323 lines
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323 lines
7.3 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of HOST.CONF</TITLE>
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</HEAD><BODY>
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<H1>HOST.CONF</H1>
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Section: Linux System Administration (5)<BR>Updated: 2019-03-06<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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host.conf - resolver configuration file
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<A NAME="lbAC"> </A>
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<H2>DESCRIPTION</H2>
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The file
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<I>/etc/host.conf</I>
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contains configuration information specific to the resolver library.
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It should contain one configuration keyword per line, followed by
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appropriate configuration information.
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The following keywords are recognized:
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<DL COMPACT>
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<DT id="1"><I>trim</I>
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<DD>
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This keyword may be listed more than once.
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Each time it should be
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followed by a list of domains, separated by colons (':'), semicolons
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(';') or commas (','), with the leading dot.
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When set, the
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resolver library will automatically trim the given domain name from the
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end of any hostname resolved via DNS.
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This is intended for use with
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local hosts and domains.
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(Related note:
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<I>trim</I>
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will not affect hostnames gathered via NIS or the
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<B><A HREF="/cgi-bin/man/man2html?5+hosts">hosts</A></B>(5)
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file.
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Care should be taken to
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ensure that the first hostname for each entry in the hosts file is
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fully qualified or unqualified, as appropriate for the local
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installation.)
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<DT id="2"><I>multi</I>
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<DD>
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Valid values are
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<I>on</I> and <I>off</I>.
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If set to
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<I>on</I>,
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the resolver library will return all valid addresses for a host that
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appears in the
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<I>/etc/hosts</I>
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file,
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instead of only the first.
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This is
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<I>off</I>
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by default, as it may cause a substantial performance loss at sites
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with large hosts files.
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<DT id="3"><I>reorder</I>
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<DD>
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Valid values are
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<I>on</I> and <I>off</I>.
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If set to
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<I>on</I>,
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the resolver library
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will attempt to reorder host addresses so that local addresses
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(i.e., on the same subnet) are listed first when a
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3)
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is performed.
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Reordering is done for all lookup methods.
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The default value is
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<I>off</I>.
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</DL>
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<A NAME="lbAD"> </A>
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<H2>ENVIRONMENT</H2>
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The following environment variables can be used to allow users to
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override the behavior which is configured in
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<I>/etc/host.conf</I>:
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<DL COMPACT>
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<DT id="4"><B>RESOLV_HOST_CONF</B>
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<DD>
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If set, this variable points to a file that should be read instead of
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<I>/etc/host.conf</I>.
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<DT id="5"><B>RESOLV_MULTI</B>
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<DD>
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Overrides the
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<I>multi</I>
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command.
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<DT id="6"><B>RESOLV_REORDER</B>
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<DD>
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Overrides the
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<I>reorder</I>
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command.
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<DT id="7"><B>RESOLV_ADD_TRIM_DOMAINS</B>
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<DD>
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A list of domains, separated by colons (':'), semicolons (';') or
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commas (','), with the leading dot, which will be added to the list of
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domains that should be trimmed.
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<DT id="8"><B>RESOLV_OVERRIDE_TRIM_DOMAINS</B>
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<DD>
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A list of domains, separated by colons (':'), semicolons (';') or
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commas (','), with the leading dot, which will replace the list of
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domains that should be trimmed.
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Overrides the
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<I>trim</I>
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command.
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</DL>
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<A NAME="lbAE"> </A>
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<H2>FILES</H2>
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<DL COMPACT>
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<DT id="9"><I>/etc/host.conf</I>
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<DD>
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Resolver configuration file
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<DT id="10"><I>/etc/resolv.conf</I>
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<DD>
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Resolver configuration file
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<DT id="11"><I>/etc/hosts</I>
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<DD>
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Local hosts database
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</DL>
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<A NAME="lbAF"> </A>
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<H2>NOTES</H2>
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The following differences exist compared to the original implementation.
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A new command
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<I>spoof</I>
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and a new environment variable
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<B>RESOLV_SPOOF_CHECK</B>
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can take arguments like
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<I>off</I>, <I>nowarn</I>, and <I>warn</I>.
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Line comments can appear anywhere and not only at the beginning of a line.
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<A NAME="lbAG"> </A>
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<H3>Historical</H3>
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The
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<B><A HREF="/cgi-bin/man/man2html?5+nsswitch.conf">nsswitch.conf</A></B>(5)
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file is the modern way of controlling the order of host lookups.
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<P>
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In glibc 2.4 and earlier, the following keyword is recognized:
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<DL COMPACT>
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<DT id="12"><I>order</I>
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<DD>
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This keyword specifies how host lookups are to be performed.
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It should be followed by one or more lookup methods, separated by commas.
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Valid methods are
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<I>bind</I>, <I>hosts</I>, and <I>nis</I>.
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<DT id="13"><B>RESOLV_SERV_ORDER</B>
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<DD>
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Overrides the
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<I>order</I>
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command.
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</DL>
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<P>
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Since glibc 2.0.7, and up through glibc 2.24, the following keywords and environment variable have
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been recognized but never implemented:
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<DL COMPACT>
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<DT id="14"><I>nospoof</I>
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<DD>
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Valid values are
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<I>on</I> and <I>off</I>.
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If set to
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<I>on</I>,
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the resolver library will attempt to prevent hostname spoofing to
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enhance the security of
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<B>rlogin</B> and <B>rsh</B>.
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It works as follows: after performing a host address lookup,
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the resolver library will perform a hostname lookup for that address.
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If the two hostnames
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do not match, the query fails.
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The default value is
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<I>off</I>.
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<DT id="15"><I>spoofalert</I>
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<DD>
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Valid values are
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<I>on</I> and <I>off</I>.
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If this option is set to
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<I>on</I>
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and the
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<I>nospoof</I>
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option is also set,
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the resolver library will log a warning of the error via the
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syslog facility.
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The default value is
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<I>off</I>.
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<DT id="16"><I>spoof</I>
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<DD>
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Valid values are
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<I>off</I>, <I>nowarn</I>, and <I>warn</I>.
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If this option is set to
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<I>off</I>,
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spoofed addresses are permitted and no warnings will be emitted
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via the syslog facility.
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If this option is set to
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<I>warn</I>,
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the resolver library will attempt to prevent hostname spoofing to
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enhance the security and log a warning of the error via the syslog
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facility.
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If this option is set to
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<I>nowarn</I>,
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the resolver library will attempt to prevent hostname spoofing to
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enhance the security but not emit warnings via the syslog facility.
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Setting this option to anything else is equal to setting it to
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<I>nowarn</I>.
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<DT id="17"><B>RESOLV_SPOOF_CHECK</B>
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<DD>
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Overrides the
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<I>nospoof</I>, <I>spoofalert</I>, and <I>spoof</I>
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commands in the same way as the
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<I>spoof</I>
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command is parsed.
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Valid values are
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<I>off</I>, <I>nowarn</I>, and <I>warn</I>.
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</DL>
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<A NAME="lbAH"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+gethostbyname">gethostbyname</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?5+hosts">hosts</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?5+nsswitch.conf">nsswitch.conf</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?5+resolv.conf">resolv.conf</A></B>(5),
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<B><A HREF="/cgi-bin/man/man2html?7+hostname">hostname</A></B>(7),
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<B><A HREF="/cgi-bin/man/man2html?8+named">named</A></B>(8)
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<A NAME="lbAI"> </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="18"><A HREF="#lbAB">NAME</A><DD>
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<DT id="19"><A HREF="#lbAC">DESCRIPTION</A><DD>
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<DT id="20"><A HREF="#lbAD">ENVIRONMENT</A><DD>
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<DT id="21"><A HREF="#lbAE">FILES</A><DD>
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<DT id="22"><A HREF="#lbAF">NOTES</A><DD>
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<DL>
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<DT id="23"><A HREF="#lbAG">Historical</A><DD>
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</DL>
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<DT id="24"><A HREF="#lbAH">SEE ALSO</A><DD>
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<DT id="25"><A HREF="#lbAI">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: 00:06:03 GMT, March 31, 2021
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</BODY>
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</HTML>
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