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# (C) Copyright IBM Corp. 2004, 2005, 2006
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<title>conmux - the console multiplexor</title>
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<h1>conmux - the console multiplexor</h1>
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<p><em>conmux</em>, the console multiplexor is a system designed to abstract
the concept of a console.  That is to provide a virtualised machine interface,
including access to the console and the 'switches' on the front panel; the
/dev/console stream and the reset button.  It creates the concept of a virtual
console server for multiple consoles and provides access to and sharing of
consoles connected to it.

<p>There are two main motivations for wanting to do this.  Firstly, we have
many different machine types with vastly differing access methodologies for
their consoles and for control functions (VCS, HMC, Annex) and we neither want
to know what they are nor how they function.  Secondly, most console sources
are single access only and we would like to be able to share the console data
between many consumers including users.

<h2>Basic Usage</h2>

<p>The main interface to the consoles is via the <code>console</code>
program.  This connects us to the console server for the machine and allows us
to interact with it, including issuing <i>out-of-band</i> commands to control
the machine.

<div class="example">$ console &lt;host&gt;/&lt;console&gt;
</div>

<p>In the example below  we indicate that the console we require is located on
the virtual console server <code>consoles.here.com</code> and the
specific console is <code>elm3b70</code>.

<div class="example">$ console consoles.here.com/elm3b70
Connected to elm3b70 console (~$quit to exit)

Debian GNU/Linux 3.1 elm3b70 ttyS0

elm3b70 login:
</div>

<p>Once connected we can interact normally with the console stream.  To
perform front pannel operation such as peforming an <em>hard reset</em> we
switch to command mode.  This is achieved using the escape sequence
<code>~$</code>.  Nore the prompt <code>Command&gt;</code>

<div class="example">elm3b70 login: <em>~$</em>
Command&gt; quit
Connection closed
$
</div>

<h2>Command Summary</h2>

<p>The following commands are generally available:

<p><table class="quote" rules="all" frame="box">

<tr><th>Command<th>Description</tr>

<tr><td>quit<td>quit this console session, note that this disconnects us from
the session it does not affect the integity of the session itself.</tr>

<tr><td>hardreset<td>force a hard reset on the machine, this may be a simple
reset or a power off/on sequence whatever is required by this system.</tr>

</table>

<h2>Architecture</h2>

<p>The conmux provides a virtual console multiplexor system reminicent of
an Annex terminal server.  You refer to the conmux <em>server</em> and
<em>lines</em>, unlike an Annex lines are referred to by mnemonic names.
Above we referred to the console for <code>elm3b70</code> 'connected to' the
server <code>consoles.here.com</cond>.  A virtual console server consists
of a number of server processes.  One <code>conmux-registry</code> server,
several <code>conmux</code> servers and optionally several <em>helper</em>
processes.

<p><code>conmux-registry</code>: a server is defined by the server registry.
This maintains the mnemonic name to current server location relation.  When
a client wishes to attach to a console on a server, the registry is first
queried to locate the server currently handling that console.

<p><code>conmux</code>: for each connected console there is a corresponding
console multiplexor.  This process is responsible for maintaining the
connection to the console and for redistributing the output to the various
connected clients.  It is also responsible for handling "panel" commands
from the client channels.

<p><code>autoboot-helper</code>: an example helper which aids systems which
are not capable of an automatic reboot.  It connects to a console and watches
for tell-tale reboot activity, preforming a "panel" <em>hardreset</em> when
required.  This provides the impression of seamless reboot for systems
which this does not work.

<h2>Configuration</h2>

<h3>conmux-registry</h3>

<p>Configuration of this service is very simple.  Supplying the default
registry port (normally 63000) and the location for the persistant registry
database.

<h3>conmux</h3>

<p>Configuration of each conmux is complex.  Each has a listener, payload
and optionally one or more panel commands.  Configuration is provided via
a per console configuration file.  This file consists of lines defining each
element:

<p><code>listener &lt;server&gt;/&lt;name&gt;</code>:
defines the name of this console port as it appears in the registry.

<p><code>socket &lt;name&gt; &lt;title&gt; &lt;host&gt;:&lt;port&gt;</code>: 
defines a console payload connected to a tcp socket on the network.
<code>name</code> defines this payload within the multiplexor,
<code>title</code> is announced to the connecting clients.

<p><code>application &lt;name&gt; &lt;title&gt; &lt;cmd&gt;</code>:
defines a console payload which is accessed by running a specific command.
<code>name</code> defines this payload within the multiplexor,
<code>title</code> is announced to the connecting clients.

<p><code>command &lt;panel&gt; &lt;message&gt; &lt;cmd&gt;</code>:
defines a panel command for the preceeding payload, triggerd when
<code>panel</code> is typed at the command prompt.  <code>message</code>
is announced to the user community.  <code>cmd</cmd> will be actually
executed.

<p>For example here is the configuration for a NUMA-Q system which is rebooted
using a remote VCS console and for which the real console channel is
on an Annex terminal server:

<div class="example">listener localhost/elm3b130
socket console 'elm3b130 console' console.server.here.com:2040
  command 'hardreset' 'initated a hard reset' \
      './reboot-numaq vcs 1.2.3.4 elm3b130 12346 Administrator password'
</div>

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