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Bug#567468: (boot time consequences of) Linux mdadm superblock question.

also sprach Daniel Reurich <daniel@centurion.net.nz> [2010.02.19.0351 +0100]:
> But if a generated 'system uuid' value (I just suggested the root fs
> UUID because it would be highly unlikely to be unchanged, and nobody
> would be likely to fiddle with it) was copied into a file
> called /etc/system_uuid and copied into the initrd, then we could add
> put into mdadms hook script in initramfs-tools, to verify and update the
> homehost variable in the boot time required raid volumes when ever a new
> initrd is installed.  (This generally happens on debian whenever a
> kernel is installed and mdadm is installed or upgraded.

Neil's point is that no such value exists. The root filesystem UUID
is not available when the array is created. And updating the
homehost in the RAID metadata at boot time would defeat the purpose
of homehost in the first place.

> As an added protection we could include checks in mdadm shutdown
> script a check that warns when mdadm.conf doesn't exist and the
> /etc/system_uuid doesn't match the homehost value in the boottime
> assembled raid volumes.  If we did use the root filesystem UUID
> for this, we could compare that as well.

Debian has no policy for this. There is no way to warn a user and
interrupt the shutdown process.

> It would be useful to have a tool similar to /bin/hostname that
> could be used to create|read|verify|update the system uuid, which
> would update all the relevant locations which store and check
> against this system uuid.

Yes, it would be useful to have a system UUID that could be
generated by the installer and henceforth written to the newly
installed system. This is probably something the LSB should push.
But you could also bring it up for discussion on debian-devel.

martin | http://madduck.net/ | http://two.sentenc.es/
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 for everyone in good society
 holds exactly the same opinion."
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