Bug#756593: busybox's switch_root makes read-only NFS root read/write

[Michael Tokarev <mjt@tls.msk.ru>]

01.08.2014 15:37, Zimmermann, Alexander wrote:

> As you can see, we use a vanilla 3.14 Kernel, patched w/ official AUFS patch (see
> http://aufs.sourceforge.net)

I too use aufs here, for a very long time.  But I never tried
nfs-root together with aufs, I used if in slightly different
scenarios.

> To enable/disable AUFS we use a patched version of the root-ro script (see
> https://help.ubuntu.com/community/aufsRootFileSystemOnUsbFlash) in our initramfs.
> The script is located under /etc/initramfs-tools/scripts/init-bottom/. 
> 
>> Where do you set breakpoints?
> 
> To ensure that the root-to script isn’t the culprit, I disabled it (and therefore
> AUFS too) via cmdline parameter root-ro=false and put a breakpoint right after
> (break=init). At the breakpoint, the NFS mount was still ro.
> 
> I put another „breakpoint“ in /etc/rc3.d/S01* start script to verify the mount
> right after switch_root. Here, the mount was already rw.

You can also write a small script - a wrapper for /sbin/init which will
show you the mount info and exec /sbin/init, and run it with init=yourscript.

> Let me double check that AUFS is not broken. I try to boot a vanilla kernel.
> I will come back to you w/ the results.
> 
> Alex
> 
> —-
> As a side note, if we boot w/ AUFS, the mount points are right.

That's even more interesting :)

Thanks,

/mjt