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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | BUGS | SEE ALSO | COLOPHON |
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daemon(3) Library Functions Manual daemon(3)
daemon - run in the background
Standard C library (libc, -lc)
#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 │
└──────────────────────────────────────┴───────────────┴─────────┘
A similar function appears on the BSDs.
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.
None.
4.4BSD.
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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 daemon(3)
Pages that refer to this page: fork(2), daemon(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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