I have just installed Ubuntu 10.10 using the guide: Guide to install any linux distro you please....and also grafs latest kernel updates(precompiled)
After the installation I shut down PS3, launched lv2patcher, Pressed X at the Linux Entry.
In petitboot I got 2 new entries:
linux: var petitboot mnt sda5 boot vmlinux initrd var petitboot mnt sda5 boot initrd img root dev sda1 quiet video ps3fb mode 5
and another one with "old"
Whenever I select either of these entries I get the following messages:
mount: mounting dev sda1 on root failed: invalid argument
mount: mounting dev on root dev failed: no such file or directory
mount: mounting proc on root proc failed: no such file or directory
target filesystem doesn't have requested sbin init
no init found. try passing init bootarg

What should I do in order to boot Ubuntu?

Playstation 3 Slim 320GB
Image used: ubuntu 10 10 alternate powerpc ps3 iso
Installed on a external HDD 2.5 with 3 Partitions:
Partition1: ext4 39.74GB
Partition2: swap 0.26GB
Partition3: fat32 40GB
CFW: 3.55.2 Rebug with Update 4.

Other questions:
Can I directly boot to Linux via XMB?

I cannot type symbols are used in links even if I have 30+ posts and being a member over than 1 month...