Debian pauses /usr merge file moves

[Posted May 17, 2023 by corbet]

The Debian Technical Committee has announced a new moratorium on moving files from the root into /usr, a necessary part of its UsrMerge project. Many distributions have made this change, but Debian has had more difficulties than most; LWN last looked at this project one year ago.

This moratorium lasts until we vote to repeal it. We expect to do that during the trixie development cycle, and sooner rather than later. We will continue to facilitate efforts to resolve the remaining issues that stand in the way of safely repealing the moratorium.

Trixie is the codename for Debian 13, the upcoming major release cycle.

Note: this item originally ran with a headline saying that the /usr merge had been paused, which is evidently not accurate.

Debian pauses its /usr merge — again

Posted May 17, 2023 13:42 UTC (Wed) by bluca (subscriber, #118303) [Link] (1 responses)

The title is incorrect, it is not paused. This is just required as part of the continuing work, because some of it needs to happen in the next dev cycle. Moving files by hand was never part of it.

Debian pauses its /usr merge — again

Posted May 17, 2023 18:18 UTC (Wed) by smcv (subscriber, #53363) [Link]

Yes, this is a misleading writeup of a Debian-internal announcement. One specific action that is mostly internal to Debian, which some developers wanted to push ahead with after the bookworm release, has been paused.

On a merged-/usr system (which will include all Debian 12 and Debian 13 systems, both new installations and upgrades), both /bin/cat and /usr/bin/cat exist, but dpkg is only aware of one of those paths (/bin/cat in this case); in dpkg jargon, the other is said to be an alias. The specific action that should not proceed until further notice is: swapping the path that dpkg considers to be canonical, for example from /bin/cat to /usr/bin/cat.

Debian pauses its /usr merge — again

Posted May 17, 2023 13:52 UTC (Wed) by rweikusat2 (subscriber, #117920) [Link] (8 responses)

The idocy of this whole project is nicely exemplified by that fact that it's not supposed to get rid of /usr. That could have been accomplished by ln -s / /usr instead of an insanely complicate scheme to move some files sitting in a hierarchy directly below / one level down in the filesystem while creating loads of symlinks to create the impression that this hadn't been done.

Debian pauses its /usr merge — again

Posted May 17, 2023 14:02 UTC (Wed) by bluca (subscriber, #118303) [Link] (1 responses)

You clearly do not understand what this is about, which is fine - but maybe it would be better to reframe from throwing around insults on things you do not fully grasp

Debian pauses its /usr merge — again

Posted May 17, 2023 18:11 UTC (Wed) by rweikusat2 (subscriber, #117920) [Link]

I'm extremely glad to see that the default mode of operation of the open sausage community with regards to opinions differing from those of what it considers to be established authorities is still content-free abuse. Anything else would admittedly have surprise me greatly, though.

:-)

Debian pauses its /usr merge — again

Posted May 17, 2023 14:10 UTC (Wed) by kilobyte (subscriber, #108024) [Link]

Exactly. Why should we suffer just because someone ran out of disk space on an early install, and had to move some programs to the drive meant for use files?

Debian pauses its /usr merge — again

Posted May 17, 2023 20:49 UTC (Wed) by mjg59 (subscriber, #23239) [Link] (4 responses)

Merely symlinking /usr to / doesn't allow separation of the OS from its configuration and other mutable content. The more complicated approach makes it possible to do a bunch of interesting things that would be significantly harder (or impossible) to achieve with the naive approach. In general, if a proposal seems needlessly complicated, it's worth spending some time figuring out why people chose the more complicated approach rather than immediately assuming that it's "idocy".

Debian pauses its /usr merge — again

Posted May 17, 2023 22:36 UTC (Wed) by jhe (subscriber, #164815) [Link] (3 responses)

People who wanted mutable and immutable data split are using overlayfs by now. The /usr move is causing more troubles for the same effect.

Debian pauses its /usr merge — again

Posted May 18, 2023 0:49 UTC (Thu) by mjg59 (subscriber, #23239) [Link] (2 responses)

No, that's solving a different problem. The goal isn't for the underlying OS to remain untouched as you tamper with things above it, it's for the visible representation of the OS to remain untouched other than local configuration and state. Overlayfs isn't a great way of managing that, and as a bonus you get to break various filesystem semantics in weird ways (see: using overlayfs on Debian breaks upgrades)

Debian pauses its /usr merge — again

Posted May 18, 2023 11:31 UTC (Thu) by jhe (subscriber, #164815) [Link] (1 responses)

Regarding "using overlayfs on Debian breaks upgrades", you need to back that up and explain why its not a problem for Docker folks who apparently do it all the time.

Debian pauses its /usr merge — again

Posted May 18, 2023 17:35 UTC (Thu) by mjg59 (subscriber, #23239) [Link]

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1008202

Debian pauses its /usr merge — again

Posted May 17, 2023 14:16 UTC (Wed) by pdewacht (subscriber, #47633) [Link] (3 responses)

What does this mean for the Debian 12, which will be released next month? Is there anything I as a Debian user should be aware of?

Debian pauses its /usr merge — again

Posted May 17, 2023 14:30 UTC (Wed) by bluca (subscriber, #118303) [Link]

Not really, anything relevant will be listed in the release notes as always

Debian pauses its /usr merge — again

Posted May 17, 2023 17:42 UTC (Wed) by amacater (subscriber, #790) [Link] (1 responses)

A fresh install of 12 already has the merged user transition in it, as far as I can see. Likewise a fresh install of Debian 11. The difficulty comes with upgrading a system that has not already been merged. Discussions are ongoing as to how best to do this and there are still differences of opinion as to the best way to tackle the issue.

TL;DR - If you do a new install, you shouldn't need to worry. Debian 12 is shaping up well.

[Full disclosure: I'm a Debian developer but have no viewpoint on how easy/difficult the necessary work for the full merged /usr transition is going to be.]

Debian pauses its /usr merge — again

Posted May 17, 2023 18:11 UTC (Wed) by smcv (subscriber, #53363) [Link]

Upgrading to Debian 12 also works fine in practice. The main issue when upgrading an older Debian installation (originally installed as Debian 10 or older) is that switching it to merged-/usr can fail is if its root filesystem is on overlayfs, which in practice is most common for Docker and similar containers. The workaround is to re-create the container instead of upgrading it, which is generally preferred for Docker anyway.

The change that the technical committee is asking Debian contributors to avoid for now is mostly only visible/relevant to Debian contributors, and is to do with changing which of the two possible paths (for example /bin/foo or /usr/bin/foo) is considered to be the canonical path by dpkg. On end-user systems, the compatibility symlinks mean that both /bin/foo and /usr/bin/foo exist; that is not new, and is not changing.

Debian pauses its /usr merge — again

Posted May 17, 2023 16:40 UTC (Wed) by nickodell (subscriber, #125165) [Link] (7 responses)

I just looked at one of my Debian boxes, and it seems that it's already had this merge applied. (Which is a point in favor of people who say this can be done without much fanfare, since they managed to do it without breaking anything or making me notice.) It's not a new install, either - this is running Debian 10.
So what's being voted on here?

Debian pauses its /usr merge — again

Posted May 17, 2023 16:50 UTC (Wed) by bluca (subscriber, #118303) [Link] (6 responses)

It's just procedural to ensure we can keep working on a few remaining things in the background safely in the next dev cycle. The title is highly misleading.

Debian pauses its /usr merge — again

Posted May 17, 2023 17:49 UTC (Wed) by ovitters (guest, #27950) [Link]

Ah, the bit about Debian 12 must be seen as that it really only is for that version and does not apply to anything newer/older? I didn't get that out of the announcement.

Debian pauses its /usr merge — again

Posted May 17, 2023 17:54 UTC (Wed) by archaic (subscriber, #111970) [Link] (4 responses)

The title is misleading because the technical committee didn't understand the definition of moratorium, which is:

a temporary suspension of an activity or law until future consideration warrants lifting the suspension

The TC's email was subjected with:

Reinstatement of merged-/usr file movement moratorium

Therefore, they (the TC, not LWN) said they were "reinstating" the "suspension". I agree the article's title is misleading, but it does accurately reflect Debian's title, if not content.

Debian pauses its /usr merge — again

Posted May 17, 2023 18:25 UTC (Wed) by smcv (subscriber, #53363) [Link]

The announcement concerns an activity that is internal to Debian (changing the canonical paths of non-/usr files in dpkg's database of package contents, so that dpkg considers the official path of cat to be /usr/bin/cat instead of /bin/cat, and so on), which some Debian developers wanted to push ahead with immediately after the bookworm release.

That activity has been temporarily suspended, but we expect it to become desirable in future, after some technical issues that block it have been resolved; so by the definition you cited, this is indeed a moratorium.

This does not affect whether /usr is merged on end-user systems: it only affects the state of the dpkg database and the contents of new .deb files. So it is misleading to summarize this as the /usr merge having been paused.

Debian pauses its /usr merge — again

Posted May 17, 2023 18:28 UTC (Wed) by bluca (subscriber, #118303) [Link] (2 responses)

The TC's email is correct, the article is not, because it misunderstands and misleads on what this is really about. There is no "pause".

Debian pauses its /usr merge — again

Posted May 17, 2023 18:36 UTC (Wed) by dullfire (guest, #111432) [Link] (1 responses)

The above comment is misleading. There is a pause according to the email (e.g. see the defintion: https://www.dictionary.com/browse/moratorium), however as smcv pointed out it's not the whole usr merge project, but file relocations that are "paused" (at least according to the email and smcv)

Debian pauses its /usr merge — again

Posted May 17, 2023 18:55 UTC (Wed) by bluca (subscriber, #118303) [Link]

The article is misleading. Manual file relocations were never "unpaused" in the first place, as that's not how we are going to handle it.