Re: anticipating the upstart migration

[Gabor Gombas <gombasg@sztaki.hu>]

On Tue, Oct 10, 2006 at 05:25:57PM -0400, Eric Dorland wrote:

> Shouldn't it be possible to move the alternatives around in an atomic
> fashion? ln -sf bar foo.tmp ; mv foo.tmp foo . Or am I missing
> something? 

- If you set up the alternatives in preinst, then there is a time when
  the symlink exists but the pointed binary hasn't been unpacked yet ->
  unbootable system.
- If you set up the alternatives in postinst, there is a time when there
  is no /sbin/init at all -> unbootable system.

It's not enough to install a single link atomically. Unpacking
/sbin/init.upstart AND setting the /sbin/init symlink AND setting the
/etc/alternatives/init symlink _together_ would have to be atomic.

Gabor

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     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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