Failsafe X Window server with automatic switch-over | Classroom situation Display wall with multiple X Window servers

# Failsafe X Window server with automatic switch-over

The Failsafe option (Failsafe operation) combined with the scripting capability of the configuration tool (XmetaXtool: control and integration) allows to configure a failsafe X Window server. However, the XmetaX proxy must be executed on a failsafe host. Here, two single-headed X terminals — one and two — act as X Window servers. The common configuration file is specialized through the variable $terminal (Variables):

    # /etc/opt/XSOXmetaX/terminal.conf

    options +DynamicServer +Failsafe
    screen $terminal
        display $terminal:0.0
        clipX 0
        failsafeTimeout 10

The fact that one of the X terminals can fail, has two consequences:

When starting the XmetaX proxy it is not clear which of the X terminals is actually up.

If an X terminal fails during runtime, it is deleted from the configuration automatically due to the Failsafe option, and the other terminal has to be included into the configuration.

The following shell script covers both problems:

    #!/bin/sh
    # /etc/opt/XSOXmetaX/failsafe

    DISPLAY=:0.0 export DISPLAY
    export terminal
    for terminal in one two
    do
        /opt/XSOXmetaX/bin/xmetax /etc/opt/XSOXmetaX/terminal.conf &
        sleep 60
        if /opt/XSOXmetaX/bin/xmetaxtool -print > /dev/null
        then
            break
        fi
        if [ "$terminal" = "two" ]
        then
            echo "$0: No server available" 1>&2
            exit 1
        fi
    done

    /opt/XSOXmetaX/bin/xmetaxtool -events \
        | while read type terminal detail
    do
        case $detail
        in destroyed)
            case $terminal
            in one)
                 terminal=two
            ;; two)
                 terminal=one
            ;; esac
            echo "$0: Switching to server $terminal" 1>&2
            if /opt/XSOXmetaX/bin/xmetaxtool -nogui \
                /etc/opt/XSOXmetaX/terminal.conf
            then
                :
            else
                exit $?
            fi
        ;; esac
    done

In the second part, the shell script continuously reads and processes configuration changes (Reporting configuration changes): if a screen is deleted from the configuration, the respective other one is configured.

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Classroom situation
Display wall with multiple X Window servers

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