DAEMON(3)		   Linux Programmer's Manual		     DAEMON(3)



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 suc-
       cess daemon() returns zero.  If an error occurs,	 daemon()  returns  -1
       and  sets errno to any of the errors specified for the fork(2) and set-
       sid(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), set-
       sid(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)

COLOPHON
       This  page  is  part of release 4.10 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/.



GNU				  2016-03-15			     DAEMON(3)