208 lines
4.9 KiB
HTML
208 lines
4.9 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of DAEMON</TITLE>
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</HEAD><BODY>
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<H1>DAEMON</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-11-26<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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daemon - run in the background
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<B>#include <<A HREF="file:///usr/include/unistd.h">unistd.h</A>></B>
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<P>
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<B>int daemon(int </B><I>nochdir</I><B>, int </B><I>noclose</I><B>);</B>
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>daemon</B>():
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<PRE>
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Since glibc 2.21:
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_DEFAULT_SOURCE
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In glibc 2.19 and 2.20:
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_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
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Up to and including glibc 2.19:
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_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
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</PRE>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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The
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<B>daemon</B>()
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function is for programs wishing to detach themselves from the
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controlling terminal and run in the background as system daemons.
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<P>
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If
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<I>nochdir</I>
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is zero,
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<B>daemon</B>()
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changes the process's current working directory
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to the root directory ("/");
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otherwise, the current working directory is left unchanged.
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<P>
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If
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<I>noclose</I>
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is zero,
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<B>daemon</B>()
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redirects standard input, standard output and standard error
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to
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<I>/dev/null</I>;
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otherwise, no changes are made to these file descriptors.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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(This function forks, and if the
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2)
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succeeds, the parent calls
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<B><A HREF="/cgi-bin/man/man2html?2+_exit">_exit</A></B>(2),
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so that further errors are seen by the child only.)
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On success
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<B>daemon</B>()
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returns zero.
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If an error occurs,
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<B>daemon</B>()
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returns -1 and sets
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<I>errno</I>
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to any of the errors specified for the
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2)
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and
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<B><A HREF="/cgi-bin/man/man2html?2+setsid">setsid</A></B>(2).
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<A NAME="lbAF"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>daemon</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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<A NAME="lbAG"> </A>
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<H2>CONFORMING TO</H2>
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Not in POSIX.1.
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A similar function appears on the BSDs.
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The
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<B>daemon</B>()
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function first appeared in 4.4BSD.
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<A NAME="lbAH"> </A>
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<H2>NOTES</H2>
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The glibc implementation can also return -1 when
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<I>/dev/null</I>
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exists but is not a character device with the expected
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major and minor numbers.
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In this case,
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<I>errno</I>
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need not be set.
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<A NAME="lbAI"> </A>
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<H2>BUGS</H2>
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The GNU C library implementation of this function was taken from BSD,
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and does not employ the double-fork technique (i.e.,
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+setsid">setsid</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2))
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that is necessary to ensure that the resulting daemon process is
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not a session leader.
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Instead, the resulting daemon
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<I>is</I>
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a session leader.
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On systems that follow System V semantics (e.g., Linux),
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this means that if the daemon opens a terminal that is not
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already a controlling terminal for another session,
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then that terminal will inadvertently become
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the controlling terminal for the daemon.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?2+setsid">setsid</A></B>(2),
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<B><A HREF="/cgi-bin/man/man2html?7+daemon">daemon</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+logrotate">logrotate</A></B>(8)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="1"><A HREF="#lbAB">NAME</A><DD>
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<DT id="2"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="3"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="4"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="5"><A HREF="#lbAF">ATTRIBUTES</A><DD>
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<DT id="6"><A HREF="#lbAG">CONFORMING TO</A><DD>
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<DT id="7"><A HREF="#lbAH">NOTES</A><DD>
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<DT id="8"><A HREF="#lbAI">BUGS</A><DD>
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<DT id="9"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="10"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:38 GMT, March 31, 2021
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</BODY>
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</HTML>
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