The case for the /usr merge [LWN.net]

The case for the /usr merge

Posted Jan 27, 2012 12:39 UTC (Fri) by bluss (guest, #47454)
Parent article: The case for the /usr merge

Snapshotting is a claimed feature, yet /etc and /var usually change with package upgrades and installations. If you rollback /usr, you will have to rollback /etc and /var as well.

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The case for the /usr merge

Posted Jan 27, 2012 19:48 UTC (Fri) by BenHutchings (subscriber, #37955) [Link] (1 responses)

Yes, I noticed that too. Changes to /usr should already be easily reversible by downgrading the package. Changes to /etc and /var may not be reversible without resort to backups, and that's where the snapshot feature might be more useful.

The case for the /usr merge

Posted Jan 28, 2012 2:30 UTC (Sat) by russell (guest, #10458) [Link]

Snapshotting is never going to be an atomic operation, this is a false argument for unified /usr. What happens if a package is being installed when the snapshot takes place. e.g. parallel installation of a tarball by someone else. If you roll back you end up with something half installed.

So you have to procedurally "quiesce" the system FS to avoid race conditions. Given that, what's the difference between snapshotting one FS or 3,4,5,etc?

The only reliable way to manage the system is to use the package manager to undo the changes as it currently does. And if this is not possible, because the system won't run the package manager. Shame the sys admin who broke it for being so careless.