The theory behind Ubuntu Core is that it's a stripped, very light-weight version of Ubuntu for the cloud or server installations. It's a nice theory, but I found the practise a little less idyllic.
- https://wiki.ubuntu.com/Core (page shows latest release as 14.04, but there's a 15.04 release that's smaller than the 14.04 release)
- 15.04 amd64 tarball (gzip) is 47MB
- note: tarball, not bootable installer: the install process is rather ugly
- I used a gparted live ISO in VirtualBox to do the drive set-up
- then following these instructions: http://askubuntu.com/questions/67001/what-commands-are-needed-to-install-ubuntu-core (the instructions on the "Core" page are pretty weak)
- the gparted live CD balked at the chroot command
- tried it with Debian netinst disk in Rescue mode ... chroot worked
- interesting problem: the instructions at askubuntu.com say to use the command apt-get install linux-{headers,image}-generic: this doesn't work in the Debian rescue environment as the shell is unable to expand the "{headers,image}" construct, so I ran the command twice, once with "linux-headers-generic" and once with "linux-image-generic"
- the headers used a lot of space
- the kernel ("linux-image-generic") downloaded 99MB including not only the kernel but a huge number of deps, which then expanded to ~360MB on disk
- by which time "Core" is no longer looking like a lightweight choice
- after rebooting, the system boots ... but I couldn't log in: /etc/shadow shows root's password as "*", so I had to use a boot disk to change that from "*" to ""
- reboot, login as root with no password as it's been set to blank
- but I couldn't use passwd to change root's password because / was mounted ro
- fixed with mount -o remount,rw /
- this may be because I've managed to create a bizarro hybrid of Ubuntu with a Debian GRUB (presumably because I was using a Debian rescue environment
- grub-install /dev/sda in an attempt to get the Ubuntu version of GRUB going on
- reboot
- lots of errors during boot (appeared to be the same as previously), but the system comes up okay
- df -h: "df: cannot read table of mounted file systems: No such file or directory"
- that's right, there's no /etc/mtab
- grep -v rootfs /proc/mounts > /etc/mtab (nifty - one of those little fixes you can find on the internet)
- didn't work first try because the FS is again mounted ro - fixed as above, rerun
- df now works as expected
- / is 779M
- apt-get clean gets us to / being 663M
- at this point though, the .VDI file is already 1008MB in size: I can make a usable (and better equipped and less error-prone) Debian system more easily: it's slightly larger, but it works and is much easier to deal with
- and so ends the Ubuntu Core experiment