Re: Live File System
On Tue, 22 Feb 2000, J.A. Bezemer wrote:
>
> On Tue, 22 Feb 2000, Ari Makela wrote:
>
> > I'm interested in contributing to the developement of the installation
> > of Debian GNU/Linux. When this was discussed in debian-devel I came to
> > think that I could work with live file system. A bootable CD with a
> > bootable floppy for those systems that cannot boot from a CD. It would
> > be a good thing for fixing systems and for installing Debian.
> >
> > It was pointed out that this has been discussed before, probably six
> > months earlier, and that I should ask from debian-cd.
> >
> > So, is someone working with this? If yes, I'd be willing to help, if
> > not I'd be interested to start working with it.
>
> AFAIK, there's no one working on this at the moment, but we would welcome any
> kind of contribution.
I have had some plans for over a year, but haven't found the time to
devote to the project.
>
> There are, as I see it, several possibilities for a "live" filesystem. The
> first thing would be to decide what's our best option, and work from there.
> I think of two possible (orthogonal) categories:
>
> read-only read/write
> +-----------------------------------------
> size: small | current rescue disk
> medium |
> large |
>
> This is about the functionality as seen from the user, _not_ yet how to
> achieve it.
First: A "live" file system usually implies booting off a CD and not
putting much, if anything on the target machine's HD.
Given that as the starting point, the difficulty with the above is that
you can't boot a system that has all of root read-only. /dev, /etc, and
/var must be read-write for the system to run.
>
> Size: small: barely enough tools to do some basic system administration;
> intended to be single-user (namely root)
> medium: basic multi-user without fancy stuff, no X etc. Something
> like the current base system (probably a little bit larger)
> large: Full-featured system, with X, mp3-player(!! ;-), gimp, gnome
> etc. Something like on the Corel CD (well, I've only seen the
> directory listing ;-)
If the starting point is a CD, why start with anything less than the most
complete system you can deliver. Just because the system has a web
brouser, doesn't mean you have to use it to do rescue work. ;-)
>
> Writable: no: Users can take a look, but not change anything big. Some
> pre-defined limited number of config files (hostname, X config,
> etc) copied at startup from DOS/Win partition; /home mounted
> from DOS/Win partition (UMSDOS or ext2 loopback)
> yes: Users can change anything they want, (un)install packages
> etc.
>
> To me, a relatively large read/write system seems the best option. Allows new
> users to fully exploit Debian's possibilities without repartitioning and
> installing. When they want to use the system "for real", repartitioning and
> copying is all that's needed.
You imply here that such a system would be "copied" into a file on the HD
of the target system? This is more like the "Drop in Debian" that I used
to distribute.
>
> I hope everyone can agree with this "fundamental analysis"; if not please
> speak up now.
>
> Then the question of "how". Let's say first that we do not intend to use much
> of the user's harddisk space. So it's (at least at this time) not an option to
> simply prepare a large ext2 loopback and copy it to the harddisk and run from
> there in read/write.
>
> This means that there's got to be some kind of hybrid CD - harddisk system,
> with the users' changes residing on the harddisk. At the moment I see two
> options for that:
>
> - An small ext2 loopback on harddisk with lots of symlinks to a fs
> on the CD (may be ext2 loopback, but I think RockRidge is lots faster)
>
> - Use an Overlay filesystem, details on
> http://home.att.net/~artnaseef/ovlfs/ovlfs.html
>
> Any other options?
Well, I had seen the volatile portions of the file system residing in
ram-disk, with the option to put /etc, /dev, and /var in a loop mounted
file on the HD so that the system can be "maintained"
This involves having a loop mountable file on the CD that contains the
complete file system image. This gets mounted on the ramdisk, say on
/mnt/live, and the directories that need to be volatile are copied into
either the ram-disk, or the file on the HD. Links get created on the
ram-disk that link all the primary directories from the CD and possibly
the HD file to their proper places on the root file system. The hard part
is next: hardware detection. For a live Debian delivered on a CD, the
system is going to need to recognize the various hardware on the system,
and configure the system accordingly. Since you must do this on the fly,
there is some small penalty at bootup if you don't want any file on the
HD, but bootup is sooooo long now that it can hardly matter.
Luck,
Dwarf
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