RFC- 'persistance' is on LiveCD wishlist - what does it mean?

[Douglas McClendon]

On the Fedora LiveCD wiki's wishlist, is 'persistance' -

http://fedoraproject.org/wiki/FedoraLiveCD

"
     * Persistence; e.g. the ability to save livecd changes (e.g. installed 
software) to a USB stick instead of tmpfs
     * LiveCD content + persistence all on a 1GB USB stick image
"

While I have plenty of ideas for this, and have vague memories of seeing other 
distributions do it, I'd like to get a feel for what the fedora community 
actually wants.  I.e. lets design this feature.  How should it work from the end 
user perspective?

Also, there are a bazillion distros and livecds out there, if you happen to know 
of any that do this in a way that you like, please mention them.

-dmc

[Jeroen van Meeuwen]

Douglas McClendon wrote:
>  On the Fedora LiveCD wiki's wishlist, is 'persistance' -
>  
>  http://fedoraproject.org/wiki/FedoraLiveCD
>  
>  "
>      * Persistence; e.g. the ability to save livecd changes (e.g.
>  installed software) to a USB stick instead of tmpfs
>      * LiveCD content + persistence all on a 1GB USB stick image
>  "
>  
>  While I have plenty of ideas for this, and have vague memories of seeing
>  other distributions do it, I'd like to get a feel for what the fedora
>  community actually wants.  I.e. lets design this feature.  How should it
>  work from the end user perspective?
>  
>  Also, there are a bazillion distros and livecds out there, if you happen
>  to know of any that do this in a way that you like, please mention them.
>   
The first feature requests that when booting some media that you can't
commit changes to, changes in tmpfs should be saved to a USB stick or
something similar that holds a filesystem that we /can/ commit to, so
that when you boot it again, you can roll-forward the changes from the
'tmpfs' on that medium and continue like it's a normal system. Does it
make sense?

The second just wants USB media like the LiveCD but with a real RW
filesystem.

Kind regards,

Jeroen van Meeuwen
-kanarip

[Jeremy Katz]

On Mon, 2007-07-16 at 23:30 +0200, Jeroen van Meeuwen wrote:
>  The first feature requests that when booting some media that you
> can't
>  commit changes to, changes in tmpfs should be saved to a USB stick or
>  something similar that holds a filesystem that we /can/ commit to, so
>  that when you boot it again, you can roll-forward the changes from the
>  'tmpfs' on that medium and continue like it's a normal system. Does it
>  make sense? 
This is really the important one, see my other response for more
details.

>  The second just wants USB media like the LiveCD but with a real RW
>  filesystem. 
I think that for this, you should just install to the USB stick.  That
should work these days and if it doesn't, then we should just fix it
rather than papering over by allowing something like this.

Jeremy

[Jeroen van Meeuwen]

Jeremy Katz wrote:
>  On Mon, 2007-07-16 at 23:30 +0200, Jeroen van Meeuwen wrote:
> > The first feature requests that when booting some media that you can't
> > commit changes to, changes in tmpfs should be saved to a USB stick or
> > something similar that holds a filesystem that we /can/ commit to, so
> > that when you boot it again, you can roll-forward the changes from the
> > 'tmpfs' on that medium and continue like it's a normal system. Does it
> > make sense?
>  
>  This is really the important one, see my other response for more
>  details.
>  
> > The second just wants USB media like the LiveCD but with a real RW
> > filesystem.
>  
>  I think that for this, you should just install to the USB stick.  That
>  should work these days and if it doesn't, then we should just fix it
>  rather than papering over by allowing something like this.
>   
Right. Mind that it's not me who created the wish-list, I think it was
David in the early days after FUDCon in Boston.

The second (USB sticks) seems far more important to me then the
stateless-but-persistent one.

Kind regards,

Jeroen van Meeuwen
-kanarip

[Jeremy Katz]

On Tue, 17 Jul 2007 00:22:49 +0200
Jeroen van Meeuwen <kanarip(a)kanarip.com&gt; wrote:
>  Jeremy Katz wrote:
>  > On Mon, 2007-07-16 at 23:30 +0200, Jeroen van Meeuwen wrote:
>  >> The second just wants USB media like the LiveCD but with a real RW
>  >> filesystem.
>  > 
>  > I think that for this, you should just install to the USB stick.
>  > That should work these days and if it doesn't, then we should just
>  > fix it rather than papering over by allowing something like this.
>  > 
>  
>  Right. Mind that it's not me who created the wish-list, I think it was
>  David in the early days after FUDCon in Boston.
>  
>  The second (USB sticks) seems far more important to me then the
>  stateless-but-persistent one. 
USB sticks play a big part in the first and really are in a lot of ways
the more interesting case especially if you then do the second step of
having an encrypted home dir setup. I ran with the second half of this
while waiting on a replacement drive for my laptop; with work to make
it easy to setup and to fix the weirdnesses (of which lack of
persistence was the biggest as I had to keep reinstalling the packages
I had forgotten in my config), this could be really compelling to use
on a regular basis

Jeremy

[Jeremy Katz]

On Mon, 2007-07-16 at 16:03 -0500, Douglas McClendon wrote:
>  While I have plenty of ideas for this, and have vague memories of
> seeing other 
>  distributions do it, I'd like to get a feel for what the fedora community 
>  actually wants.  I.e. lets design this feature.  How should it work from the end 
>  user perspective? 
The crux of the idea is that you have a file on some form of read/write
device that can store changes that you've made to the system.  So, eg,
if I boot with the live image (either off of CD or a usb key) and
install emacs because I can't use a system without emacs, those changes
are saved and the next time I boot, I have my emacs installed already.  

The simple and obvious way to do this is to be able to look for a file
with a certain name (based on a UUID from the live image) located on
either a USB key or a hard drive and then layer that as our snapshot dev
rather than a sparse file in memory.  That then leaves a few questions:

1) Do we then mount every partition we can find in the initramfs to get
to the persistence file (with an option to disable, obviously)?  Or do
we require the device info to be specified in the bootloader.  The first
has the advantage of more "just working".  The second is better for the
case of not touching things and thus being a little bit safer. 

2) How do we do the initial set up of this file?  It's easy enough once
they've booted the image to say "set up a persistence file for future
use" and be able to prompt for where to keep it, etc.  But then do we
try to snapshot to it immediately and save any changes they've already
made?  Obviously this is better from a user perspective, but may be
tricky to do sanely

3) When doing an install from the live image, do we keep the changes?
If so, how does that interact with some of the hacky things we currently
do in the live init script such as user addition and disabling
firstboot?

I somewhat suspect that the answer is to get together the quick path for
each of these (explicit specification of where the persistence is,
require manual set up) and just see how things work.

Jeremy

[Douglas McClendon]

Jeremy Katz wrote:

>  
>  I somewhat suspect that the answer is to get together the quick path for
>  each of these (explicit specification of where the persistence is,
>  require manual set up) and just see how things work. 
I agree, and was planning on going ahead and trying out some ideas myself.  I
just want to make sure I take into consideration any particular use-cases that
people may already have in mind.  And in particular, I'm hoping that if a good
end-user implementation already exists somewhere that I'm oblivious to, that
someone mentions it.


Knoppix, at least from what I see, still uses unionfs, so thats not interesting 
for us.

ubuntu also uses unionfs, and their persistence support looks like a mess right now-

https://help.ubuntu.com/community/LiveCDPersistence

googling for "[gentoo/suse/mandriava] livecd persistence" didn't yield
anything 
immediately obvious (look I managed to spell it correctly there :)


Anyway, I'll see what I can do in the next week or two.


-dmc