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Dan
Asked: 2018-12-28 03:27:56 +0800 CST

Samba Internal DNS - Systemd resolve safe to disable?

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So I had a Ubuntu 16.04 instance running a samba ad dc, I upgraded to 18.04 and when starting samba I was getting the error;

[2018/12/27 11:09:56.483755, 0] ../source4/dsdb/dns/dns_update.c:290(dnsupdate_nameupdate_done)
../source4/dsdb/dns/dns_update.c:290: Failed DNS update - with error code 110

After some digging and running sudo lsof -i :53 I could see 

systemd-r  767 systemd-resolve   12u  IPv4  18656      0t0  UDP 127.0.0.53:domain 
systemd-r  767 systemd-resolve   13u  IPv4  18657      0t0  TCP 127.0.0.53:domain (LISTEN)
samba     1594            root   36u  IPv6  23058      0t0  TCP *:domain (LISTEN)
samba     1594            root   38u  IPv6  23059      0t0  UDP *:domain

Which lead me to disable systemd-resolve using the instructions here, this has fixed all my problems within the network (other domain machines not being able to apt-get update etc) but im worndering is disabling systemd-resolve safe ?

Edit

This is a VM running on vsphere 6.0 its a bridged networked. Netplan folder is empty after the upgrade (which Ive just remembered should have to be set) the old network details /etc/network/interfaces is set to; 

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto ens160
iface ens160 inet static
address 192.168.2.23
netmask 255.255.255.0
gateway 192.168.2.254

dns-nameservers 192.168.2.23
dns-search MYDOMAINNAME.co.uk

I can manually set the resolv.conf (after removing the sym link) to the following and it works

nameserver 192.168.2.23
nameserver 127.0.0.53
search MYDOMAIN.co.uk
DNSStubListener=no
networking samba dns 16.04 18.04

1 Answers

  1. Re-enable systemd-resolve.

    Two possibilities...

    1. Regarding dnsmasq and systemd-resolved...

    Do a ps auxc | grep -i dns and ps auxc | grep -i resolv and look for dnsmasq and systemd-resolved, and if both are running, you need to disable the DNS part of systemd-resolved by editing /etc/systemd/resolved.conf and...

    change:

    #DNSStubListener=yes

    to:

    DNSStubListener=no

    then restart systemd-resolve and dnsmasq, or reboot.

    1. you MAY need to reset the symlink that is /etc/resolv.conf (if dnsmasq is not running)...

    sudo mv /etc/resolv.conf /etc/resolv.conf.OLD # save the old symlink

    sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf # create new symlink

    Update #1:

    Many details of this installation came forward in the comments, and we still don't have a final working solution. Here are some points to recognize...

    DNSStubListener=no does not belong in /etc/resolv.conf. (/etc/resolv.conf should not (normally) be edited directly). It's an edit to /etc/systemd/resolved.conf. DNS= can also be edited there to add DNS server addresses.

    /etc/resolv.conf should be a symlink, linked to one of two possible locations in /run.

    NEW -> /run/systemd/resolve/resolv.conf
OLD -> ../run/resolvconf/resolv.conf

    and should contain either 127.0.0.53 (or 127.0.0.1 if dnsmasq was running), or DNS nameserver addresses, or your router's address (ex: 192.168.1.1)

    If you're going to use NetworkManager instead of netplan, then /etc/netplan should contain at least one .yaml file containing...

    network:
  version: 2
  renderer: NetworkManager

    followed by...

    sudo netplan generate # generate config files

    sudo netplan apply # apply configuration

    If you're using NetworkManager, then /etc/NetworkManager/NetworkManager.conf should exist... and should look something like...

    [main]
plugins=ifupdown,keyfile

[ifupdown]
managed=false

[device]
wifi.scan-rand-mac-address=no

    If dnsmasq AND systemd-resolve are running, then you should do #1 in my answer.

    If dnsmasq is not running, and systemd-resolve is running, then you should do #2 in my answer.

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