On 30/10/10 10:50 PM, nomad Bellcam wrote:
> Date: Sat, 30 Oct 2010 22:35:19 -0400
> From: [1]...@aerobiology.ca
> To: [2]damonswir...@hotmail.com
> Subject: Re: ro first branch
>
> On 30/10/10 09:26 PM, nomad Bellcam wrote:
> > hello,
> >
> > it is unclear to me from the docs and man page whether is is possible
to
> > have a rw aufs file system with a ro "first (upper-most) branch. the
man
> > page says "The default branch permission for the first branch is
ârwâ,
and
> > the rest is âro.â" and "When you mount or remount your union without
âo ro
> > common mount option and without writable branch, aufs will warn you
that the
> > first branch should be writable." but i cannot find any more info
regarding
> > this.
> >
> > what i want to do is this:
> >
> > mount -t aufs -o br:one=ro:two=rw none base
> >
> > this works, but when i try to write to base i cannot (ro file system).
i am
> > not sure why aufs will not simply write to "two"
> >
> > if this is not possible, what is the best solution for keeping "one"
at the
> > top of the stack? i thought of making a dummy empty directory an
mounting
> > it like this:
> >
> > mount -t aufs -o br:dummy=rw:one=ro:two=rw none base
> >
> > is this the recommended way?
> >
> > sincerely,
> >
> > proctor
>
> What's the end goal of this, exactly? I mean, why can't you mount -o
> br:two=rw:one=ro ?? No matter what, the read-write branch -must- stand
> on top of the reference (read-only) branches, as that's the only way for
> it to actually work like a regular fs whenever a change is made.
> What's the end goal of this, exactly? I mean, why can't you mount -o
> br:two=rw:one=ro ??
what i am trying to accomplish is mounting user-defined changes to a file
system from a live-cd (knoppix).
i want to be able to make changes to the base knoppix system (using a rw
aufs overlay on e.g. usb stick).
then i want to burn the resulting "changes file" to the dvd and mount them
from there. since
they no longer reside on a writeable media i must use "ro" (i believe). but
i still require them to
be the "highest level changes" made to the system at that point.
with "one" being my custom changes and "two" being the base knoppix system,
i can do
br:two=rw:one=r
but (i believe) any files that are in both "one" and "two" would only be
visible in "two" (the highest level overlay)
in this case. is this assumption/understanding correct?
OK so to reiterate:
- You have the livecd (i'll call it 'x')
- You have your user-defined changes to the livecd (i'll call it 'y')
So firstly what you're doing is you mount -o br:y=rw,x=ro to make the image
for 'y', right? Then you burn it to DVD, so that it becomes read-only.
So then what you need, if I'm understanding this properly, is a -third- fs
(say, a tmpfs) 'z' that serves as your rw branch when you're using the dvd.
Then you can mount -o br:z=rw,y=ro,x=ro ... it will be up to you whether or
not any changes in 'z' get written back to 'y' or not.
References
1. mailto:i...@aerobiology.ca
2. mailto:damonswir...@hotmail.com
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