal that will invoke the handler, and
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.I code
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is additional information about the interrupt condition. Currently,
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.I code
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is always zero. The handler should probably also be compiled using the
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.B "#pragma databank 1"
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directive, in the event
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.I func
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is not in the same bank as the C global data segment
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.RI ( func
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is called with the data bank equal to the program bank).
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.LP
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Orca/C already provides a
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.BR signal
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function, but it doesn't do very much. GNO's <signal.h> file replaces
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the one that comes with Orca/C.
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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, \-1 is returned and the global variable
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.IR errno
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is set to indicate the error.
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.SH ERRORS
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.BR 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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.RS
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.IP \fBEINVAL\fR
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.IR Sig
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is not a valid signal number.
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.IP \fBEINVAL\fR
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An attempt is made to ignore or supply a handler for
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.BR SIGKILL
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or
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.BR SIGSTOP .
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.IP \fBEINVAL\fR
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An attempt is made to ignore
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.BR SIGCONT
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(by default
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.BR SIGCONT
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is ignored).
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.SH SEE ALSO
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.BR kill (1),
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.BR execve (2),
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.BR fork (2),
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.BR kill (2),
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.BR sigblock (2),
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.BR sigsetmask (2),
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.BR wait (2),
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.BR tty (4)
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.SH HISTORY
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A
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.BR signal
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facility appeared in 4.0BSD.
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