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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
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DAEMON(3) Linux Programmer's Manual DAEMON(3)
daemon - run in the background
#include <unistd.h>
int daemon(int nochdir, int noclose);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
daemon():
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.
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).
┌──────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────┼───────────────┼─────────┤
│daemon() │ Thread safety │ MT-Safe │
└──────────┴───────────────┴─────────┘
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.
fork(2), setsid(2), daemon(7), logrotate(8)
This page is part of release 5.10 of the Linux man-pages project.
A description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-11-26 DAEMON(3)
Pages that refer to this page: fork(2), daemon(7)
Copyright and license for this manual page
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