How to Install Debian on SheevaPlug supplied SD card?

The best approach would probably have been to start with a plain factory build. The process that we used to configure your system is very similar to one of the procedures listed at cyrius.com. This one:

http://www.cyrius.com/debian/kirkwood/sheevaplug/install.html

Now, I haven't performed an Ubuntu install but I know a man who has, and the advice that was given to me is that this second method is more versatile, and allows for greater choice in the resulting configuration:

http://www.cyrius.com/debian/kirkwood/sheevaplug/unpack.html

Although this second article doesn't explicitly state it, the instructions there provide examples for writing the filesystem to an SD card that is mounted in the SheevaPlug. Right now, on your plug, you cannot do this, since the only bootable operating system that you have relies on using that SD card slot for the operating system. However (and I haven't tested this), you should be able to use a different PC (ie your desktop), with a card reader / writer, to write to a new card.

In both cases there is an issue with the U-Boot config; you have to make sure that the settings that allow your system to boot now are the same as the settings that would allow you to boot from the debian card.

If I were in your shoes I would:

Make sure I can read and write SD cards on a PC other than the Sheevaplug
Using that reader / writer, make an image of your current SD card to a file on your PC. Keep this image safe; it will enable you to restore your system to its current state if you ever break the configuration on the SD card. You can also take snapshots from time to time in the future.
Obtain a second SD card
Unpack the image listed on the cyrius.com page and copy it to your second SD card using card reader / writer and your PC (not the Sheevaplug)
Review, copy, check and re-check the U-Boot settings. Follow the instructions on the cyrius.com Unpack page and test your SheevaPlug for booting from this second card.
Congratulations! You now have a plug that can be booted into either debian or Ubuntu, simply by switching SD cards.
Take snapshots of these cards from time to time.

I don't think that partitioning is critical. Solid state memory should be truly Random in its access. The defaults suggested on other sites should be fine. If you want to create a separate partition and mount it, you should be OK. But I'm not convinced that logical partitions are useful on an SD card. The card you are currently using should show this:

~# df -h Filesystem Size Used Avail Use% Mounted on tmpfs 251M 0 251M 0% /lib/init/rw varrun 251M 36K 251M 1% /var/run varlock 251M 0 251M 0% /var/lock udev 251M 116K 251M 1% /dev tmpfs 251M 0 251M 0% /dev/shm rootfs 3.7G 368M 3.1G 11% /

and this:

~# fdisk -l /dev/mmcblk0 Disk /dev/mmcblk0: 3965 MB, 3965190144 bytes 4 heads, 16 sectors/track, 121008 cylinders Units = cylinders of 64 * 512 = 32768 bytes Disk identifier: 0x00000000 Device Boot Start End Blocks Id System /dev/mmcblk0p1 1 123 3928 83 Linux /dev/mmcblk0p2 124 121008 3868320 83 Linux

Whereas the cyrius page suggests this:

Device Boot Start End Blocks Id System /dev/sda1 * 1 110 883543+ 83 Linux /dev/sda2 111 125 120487+ 82 Linux swap

There may be an implication here with regard to the boot address. I haven't had a chance to test either of these procedures, but I hope to try them out soon.

Hope this helps.