[Fedora-livecd-list] livecd fs format

[Frederick Grose]

On Mon, Oct 24, 2011 at 9:02 AM, Mr Dash Four
<mr.dash.four at googlemail.com>wrote:

>
> >> 1. How is the LiveCD file system constructed/built? I've read a variety
> >> of articles and it seems that it is close to the UnionFS (rom+ram
> >> "partitions"), but I am not sure that is used with the new versions of
> >> Linux. I see there are multiple loop mounts on the system, but can't
> >> figure out what they are.
> >>
> >
> > It is originally written into an ext4 image. That image is then compacted
> > and then written to a squashfs file system.
> >
> I am aware of all that - squashfs.img is constructed (which encapsulates
> the real ext3/4 partition in a separate file - ext4.img I think it was
> called), but what I was after is how is this actually mounted on the
> live system so that it is "read-write"? From what I can see there are
> multiple loop partitions used (in conjunction with dm), but this is as
> far as my knowledge goes, unfortunately.
>
> >> 2. My understanding is that all files that are modified in the "live"
> >> image are stored "separately" on a "ram partition". If that is indeed
> >> the case, can I look at what has been "modified" during the live
> >> session? This is easily visible and implemented in UnionFS by a simple
> >> "ls" on the ram (i.e. the read-write) part of the UnionFS, but I am not
> >> sure how this is organised on the LiveCD system.
> >>
> >
> > A dm overlay is used. This can either be ram or separate overlay spaces
> > for /home and/or /.
> I don't have /home, so just /. Could you tell me how is it actually done
> at boot up and how is it made "read-write"? I presume there must be some
> sort of space where this information is written - I assume it is the
> ram, but I am not 100% sure.
>
> >  I don't think this makes it easy to look at just what's
> > changed (in terms of efficiency, not commands). You can use find to find
> > files with a recent ctime, but you'd need to check every file.
> >
> I know that, but, as you rightly pointed out, I have to trash the whole
> / partition and even then this won't be a complete solution as I also
> need to know the time when the system booted up - it is all a bit
> clumsy, there must be a better solution to this.
> --
>

See http://wiki.sugarlabs.org/go/LiveOS_image for a page on these issues.

           --Fred
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