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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
	"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
<!ENTITY COMMANDNAME "mandos-client">
<!ENTITY TIMESTAMP "2019-02-10">
<!ENTITY % common SYSTEM "../common.ent">
%common;
]>

<refentry xmlns:xi="http://www.w3.org/2001/XInclude">
  <refentryinfo>
    <title>Mandos Manual</title>
    <!-- NWalsh’s docbook scripts use this to generate the footer: -->
    <productname>Mandos</productname>
    <productnumber>&version;</productnumber>
    <date>&TIMESTAMP;</date>
    <authorgroup>
      <author>
	<firstname>Björn</firstname>
	<surname>Påhlsson</surname>
	<address>
	  <email>belorn@recompile.se</email>
	</address>
      </author>
      <author>
	<firstname>Teddy</firstname>
	<surname>Hogeborn</surname>
	<address>
	  <email>teddy@recompile.se</email>
	</address>
      </author>
    </authorgroup>
    <copyright>
      <year>2008</year>
      <year>2009</year>
      <year>2010</year>
      <year>2011</year>
      <year>2012</year>
      <year>2013</year>
      <year>2014</year>
      <year>2015</year>
      <year>2016</year>
      <year>2017</year>
      <year>2018</year>
      <year>2019</year>
      <holder>Teddy Hogeborn</holder>
      <holder>Björn Påhlsson</holder>
    </copyright>
    <xi:include href="../legalnotice.xml"/>
  </refentryinfo>
  
  <refmeta>
    <refentrytitle>&COMMANDNAME;</refentrytitle>
    <manvolnum>8mandos</manvolnum>
  </refmeta>
  
  <refnamediv>
    <refname><command>&COMMANDNAME;</command></refname>
    <refpurpose>
      Client for <application>Mandos</application>
    </refpurpose>
  </refnamediv>
  
  <refsynopsisdiv>
    <cmdsynopsis>
      <command>&COMMANDNAME;</command>
      <group>
	<arg choice="plain"><option>--connect
	<replaceable>ADDRESS</replaceable><literal>:</literal
	><replaceable>PORT</replaceable></option></arg>
	<arg choice="plain"><option>-c
	<replaceable>ADDRESS</replaceable><literal>:</literal
	><replaceable>PORT</replaceable></option></arg>
      </group>
      <sbr/>
      <group rep='repeat'>
	<arg choice="plain"><option>--interface
	<replaceable>NAME</replaceable><arg rep='repeat'
	>,<replaceable>NAME</replaceable></arg></option></arg>
	<arg choice="plain"><option>-i <replaceable>NAME</replaceable
	><arg rep='repeat'>,<replaceable>NAME</replaceable></arg
	></option></arg>
      </group>
      <sbr/>
      <group>
	<arg choice="plain"><option>--pubkey
	<replaceable>FILE</replaceable></option></arg>
	<arg choice="plain"><option>-p
	<replaceable>FILE</replaceable></option></arg>
      </group>
      <sbr/>
      <group>
	<arg choice="plain"><option>--seckey
	<replaceable>FILE</replaceable></option></arg>
	<arg choice="plain"><option>-s
	<replaceable>FILE</replaceable></option></arg>
      </group>
      <sbr/>
      <group>
	<arg choice="plain"><option>--tls-privkey
	<replaceable>FILE</replaceable></option></arg>
	<arg choice="plain"><option>-t
	<replaceable>FILE</replaceable></option></arg>
      </group>
      <sbr/>
      <group>
	<arg choice="plain"><option>--tls-pubkey
	<replaceable>FILE</replaceable></option></arg>
	<arg choice="plain"><option>-T
	<replaceable>FILE</replaceable></option></arg>
      </group>
      <sbr/>
      <arg>
	<option>--priority <replaceable>STRING</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--dh-bits <replaceable>BITS</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--dh-params <replaceable>FILE</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--delay <replaceable>SECONDS</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--retry <replaceable>SECONDS</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--network-hook-dir
	<replaceable>DIR</replaceable></option>
      </arg>
      <sbr/>
      <arg>
	<option>--debug</option>
      </arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>&COMMANDNAME;</command>
      <group choice="req">
	<arg choice="plain"><option>--help</option></arg>
	<arg choice="plain"><option>-?</option></arg>
      </group>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>&COMMANDNAME;</command>
      <arg choice="plain"><option>--usage</option></arg>
    </cmdsynopsis>
    <cmdsynopsis>
      <command>&COMMANDNAME;</command>
      <group choice="req">
	<arg choice="plain"><option>--version</option></arg>
	<arg choice="plain"><option>-V</option></arg>
      </group>
    </cmdsynopsis>
  </refsynopsisdiv>
  
  <refsect1 id="description">
    <title>DESCRIPTION</title>
    <para>
      <command>&COMMANDNAME;</command> is a client program that
      communicates with <citerefentry><refentrytitle
      >mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>
      to get a password.  In slightly more detail, this client program
      brings up network interfaces, uses the interfaces’ IPv6
      link-local addresses to get network connectivity, uses Zeroconf
      to find servers on the local network, and communicates with
      servers using TLS with a raw public key to ensure authenticity
      and confidentiality.  This client program keeps running, trying
      all servers on the network, until it receives a satisfactory
      reply or a TERM signal.  After all servers have been tried, all
      servers are periodically retried.  If no servers are found it
      will wait indefinitely for new servers to appear.
    </para>
    <para>
      The network interfaces are selected like this: If any interfaces
      are specified using the <option>--interface</option> option,
      those interface are used.  Otherwise,
      <command>&COMMANDNAME;</command> will use all interfaces that
      are not loopback interfaces, are not point-to-point interfaces,
      are capable of broadcasting and do not have the NOARP flag (see
      <citerefentry><refentrytitle>netdevice</refentrytitle>
      <manvolnum>7</manvolnum></citerefentry>).  (If the
      <option>--connect</option> option is used, point-to-point
      interfaces and non-broadcast interfaces are accepted.)  If any
      used interfaces are not up and running, they are first taken up
      (and later taken down again on program exit).
    </para>
    <para>
      Before network interfaces are selected, all <quote>network
      hooks</quote> are run; see <xref linkend="network-hooks"/>.
    </para>
    <para>
      This program is not meant to be run directly; it is really meant
      to run as a plugin of the <application>Mandos</application>
      <citerefentry><refentrytitle>plugin-runner</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>, which runs in the
      initial <acronym>RAM</acronym> disk environment because it is
      specified as a <quote>keyscript</quote> in the <citerefentry>
      <refentrytitle>crypttab</refentrytitle><manvolnum>5</manvolnum>
      </citerefentry> file.
    </para>
  </refsect1>
  
  <refsect1 id="purpose">
    <title>PURPOSE</title>
    <para>
      The purpose of this is to enable <emphasis>remote and unattended
      rebooting</emphasis> of client host computer with an
      <emphasis>encrypted root file system</emphasis>.  See <xref
      linkend="overview"/> for details.
    </para>
  </refsect1>
  
  <refsect1 id="options">
    <title>OPTIONS</title>
    <para>
      This program is commonly not invoked from the command line; it
      is normally started by the <application>Mandos</application>
      plugin runner, see <citerefentry><refentrytitle
      >plugin-runner</refentrytitle><manvolnum>8mandos</manvolnum>
      </citerefentry>.  Any command line options this program accepts
      are therefore normally provided by the plugin runner, and not
      directly.
    </para>
    
    <variablelist>
      <varlistentry>
	<term><option>--connect=<replaceable
	>ADDRESS</replaceable><literal>:</literal><replaceable
	>PORT</replaceable></option></term>
	<term><option>-c
	<replaceable>ADDRESS</replaceable><literal>:</literal
	><replaceable>PORT</replaceable></option></term>
	<listitem>
	  <para>
	    Do not use Zeroconf to locate servers.  Connect directly
	    to only one specified <application>Mandos</application>
	    server.  Note that an IPv6 address has colon characters in
	    it, so the <emphasis>last</emphasis> colon character is
	    assumed to separate the address from the port number.
	  </para>
	  <para>
	    Normally, Zeroconf would be used to locate Mandos servers,
	    in which case this option would only be used when testing
	    and debugging.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--interface=<replaceable
	>NAME</replaceable><arg rep='repeat'>,<replaceable
	>NAME</replaceable></arg></option></term>
	<term><option>-i
	<replaceable>NAME</replaceable><arg rep='repeat'>,<replaceable
	>NAME</replaceable></arg></option></term>
	<listitem>
	  <para>
	    Comma separated list of network interfaces that will be
	    brought up and scanned for Mandos servers to connect to.
	    The default is the empty string, which will automatically
	    use all appropriate interfaces.
	  </para>
	  <para>
	    If the <option>--connect</option> option is used, and
	    exactly one interface name is specified (except
	    <quote><literal>none</literal></quote>), this specifies
	    the interface to use to connect to the address given.
	  </para>
	  <para>
	    Note that since this program will normally run in the
	    initial RAM disk environment, the interface must be an
	    interface which exists at that stage.  Thus, the interface
	    can normally not be a pseudo-interface such as
	    <quote>br0</quote> or <quote>tun0</quote>; such interfaces
	    will not exist until much later in the boot process, and
	    can not be used by this program, unless created by a
	    <quote>network hook</quote> — see <xref
	    linkend="network-hooks"/>.
	  </para>
	  <para>
	    <replaceable>NAME</replaceable> can be the string
	    <quote><literal>none</literal></quote>; this will make
	    <command>&COMMANDNAME;</command> only bring up interfaces
	    specified <emphasis>before</emphasis> this string.  This
	    is not recommended, and only meant for advanced users.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--pubkey=<replaceable
	>FILE</replaceable></option></term>
	<term><option>-p
	<replaceable>FILE</replaceable></option></term>
	<listitem>
	  <para>
	    OpenPGP public key file name.  The default name is
	    <quote><filename>/conf/conf.d/mandos/pubkey.txt</filename
	    ></quote>.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--seckey=<replaceable
	>FILE</replaceable></option></term>
	<term><option>-s
	<replaceable>FILE</replaceable></option></term>
	<listitem>
	  <para>
	    OpenPGP secret key file name.  The default name is
	    <quote><filename>/conf/conf.d/mandos/seckey.txt</filename
	    ></quote>.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--tls-pubkey=<replaceable
	>FILE</replaceable></option></term>
	<term><option>-T
	<replaceable>FILE</replaceable></option></term>
	<listitem>
	  <para>
	    TLS raw public key file name.  The default name is
	    <quote><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename
	    ></quote>.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term><option>--tls-privkey=<replaceable
	>FILE</replaceable></option></term>
	<term><option>-t
	<replaceable>FILE</replaceable></option></term>
	<listitem>
	  <para>
	    TLS secret key file name.  The default name is
	    <quote><filename>/conf/conf.d/mandos/tls-privkey.pem</filename
	    ></quote>.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term><option>--priority=<replaceable
	>STRING</replaceable></option></term>
	<listitem>
	  <xi:include href="../mandos-options.xml"
		      xpointer="priority"/>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--dh-bits=<replaceable
	>BITS</replaceable></option></term>
	<listitem>
	  <para>
	    Sets the number of bits to use for the prime number in the
	    TLS Diffie-Hellman key exchange.  The default value is
	    selected automatically based on the GnuTLS security
	    profile set in its priority string.  Note that if the
	    <option>--dh-params</option> option is used, the values
	    from that file will be used instead.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--dh-params=<replaceable
	>FILE</replaceable></option></term>
	<listitem>
	  <para>
	    Specifies a PEM-encoded PKCS#3 file to read the parameters
	    needed by the TLS Diffie-Hellman key exchange from.  If
	    this option is not given, or if the file for some reason
	    could not be used, the parameters will be generated on
	    startup, which will take some time and processing power.
	    Those using servers running under time, power or processor
	    constraints may want to generate such a file in advance
	    and use this option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term><option>--delay=<replaceable
	>SECONDS</replaceable></option></term>
	<listitem>
	  <para>
	    After bringing a network interface up, the program waits
	    for the interface to arrive in a <quote>running</quote>
	    state before proceeding.  During this time, the kernel log
	    level will be lowered to reduce clutter on the system
	    console, alleviating any other plugins which might be
	    using the system console.  This option sets the upper
	    limit of seconds to wait.  The default is 2.5 seconds.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term><option>--retry=<replaceable
	>SECONDS</replaceable></option></term>
	<listitem>
	  <para>
	    All Mandos servers are tried repeatedly until a password
	    is received.  This value specifies, in seconds, how long
	    between each successive try <emphasis>for the same
	    server</emphasis>.  The default is 10 seconds.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term><option>--network-hook-dir=<replaceable
	>DIR</replaceable></option></term>
	<listitem>
	  <para>
	    Network hook directory.  The default directory is
	    <quote><filename class="directory"
	    >/lib/mandos/network-hooks.d</filename></quote>.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--debug</option></term>
	<listitem>
	  <para>
	    Enable debug mode.  This will enable a lot of output to
	    standard error about what the program is doing.  The
	    program will still perform all other functions normally.
	  </para>
	  <para>
	    It will also enable debug mode in the Avahi and GnuTLS
	    libraries, making them print large amounts of debugging
	    output.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--help</option></term>
	<term><option>-?</option></term>
	<listitem>
	  <para>
	    Gives a help message about options and their meanings.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--usage</option></term>
	<listitem>
	  <para>
	    Gives a short usage message.
	  </para>
	</listitem>
      </varlistentry>
      
      <varlistentry>
	<term><option>--version</option></term>
	<term><option>-V</option></term>
	<listitem>
	  <para>
	    Prints the program version.
	  </para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  
  <refsect1 id="overview">
    <title>OVERVIEW</title>
    <xi:include href="../overview.xml"/>
    <para>
      This program is the client part.  It is a plugin started by
      <citerefentry><refentrytitle>plugin-runner</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry> which will run in
      an initial <acronym>RAM</acronym> disk environment.
    </para>
    <para>
      This program could, theoretically, be used as a keyscript in
      <filename>/etc/crypttab</filename>, but it would then be
      impossible to enter a password for the encrypted root disk at
      the console, since this program does not read from the console
      at all.  This is why a separate plugin runner (<citerefentry>
      <refentrytitle>plugin-runner</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>) is used to run
      both this program and others in in parallel,
      <emphasis>one</emphasis> of which (<citerefentry>
      <refentrytitle>password-prompt</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>) will prompt for
      passwords on the system console.
    </para>
  </refsect1>
  
  <refsect1 id="exit_status">
    <title>EXIT STATUS</title>
    <para>
      This program will exit with a successful (zero) exit status if a
      server could be found and the password received from it could be
      successfully decrypted and output on standard output.  The
      program will exit with a non-zero exit status only if a critical
      error occurs.  Otherwise, it will forever connect to any
      discovered <application>Mandos</application> servers, trying to
      get a decryptable password and print it.
    </para>
  </refsect1>
  
  <refsect1 id="environment">
    <title>ENVIRONMENT</title>
    <variablelist>
      <varlistentry>
	<term><envar>MANDOSPLUGINHELPERDIR</envar></term>
	<listitem>
	  <para>
	    This environment variable will be assumed to contain the
	    directory containing any helper executables.  The use and
	    nature of these helper executables, if any, is
	    purposefully not documented.
	</para>
	</listitem>
      </varlistentry>
    </variablelist>
    <para>
      This program does not use any other environment variables, not
      even the ones provided by <citerefentry><refentrytitle
      >cryptsetup</refentrytitle><manvolnum>8</manvolnum>
    </citerefentry>.
    </para>
  </refsect1>
  
  <refsect1 id="network-hooks">
    <title>NETWORK HOOKS</title>
    <para>
      If a network interface like a bridge or tunnel is required to
      find a Mandos server, this requires the interface to be up and
      running before <command>&COMMANDNAME;</command> starts looking
      for Mandos servers.  This can be accomplished by creating a
      <quote>network hook</quote> program, and placing it in a special
      directory.
    </para>
    <para>
      Before the network is used (and again before program exit), any
      runnable programs found in the network hook directory are run
      with the argument <quote><literal>start</literal></quote> or
      <quote><literal>stop</literal></quote>.  This should bring up or
      down, respectively, any network interface which
      <command>&COMMANDNAME;</command> should use.
    </para>
    <refsect2 id="hook-requirements">
      <title>REQUIREMENTS</title>
      <para>
	A network hook must be an executable file, and its name must
	consist entirely of upper and lower case letters, digits,
	underscores, periods, and hyphens.
      </para>
      <para>
	A network hook will receive one argument, which can be one of
	the following:
      </para>
      <variablelist>
	<varlistentry>
	  <term><literal>start</literal></term>
	  <listitem>
	    <para>
	      This should make the network hook create (if necessary)
	      and bring up a network interface.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><literal>stop</literal></term>
	  <listitem>
	    <para>
	      This should make the network hook take down a network
	      interface, and delete it if it did not exist previously.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><literal>files</literal></term>
	  <listitem>
	    <para>
	      This should make the network hook print, <emphasis>one
	      file per line</emphasis>, all the files needed for it to
	      run.  (These files will be copied into the initial RAM
	      filesystem.)  Typical use is for a network hook which is
	      a shell script to print its needed binaries.
	    </para>
	    <para>
	      It is not necessary to print any non-executable files
	      already in the network hook directory, these will be
	      copied implicitly if they otherwise satisfy the name
	      requirements.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><literal>modules</literal></term>
	  <listitem>
	    <para>
	      This should make the network hook print, <emphasis>on
	      separate lines</emphasis>, all the kernel modules needed
	      for it to run.  (These modules will be copied into the
	      initial RAM filesystem.)  For instance, a tunnel
	      interface needs the
	      <quote><literal>tun</literal></quote> module.
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
      <para>
	The network hook will be provided with a number of environment
	variables:
      </para>
      <variablelist>
	<varlistentry>
	  <term><envar>MANDOSNETHOOKDIR</envar></term>
	  <listitem>
	    <para>
	      The network hook directory, specified to
	      <command>&COMMANDNAME;</command> by the
	      <option>--network-hook-dir</option> option.  Note: this
	      should <emphasis>always</emphasis> be used by the
	      network hook to refer to itself or any files in the hook
	      directory it may require.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><envar>DEVICE</envar></term>
	  <listitem>
	    <para>
	      The network interfaces, as specified to
	      <command>&COMMANDNAME;</command> by the
	      <option>--interface</option> option, combined to one
	      string and separated by commas.  If this is set, and
	      does not contain the interface a hook will bring up,
	      there is no reason for a hook to continue.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><envar>MODE</envar></term>
	  <listitem>
	    <para>
	      This will be the same as the first argument;
	      i.e. <quote><literal>start</literal></quote>,
	      <quote><literal>stop</literal></quote>,
	      <quote><literal>files</literal></quote>, or
	      <quote><literal>modules</literal></quote>.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><envar>VERBOSITY</envar></term>
	  <listitem>
	    <para>
	      This will be the <quote><literal>1</literal></quote> if
	      the <option>--debug</option> option is passed to
	      <command>&COMMANDNAME;</command>, otherwise
	      <quote><literal>0</literal></quote>.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><envar>DELAY</envar></term>
	  <listitem>
	    <para>
	      This will be the same as the <option>--delay</option>
	      option passed to <command>&COMMANDNAME;</command>.  Is
	      only set if <envar>MODE</envar> is
	      <quote><literal>start</literal></quote> or
	      <quote><literal>stop</literal></quote>.
	    </para>
	  </listitem>
	</varlistentry>
	<varlistentry>
	  <term><envar>CONNECT</envar></term>
	  <listitem>
	    <para>
	      This will be the same as the <option>--connect</option>
	      option passed to <command>&COMMANDNAME;</command>.  Is
	      only set if <option>--connect</option> is passed and
	      <envar>MODE</envar> is
	      <quote><literal>start</literal></quote> or
	      <quote><literal>stop</literal></quote>.
	    </para>
	  </listitem>
	</varlistentry>
      </variablelist>
      <para>
	A hook may not read from standard input, and should be
	restrictive in printing to standard output or standard error
	unless <varname>VERBOSITY</varname> is
	<quote><literal>1</literal></quote>.
      </para>
    </refsect2>
  </refsect1>
  
  <refsect1 id="files">
    <title>FILES</title>
    <variablelist>
      <varlistentry>
	<term><filename>/conf/conf.d/mandos/pubkey.txt</filename
	></term>
	<term><filename>/conf/conf.d/mandos/seckey.txt</filename
	></term>
	<listitem>
	  <para>
	    OpenPGP public and private key files, in <quote>ASCII
	    Armor</quote> format.  These are the default file names,
	    they can be changed with the <option>--pubkey</option> and
	    <option>--seckey</option> options.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><filename>/conf/conf.d/mandos/tls-pubkey.pem</filename
	></term>
	<term><filename>/conf/conf.d/mandos/tls-privkey.pem</filename
	></term>
	<listitem>
	  <para>
	    Public and private raw key files, in <quote>PEM</quote>
	    format.  These are the default file names, they can be
	    changed with the <option>--tls-pubkey</option> and
	    <option>--tls-privkey</option> options.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><filename
	class="directory">/lib/mandos/network-hooks.d</filename></term>
	<listitem>
	  <para>
	    Directory where network hooks are located.  Change this
	    with the <option>--network-hook-dir</option> option.  See
	    <xref linkend="network-hooks"/>.
	  </para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
  
  <refsect1 id="bugs">
    <title>BUGS</title>
    <xi:include href="../bugs.xml"/>
  </refsect1>
  
  <refsect1 id="example">
    <title>EXAMPLE</title>
    <para>
      Note that normally, command line options will not be given
      directly, but via options for the Mandos <citerefentry
      ><refentrytitle>plugin-runner</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>.
    </para>
    <informalexample>
      <para>
	Normal invocation needs no options, if the network interfaces
	can be automatically determined:
      </para>
      <para>
	<userinput>&COMMANDNAME;</userinput>
      </para>
    </informalexample>
    <informalexample>
      <para>
	Search for Mandos servers (and connect to them) using one
	specific interface:
      </para>
      <para>
	<!-- do not wrap this line -->
	<userinput>&COMMANDNAME; --interface eth1</userinput>
      </para>
    </informalexample>
    <informalexample>
      <para>
	Run in debug mode, and use custom keys:
      </para>
      <para>

<!-- do not wrap this line -->
<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --tls-pubkey keydir/tls-pubkey.pem --tls-privkey keydir/tls-privkey.pem</userinput>

      </para>
    </informalexample>
    <informalexample>
      <para>
	Run in debug mode, with custom keys, and do not use Zeroconf
	to locate a server; connect directly to the IPv6 link-local
	address <quote><systemitem class="ipaddress"
	>fe80::aede:48ff:fe71:f6f2</systemitem></quote>, port 4711,
	using interface eth2:
      </para>
      <para>

<!-- do not wrap this line -->
<userinput>&COMMANDNAME; --debug --pubkey keydir/pubkey.txt --seckey keydir/seckey.txt --tls-pubkey keydir/tls-pubkey.pem --tls-privkey keydir/tls-privkey.pem --connect fe80::aede:48ff:fe71:f6f2:4711 --interface eth2</userinput>

      </para>
    </informalexample>
  </refsect1>
  
  <refsect1 id="security">
    <title>SECURITY</title>
    <para>
      This program is set-uid to root, but will switch back to the
      original (and presumably non-privileged) user and group after
      bringing up the network interface.
    </para>
    <para>
      To use this program for its intended purpose (see <xref
      linkend="purpose"/>), the password for the root file system will
      have to be given out to be stored in a server computer, after
      having been encrypted using an OpenPGP key.  This encrypted data
      which will be stored in a server can only be decrypted by the
      OpenPGP key, and the data will only be given out to those
      clients who can prove they actually have that key.  This key,
      however, is stored unencrypted on the client side in its initial
      <acronym>RAM</acronym> disk image file system.  This is normally
      readable by all, but this is normally fixed during installation
      of this program; file permissions are set so that no-one is able
      to read that file.
    </para>
    <para>
      The only remaining weak point is that someone with physical
      access to the client hard drive might turn off the client
      computer, read the OpenPGP and TLS keys directly from the hard
      drive, and communicate with the server.  To safeguard against
      this, the server is supposed to notice the client disappearing
      and stop giving out the encrypted data.  Therefore, it is
      important to set the timeout and checker interval values tightly
      on the server.  See <citerefentry><refentrytitle
      >mandos</refentrytitle><manvolnum>8</manvolnum></citerefentry>.
    </para>
    <para>
      It will also help if the checker program on the server is
      configured to request something from the client which can not be
      spoofed by someone else on the network, like SSH server key
      fingerprints, and unlike unencrypted <acronym>ICMP</acronym>
      echo (<quote>ping</quote>) replies.
    </para>
    <para>
      <emphasis>Note</emphasis>: This makes it completely insecure to
      have <application >Mandos</application> clients which dual-boot
      to another operating system which is <emphasis>not</emphasis>
      trusted to keep the initial <acronym>RAM</acronym> disk image
      confidential.
    </para>
  </refsect1>
  
  <refsect1 id="see_also">
    <title>SEE ALSO</title>
    <para>
      <citerefentry><refentrytitle>intro</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>cryptsetup</refentrytitle>
      <manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>crypttab</refentrytitle>
      <manvolnum>5</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>mandos</refentrytitle>
      <manvolnum>8</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>password-prompt</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>,
      <citerefentry><refentrytitle>plugin-runner</refentrytitle>
      <manvolnum>8mandos</manvolnum></citerefentry>
    </para>
    <variablelist>
      <varlistentry>
	<term>
	  <ulink url="http://www.zeroconf.org/">Zeroconf</ulink>
	</term>
	<listitem>
	  <para>
	    Zeroconf is the network protocol standard used for finding
	    Mandos servers on the local network.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <ulink url="http://www.avahi.org/">Avahi</ulink>
	</term>
      <listitem>
	<para>
	  Avahi is the library this program calls to find Zeroconf
	  services.
	</para>
      </listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <ulink url="https://www.gnutls.org/">GnuTLS</ulink>
	</term>
      <listitem>
	<para>
	  GnuTLS is the library this client uses to implement TLS for
	  communicating securely with the server, and at the same time
	  send the public key to the server.
	</para>
      </listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  <ulink url="https://www.gnupg.org/related_software/gpgme/"
		 >GPGME</ulink>
	</term>
	<listitem>
	  <para>
	    GPGME is the library used to decrypt the OpenPGP data sent
	    by the server.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  RFC 4291: <citetitle>IP Version 6 Addressing
	  Architecture</citetitle>
	</term>
	<listitem>
	  <variablelist>
	    <varlistentry>
	      <term>Section 2.2: <citetitle>Text Representation of
	      Addresses</citetitle></term>
	      <listitem><para/></listitem>
	    </varlistentry>
	    <varlistentry>
	      <term>Section 2.5.5.2: <citetitle>IPv4-Mapped IPv6
	      Address</citetitle></term>
	      <listitem><para/></listitem>
	    </varlistentry>
	    <varlistentry>
	    <term>Section 2.5.6, <citetitle>Link-Local IPv6 Unicast
	    Addresses</citetitle></term>
	    <listitem>
	      <para>
		This client uses IPv6 link-local addresses, which are
		immediately usable since a link-local addresses is
		automatically assigned to a network interface when it
		is brought up.
	      </para>
	    </listitem>
	    </varlistentry>
	  </variablelist>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  RFC 5246: <citetitle>The Transport Layer Security (TLS)
	  Protocol Version 1.2</citetitle>
	</term>
      <listitem>
	<para>
	  TLS 1.2 is the protocol implemented by GnuTLS.
	</para>
      </listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  RFC 4880: <citetitle>OpenPGP Message Format</citetitle>
	</term>
      <listitem>
	<para>
	  The data received from the server is binary encrypted
	  OpenPGP data.
	</para>
      </listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  RFC 7250: <citetitle>Using Raw Public Keys in Transport
	  Layer Security (TLS) and Datagram Transport Layer Security
	  (DTLS)</citetitle>
	</term>
      <listitem>
	<para>
	  This is implemented by GnuTLS in version 3.6.6 and is, if
	  present, used by this program so that raw public keys can be
	  used.
	</para>
      </listitem>
      </varlistentry>
      <varlistentry>
	<term>
	  RFC 6091: <citetitle>Using OpenPGP Keys for Transport Layer
	  Security</citetitle>
	</term>
      <listitem>
	<para>
	  This is implemented by GnuTLS before version 3.6.0 and is,
	  if present, used by this program so that OpenPGP keys can be
	  used.
	</para>
      </listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>

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