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1.\" $OpenBSD: pidfile.3,v 1.8 2025/06/06 22:01:40 schwarze Exp $
2.\" $NetBSD: pidfile.3,v 1.2 2001/04/12 22:34:31 sommerfeld Exp $
3.\"
4.\" Copyright (c) 1999 The NetBSD Foundation, Inc.
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7.\" This code is derived from software contributed to The NetBSD Foundation
8.\" by Jason R. Thorpe.
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31.Dd $Mdocdate: June 6 2025 $
32.Dt PIDFILE 3
33.Os
34.Sh NAME
35.Nm pidfile
36.Nd write a daemon pid file
37.Sh SYNOPSIS
38.Lb libutil
39.In util.h
40.Ft int
41.Fn pidfile "const char *basename"
42.Sh DESCRIPTION
43.Fn pidfile
44writes a file containing the process ID of the program to the
45.Pa /var/run
46directory.
47The file name has the form
48.Pa /var/run/basename.pid .
49If the
50.Ar basename
51argument is NULL,
52.Nm
53will determine the program name and use that instead.
54.Pp
55The pid file can be used as a quick reference if
56the process needs to be sent a signal.
57When the program exits, the pid file will be removed automatically,
58unless the program receives a fatal signal.
59.Sh RETURN VALUES
60.Fn pidfile
61returns 0 on success and -1 on failure.
62.Sh SEE ALSO
63.Xr atexit 3
64.Sh HISTORY
65The
66.Nm
67function call appeared in
68.Ox 3.0 .
69.Sh CAVEATS
70If
71.Fn pidfile
72is called multiple times with different
73.Ar basename ,
74only the last pidfile will be removed upon exit.
75.Pp
76.Fn pidfile
77uses
78.Fn atexit
79to ensure the pidfile is unlinked at program exit.
80However, programs that use the
81.Fn _exit
82function (for example, in signal handlers)
83will not trigger this behaviour.