.\" Copyright (c) 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 4. Neither the name of the University 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 REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)daemon.3 8.1 (Berkeley) 6/9/93 .\" $FreeBSD: src/lib/libc/gen/daemon.3,v 1.15 2007/01/09 00:27:53 imp Exp $ .\" .Dd June 9, 1993 .Dt DAEMON 3 .Os .Sh NAME .Nm daemon .Nd run in the background .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In stdlib.h .Ft int .Fn daemon "int nochdir" "int noclose" .Sh DESCRIPTION The .Fn daemon function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons. On Mac OS X, the use of this API is discouraged in favor of using .Xr launchd 8 . .Pp Unless the argument .Fa nochdir is non-zero, .Fn daemon changes the current working directory to the root .Pq Pa / . .Pp Unless the argument .Fa noclose is non-zero, .Fn daemon will redirect standard input, standard output, and standard error to .Pa /dev/null . .Sh RETURN VALUES .Rv -std daemon .Sh ERRORS The .Fn daemon function may fail and set .Va errno for any of the errors specified for the library functions .Xr fork 2 and .Xr setsid 2 . .Sh SEE ALSO .Xr fork 2 , .Xr setsid 2 , .Xr sigaction 2 .Sh HISTORY The .Fn daemon function first appeared in .Bx 4.4 . .Sh CAVEATS Unless the .Fa noclose argument is non-zero, .Fn daemon will close the first three file descriptors and redirect them to .Pa /dev/null . Normally, these correspond to standard input, standard output, and standard error. However, if any of those file descriptors refer to something else, they will still be closed, resulting in incorrect behavior of the calling program. This can happen if any of standard input, standard output, or standard error have been closed before the program was run. Programs using .Fn daemon should therefore either call .Fn daemon before opening any files or sockets, or verify that any file descriptors obtained have values greater than 2. .Pp The .Fn daemon function temporarily ignores .Dv SIGHUP while calling .Xr setsid 2 to prevent a parent session group leader's calls to .Xr fork 2 and then .Xr _exit 2 from prematurely terminating the child process.