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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ATTRIBUTES |VERSIONS |STANDARDS |HISTORY |BUGS |SEE ALSO |COLOPHON | |
daemon(3) Library Functions Manualdaemon(3)daemon - run in the background
Standard C library (libc,-lc)
#include <unistd.h>int daemon(intnochdir, intnoclose); Feature Test Macro Requirements for glibc (seefeature_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)
Thedaemon() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons. Ifnochdir is zero,daemon() changes the process's current working directory to the root directory ("/"); otherwise, the current working directory is left unchanged. Ifnoclose 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 thefork(2) succeeds, the parent calls_exit(2), so that further errors are seen by the child only.) On successdaemon() returns zero. If an error occurs,daemon() returns -1 and setserrno to any of the errors specified for thefork(2) andsetsid(2).
For an explanation of the terms used in this section, seeattributes(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 daemonis 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 theman-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 isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17daemon(3)Pages that refer to this page:fork(2), daemon(7)
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