I posted the below on the Ubuntu forum, however I respost it here, because I am unsure to what extent I hitting a Turnkey issue rather than an Ubuntu issue. For instance, it would appear that with Turnkey there is no "sudo" command, yet I can't ever remember coming across any Ubuntu documentation that doesn't expect "sudo" to be available.
root@lamp /home/gt# apt-get install ubuntu-restricted-extras Reading package lists... Done Building dependency tree Reading state information... Done E: Couldn't find package ubuntu-restricted-extras