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daemon - run in the background
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 calling 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
Not in POSIX.1-2001. 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.
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