Manpage of DAEMON

DAEMON

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

NAME

daemon - run in the background  

SYNOPSIS

#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)
 

DESCRIPTION

The daemon() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons.

If nochdiris zero, daemon() changes the process's current working directory to the root directory ("/"); otherwise, the current working directory is left unchanged.

If nocloseis zero, daemon() redirects standard input, standard output and standard error to /dev/null; otherwise, no changes are made to these file descriptors.  

RETURN VALUE

(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 errnoto any of the errors specified for the fork(2) and setsid(2).  

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).
InterfaceAttributeValue
daemon() Thread safetyMT-Safe
 

CONFORMING TO

Not in POSIX.1. A similar function appears on the BSDs. The daemon() function first appeared in 4.4BSD.  

NOTES

The glibc implementation can also return -1 when /dev/nullexists but is not a character device with the expected major and minor numbers. In this case, errnoneed not be set.  

BUGS

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 isa 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.  

SEE ALSO

fork(2), setsid(2)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ATTRIBUTES
CONFORMING TO
NOTES
BUGS
SEE ALSO

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