[Feature Suggestion] UsrMove continued

Serge sergemdev at gmail.com
Fri Oct 12 01:37:23 UTC 2012

2012/10/11 Adam Williamson wrote:

> A proposal to change the filesystem that was synchronized with and
> planned to continue to be identical to (or at least fully compatible
> with) how it's done in Android and Solaris, with the participation of
> Google and Oracle, would be a more interesting proposal

Why doing identical if we can do it better?

Solaris implemented UsrMove (or rather /sbin-move in their case) in
a very weird way. Their initramfs has non-empty /usr directory which
contains the files from former /sbin and /lib, necessary to mount /usr.
Real /usr is just mounted on top of them hiding the old /usr content.
But, I guess you already knew that, since even original UsrMove page
mentions "Minimize difference to other Unixes, such as Solaris".
I remember someone had even blogged about that [1].

Androids implemented it differently, they also use initramfs for the root
filesystem layout. But they do not reuse existing directories, instead
they created a set of new directories (/system, /data, /cache...) and
then put symlinks there (i.e. /etc -> /system/etc).

I tried to make it better. To minimize changes I reused existing/known
directories so that their names still matched their content.

>> Turning /lib into /usr/lib was also incompatible with every other
>> Linux distro, nevertheless it's already done.
> As was already said, that change also had clear concrete benefits; the
> incompatibility was acknowledged as a drawback, but the benefit was
> traded off against the drawback, and it won. Your proposal seems short
> on clear concrete benefits

Actually my proposal is based on same benefits, it just adds more
(simpler diskless NFS stations, multiple OSes on same partition, etc).
It was aiming for a simple layout, and I made it as simple as I could.
It was trying to separate different resources, and I separated them,
grouping same resources into same directories. And so on.
You can compare initial email with UsrMove wiki page. Or are there
other UsrMove benefits that were not listed on a wiki page?

[1] https://plus.google.com/u/0/115547683951727699051/posts/DiGcrjDaKEb

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