Stefan Bader wrote in #2:
> Would it be an option to do nothing (not touch resolv.conf)
> if there is neither an active interface with dhcp nor
> dns-server lines in /etc/network/interfaces?


The aforementioned "link-tail-to-original" approximates this.


Stéphane Graber wrote in #5:
> the exact failing case is:
> 1) Installed system [...] using DHCP configuration [...]
> 2) Post-install, turned the system into static [...]
> 3) Upgraded [...] to Precise which added resolvconf


If this is the only case then we might be able to get away with (1) detecting 
this case and then (2) turning on link-tail-to-original, (3) assuming that the 
admin who manually switches from DHCP to static is competent to edit 
configuration files, (4) notifying the admin that information needs to be moved 
from /etc/resolvconf/resolv.conf.d/original to /etc/network/interfaces.


Stéphane Graber continued:
> I'd be against a link-tail-to-original by default as it'd mostly be confusing 
> on systems where the DNS configuration is dynamic


Agreed.  It's something to do only in the case described.  It was designed for 
exactly that case.


Stéphane Graber also wrote:
> An option would be to use link-tail-to-original but only if we
> detect that we have interfaces in /etc/network/interfaces
> that are marked as auto but don't have dns- fields
> (easy to check with ifquery) and that we don't have
> Network Manager on the system.

and Stefan Bader wrote in #6:
> If I understand correctly things are bad if
> 1. there is no active/auto [logical] interface [...] that uses dhcp, and
> 2. there is no active/auto [logical] interface [...] with dns-nameservers, and
> 3. there are nameservers defined in resolv.conf


Worry: Physical interfaces are marked "auto" but the "dns-" fields are in 
logical interface stanzas.  So we have to assume that only logical interface 
stanzas are used that are named like the corresponding physical interface.

Worry: Configuration can be split across multiple files by means of the
"source" feature.

Can we boil the proposal down to this?:

If there is nameserver information in the original /etc/resolv.conf and
there is no physical interface marked "auto" in /e/n/i for which there
is a logical interface definition in /e/n/i that could supply nameserver
information dynamically (i.e., either a logical interface with the
"dhcp" method or a logical interface with the "static" method and "dns-"
lines) then adjust link-tail-to-original's default value to "true" and
its priority to "critical" ("will  probably break the system without
user intervention").

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https://bugs.launchpad.net/bugs/923685

Title:
  New resolver package overwrites manually created resolv.conf on server

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