We should grep for "dns-nameservers" and not just for "dns-" in step 5
in the algorithm.
The algorithm will still fail in a case like this:
=== /e/n/i ===
auto eth0
iface eth0 inet static
address 192.168.0.2
netmask 255.255.255.0
iface foo inet static
dns-nameservers 1.2.3.4
================
In this case the algorithm will fail to link tail to original (and thus,
fail to cause /sbin/resolvconf to include the original as the tail of
resolv.conf) because it will see a dns-nameservers line in a logical
interface even though that logical interface isn't used. Perhaps we
should only refrain from linking tail to original due to the presence of
a dns-nameservers line if the default mapping is used and the dns-
nameservers line found is in a logical interface definition whose name
is listed on an "auto" line. That would be safer. (Remember, the
consequences of wrongly omitting the link are worse than the
consequences of wrongly creating it.)
We can refine the algorithm even further but we will never be able to
make it work perfectly under all possible circumstances. I've mentioned
the "mapping" and "source" features but there are other ways in which
the networking configuration may have been customized by the admin.
There's no limit to what people may have put onto "up" lines.
Because we can end up with tail linked to original in cases where it's
not appropriate, it is important to minimize the negative consequences
of this.
I see one small way of reducing the possible negative impact of an
unneeded tail->original. Consider that /sbin/resolvconf composes a
resolv.conf file from:
head
base + dynamic content, ordered according to /etc/resolvconf/interface-order
tail
For nameserver addresses it's fine to include them in the tail file
because any dynamically added addresses will precede them and thus
override them.
For "domain" and "search" lines it's not fine since, according to
resolv.conf(5), the last instance wins. Thus a "domain" or "search"
line in the original file will always override the dynamic "search"
line.
It would thus be better to include "domain" and "search" lines from the
original file in the head file and not in the tail file.
What I would propose is that instead of creating a symlink, the
installation program splits up the original file into "head-from-
original" (containing domain and/or search lines) and "tail-from-
original" (including nameserver lines and anything else) and that
/sbin/resolvconf builds resolv.conf from
head
head-from-original
base + dynamic content
tail-from-original
tail
--
Thomas
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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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