From LinuxMCE wiki
This wiki is for the many of us out there that are new to linux and don't know the general commands used to find/edit/troublehoot. It also describes a lot of regularly used files for troublehooting. I will just use the core in my examples, but you can do this for any md also.
Logging Into A Terminal On Core Or MD
A lot of troubleshooting is done from a terminal, which is different than a windows or kde environment
- On the core/hybrid itself press ctrl-alt-f1 for what i call terminal 1, you can also use f2, f3 or f4 and have 4 terminals open at the same time
- From a windows box download putty which is a free ssh (secure shell) program to telnet into your core/hybrid
- Download here 
- Open the program and for the core/hybrid use 192.168.80.1 for the Host Name (or IP address) and click the 'Open' button
You are now in a command terminal on your core.
For most of the changes you want to make or installing new software you have to become 'root' (equivalent to administrator in win)
- If you are worried about messing stuff up, just use the 'sudo' command to become root just for that command, this is generally recommended for novice users of linux
- kubuntu will ask you for a password when you do, enter the password you used to setup the first account while installing kubuntu. kubuntu will only ask you for your password once per session===
- If you want to become 'root' and stay that way use the 'sudo -i' command and answer the password
You are now root on the system or can use a command as root
Viewing And Editing Files
For this example i'll use your video setup file xorg.conf
- location /etc/X11/xorg.conf
This file is used to store all your videocard settings, a lot of simple fixes can be made in here like changing the driver from vesa to nvidia and vice versa.
- To view you xorg.conf just use the 'cat' command:
To edit xorg.conf use any of the editors available, in kubuntu 'vi' is always available, i use 'nano'
- if you don't have nano, you can use the following command to install it
sudo apt-get install nano
- after installing nano, just use:
nano /etc/X11/xorg.conf to edit the file
you can now view and edit your xorg.conf, ofcourse you can use these same commands to view/edit any other file
Checking versions of installed software
With this command you can check the versions of the software installed
Ofcourse getting this whole list is difficult to navigate, and you can ask for only one piece as follows, for this example mythtv is used
dpkg -l | grep mythtv
This should give you a list like this with only the mythtv versions:
ii mythtv-backend 2:0.21.0+fixes-22228-openglvdpau2-0ubuntu2 A personal video recorder application (serve ii mythtv-common 2:0.21.0+fixes-22228-openglvdpau2-0ubuntu2 A personal video recorder application (commo ii mythtv-frontend 2:0.21.0+fixes-22228-openglvdpau2-0ubuntu2 A personal video recorder application (clien ii mythtv-transcode-utils 2:0.21.0+fixes-22228-openglvdpau2-0ubuntu2 Utilities used for transcoding MythTV tasks ii pluto-mythtv-player 184.108.40.206.09091422296 <insert up to 60 chars description>
As you can see this system is running mythtv version 0.21.0 (the vdpau2 gives away it's also using the avenard depot)
Getting a missing key for a certain package
In the latest install the md's medibuntu package key was not set correctly, which gives an error on apt-get update, you can correct this by typing the following.
wget http://packages.medibuntu.org/medibuntu-key.gpg sudo apt-key add medibuntu-key.gpg
This should add the key to your package manager, do another apt-get update and you should get no errors
Changing root password for an MD
Figure out the device number of your MD when it was created. On the Core/Hybrid start a terminal ctrl-alt-f1 and login with your login and password you used when you installed kubuntu. Become root as above sudo -i and put in the password again. Now navigate to /usr/pluto/diskless/ and look this directory, it should have a number in there that is the same as your md. Now type chroot ## (where ## is the number of the md device) type passwd it asks you to put a new root password in twice, do it and the root password for that md is changed. type exit or just go back to lmce by keystroke ctrl-alt-f7
This is a start and i will be adding to this wiki while i figure out commands on kubuntu and while troubleshooting, please feel free to add your commands at any time
a much more elaborate explanation and list of commands is found here at ubuntu.com