DAEMON(3C) Standard C Library Functions DAEMON(3C)

NAME

daemon - basic daemonization function

SYNOPSIS

#include <stdlib.h>

int daemon(int nochdir, int noclose);

DESCRIPTION

The daemon() function provides a means for applications to run in the
background.


This function ensures that the process calling this function:

o runs in the background

o detaches from the controlling terminal

o forms a new process group

o is not a session group leader.


The arguments to this function are treated as boolean variables and
are evaluated using negative logic.


If the nochdir argument is zero the working directory will be changed
to the root directory (/); otherwise it will not be.


If the noclose argument is zero the descriptors 0, 1, and 2 (normally
corresponding to standard input, output and error output, depending
on the application) will be redirected to /dev/null; otherwise they
will not be.

RETURN VALUES

Upon successful completion, daemon() returns 0. Otherwise it returns
-1 and sets errno to the values specified for fork(2), setsid(2),
open(2), and dup(2).


If daemon() is called with noclose set to 0 and fails to redirect
descriptors 0, 1, and 2 to /dev/null, those descriptors are not
guaranteed to be the same as before the call.

EXAMPLES

Example 1: Using daemon to run a process in the background.

The main() function of a network server could look like this:


int background; /* background flag */

/* Load and verify the configuration. */

/* Go into background. */
if (background && daemon(0, 0) < 0)
err(1, "daemon");

/* Process requests here. */

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+

SEE ALSO

Intro(2), dup(2), fork(2), open(2), setsid(2), attributes(7)

September 15, 2009 DAEMON(3C)