Installing Ubuntu and Arch Linux on 500gb external hard drive

[sudo_smith]

I have an 500gb external usb hard drive. I wanted to install a couple of linux operating systems including Ubuntu and Arch Linux. I have installed Ubuntu 11.10 and it works fine. I can't figure out though how to install Arch Linux on the remaining hard drive. I have included a screenshot of my external hard drive from gparted. So the 25gb that i labeled arch thats the part that I wan't arch linux installed on.

[charleseddy]

It should be relatively straightforward. Boot into your Arch Linux installation disk, and during the installation process, select a custom partition table. Then give the mount point of / (just a slash, nothing else) to the Arch partition, which will make it the one where the data is installed. You can also give a mount point to your Ubuntu partition (for instance, /ubuntu or /media/ubuntu) so that it's automounted each time you start your Arch session and you can access the data.

[sudo_smith]

It should be relatively straightforward. Boot into your Arch Linux installation disk, and during the installation process, select a custom partition table. Then give the mount point of / (just a slash, nothing else) to the Arch partition, which will make it the one where the data is installed. You can also give a mount point to your Ubuntu partition (for instance, /ubuntu or /media/ubuntu) so that it's automounted each time you start your Arch session and you can access the data.

Ok so I created a / partition in cfdisk in the Arch Linux installation. I then selected the packages I wanted and installed it. I didn't install grub since I wan't to boot from the grub in my ubuntu. So I updated the grub and next time I rebooted it found Arch Linux on dev/sda4 (which is the partition I assigned / to). I tried to boot it and cam with this error message:

Waiting 10 seconds for device dev/sda4 ...
Root device 'dev/sda4' doesn't exist. Attempting to recreate it.
ERROR: Unable to determine major/minor number of root device '/dev/sda4'.
You are being dropped to a recovery shell
Type 'exit' to try and continue booting
sh: can't access tty; job control turned off
[ramfs /]#

I went on Ubuntu and checked gparted again and it showed /dev/sda4 as and ext4 partition with mountpoint /media/arch. I don't understand what happened. Do I have to make a /boot partition? I am using Ubuntu 11.10 and Grub 1.99

[charleseddy]

I would have let Arch remake the Grub, as I don't see why it would cause a problem...

It appears as if the error you're describing should mean that the partition is showing up as hda4 instead of sda4, described in the ArchLinux wiki here.

No need for a boot partition then, as the installation should have taken place correctly. Rebuild the grub using

sudo update grub

and see what happens. At the worst, you'll have to go in and edit the grub configuration by hand (admittedly not that much fun since Grub 2).