Temporary failure in name resolution on Ubuntu server 22.04.3 LTS

[Bo Berglund]

On Mon, 27 Nov 2023 12:27:09 -0500, Jon LaBadie <ubu at labadie.us> wrote:

>On Mon, Nov 27, 2023 at 03:25:40PM +0100, Bo Berglund wrote:
>>On Sun, 26 Nov 2023 21:33 +0100, Tom H wrote:
>>
>>> I read the ubuntu-users@ archives more or less weekly, and I've just
>>> seen your "resolv.conf" thread and your last post:
>>>
>>> https://lists.ubuntu.com/archives/ubuntu-users/2023-November/311569.html
>>>
>>> Your immediate problem can be solved by changing the "resolved"
>>> configuration since it's controlling "resolv.conf".
>>>
>>> Create "/etc/systemd/resolved.conf.d/bo.conf" [ feel free to name it
>>> something else :) ].
>>>
>>> $ /etc/systemd/resolved.conf.d/bo.conf
>>> [Resolve]
>>> DNS=the_nameservers_that_you_want_(space_separated)
>>>
>>> This should ensure that you get your nameservers in "resolv.conf".
>>
>>About the file to create:
>>Do you mean I should create *directory*
>>  /etc/systemd/resolved.conf.d
>>and then place text file bo.conf inside that dir?
>>
>>> To investigate your network setup more generally, find out what
>>> networking packages are installed with:
>>>
>>> dpkg-query -W -f='${binary:Package}\n' | grep -E
>>> 'ifupdown|netplan|network-manager|resolv'
>>>
>>> On my laptop, this command lists:
>>>
>>> libnetplan0:amd64
>....
>>> systemd-resolved
>>
>>When I try on the remote system I get this:
>>$ dpkg-query -W -f='${binary:Package}\n' | grep
>>-E'ifupdown|netplan|network-manager|resolv'
>
>
>You left out a space after -E

I just copied the command in the email...
But here it is (newsreader split the line) after space added:

$ dpkg-query -W -f='${binary:Package}\n' | grep -E
'ifupdown|netplan|network-manager|resolv'
ifupdown
libnetplan0:amd64
netplan.io
resolvconf

>
>>grep: updown|netplan|network-manager|resolv: No such file or directory
>>
>>So somehow my system does not really behave...
>>
>
>Assuming "systemd-resolved" is installed, check whether it is in use.
>
>$ systemctl status systemd-resolved

This is the result:

$ systemctl status systemd-resolved
? systemd-resolved.service - Network Name Resolution
     Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled;
vendor preset: enabled)
     Active: active (running) since Sun 2023-11-26 07:05:58 CST; 1 day 9h ago
       Docs: man:systemd-resolved.service(8)
             man:org.freedesktop.resolve1(5)

https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers

https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
   Main PID: 5669 (systemd-resolve)
     Status: "Processing requests..."
      Tasks: 1 (limit: 1013)
     Memory: 4.1M
        CPU: 886ms
     CGroup: /system.slice/systemd-resolved.service
             +-5669 /lib/systemd/systemd-resolved

>
>>I have it installed, but am not using it for my name resolution.
>>So I get:
>>
>>$ systemctl status systemd-resolved
>>? systemd-resolved.service - Network Name Resolution
>>      Loaded: loaded (/lib/systemd/system/systemd-resolved.service; disabled; vendor preset: enabled)
>>      Active: inactive (dead)
>>        Docs: man:systemd-resolved.service(8)
>>              man:org.freedesktop.resolve1(5)
>>              https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
>>              https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
>>
>>
>If you are using systemd-resolved for your DNS the reason 
>/etc/resolv.conf says "do NOT edit" is because that package
>uses files in /etc/systemd.  Specifically "resolved.conf"
>and "resolved.conf.d/*".

On my system the content of the dir is:

$ ls -la /etc/systemd/
total 64
drwxr-xr-x   5 root root  4096 Nov  6 03:17 .
drwxr-xr-x 139 root root 12288 Nov 26 08:20 ..
-rw-r--r--   1 root root  1282 Aug 21 16:11 journald.conf
-rw-r--r--   1 root root  1374 Aug 21 16:11 logind.conf
drwxr-xr-x   2 root root  4096 Apr 12  2016 network
-rw-r--r--   1 root root   846 Mar 11  2022 networkd.conf
-rw-r--r--   1 root root   670 Mar 11  2022 pstore.conf
-rw-r--r--   1 root root  1406 Aug 21 16:11 resolved.conf
-rw-r--r--   1 root root   931 Mar 11  2022 sleep.conf
drwxr-xr-x  23 root root  4096 Oct 25 02:41 system
-rw-r--r--   1 root root  1993 Aug 21 16:11 system.conf
-rw-r--r--   1 root root   748 Aug 21 16:11 timesyncd.conf
drwxr-xr-x   5 root root  4096 Oct 11 14:36 user
-rw-r--r--   1 root root  1394 Aug 21 16:11 user.conf

Note that there is no directory named
/etc/systemd/resolved.conf.d
so there is also no place for files there...

Question:
Can I manually create the dir /etc/systemd/resolved.conf.d and files therein
such that they will be recognized by the system?
And if so when are they considered?
- reboot?
- restart of the systemd-resolved service?
- anytime a networking interface is cycled (down/up)?

>In the latter directory one of my systems has a file
>"localdns.conf" containing:
>
>[Resolve]
>DNS=10.0.0.12 10.0.0.2 8.8.8.8
>FallbackDNS=9.9.9.9 
>Domains=jgcomp.com labadie.us jgcomp.org

If that could work then I can actually rescue the system by creating the extra
file with the wanted DNS servers listed...
I will try this if I get a confirmation on the issues above.

>
>-- 
>Jon H. LaBadie                  ubu at labadie.us


-- 
Bo Berglund
Developer in Sweden