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

       This  page  is  part of release 4.15 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.