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 way for applications to go into
     background.

     The function will ensure 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 options to the function are treated as boolean variables and are
     evaluated using negative logic.

     If the nochdir option is other than zero the working directory will
     not be changed to the root directory ("/"), otherwise it will be.

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

COMMENTS
  Running daemon as a service
     If the process calling daemon() is running as a smf(5) service,
     it should call daemon() as late as possible in the process of initializing
     in order to ensure that the process returns on the brink of providing
     the service (e.g. waiting for requests) and to return as much
     information as possible about eventual failures during initialization.

  Other options for setting up daemon environment
     The daemonized process might want to use the following:

       - contracts
       - tasks
       - privileges
       - umask setting

     If running under smf(5), process contracts, tasks and credential context
     are accounted for by smf(5) so this sort of daemon generally does not
     need to explicitly set them (unless being e.g. login application).

     Contracts are useful for providing fault separation, e.g.
     placing worker process groups started by the master listener process
     (the process calling daemon()) into a different contract(4) prevents
     them from being killed if the master process goes away.

     The daemon can be placed into a new task owned by a specific project(4)
     for better workload management.

     After going into background privileged daemons might want to permanently
     revoke some of the privileges(5) which they will not need anymore and
     drop some of the effective privileges until they are needed for
     specific action.

     Changing umask(2) is a good practice for daemons creating new
     files to ensure they are created with expected permissions. Since the file
     creation mask umask is inherited by child processes it is suitable to
     set it after calling daemon() and before forking child processes.

RETURN VALUES
     Upon successful completion, daemon() returns 0. Otherwise it returns -1
     in which case errno will be set to the values specified in fork(2) and
     setsid(2).

EXAMPLES

     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  attri-
     butes:

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


SEE ALSO
     attributes(5), contract(4), fork(2), Intro(2), privileges(5),
     process(4), project(4), setsid(2), smf(5), umask(2)