c6ff3a1bf7
of the typeset output, tend to make diffs harder to read and provide bad examples for new-comers to mdoc.
579 lines
16 KiB
Groff
579 lines
16 KiB
Groff
.\" Copyright (c) 1980, 1990, 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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.\" From: @(#)sigaction.2 8.2 (Berkeley) 4/3/94
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.\" $FreeBSD$
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.\"
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.Dd April 3, 1994
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.Dt SIGACTION 2
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.Os
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.Sh NAME
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.Nm sigaction
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.Nd software signal facilities
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.Sh SYNOPSIS
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.Fd #include <signal.h>
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.Bd -literal
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struct sigaction {
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/*
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* Signal handler function if flag SA_SIGINFO is not used and for
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* SIG_DFL and SIG_IGN.
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*/
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void (*sa_handler)(int);
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/* Signal handler function if flag SA_SIGINFO is used */
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void (*sa_sigaction)(int, siginfo_t *, void *);
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sigset_t sa_mask; /* signal mask to apply */
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int sa_flags; /* see signal options below */
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};
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.Ed
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.Ft int
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.Fn sigaction "int sig" "const struct sigaction *act" "struct sigaction *oact"
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.Sh DESCRIPTION
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|
The system defines a set of signals that may be delivered to a process.
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Signal delivery resembles the occurrence of a hardware interrupt:
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the signal is normally blocked from further occurrence, the current process
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context is saved, and a new one is built. A process may specify a
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|
.Em handler
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|
to which a signal is delivered, or specify that a signal is to be
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.Em ignored .
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|
A process may also specify that a default action is to be taken
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by the system when a signal occurs.
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|
A signal may also be
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.Em blocked ,
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|
in which case its delivery is postponed until it is
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|
.Em unblocked .
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|
The action to be taken on delivery is determined at the time
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of delivery.
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|
Normally, signal handlers execute on the current stack
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of the process. This may be changed, on a per-handler basis,
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|
so that signals are taken on a special
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|
.Em "signal stack" .
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|
.Pp
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|
Signal routines normally execute with the signal that caused their
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|
invocation
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|
.Em blocked ,
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|
but other signals may yet occur.
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|
A global
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|
.Em "signal mask"
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|
defines the set of signals currently blocked from delivery
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|
to a process. The signal mask for a process is initialized
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|
from that of its parent (normally empty). It
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|
may be changed with a
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|
.Xr sigprocmask 2
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|
call, or when a signal is delivered to the process.
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|
.Pp
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|
When a signal
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|
condition arises for a process, the signal is added to a set of
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|
signals pending for the process.
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|
If the signal is not currently
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|
.Em blocked
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|
by the process then it is delivered to the process.
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|
Signals may be delivered any time a process enters the operating system
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|
(e.g., during a system call, page fault or trap, or clock interrupt).
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|
If multiple signals are ready to be delivered at the same time,
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|
any signals that could be caused by traps are delivered first.
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|
Additional signals may be processed at the same time, with each
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|
appearing to interrupt the handlers for the previous signals
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before their first instructions.
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|
The set of pending signals is returned by the
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|
.Xr sigpending 2
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|
function.
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|
When a caught signal
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is delivered, the current state of the process is saved,
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|
a new signal mask is calculated (as described below),
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|
and the signal handler is invoked. The call to the handler
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|
is arranged so that if the signal handling routine returns
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|
normally the process will resume execution in the context
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|
from before the signal's delivery.
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|
If the process wishes to resume in a different context, then it
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|
must arrange to restore the previous context itself.
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|
.Pp
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|
When a signal is delivered to a process a new signal mask is
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|
installed for the duration of the process' signal handler
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|
(or until a
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|
.Xr sigprocmask
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|
call is made).
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|
This mask is formed by taking the union of the current signal mask set,
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|
the signal to be delivered, and
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|
the signal mask associated with the handler to be invoked.
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|
.Pp
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|
.Fn Sigaction
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|
assigns an action for a signal specified by
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|
.Fa sig .
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|
If
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|
.Fa act
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|
is non-zero, it
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|
specifies an action
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|
.Pf ( Dv SIG_DFL ,
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|
.Dv SIG_IGN ,
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|
or a handler routine) and mask
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|
to be used when delivering the specified signal.
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|
If
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|
.Fa oact
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|
is non-zero, the previous handling information for the signal
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|
is returned to the user.
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|
.Pp
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|
Once a signal handler is installed, it normally remains installed
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|
until another
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|
.Fn sigaction
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|
call is made, or an
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|
.Xr execve 2
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|
is performed.
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|
A signal-specific default action may be reset by
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|
setting
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|
.Fa sa_handler
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|
to
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.Dv SIG_DFL .
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|
The defaults are process termination, possibly with core dump;
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|
no action; stopping the process; or continuing the process.
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|
See the signal list below for each signal's default action.
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|
If
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|
.Fa sa_handler
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|
is
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|
.Dv SIG_DFL ,
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|
the default action for the signal is to discard the signal,
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|
and if a signal is pending,
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|
the pending signal is discarded even if the signal is masked.
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|
If
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|
.Fa sa_handler
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|
is set to
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|
.Dv SIG_IGN
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|
current and pending instances
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|
of the signal are ignored and discarded.
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|
.Pp
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|
Options may be specified by setting
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|
.Em sa_flags .
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|
The meaning of the various bits is as follows:
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|
.Bl -tag -offset indent -width SA_RESETHANDXX
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|
.It Dv SA_NOCLDSTOP
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|
If this bit is set when installing a catching function
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|
for the
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|
.Dv SIGCHLD
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|
signal,
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|
the
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|
.Dv SIGCHLD
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|
signal will be generated only when a child process exits,
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|
not when a child process stops.
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|
.It Dv SA_NOCLDWAIT
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|
If this bit is set when calling
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|
.Fn sigaction
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for the
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.Dv SIGCHLD
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signal, the system will not create zombie processes when children of
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|
the calling process exit. If the calling process subsequently issues
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|
a
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|
.Xr wait 2
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|
(or equivalent), it blocks until all of the calling process's child
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|
processes terminate, and then returns a value of -1 with errno set to
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.Dv ECHILD .
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|
.It Dv SA_ONSTACK
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|
If this bit is set, the system will deliver the signal to the process
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|
on a
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|
.Em "signal stack" ,
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|
specified with
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|
.Xr sigaltstack 2 .
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|
.It Dv SA_NODEFER
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|
If this bit is set, further occurrences of the delivered signal are
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|
not masked during the execution of the handler.
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|
.It Dv SA_RESETHAND
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|
If this bit is set, the handler is reset back to
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|
.Dv SIG_DFL
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at the moment the signal is delivered.
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|
.It Dv SA_SIGINFO
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|
If this bit is set, the handler function is assumed to be pointed to
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|
by the sa_sigaction member of struct sigaction and should match the
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|
prototype shown above or as below in
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.Sx EXAMPLES .
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|
This bit should not be set when assigning
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|
.Dv SIG_DFL
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|
or
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|
.Dv SIG_IGN .
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|
.El
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|
.Pp
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|
If a signal is caught during the system calls listed below,
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|
the call may be forced to terminate
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|
with the error
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|
.Dv EINTR ,
|
|
the call may return with a data transfer shorter than requested,
|
|
or the call may be restarted.
|
|
Restart of pending calls is requested
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|
by setting the
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|
.Dv SA_RESTART
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|
bit in
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|
.Ar sa_flags .
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|
The affected system calls include
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|
.Xr open 2 ,
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|
.Xr read 2 ,
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|
.Xr write 2 ,
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|
.Xr sendto 2 ,
|
|
.Xr recvfrom 2 ,
|
|
.Xr sendmsg 2
|
|
and
|
|
.Xr recvmsg 2
|
|
on a communications channel or a slow device (such as a terminal,
|
|
but not a regular file)
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|
and during a
|
|
.Xr wait 2
|
|
or
|
|
.Xr ioctl 2 .
|
|
However, calls that have already committed are not restarted,
|
|
but instead return a partial success (for example, a short read count).
|
|
.Pp
|
|
After a
|
|
.Xr fork 2
|
|
or
|
|
.Xr vfork 2
|
|
all signals, the signal mask, the signal stack,
|
|
and the restart/interrupt flags are inherited by the child.
|
|
.Pp
|
|
.Xr Execve 2
|
|
reinstates the default
|
|
action for all signals which were caught and
|
|
resets all signals to be caught on the user stack.
|
|
Ignored signals remain ignored;
|
|
the signal mask remains the same;
|
|
signals that restart pending system calls continue to do so.
|
|
.Pp
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|
The following is a list of all signals
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|
with names as in the include file
|
|
.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 No " terminate process" " terminal line hangup"
|
|
.It Dv SIGINT No " terminate process" " interrupt program"
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|
.It Dv SIGQUIT No " create core image" " quit program"
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|
.It Dv SIGILL No " create core image" " illegal instruction"
|
|
.It Dv SIGTRAP No " create core image" " trace trap"
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|
.It Dv SIGABRT No " create core image" Xr abort 3
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|
call (formerly
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|
.Dv SIGIOT )
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|
.It Dv SIGEMT No " create core image" " emulate instruction executed"
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|
.It Dv SIGFPE No " create core image" " floating-point exception"
|
|
.It Dv SIGKILL No " terminate process" " kill program"
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|
.It Dv SIGBUS No " create core image" " bus error"
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|
.It Dv SIGSEGV No " create core image" " segmentation violation"
|
|
.It Dv SIGSYS No " create core image" " non-existent system call invoked"
|
|
.It Dv SIGPIPE No " terminate process" " write on a pipe with no reader"
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|
.It Dv SIGALRM No " terminate process" " real-time timer expired"
|
|
.It Dv SIGTERM No " terminate process" " software termination signal"
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|
.It Dv SIGURG No " discard signal" " urgent condition present on socket"
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|
.It Dv SIGSTOP No " stop process" " stop (cannot be caught or ignored)"
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|
.It Dv SIGTSTP No " stop process" " stop signal generated from keyboard"
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|
.It Dv SIGCONT No " discard signal" " continue after stop"
|
|
.It Dv SIGCHLD No " discard signal" " child status has changed"
|
|
.It Dv SIGTTIN No " stop process" " background read attempted from control terminal"
|
|
.It Dv SIGTTOU No " stop process" " background write attempted to control terminal"
|
|
.It Dv SIGIO No " discard signal" Tn " I/O"
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|
is possible on a descriptor (see
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|
.Xr fcntl 2 )
|
|
.It Dv SIGXCPU No " terminate process" " cpu time limit exceeded (see"
|
|
.Xr setrlimit 2 )
|
|
.It Dv SIGXFSZ No " terminate process" " file size limit exceeded (see"
|
|
.Xr setrlimit 2 )
|
|
.It Dv SIGVTALRM No " terminate process" " virtual time alarm (see"
|
|
.Xr setitimer 2 )
|
|
.It Dv SIGPROF No " terminate process" " profiling timer alarm (see"
|
|
.Xr setitimer 2 )
|
|
.It Dv SIGWINCH No " discard signal" " Window size change"
|
|
.It Dv SIGINFO No " discard signal" " status request from keyboard"
|
|
.It Dv SIGUSR1 No " terminate process" " User defined signal 1"
|
|
.It Dv SIGUSR2 No " terminate process" " User defined signal 2"
|
|
.El
|
|
.Sh NOTE
|
|
The
|
|
.Fa sa_mask
|
|
field specified in
|
|
.Fa act
|
|
is not allowed to block
|
|
.Dv SIGKILL
|
|
or
|
|
.Dv SIGSTOP .
|
|
Any attempt to do so will be silently ignored.
|
|
.Pp
|
|
The following functions are either reentrant or not interruptible
|
|
by signals and are async-signal safe.
|
|
Therefore applications may
|
|
invoke them, without restriction, from signal-catching functions:
|
|
.Pp
|
|
Base Interfaces:
|
|
.Pp
|
|
.Fn _exit ,
|
|
.Fn access ,
|
|
.Fn alarm ,
|
|
.Fn cfgetispeed ,
|
|
.Fn cfgetospeed ,
|
|
.Fn cfsetispeed ,
|
|
.Fn cfsetospeed ,
|
|
.Fn chdir ,
|
|
.Fn chmod ,
|
|
.Fn chown ,
|
|
.Fn close ,
|
|
.Fn creat ,
|
|
.Fn dup ,
|
|
.Fn dup2 ,
|
|
.Fn execle ,
|
|
.Fn execve ,
|
|
.Fn fcntl ,
|
|
.Fn fork ,
|
|
.Fn fpathconf ,
|
|
.Fn fstat ,
|
|
.Fn fsync ,
|
|
.Fn getegid ,
|
|
.Fn geteuid ,
|
|
.Fn getgid ,
|
|
.Fn getgroups ,
|
|
.Fn getpgrp ,
|
|
.Fn getpid ,
|
|
.Fn getppid ,
|
|
.Fn getuid ,
|
|
.Fn kill ,
|
|
.Fn link ,
|
|
.Fn lseek ,
|
|
.Fn mkdir ,
|
|
.Fn mkfifo ,
|
|
.Fn open ,
|
|
.Fn pathconf ,
|
|
.Fn pause ,
|
|
.Fn pipe ,
|
|
.Fn raise ,
|
|
.Fn read ,
|
|
.Fn rename ,
|
|
.Fn rmdir ,
|
|
.Fn setgid ,
|
|
.Fn setpgid ,
|
|
.Fn setsid ,
|
|
.Fn setuid ,
|
|
.Fn sigaction ,
|
|
.Fn sigaddset ,
|
|
.Fn sigdelset ,
|
|
.Fn sigemptyset ,
|
|
.Fn sigfillset ,
|
|
.Fn sigismember ,
|
|
.Fn signal ,
|
|
.Fn sigpending ,
|
|
.Fn sigprocmask ,
|
|
.Fn sigsuspend ,
|
|
.Fn sleep ,
|
|
.Fn stat ,
|
|
.Fn sysconf ,
|
|
.Fn tcdrain ,
|
|
.Fn tcflow ,
|
|
.Fn tcflush ,
|
|
.Fn tcgetattr ,
|
|
.Fn tcgetpgrp ,
|
|
.Fn tcsendbreak ,
|
|
.Fn tcsetattr ,
|
|
.Fn tcsetpgrp ,
|
|
.Fn time ,
|
|
.Fn times ,
|
|
.Fn umask ,
|
|
.Fn uname ,
|
|
.Fn unlink ,
|
|
.Fn utime ,
|
|
.Fn wait ,
|
|
.Fn waitpid ,
|
|
.Fn write .
|
|
.Pp
|
|
Realtime Interfaces:
|
|
.Pp
|
|
.Fn aio_error ,
|
|
.Fn clock_gettime ,
|
|
.Fn sigpause ,
|
|
.Fn timer_getoverrun ,
|
|
.Fn aio_return ,
|
|
.Fn fdatasync ,
|
|
.Fn sigqueue ,
|
|
.Fn timer_gettime ,
|
|
.Fn aio_suspend ,
|
|
.Fn sem_post ,
|
|
.Fn sigset ,
|
|
.Fn timer_settime .
|
|
.Pp
|
|
All functions not in the above lists are considered to be unsafe
|
|
with respect to signals. That is to say, the behaviour of such
|
|
functions when called from a signal handler is undefined.
|
|
.Sh RETURN VALUES
|
|
A 0 value indicated that the call succeeded. A \-1 return value
|
|
indicates an error occurred and
|
|
.Va errno
|
|
is set to indicated the reason.
|
|
.Sh EXAMPLES
|
|
There are three possible prototypes the handler may match:
|
|
.Bl -tag -offset indent -width short
|
|
.It ANSI C:
|
|
.Fd
|
|
void handler(int);
|
|
.It Traditional BSD style:
|
|
.Fd
|
|
void handler(int, int code, struct sigcontext *scp);
|
|
.It POSIX SA_SIGINFO:
|
|
.Fd
|
|
void handler(int, siginfo_t *info, void *context);
|
|
.El
|
|
.Pp
|
|
The handler function should match the SA_SIGINFO prototype if the
|
|
SA_SIGINFO bit is set in flags.
|
|
It then should be pointed to by the
|
|
.Dv sa_siginfo
|
|
member of
|
|
.Dv struct sigaction .
|
|
Note that you should not assign SIG_DFL or SIG_IGN this way.
|
|
.Pp
|
|
If the SA_SIGINFO flag is not set, the handler function should match
|
|
either the ANSI C or traditional BSD prototype and be pointed to by
|
|
the
|
|
.Dv sa_handler
|
|
member of
|
|
.Dv struct sigaction .
|
|
In pratice,
|
|
.Fx
|
|
always sends the three arguments of the latter and since the ANSI C
|
|
prototype is a subset, both will work.
|
|
The
|
|
.Dv sa_handler
|
|
member declaration in
|
|
.Fx
|
|
include files is that of ANSI C (as required by POSIX),
|
|
so a function pointer of a BSD-style function needs to be casted to
|
|
compile without warning.
|
|
The traditional BSD style is not portable and since its capabilities
|
|
are a full subset of a SA_SIGINFO handler,
|
|
its use is deprecated.
|
|
.Pp
|
|
The
|
|
.Fa sig
|
|
argument is the signal number, one of the
|
|
.Dv SIG...
|
|
values from <signal.h>.
|
|
.Pp
|
|
The
|
|
.Fa code
|
|
argument of the BSD-style handler and the
|
|
.Dv si_code
|
|
member of the
|
|
.Dv info
|
|
argument to a SA_SIGINFO handler contain a numeric code explaning the
|
|
cause of the signal, usually one of the
|
|
.Dv SI_...
|
|
values from
|
|
<sys/signal.h> or codes specific to a signal, i.e. one of the
|
|
.Dv FPE_...
|
|
values for SIGFPE.
|
|
.Pp
|
|
The
|
|
.Fa scp
|
|
argument to a BSD-style handler points to an instance of struct
|
|
sigcontext.
|
|
.Pp
|
|
The
|
|
.Fa context
|
|
argument to a POSIX SA_SIGINFO handler points to an instance of
|
|
mcontext_t.
|
|
.Sh ERRORS
|
|
.Fn Sigaction
|
|
will fail and no new signal handler will be installed if one
|
|
of the following occurs:
|
|
.Bl -tag -width Er
|
|
.It Bq Er EFAULT
|
|
Either
|
|
.Fa act
|
|
or
|
|
.Fa oact
|
|
points to memory that is not a valid part of the process
|
|
address space.
|
|
.It Bq Er EINVAL
|
|
.Fa 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 STANDARDS
|
|
The
|
|
.Fn sigaction
|
|
function call is expected to conform to
|
|
.St -p1003.1-90 .
|
|
The
|
|
.Dv SA_ONSTACK
|
|
and
|
|
.Dv SA_RESTART
|
|
flags are Berkeley extensions,
|
|
as are the signals,
|
|
.Dv SIGTRAP ,
|
|
.Dv SIGEMT ,
|
|
.Dv SIGBUS ,
|
|
.Dv SIGSYS ,
|
|
.Dv SIGURG ,
|
|
.Dv SIGIO ,
|
|
.Dv SIGXCPU ,
|
|
.Dv SIGXFSZ ,
|
|
.Dv SIGVTALRM ,
|
|
.Dv SIGPROF ,
|
|
.Dv SIGWINCH ,
|
|
and
|
|
.Dv SIGINFO .
|
|
Those signals are available on most
|
|
.Tn BSD Ns \-derived
|
|
systems.
|
|
The
|
|
.Dv SA_NODEFER
|
|
and
|
|
.Dv SA_RESETHAND
|
|
flags are intended for backwards compatibility with other operating
|
|
systems. The
|
|
.Dv SA_NOCLDSTOP ,
|
|
and
|
|
.Dv SA_NOCLDWAIT
|
|
.\" and
|
|
.\" SA_SIGINFO
|
|
flags are featuring options commonly found in other operating systems.
|
|
.Sh SEE ALSO
|
|
.Xr kill 1 ,
|
|
.Xr kill 2 ,
|
|
.Xr ptrace 2 ,
|
|
.Xr sigaltstack 2 ,
|
|
.Xr sigblock 2 ,
|
|
.Xr sigpause 2 ,
|
|
.Xr sigpending 2 ,
|
|
.Xr sigprocmask 2 ,
|
|
.Xr sigsetmask 2 ,
|
|
.Xr sigsuspend 2 ,
|
|
.Xr sigvec 2 ,
|
|
.Xr wait 2 ,
|
|
.Xr fpsetmask 3 ,
|
|
.Xr setjmp 3 ,
|
|
.Xr siginterrupt 3 ,
|
|
.Xr sigsetops 3 ,
|
|
.Xr tty 4
|