NAME

       daemon - run in the background

LIBRARY

       Standard C library (libc, -lc)

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 │
       └───────────────────────────────────────────────────────────────┴───────────────┴─────────┘

VERSIONS

       A similar function appears on the BSDs.

       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.

STANDARDS

       None.

HISTORY

       4.4BSD.

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)