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I'm trying to resolve these two repeating errors in /var/log/syslog...

nf_conntrack: nf_conntrack: table full, dropping packet

Maximum number of concurrent DNS queries reached (max: 150)

Looking at /etc/resolv.conf...

# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.

nameserver 127.0.0.1

I know that the nameserver should be 127.0.0.53, from looking at my other 18.04 system. If I manually change (which I know I shouldn't do) 127.0.0.1 to 127.0.0.53, the errors seem to stop in syslog. Of course, a reboot sets this file back to 127.0.0.1.

How do I get resolv.conf to correctly show 127.0.0.53, and survive reboots? Am I barking up the right tree?

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    Maybe this might help: askubuntu.com/a/1057752/231142
    – Terrance
    Jul 20, 2018 at 18:50
  • @Terrance thanks for the possible lead... however, implementing the symlink change of /etc/resolv.conf didn't fix the error messages, and now dnsmasq generated error messages 'cause it noticed the symlink wasn't pointing at the "right" place any more.
    – heynnema
    Jul 20, 2018 at 21:33
  • Yeah, unfortunately I don't know yet. This Netplan seems different. However, I do know for me I don't like using netmasq. If ever I can make it so it uses my DNS server and not the built in one I get better results. I should be upgrading to 18.04 next week possibly then I might know more.
    – Terrance
    Jul 20, 2018 at 21:40
  • @Terrance and the really confusing part is knowing the relationship between systemd-resolve and dnsmasq and resolveconf... who gets the DNS query first, what do they do with it, and who/how do they pass it off to the next app?
    – heynnema
    Jul 20, 2018 at 22:01
  • 1
    You probably have dnsmasq stepping on the toes of systemd-revolved, see unix.stackexchange.com/questions/304050/…, the answers there may help. Jul 20, 2018 at 23:21

1 Answer 1

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First, thanks to @Terrance and @BernardWei for pointing me to information that ultimately helped me resolve this problem. I used parts of their links to formulate my own process to resolve the repeating error messages in syslog.

Looking at /etc/resolv.conf gives a clue. The nameserver is 127.0.0.1, and that is placed there by dnsmasq. In 18.04 it should be 127.0.0.53, placed there by systemd-resolved.

On my system, I did:

ps auxc | grep -i dns
ps auxc | grep -i resolv

And found that both dnsmasq and systemd-resolved were running, and as far as DNS is concerned, they overlap in functionality. There are two possible fixes.

Fix #1:

I uninstalled dnsmasq and dnsmasq-base (probably left over from a system prior to -29), and then restarted systemd-resolved. /etc/resolv.conf now correctly shows that the nameserver is 127.0.0.53.

Fix #2:

If you need BOTH dnsmasq and systemd-resolved running, then edit /etc/systemd/resolved.conf and change:

#DNSStubListener=yes

to:

DNSStubListener=no

and restart systemd-resolved.

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  • Glad you found a way, good to know about Fix #2, cheers. Jul 23, 2018 at 17:41
  • @heynnema I have exactly the same problem but need dnsmasq as it selves as DHCP and DNS for a WiFiHotspot running on the same machine. When setting DNSStubListener=no the flooding between 127.0.0.1 and 127.0.0.53 stops, but unfortunately my docker containers also stop working ....
    – f0rd42
    Jul 23, 2018 at 18:06
  • @f0rd42 what is in your /etc/resolv.conf? Did you restart both dnsmasq and systemd-resolved?
    – heynnema
    Jul 23, 2018 at 18:14
  • @heynnema I have given up on 18.04. Installed 16.04 and have everything working in 2% of the time I spend on 18.04 for troubleshooting :-)
    – f0rd42
    Jul 23, 2018 at 19:36

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