/mandos/release : revision 88

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<?xml version="1.0" encoding="UTF-8"?>

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"

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"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [

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<!ENTITY VERSION "1.0">

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<!ENTITY COMMANDNAME "mandos">

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<!ENTITY OVERVIEW SYSTEM "overview.xml">

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]>

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<title>&COMMANDNAME;</title>

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<productname>&COMMANDNAME;</productname>

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<productnumber>&VERSION;</productnumber>

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<firstname>Björn</firstname>

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<surname>Påhlsson</surname>

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<email>belorn@fukt.bsnet.se</email>

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</address>

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</author>

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<firstname>Teddy</firstname>

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<surname>Hogeborn</surname>

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<email>teddy@fukt.bsnet.se</email>

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</address>

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</author>

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</authorgroup>

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<holder>Teddy Hogeborn</holder>

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<holder>Björn Påhlsson</holder>

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</copyright>

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<para>

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This manual page is free software: you can redistribute it

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and/or modify it under the terms of the GNU General Public

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License as published by the Free Software Foundation,

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either version 3 of the License, or (at your option) any

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later version.

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</para>

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<para>

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This manual page is distributed in the hope that it will

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be useful, but WITHOUT ANY WARRANTY; without even the

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implied warranty of MERCHANTABILITY or FITNESS FOR A

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PARTICULAR PURPOSE. See the GNU General Public License

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for more details.

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</para>

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<para>

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You should have received a copy of the GNU General Public

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License along with this program; If not, see

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<ulink url="http://www.gnu.org/licenses/"/>.

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</para>

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</legalnotice>

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</refentryinfo>

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<refentrytitle>&COMMANDNAME;</refentrytitle>

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</refmeta>

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<refname><command>&COMMANDNAME;</command></refname>

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Sends encrypted passwords to authenticated Mandos clients

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</refpurpose>

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</refnamediv>

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<command>&COMMANDNAME;</command>

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<arg>--interface<arg choice="plain">IF</arg></arg>

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<arg>--address<arg choice="plain">ADDRESS</arg></arg>

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<arg>--priority<arg choice="plain">PRIORITY</arg></arg>

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<arg>--servicename<arg choice="plain">NAME</arg></arg>

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<arg>--configdir<arg choice="plain">DIRECTORY</arg></arg>

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<arg>--debug</arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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<arg>-a<arg choice="plain">ADDRESS</arg></arg>

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<arg>--priority<arg choice="plain">PRIORITY</arg></arg>

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<arg>--servicename<arg choice="plain">NAME</arg></arg>

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<arg>--configdir<arg choice="plain">DIRECTORY</arg></arg>

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<arg>--debug</arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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</group>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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<arg choice="plain">--version</arg>

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</cmdsynopsis>

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<command>&COMMANDNAME;</command>

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<arg choice="plain">--check</arg>

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</cmdsynopsis>

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</refsynopsisdiv>

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<title>DESCRIPTION</title>

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<para>

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<command>&COMMANDNAME;</command> is a server daemon which

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handles incoming request for passwords for a pre-defined list of

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client host computers. The Mandos server uses Zeroconf to

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announce itself on the local network, and uses TLS to

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communicate securely with and to authenticate the clients. The

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Mandos server uses IPv6 to allow Mandos clients to use IPv6

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link-local addresses, since the clients will probably not have

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any other addresses configured (see <xref linkend="overview"/>).

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Any authenticated client is then given the stored pre-encrypted

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password for that specific client.

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</para>

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</refsect1>

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<title>PURPOSE</title>

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<para>

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The purpose of this is to enable <emphasis>remote and unattended

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rebooting</emphasis> of client host computer with an

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<emphasis>encrypted root file system</emphasis>. See <xref

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linkend="overview"/> for details.

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</para>

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</refsect1>

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<title>OPTIONS</title>

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<para>

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Show a help message and exit

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</para>

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</listitem>

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</varlistentry>

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<term><literal>-i</literal>, <literal>--interface <replaceable>

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IF</replaceable></literal></term>

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<para>

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Only announce the server and listen to requests on network

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interface <replaceable>IF</replaceable>. Default is to

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use all available interfaces. <emphasis>Note:</emphasis>

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a failure to bind to the specified interface is not

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considered critical, and the server does not exit.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>-a</literal>, <literal>--address <replaceable>

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ADDRESS</replaceable></literal></term>

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<para>

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If this option is used, the server will only listen to a

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specific address. This must currently be an IPv6 address;

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an IPv4 address can be specified using the

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<quote><literal>::FFFF:192.0.2.3</literal></quote> syntax.

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Also, if a link-local address is specified, an interface

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should be set, since a link-local address is only valid on

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a single interface. By default, the server will listen to

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all available addresses.

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</para>

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</listitem>

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</varlistentry>

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PORT</replaceable></literal></term>

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<para>

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If this option is used, the server to bind to that

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port. By default, the server will listen to an arbitrary

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port given by the operating system.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--check</literal></term>

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<para>

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Run the server’s self-tests. This includes any unit

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tests, etc.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--debug</literal></term>

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<para>

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If the server is run in debug mode, it will run in the

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foreground and print a lot of debugging information. The

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default is <emphasis>not</emphasis> to run in debug mode.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--priority <replaceable>

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PRIORITY</replaceable></literal></term>

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<para>

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GnuTLS priority string for the TLS handshake with the

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clients. The default is

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<quote><literal>SECURE256:!CTYPE-X.509:+CTYPE-OPENPGP</literal></quote>.

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See <citerefentry><refentrytitle>gnutls_priority_init

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</refentrytitle><manvolnum>3</manvolnum></citerefentry>

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for the syntax. <emphasis>Warning</emphasis>: changing

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this may make the TLS handshake fail, making communication

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with clients impossible.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--servicename <replaceable>NAME</replaceable>

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</literal></term>

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<para>

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Zeroconf service name. The default is

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<quote><literal>Mandos</literal></quote>. This only needs

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to be changed this if it, for some reason, is necessary to

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run more than one server on the same

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<emphasis>host</emphasis>, which would not normally be

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useful. If there are name collisions on the same

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<emphasis>network</emphasis>, the newer server will

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automatically rename itself to <quote><literal>Mandos

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#2</literal></quote>, and so on; therefore, this option is

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not needed in that case.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--configdir <replaceable>DIR</replaceable>

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</literal></term>

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<para>

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Directory to search for configuration files. Default is

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<quote><literal>/etc/mandos</literal></quote>. See

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<citerefentry><refentrytitle>mandos.conf</refentrytitle>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>.

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</para>

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</listitem>

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</varlistentry>

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<term><literal>--version</literal></term>

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<para>

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Prints the program version and exit.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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<title>OVERVIEW</title>

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&OVERVIEW;

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<para>

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This program is the server part. It is a normal server program

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and will run in a normal system environment, not in an initial

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RAM disk environment.

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</para>

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</refsect1>

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<title>NETWORK PROTOCOL</title>

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<para>

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The Mandos server announces itself as a Zeroconf service of type

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<quote><literal>_mandos._tcp</literal></quote>. The Mandos

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client connects to the announced address and port, and sends a

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line of text where the first whitespace-separated field is the

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protocol version, which currently is

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<quote><literal>1</literal></quote>. The client and server then

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start a TLS protocol handshake with a slight quirk: the Mandos

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server program acts as a TLS <quote>client</quote> while the

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connecting Mandos client acts as a TLS <quote>server</quote>.

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The Mandos client must supply an OpenPGP certificate, and the

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fingerprint of this certificate is used by the Mandos server to

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look up (in a list read from <filename>clients.conf</filename>

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at start time) which binary blob to give the client. No other

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authentication or authorization is done by the server.

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</para>

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<table>

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<title>Mandos Protocol (Version 1)</title><tgroup cols="3"><thead>

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<row>

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<entry>Mandos Client</entry>

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<entry>Direction</entry>

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<entry>Mandos Server</entry>

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</row>

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</thead><tbody>

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<row>

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<entry>Connect</entry>

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</row>

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<row>

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</row>

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<row>

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<entry>TLS handshake <emphasis>as TLS <quote>server</quote>

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</emphasis></entry>

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<entry>TLS handshake <emphasis>as TLS <quote>client</quote>

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</emphasis></entry>

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</row>

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<row>

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<entry>OpenPGP public key (part of TLS handshake)</entry>

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</row>

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<row>

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<entry>Binary blob (client will assume OpenPGP data)</entry>

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</row>

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<row>

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<entry>Close</entry>

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</row>

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</tbody></tgroup></table>

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</refsect1>

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<title>CHECKING</title>

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<para>

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The server will, by default, continually check that the clients

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are still up. If a client has not been confirmed as being up

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for some time, the client is assumed to be compromised and is no

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longer eligible to receive the encrypted password. The timeout,

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checker program, and interval between checks can be configured

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both globally and per client; see <citerefentry>

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<refentrytitle>mandos.conf</refentrytitle>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>.

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</para>

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</refsect1>

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<title>LOGGING</title>

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<para>

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The server will send log messaged with various severity levels

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to <filename>/dev/log</filename>. With the

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<option>--debug</option> option, it will log even more messages,

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and also show them on the console.

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</para>

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</refsect1>

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<title>EXIT STATUS</title>

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<para>

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The server will exit with a non-zero exit status only when a

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critical error is encountered.

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</para>

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</refsect1>

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<title>ENVIRONMENT</title>

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<para>

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To start the configured checker (see <xref

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linkend="checking"/>), the server uses

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<filename>/bin/sh</filename>, which in turn uses

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<varname>PATH</varname> to search for matching commands if

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an absolute path is not given. See <citerefentry>

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</citerefentry>

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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<title>FILES</title>

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<para>

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Use the <option>--configdir</option> option to change where

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<command>&COMMANDNAME;</command> looks for its configurations

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files. The default file names are listed here.

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</para>

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<term><filename>/etc/mandos/mandos.conf</filename></term>

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<para>

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Server-global settings. See

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<citerefentry><refentrytitle>mandos.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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</para>

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</listitem>

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</varlistentry>

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<term><filename>/etc/mandos/clients.conf</filename></term>

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<para>

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List of clients and client-specific settings. See

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<citerefentry><refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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</para>

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</listitem>

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</varlistentry>

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<term><filename>/var/run/mandos/mandos.pid</filename></term>

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<para>

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The file containing the process id of

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<command>&COMMANDNAME;</command>.

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</para>

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</listitem>

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</varlistentry>

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<para>

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The Unix domain socket to where local syslog messages are

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sent.

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</para>

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</listitem>

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</varlistentry>

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<para>

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This is used to start the configured checker command for

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each client. See <citerefentry>

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<refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry> for details.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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<para>

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This server might, on especially fatal errors, emit a Python

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backtrace. This could be considered a feature.

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</para>

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<para>

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Currently, if a client is declared <quote>invalid</quote> due to

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having timed out, the server does not record this fact onto

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permanent storage. This has some security implications, see

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<xref linkend="CLIENTS"/>.

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</para>

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<para>

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There is currently no way of querying the server of the current

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status of clients, other than analyzing its <systemitem

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class="service">syslog</systemitem> output.

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</para>

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<para>

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There is no fine-grained control over logging and debug output.

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</para>

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<para>

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Debug mode is conflated with running in the foreground.

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</para>

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<para>

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The console log messages does not show a timestamp.

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</para>

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</refsect1>

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<title>EXAMPLE</title>

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<para>

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Normal invocation needs no options:

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</para>

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<para>

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<userinput>mandos</userinput>

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</para>

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</informalexample>

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<para>

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Run the server in debug mode, read configuration files from

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the <filename>~/mandos</filename> directory, and use the

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Zeroconf service name <quote>Test</quote> to not collide with

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any other official Mandos server on this host:

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</para>

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<para>

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<userinput>mandos --debug --configdir ~/mandos --servicename Test</userinput>

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</para>

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</informalexample>

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<para>

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Run the server normally, but only listen to one interface and

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only on the link-local address on that interface:

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</para>

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<para>

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<userinput>mandos --interface eth7 --address fe80::aede:48ff:fe71:f6f2</userinput>

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</para>

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</informalexample>

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</refsect1>

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<title>SECURITY</title>

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<title>SERVER</title>

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<para>

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Running this <command>&COMMANDNAME;</command> server program

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should not in itself present any security risk to the host

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computer running it. The program does not need any special

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privileges to run, and is designed to run as a non-root user.

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</para>

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</refsect2>

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<title>CLIENTS</title>

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<para>

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The server only gives out its stored data to clients which

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does have the OpenPGP key of the stored fingerprint. This is

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guaranteed by the fact that the client sends its OpenPGP

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public key in the TLS handshake; this ensures it to be

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genuine. The server computes the fingerprint of the key

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itself and looks up the fingerprint in its list of

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clients. The <filename>clients.conf</filename> file (see

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<citerefentry><refentrytitle>mandos-clients.conf</refentrytitle>

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<manvolnum>5</manvolnum></citerefentry>)

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<emphasis>must</emphasis> be made non-readable by anyone

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except the user running the server.

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</para>

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<para>

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As detailed in <xref linkend="checking"/>, the status of all

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client computers will continually be checked and be assumed

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compromised if they are gone for too long.

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</para>

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<para>

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If a client is compromised, its downtime should be duly noted

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by the server which would therefore declare the client

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invalid. But if the server was ever restarted, it would

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re-read its client list from its configuration file and again

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regard all clients therein as valid, and hence eligible to

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receive their passwords. Therefore, be careful when

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restarting servers if it is suspected that a client has, in

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fact, been compromised by parties who may now be running a

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fake Mandos client with the keys from the non-encrypted

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initial RAM image of the client host. What should be done in

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that case (if restarting the server program really is

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necessary) is to stop the server program, edit the

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configuration file to omit any suspect clients, and restart

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the server program.

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</para>

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<para>

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For more details on client-side security, see

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<citerefentry><refentrytitle>password-request</refentrytitle>

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<manvolnum>8mandos</manvolnum></citerefentry>.

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</para>

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</refsect2>

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</refsect1>

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<term>

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<refentrytitle>password-request</refentrytitle>

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<manvolnum>8mandos</manvolnum>

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</citerefentry>

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</term>

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<para>

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This is the actual program which talks to this server.

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Note that it is normally not invoked directly, and is only

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run in the initial RAM disk environment, and not on a

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fully started system.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink url="http://www.zeroconf.org/">Zeroconf</ulink>

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</term>

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<para>

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Zeroconf is the network protocol standard used by clients

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for finding this Mandos server on the local network.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink url="http://www.avahi.org/">Avahi</ulink>

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</term>

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<para>

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Avahi is the library this server calls to implement

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Zeroconf service announcements.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<ulink

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url="http://www.gnu.org/software/gnutls/">GnuTLS</ulink>

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</term>

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<para>

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GnuTLS is the library this server uses to implement TLS for

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communicating securely with the client, and at the same time

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confidently get the client’s public OpenPGP key.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<citation>RFC 4291: <citetitle>IP Version 6 Addressing

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Architecture</citetitle>, section 2.5.6, Link-Local IPv6

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Unicast Addresses</citation>

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</term>

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<para>

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The clients use IPv6 link-local addresses, which are

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immediately usable since a link-local addresses is

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automatically assigned to a network interfaces when it is

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brought up.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<citation>RFC 4346: <citetitle>The Transport Layer Security

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(TLS) Protocol Version 1.1</citetitle></citation>

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</term>

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<para>

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TLS 1.1 is the protocol implemented by GnuTLS.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<citation>RFC 4880: <citetitle>OpenPGP Message

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Format</citetitle></citation>

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</term>

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<para>

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The data sent to clients is binary encrypted OpenPGP data.

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</para>

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</listitem>

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</varlistentry>

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<term>

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<citation>RFC 5081: <citetitle>Using OpenPGP Keys for

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Transport Layer Security</citetitle></citation>

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</term>

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<para>

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This is implemented by GnuTLS and used by this server so

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that OpenPGP keys can be used.

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</para>

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</listitem>

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</varlistentry>

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</variablelist>

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</refsect1>

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</refentry>