daemon - run in the background
int daemon(int nochdir, int noclose);
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)
() function is for programs wishing to detach themselves from
the controlling terminal and run in the background as system daemons.
is zero, daemon
() changes the process's current working
directory to the root directory ("/"); otherwise, the current
working directory is left unchanged.
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
, so that further errors are seen by the child only.) On
() returns zero. If an error occurs, daemon
returns -1 and sets errno
to any of the errors specified for the
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
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
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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