run in the background
daemon(int nochdir, int
Macro Requirements for glibc (see
_BSD_SOURCE || (_XOPEN_SOURCE &&
_XOPEN_SOURCE < 500)
daemon() function is for programs wishing to detach
themselves from the controlling terminal and run in the
background as system daemons.
nochdir is zero, daemon() changes the
process’s current working directory to the root
directory ("/"); otherwise, the current working
directory is left unchanged.
noclose is zero, daemon() redirects standard
input, standard output and standard error to
/dev/null; otherwise, no changes are made to these
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).
explanation of the terms used in this section, see
Not in POSIX.1.
A similar function appears on the BSDs. The daemon()
function first appeared in 4.4BSD.
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.
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