.\"	$NetBSD: pidfile.3,v 1.8 2002/10/01 19:36:30 wiz Exp $
.\"	$DragonFly: src/lib/libutil/pidfile.3,v 1.2 2005/05/22 17:48:57 liamfoy Exp $
.\"
.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jason R. Thorpe.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"    must display the following acknowledgement:
.\"        This product includes software developed by the NetBSD
.\"        Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation 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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\"
.Dd June 5, 1999
.Dt PIDFILE 3
.Os
.Sh NAME
.Nm pidfile
.Nd write a daemon pid file
.Sh LIBRARY
.Lb libutil
.Sh SYNOPSIS
.In sys/types.h
.In libutil.h
.Ft int
.Fn pidfile "const char *basename"
.Sh DESCRIPTION
.Fn pidfile
writes a file containing the process ID of the program to the
.Pa /var/run
directory.
The file name has the form
.Pa /var/run/basename.pid .
If the
.Ar basename
argument is NULL,
.Nm
will determine the program name and use that instead.
.Pp
The pid file can be used as a quick reference if
the process needs to be sent a signal.
When the program exits, the pid file will be removed automatically, unless
the program receives a fatal signal.
.Pp
Note that only the first invocation of
.Nm
causes a pid file to be written; subsequent invocations have no effect
unless a new
.Ar basename
is supplied.
If called with a new
.Ar basename ,
.Fn pidfile
will remove the old pid file and write the new one.
.Sh RETURN VALUES
.Fn pidfile
returns 0 on success and -1 on failure.
.Sh SEE ALSO
.Xr atexit 3
.Sh HISTORY
The
.Nm
function call appeared in
.Nx 1.5 .
.Sh BUGS
.Fn pidfile
uses
.Xr atexit 3
to ensure the pidfile is unlinked at program exit.
However, programs that use the
.Xr _exit 2
function (for example, in signal handlers)
will not trigger this behaviour.