97 lines
3.5 KiB
Groff
97 lines
3.5 KiB
Groff
.\" $NetBSD: shutdownhook_establish.9,v 1.8 2003/02/14 15:20:22 grant Exp $
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.\"
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.\" Copyright (c) 1994 Christopher G. Demetriou
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.\" 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 for the
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.\" NetBSD Project. See http://www.NetBSD.org/ for
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.\" information about NetBSD.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" <<Id: LICENSE,v 1.2 2000/06/14 15:57:33 cgd Exp>>
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.\"
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.Dd November 13, 1995
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.Dt SHUTDOWNHOOK_ESTABLISH 9
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.Os
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.Sh NAME
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.Nm shutdownhook_establish ,
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.Nm shutdownhook_disestablish
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.Nd add or remove a shutdown hook
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.Sh SYNOPSIS
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.Ft void *
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.Fn shutdownhook_establish "void (*fn)(void *)" "void *arg"
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.Ft void
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.Fn shutdownhook_disestablish "void *cookie"
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.Sh DESCRIPTION
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The
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.Fn shutdownhook_establish
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function adds
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.Fa fn
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to the list of hooks invoked by
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.Xr doshutdownhooks 9
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at shutdown.
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When invoked, the hook function
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.Fa fn
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will be passed
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.Fa arg
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as its only argument.
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.Pp
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The
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.Fn shutdownhook_disestablish
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function removes the hook described by the opaque pointer
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.Fa cookie
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from the list of hooks to be invoked at shutdown.
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If
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.Fa cookie
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is invalid, the result of
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.Fn shutdownhook_disestablish
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is undefined.
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.Pp
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Shutdown hooks should be used to perform one-time activities
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that must happen immediately before the kernel exits.
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Because of the environment in which they are run, shutdown hooks cannot
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rely on many system services (including file systems, and timeouts
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and other interrupt-driven services), or even basic system
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integrity (because the system could be rebooting after a crash).
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.Sh RETURN VALUES
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If successful,
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.Fn shutdownhook_establish
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returns an opaque pointer describing the newly-established
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shutdown hook.
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Otherwise, it returns NULL.
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.Sh EXAMPLES
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It may be appropriate to use a shutdown hook to
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disable a device that does direct memory access, so that
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the device will not try to access memory while the system
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is rebooting.
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.Pp
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It may be appropriate to use a shutdown hook to
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inform watchdog timer hardware that the operating system
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is no longer running.
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.Sh SEE ALSO
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.Xr doshutdownhooks 9
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.Sh BUGS
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The names are clumsy, at best.
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