daemon - run in the background
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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)
The 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 file
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
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)) 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
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