man pages section 3: Basic Library Functions

Exit Print View

Updated: July 2014
 
 

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:

  • runs in the background

  • detaches from the controlling terminal

  • forms a new process group

  • 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(5) 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(5)