NAME

       daemon - run in the background

SYNOPSIS

       #include <unistd.h>

       int daemon(int nochdir, int noclose);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       daemon():
           Since glibc 2.21:
               _DEFAULT_SOURCE
           In glibc 2.19 and 2.20:
               _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
           Up to and including glibc 2.19:
               _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

DESCRIPTION

       The  daemon() function is for programs wishing to detach themselves from the controlling terminal and run
       in the background as system daemons.

       If nochdir is zero, daemon() changes the process's current working directory to the root directory ("/");
       otherwise, the current working directory is left unchanged.

       If  noclose  is zero, daemon() redirects standard input, standard output and standard error to /dev/null;
       otherwise, no changes are made to these file descriptors.

RETURN VALUE

       (This function forks, and if the fork(2) succeeds, the parent calls _exit(2), so that further errors  are
       seen  by the child only.)  On success daemon() returns zero.  If an error occurs, daemon() returns -1 and
       sets errno to any of the errors specified for the fork(2) and setsid(2).

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌──────────┬───────────────┬─────────┐
       │Interface │ Attribute     │ Value   │
       ├──────────┼───────────────┼─────────┤
       │daemon()  │ Thread safety │ MT-Safe │
       └──────────┴───────────────┴─────────┘

CONFORMING TO

       Not in POSIX.1.  A similar function appears on the BSDs.  The daemon() function first appeared in 4.4BSD.

NOTES

       The glibc implementation can also return -1 when /dev/null exists but is not a character device with  the
       expected major and minor numbers.  In this case, errno need not be set.

BUGS

       The GNU C library implementation of this function was taken from BSD, and does not employ the double-fork
       technique (i.e., fork(2), setsid(2), fork(2)) that is necessary  to  ensure  that  the  resulting  daemon
       process  is  not  a  session leader.  Instead, the resulting daemon is a session leader.  On systems that
       follow System V semantics (e.g., Linux), this means that if the daemon  opens  a  terminal  that  is  not
       already  a  controlling  terminal  for  another session, then that terminal will inadvertently become the
       controlling terminal for the daemon.

SEE ALSO

       fork(2), setsid(2), daemon(7), logrotate(8)

COLOPHON

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