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30.Dd $Mdocdate: May 18 2016 $
31.Dt DAEMON 3
32.Os
33.Sh NAME
34.Nm daemon
35.Nd run in the background
36.Sh SYNOPSIS
37.In stdlib.h
38.Ft int
39.Fn daemon "int nochdir" "int noclose"
40.Sh DESCRIPTION
41The
42.Fn daemon
43function is for programs wishing to detach themselves from the
44controlling terminal and run in the background as system daemons.
45.Pp
46If the argument
47.Fa nochdir
48is zero,
49.Fn daemon
50changes the current working directory to the root
51.Pq Pa / .
52.Pp
53If the argument
54.Fa noclose
55is zero,
56.Fn daemon
57redirects standard input, standard output and standard error to
58.Pa /dev/null .
59.Sh RETURN VALUES
60Upon success,
61.Fn daemon
62returns 0; otherwise \-1 is returned.
63.Sh ERRORS
64The function
65.Fn daemon
66may fail and set
67.Va errno
68for any of the errors specified for the library functions
69.Xr fork 2
70and
71.Xr setsid 2 .
72.Sh SEE ALSO
73.Xr fork 2 ,
74.Xr setsid 2
75.Sh HISTORY
76The
77.Fn daemon
78function first appeared in
79.Bx 4.4 .
80.Sh CAVEATS
81If the
82.Ar noclose
83argument is zero,
84.Fn daemon
85closes the first three file descriptors and redirects them to
86.Pa /dev/null .
87Normally, these correspond to standard input, standard output and
88standard error.
89However, if any of those file descriptors refer to something else they
90will still be closed, resulting in incorrect behavior of the calling program.
91This can happen if any of standard input, standard output or standard error
92have been closed before the program was run.
93Programs using
94.Fn daemon
95should therefore make sure to either call
96.Fn daemon
97before opening any files or sockets or, alternately, verifying that
98any file descriptors obtained have a value greater than 2.
99