227 lines
5.0 KiB
HTML
227 lines
5.0 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 GETHOSTID</TITLE>
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</HEAD><BODY>
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<H1>GETHOSTID</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<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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gethostid, sethostid - get or set the unique identifier of the current host
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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>long gethostid(void);</B>
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<BR>
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<B>int sethostid(long </B><I>hostid</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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<BR>
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<B>gethostid</B>():
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<DL COMPACT><DT id="1"><DD>
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_BSD_SOURCE || _XOPEN_SOURCE >= 500
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</DL>
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<B>sethostid</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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<B>gethostid</B>()
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and
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<B>sethostid</B>()
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respectively get or set a unique 32-bit identifier for the current machine.
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The 32-bit identifier is intended to be unique among all UNIX systems in
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existence.
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This normally resembles the Internet address for the local
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machine, as returned by
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3),
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and thus usually never needs to be set.
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<P>
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The
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<B>sethostid</B>()
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call is restricted to the superuser.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<B>gethostid</B>()
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returns the 32-bit identifier for the current host as set by
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<B>sethostid</B>().
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<P>
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On success,
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<B>sethostid</B>()
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returns 0; on error, -1 is returned, and
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<I>errno</I>
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is set to indicate the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<B>sethostid</B>()
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can fail with the following errors:
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<DL COMPACT>
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<DT id="2"><B>EACCES</B>
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<DD>
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The caller did not have permission to write to the file used
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to store the host ID.
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<DT id="3"><B>EPERM</B>
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<DD>
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The calling process's effective user or group ID is not the same
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as its corresponding real ID.
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</DL>
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<A NAME="lbAG"> </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>gethostid</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe hostid env locale<BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>sethostid</B>()
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</TD><TD>Thread safety</TD><TD>MT-Unsafe const:hostid<BR></TD></TR>
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</TABLE>
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<P>
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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4.2BSD; these functions were dropped in 4.4BSD.
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SVr4 includes
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<B>gethostid</B>()
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but not
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<B>sethostid</B>().
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<P>
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POSIX.1-2001 and POSIX.1-2008 specify
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<B>gethostid</B>()
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but not
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<B>sethostid</B>().
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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In the glibc implementation, the
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<I>hostid</I>
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is stored in the file
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<I>/etc/hostid</I>.
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(In glibc versions before 2.2, the file
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<I>/var/adm/hostid</I>
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was used.)
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<P>
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In the glibc implementation, if
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<B>gethostid</B>()
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cannot open the file containing the host ID,
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then it obtains the hostname using
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<B><A HREF="/cgi-bin/man/man2html?2+gethostname">gethostname</A></B>(2),
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passes that hostname to
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname_r">gethostbyname_r</A></B>(3)
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in order to obtain the host's IPv4 address,
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and returns a value obtained by bit-twiddling the IPv4 address.
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(This value may not be unique.)
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<A NAME="lbAJ"> </A>
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<H2>BUGS</H2>
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It is impossible to ensure that the identifier is globally unique.
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<A NAME="lbAK"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?1+hostid">hostid</A></B>(1),
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3)
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<A NAME="lbAL"> </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="4"><A HREF="#lbAB">NAME</A><DD>
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<DT id="5"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="6"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="7"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="8"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="9"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="10"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="11"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="12"><A HREF="#lbAJ">BUGS</A><DD>
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<DT id="13"><A HREF="#lbAK">SEE ALSO</A><DD>
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<DT id="14"><A HREF="#lbAL">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: 00:05:44 GMT, March 31, 2021
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</BODY>
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</HTML>
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