Tuesday, October 21, 2014

Improving LTSP scripting facility

One thing that has been a pain with LTSP is that the scripts in /usr/share/ltsp/screen.d which control what launches on the thin client are all contained within the build image.  Any change/customization to those scripts then requires a rebuild/redeployment of the image.

I thought why not just use the tftp client to pull the script from the TFTP server instead.  Turns out this is quite easy to do.  I added the following script to the screen.d directory, and called it "tftp" (which was just based on one of the existing init scripts):


#full path to file (excluding /var/lib/tftpboot)
file=`basename $filepath`

if [ -n "$SERVER" ]; then
    tftp "$SERVER" -c get ${filepath} $script_temp
    # only execute if it has non-zero size.
    if [ -s "$script_temp" ]; then
        mv "$script_temp" /usr/share/ltsp/screen.d/${file}
        chmod 777 /usr/share/ltsp/screen.d/${file}
        exec /bin/bash /usr/share/ltsp/screen.d/${file}
        rm "$script_temp"
        sleep 15
        exec /bin/bash --login
Now in lts.conf I can do somthing like:

SCREEN_01 = tftp /ltsp-trusty/amd64/firefox

Now I have built the "/var/lib/tftpboot/ltsp-trusty/amd64/firefox" script on the TFTP server and it can easily/quickly customized as needed.

Here is an example (requires "apt-get install firefox openbox" in the ltsp-chroot image):


. /usr/share/ltsp/screen-x-common

export HOME="${HOME:-/root}" USER="${USER:-root}"
mkdir -p /root/.config/openbox
echo "/usr/bin/firefox http://somesite.biz" >> /root/.config/openbox/autostart
chmod 755 /root/.config/openbox/autostart

# The following logic is described at the top of xinitrc.
if [ -x /usr/share/ltsp/xinitrc ]; then
    xinit /usr/share/ltsp/xinitrc "$COMMAND" -- "$DISPLAY" "vt${TTY}" $X_ARGS >/dev/null
    eval "xinit $COMMAND -- $DISPLAY vt${TTY} $X_ARGS >/dev/null"

if [ $? -ne 0 ]; then
    echo "Xserver failed, falling back to a text shell" >&2
    exec /bin/bash --login

So simple things like having one thin-client launch firefox and another launch NX player, is easy thru lts.conf and script manipulation - no rebuilding of images required (apart from package installation of course).

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