Conmux - Original Documentation

conmux, 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.

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. Basic Usage

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

$ console <host>/<console>

In the example below we indicate that the console we require is located on the virtual console server and the specific console is elm3b70.

$ console
Connected to elm3b70 console (~$quit to exit) Debian GNU/Linux 3.1 elm3b70 ttyS0
elm3b70 login:

Once connected we can interact normally with the console stream. To perform front pannel operation such as peforming an hard reset we switch to command mode. This is achieved using the escape sequence ~$. Note the prompt Command>

elm3b70 login: ~$
Command> quit
Connection closed $

Command Summary

The following commands are generally available:

Command Description
quit quit this console session, note that this disconnects us from the session it does not affect the integity of the session itself.
hardreset 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.


The conmux provides a virtual console multiplexor system reminicent of an Annex terminal server. You refer to the conmux server and lines, unlike an Annex lines are referred to by mnemonic names. Above we referred to the console for elm3b70 ‘connected to’ the server A virtual console server consists of a number of server processes. One conmux-registry server, several conmux servers and optionally several helper processes.

conmux-registry: 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.

conmux: 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.

autoboot-helper: 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” hardreset when required. This provides the impression of seamless reboot for systems which this does not work. Configuration conmux-registry

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

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:

listener <server>/<name>: defines the name of this console port as it appears in the registry.

socket <name> <title> <host>:<port>: defines a console payload connected to a tcp socket on the network. name defines this payload within the multiplexor, title is announced to the connecting clients.

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

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

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:

listener localhost/elm3b130
socket console 'elm3b130 console'
command 'hardreset' 'initated a hard reset' \ './reboot-numaq vcs elm3b130 12346 Administrator password'