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       daemon - run in the background


       #include <unistd.h>

       int daemon(int nochdir, int noclose);

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

       daemon(): _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)


       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.


       (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


       For  an  explanation  of  the  terms  used   in   this   section,   see

       │InterfaceAttributeValue   │
       │daemon()  │ Thread safety │ MT-Safe │


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


       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.


       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.


       fork(2), setsid(2)


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