daemon - run in the background
int daemon(int nochdir, int
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
Since glibc 2.21:
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)
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 setsid(2).
For an explanation of the terms used in this section, see attributes(7).
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.
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