[Fedora-livecd-list] Re: How do I save and restore my overlay?

Sun Jul 27 02:20:22 UTC 2008

Douglas -

Thanks again for the reply.

Douglas McClendon <dmc.fedora at filteredperception.org> wrote:
> Message: 1
> Date: Fri, 25 Jul 2008 23:53:41 -0700
> From: Douglas McClendon <dmc.fedora at filteredperception.org>
> Subject: Re: [Fedora-livecd-list] Re:  How do I save and restore my
>                overlay?
> To: fedora-livecd-list at redhat.com
> Message-ID: <488AC9F5.5060905 at filteredperception.org>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> 
> martin.x.long at jpmchase.com wrote: 
> > Douglas McClendon <dmc.fedora at filteredperception.or wrote:
> > 
> >  >If that doesn't help or answer you question, try to add more detail 
to
> >  >your question.
> > 
> > Douglas -
> > 
> > Thanks for the reply. 
> > 
> > I use the live usb tools to create my live USB stick with a 2047 MB 
> > overlay.  I boot from it and let it run updates. I reboot the LiveUSB 
to 
> > make sure it still boots, then I shut down.  I boot a system on a copy 

> > of Fedora 9 on the hard drive and plug in my Live USB so I can see the 

> > files on my USB stick. 
> > 
> > I see 2 folders:
> > LiveOS
> > and
> > syslinux
> > 
> > in the LiveOS folder I see three files:
> > osmin.img
> > overlay-FEDORA-3099-53F2
> > and
> > squashfs.img
> > 
> > ======
> > assumptions
> > 
> > squashfs.img looks to be the size of the live iso
> > overlay-FEDORA-3099-53F2 looks to be the size of the overlay and has 
> > overlay in the file name
> > osmin.img is only 8k probably a boot strap, I'm not sure.
> 
> osmin.img is part of an optimization used during the install-to-disk
> process.  Interesting long story, but should not be relevant here.
> 
> > =======
> > 
> > I'm sorry, I can't find anything on the LiveUSB file structure on the 
> > WiKi.  I've signed on as a writer for the Fedore project so I'd like 
to 
> > write it once I figure out what it is.
> 
> Sounds like a good plan.  I don't have the free time I used to when I
> was happily unemployed, but I'll try to help.
> 
> 
> > I was hoping that I could backup the overlay file and the syslinux 
> > folder from my completely updated LiveUSB stick and restore them to a 
> > newly built LiveUSB from my backup.
> 
> I think this should work, but there may be some subtle wording here.
> What you said almost sounds like boiling down to doing a straight
> duplication of a LiveUSB, which AFAIK should work.  To the extent that
> it doesn't work, we should focus on how what you are doing is different
> than a pure duplication.
> 
> > 
> >  > I'm not entirely sure what you mean.  One thing that is possible is 
to
> >  > copy the overlay file from one liveusb and put it on another. 
Though
> >  > the format of the overlay file is inherently tied to the specific 
liveos
> >  > it was originally with.  I.e. you won't be able to copy an overlay 
file
> >  > from an f9-x86 liveusb onto an f9-x64 or f10-x86 liveusb.  Or even 
a
> >  > customized f9-x86 liveusb that you created with 
livecd-creator/tools.
> > 
> > Nothing fancy - The same USB stick, built in the same way with the 
same 
> > iso and the same overlay size.
> > 
> > The overlay file name changes.  I've given the updated file (the 
overlay 
> > that was part of the LiveUSB for all of the updates) the same name as 
> > the new file that is created and left the updated file with its 
original 
> > name. I've overwritten just the overlay itself and the overlay and 
every 
> > combinarion of the osmin.img and squashfs.img files.
> 
> This sounds reasonable.  Now, if this is a new LiveUSB built from the
> same LiveCD, the osmin.img and squashfs.img should be 100% identical.
> Same file sizes, same md5sums.  If they aren't, mention that.
> 

I always build from the same .iso using a script so everything is built 
identically.  The overlay file name does change every time though.

> 
> > 
> > I could never get it to boot.  The boot starts but then hangs.
> 
> What is the last thing you see when it hangs?
> 

=================================================
Decompressing Linux... done.
Booting the kernel.
sd 2:0:0:0: [sdb] Assuming drive cache: write through
sd 2:0:0:0: [sdb] Assuming drive cache: write through

----------------------------------------------------------
WARNING: Cannot find root file system!
----------------------------------------------------------

Create symlink /dev/root and then exit this shell to continue the boot 
sequence.

bash-3.2#
=================================================

I can't find the symlink command anywhere in this limited recovery shell. 
I don't know where this little root directory is so I can move commands 
and scripts into it (before I back up) to help me recover or avoid banging 
out to this shell.

> 
> > Ideally, it would be great to specify the overlay and the syslinyx 
> > folder that goes with that overlay in the command line to build the 
> > LiveUSB.
> 
> Unfortunately the syslinux folder is hard coded and is a limitation of
> syslinux (actually you get 2 or 3 choices, but not an arbitrary choice).
>   The overlay file name is part of our code, and is keyed off of the
> UUID of the usb disk (in this case).  I can't say off the top of my head
> (it's been awhile) whether making the filename specifiable on the
> commandline is trivial or not.
> 
> > 
> > At this point I would be thrilled if I could get a set of manual steps 

> > together to have an updated system without going through the update 
> > process.  I loose a day each time.
> 
> If I find the time, I'll try to reproduce your problem.  An absolute
> brute-force method that should work for identical sized usbsticks would
> be a bit for bit copy.  I.e. if you set up one 4G LiveUSB and it works,
> you should be able to plug it in, and if it is seen as perhaps /dev/sdX
> and then you plug in another 4G usbstick seen as /dev/sdY, you should be
> able to run
> 
> dd if=/dev/sdX of=/dev/sdY

I actually started with something like this only created an output file of 
/usr/MLONG01/usbiso.  This was ok with my 1 gig stick but it was to small 
to install apps and run updates, so I upgraded.

I could actually restore a bootable USB from that file which would work in 
a pinch.  The problem is that I'm using a 16Gig USB stick and my back up 
files would be 16Gig each and take hours to create and restore.  It 
actually takes longer than building the bootable USB and running the 
updates.  On the plus side I can do a restore without an internet 
connection or interaction.  Unfortunately, these files are just too big to 
work with. 

> 
> and get a working clone.  (note, you may have the partition visible as
> /dev/sdX1, but use the whole device as above for the duplication).
> 
> > 
> >  > From an engineering standpoint, of course anything is possible. One
> >  > use case I see, is to use the persistence feature to add an entry 
to
> >  > fstab, such that say, /mnt/data mounts to a ext3fs image located on 
a
> >  > file on your liveusb.  You can then add a user that has a home 
directory
> >  > under there, and perhaps install applications under there.  In this 
way,
> >  > you could then copy that ext3fs image file to an f10 liveusb, and 
then
> >  > only have to re-do the fstab and passwd modifications, such that
> >  > everything now pretty much looks the same.
> > 
> > Your suggestion of building a file structure that would transcend 
> > different releases would be awesome but alas I need to crawl before I 
> > can run.
> > 
> > Any help would be greatly appreciated.
> 
> Hope the above helps.  And as mentioned, if I find the time, I'll try to
> reproduce your less brute-force method of copying, which sounds pretty
> reasonable, but clearly isn't working for some reason or another.
> 
> And just post any wiki/work-in-progress and I'll be happy to provide
> feedback.

What I know of the LiveUSB file structure is not yet WiKiworthy.
Are my assumptions correct regarding squashfs.img and 
overlay-FEDORA-3099-53F2?
> 
> -dmc
> 
Thanks Again

Martin

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