[Bug 1032855] Re: resolvconf modifies real file /etc/resolv.conf in lieu of /run/resolvconf/resolv.conf

Sat Aug 4 17:28:19 UTC 2012

Hi vorlon,

thanks again for your message. I just tried to convert this bug into a
question but launchpad wouldn't let me since it seems that should've
been done before turning it into invalid.

Please don't rush an answer since, at least for me, it is now more of a
will for understanding what happens than a bug in need of a fix.

On 03/08/12 22:17, Steve Langasek wrote:
> On Sat, Aug 04, 2012 at 12:44:34AM -0000, MarianoAbsatz wrote:
>> So Network Manager and dhclient are NOT currently invoking resolvconf,
>> BUT they're actually handling /etc/resolv.conf by themselves?
>
> This will definitely be the case for dhclient.  It may or may not also be
> the case for NM, depending on how NM decides whether to invoke resolvconf
> vs. editing directly.  (I haven't looked closely at the details.)
>
>> This is not what the manpage implies (or what I understand form it)
>
> If you can point to particular language in the manpage which contradicts
> this, we should fix it.

Quoting http://manpages.ubuntu.com/manpages/precise/man8/resolvconf.8.html section PUBLICATION:
      Normally  resolvconf  is  run  only by hook scripts attached to network
       interface configurers such as pppd(8) (for  ppp  interfaces),  to  DHCP
       clients  such  as dhclient(8), to ifup(8) and ifdown, and to DNS caches
       such as dnsmasq(8) (for the loopback interface).   These  hook  scripts
       furnish  resolvconf  with  information about nameservers.  For example,
       dhclient  receives  one  or  more  nameserver  addresses   during   its
       negotiation  with  the DHCP server; its hook script /etc/dhcp/dhclient-
       enter-hooks.d/resolvconf pushes this information to resolvconf.

>From this paragraph I understand that resolvconf is invoked by dhclient.

Below that, in section PUBLICATION:

      The  most  important  piece  of  software  that   subscribes   to   the
       notification  service  is  the  set of functions that make up the GNU C
       Library resolver(3).   When  nameserver  information  is  updated,  the
       script    /etc/resolvconf/update.d/libc    writes    a   new   resolver
       configuration file to /run/resolvconf/resolv.conf  and  then  runs  the
       scripts  in  /etc/resolvconf/update-libc.d/.   To make the resolver use
       the dynamically generated resolver configuration file the administrator
       should   ensure   that   /etc/resolv.conf   is   a   symbolic  link  to
       /run/resolvconf/resolv.conf.   This   link   is   never   modified   by
       resolvconf(8).  If you find that /etc/resolv.conf is not being updated,
       check to make sure that the link is intact.

>From this paragraph I understand that resolvconf modifies
/run/resolvconf/resolv.conf AND NOT /etc/resolv.conf

After reading these two paragraph I thought (though I can be wrong)
that:

1) dhclient doesn't handle /etc/resolv.conf directly but, instead, invokes resolvconf
2) resolvconf NEVER modifies /etc/resolv.conf but, instead, modifies /run/resolvconf/resolv.conf

3) (implied by me) If dhclient doesn't modify /etc/resolv.conf directly
AND neither does resolvconf, then, if /etc/resolv.conf is NOT a symlink
to /run/resolvconf/resolv.conf, no one (at least not dhclient or
resolvconf) would mess with it (at least on a small server with hardly
any non-official-ubuntu software installed/configured).

Stéphane's article at http://www.stgraber.org/2012/02/24/dns-in-
ubuntu-12-04/ also implies something similar (although he clearly
doesn't recommend it) when he writes:

 * I really don’t want resolvconf, how can I disable it?
   I certainly wouldn’t recommend disabling resolvconf 
   but you can do it by making /etc/resolv.conf a regular 
   file instead of a symlink.
   Though please note that you may then be getting 
   inconsistent /etc/resolv.conf when multiple software are 
   fighting to change it.

Since I thought the only piece of software that might be "fighting" for
it was dhclient and I had that covered by 3) above, I went ahead.

>
>> Who/what are using resolvconf, then?
>
> By default, when /etc/resolv.conf is not a symlink, nothing is.

Does this imply that dhclient checks whether /etc/resolv.conf is a
symlink and, if true, it calls resolvconf and otherwise, it messes with
/etc/resolv.conf directly?

Maybe then I have to mess with dhclient and convince it NOT to handle
/etc/resolv.conf at all.

** Converted to question:
   https://answers.launchpad.net/ubuntu/+source/resolvconf/+question/205014

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https://bugs.launchpad.net/bugs/1032855

Title:
  resolvconf modifies real file /etc/resolv.conf in lieu of
  /run/resolvconf/resolv.conf

Status in “resolvconf” package in Ubuntu:
  Invalid

Bug description:
  I manually compiled and installed the unbound DNS resolver on my 12.04
  server (upgraded from a 10.04).

  Yesterday, after reading http://www.stgraber.org/2012/02/24/dns-in-
  ubuntu-12-04/ and
  http://manpages.ubuntu.com/manpages/precise/man8/resolvconf.8.html I
  took the "minimum breakage path" and simply erased the symlink
  /etc/resolv.conf (which points to /run/resolvconf/resolv.conf) and
  created a plain file for /etc/resolv.conf using ::1 as my only
  resolver.

  However, today I found that the file /etc/resolv.conf had been
  rewritten with the same contents it had before.

  Checking a little I found the file modification time was 12:35 and
  found the following on my syslog:

  Aug  3 12:35:40 abako dhclient: DHCPREQUEST of 66.228.40.90 on eth0 to 207.192.68.72 port 67
  Aug  3 12:35:40 abako dhclient: DHCPACK of 66.228.40.90 from 207.192.68.72
  Aug  3 12:35:40 abako dhclient: bound to 66.228.40.90 -- renewal in 38228 seconds.

  So, the primary cuplrit seems to be resolvconf.

  What's more, the file modification time for
  /run/resolvconf/resolv.conf is on June 20th (the day I upgraded from
  10.04 to 12.04.

  So, IMHO, either resolvconf has a bug or the following paragraph of
  its manpage is plain wrong:

        The  most  important  piece  of  software  that   subscribes   to   the
         notification  service  is  the  set of functions that make up the GNU C
         Library resolver(3).   When  nameserver  information  is  updated,  the
         script    /etc/resolvconf/update.d/libc    writes    a   new   resolver
         configuration file to /run/resolvconf/resolv.conf  and  then  runs  the
         scripts  in  /etc/resolvconf/update-libc.d/.   To make the resolver use
         the dynamically generated resolver configuration file the administrator
         should   ensure   that   /etc/resolv.conf   is   a   symbolic  link  to
         /run/resolvconf/resolv.conf.   This   link   is   never   modified   by
         resolvconf(8).  If you find that /etc/resolv.conf is not being updated,
         check to make sure that the link is intact.

  FWIW, resolvconf's version is 1.63ubuntu14

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