man pages section 3: Basic Library Functions

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Updated: July 2014



daemon - basic daemonization function


#include <stdlib.h>

int daemon(int nochdir, int noclose);


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.


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. */


See attributes(5) for descriptions of the following attributes:

Interface Stability

See also

Intro(2), dup(2), fork(2), open(2), setsid(2), attributes(5)