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\"      @(#)daemon.3    8.1 (Berkeley) 6/9/93
\"
Dd September 3, 1999
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.
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
On return 0 indicates success with \-1 indicating error.
Sh ERRORS
The function
Fn daemon
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
Sh HISTORY
The
Fn daemon
function first appeared in
Bx 4.4 .
Sh CAVEATS
Unless the
Ar 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 make sure to either call
Fn daemon
before opening any files or sockets or, alternately, verifying that
any file descriptors obtained have a value greater than 2.
Sh BUGS
Fn daemon
uses
Fn fork
as part of its tty detachment mechanism.
Consequently the process id changes when
Fn daemon
is invoked.
Processes employing
Fn daemon
can not be reliably waited upon until
Fn daemon
has been invoked.

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