[Fedora-livecd-list] alternative rebootless installer, was Re: kexec instead of rebooting at the end of the install?

[Jane Dogalt]

--- Matthew Miller <mattdm at mattdm.org> wrote:

> So, tell me -- is this a crazy idea?

Certainly no crazier than this idea I mentioned on the livecd list-

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Rebootless Installer - Implementation Outline
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Goal: A cd/dvd/bluray iso which serves as both a traditional livecd, and a
traditional install cd (functionally akin to current ubuntu stuffs, but
radically different implementation, as well as 'rebootless' feature)

1) take your linux distro (i.e. fc6).  Create a "hardware agnostic" minimal
(but useful) installation.  I.e. resulting install image can be booted on any
supported hardware, and all hardware configuration is done during normal system
boot.  I.e. the type of system installation you would put on a traditional
'livecd'.  Now put this on a livecd, but with a cutting edge boot method such
as...

2) the latest linux-from-scratch livecd implements a particularly novel livecd
system.  Traditionally, various implementations have usually used ram based
tmpfs, combined with rom based cd/dvd iso9660, zisofs, squashfs.  Along with
some bindmounting, or unionfs to get a nice copy-on-write action going.

The latest LFS livecd however uses a radical method of storing the system as an
ext3 filesystem image (sparse file) on the cd/dvd iso9660 fs, but compressed
with zisofs.  Then, during early boot, a tmpfs is created, and a large sparse
file is created in tmpfs.  This sparse file in tmpfs is then used as a
devicemapper snapshot device, allowing an alternate COW mechanism to the
traditional unionfs mechanism.  Now, extending the radicalism-

3) make the following change to (2):  Instead of using the sparse file image on
dvd, and in tmpfs, use device mapper mirrors for both, initially created as
broken mirrors, with the unbroken half being the same image used in (2).

4) now, one can implement an installer application on the livecd like so:

- have user create target partitions the traditional way
- now, to install, just set the target partitions as the unbroken halfs of the
device mapper mirrors created in (3).  Then let the device mapper "install" the
system by repairing the mirror.
- once the mirror is unbroken, manually rebreak it, the opposite way, so the
tmpfs image, and cd/dvd rom can be discarded/forgotten-about/unmounted/ejected.
- thus once the installer has completed, the same livecd system that the user
has been looking at and playing with, _*has become the installed system*_.  No
reboot is necessary, except for normal kernel maintenance as released updates
dictate.
- one beneficial side effect, is that the system will be prepared from the
beginning for the user to optionally add another disk to be used to 'fix' the
broken mirror.  (or alternately the bootscripts could remove the broken mirror
cruft during the next reboot, so it looks like a perfectly 'normal' system).

- one last note, I haven't actually experimented with all of this, but I'm
guessing that it's also possible to make the COW dm-snapshot device disappear
by "writing back" it's contents to the main image.  Otherwise one would have to
keep around the original small system image (which isn't necessarily a useless
side effect).

-jdog


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