[tor-bugs] #34115 [Internal Services/Tor Sysadmin Team]: review the impact of usrmerge

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#34115: review the impact of usrmerge
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 Reporter:  anarcat                              |          Owner:  anarcat
     Type:  defect                               |         Status:
                                                 |  assigned
 Priority:  High                                 |      Milestone:
Component:  Internal Services/Tor Sysadmin Team  |        Version:
 Severity:  Major                                |     Resolution:
 Keywords:                                       |  Actual Points:
Parent ID:                                       |         Points:
 Reviewer:                                       |        Sponsor:
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Old description:

> Debian buster shipped with a "merged `/usr`", which means that `/bin`,
> `/lib` and `/sbin` are now symlinks to their counterparts in `/usr`.
> There are concerns that this behavior is buggy and triggers problems in
> all sorts of places. In particular, the `dpkg` maintainers are quite
> unhappy about the change and do not support it as a configuration:
>
> https://wiki.debian.org/Teams/Dpkg/MergedUsr
>
> ... which is disturbing, considering the `dpkg` is such a core component
> of a Debian system.
>
> That wiki page provides a hackish script to "migrate away" from usrmerge
> but no one, as far as I know, has done that in production. It definitely
> looks nasty.
>
> We should consider whether:
>
>  1. [ ] this is a real problem
>  2. [x] which machines have usrmerge
>  3. [ ] whether new machines should have it
>  4. [ ] whether we need to fix old machines

New description:

 Debian buster shipped with a "merged `/usr`", which means that `/bin`,
 `/lib` and `/sbin` are now symlinks to their counterparts in `/usr`. There
 are concerns that this behavior is buggy and triggers problems in all
 sorts of places. In particular, the `dpkg` maintainers are quite unhappy
 about the change and do not support it as a configuration:

 https://wiki.debian.org/Teams/Dpkg/MergedUsr

 ... which is disturbing, considering the `dpkg` is such a core component
 of a Debian system.

 That wiki page provides a hackish script to "migrate away" from usrmerge
 but no one, as far as I know, has done that in production. It definitely
 looks nasty.

 We should consider :

  * [ ] whether this is a real problem (probably?)
  * [x] which machines have usrmerge (20 machines or 27%, detailed below)
  * [x] whether new machines should have it (probably not? not having
 usrmerge is *not* a problem, and having it has risks, so let's not risk
 it?)
  * [ ] whether we need to fix old machines

 There are two ways of fixing the installers:

  * pass `--no-merged-usr` to deboostrap
  * use `mmdebstrap`

 The latter has the advantage of being faster, at the cost of being
 possibly less reliable and compatible.

 Next steps:

  1. [ ] fix cloud installer
  2. [ ] fix robot installer
  3. [ ] fix ganeti installer - reported as [https://bugs.debian.org/cgi-
 bin/bugreport.cgi?bug=959745 bug 959745]

--

Comment (by anarcat):

 i have filed [https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=959745 bug
 959745] against ganeti-instance-debootstrap to see if that can be
 customized. it seems we should be able to override the `debootstrap` call
 by defining a function in the variants config file, which remains to be
 tested.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34115#comment:2>
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