Issue & Setup
So, i noticed that there are a lot of posts more-or-less about this issue, but this is the one that came up for me in a web search, so this is the one i'm going to reply to; my apologies if there is a more appropriate place.
I hope to outline a [temporary?] solution here.
I have encountered a similar issue. After running
$ pihole-up
about an hour ago, unbound DNS resolution broke for me, as did the pi-hole web interface. Details about my setup:
My pi-hole is set up to do its own DNS resolution via unbound, as outlined at:
https://docs.pi-hole.net/guides/dns/unbound/
I typically do all maintenance via ssh, so, to be fair, it's possible that the web interface has been broken for a while without my noticing. In any case.
It looks like maybe some config files got totally clobbered in the upgrade process? My solution:
[Temporary?] Solution
First, i logged into my router and changed DNS resolution back to allowing my ISP to do it, as a temporary measure; i'm not sure whether this is necessary, but it made getting online /at all/ much more convenient.
At this point, DNS resolution on the pi-hole itself seemed to come back, as the commands
$ dig fail01.dnssec.works @127.0.0.1 -p 5335
and
$ dig dnssec.works @127.0.0.1 -p 5335
began returning the expected results, although it's possible that some reboots of the pi-hole that ended up being necessary were the cause of this, i'm not certain.
Second, i took the advice here and killed lighttpd, via
$ sudo service lighttpd stop
I have not yet disabled lighttpd entirely [edit: i have done now, as this appears to be a normal part of the v6 update process; see the "Edit: Additional Info" section below]; i will mess around with whether this is necessary in the coming days, but for now i just wanted to get things working again over the weekend.
Once lighttpd was killed, i was able to access the web interface again. /However,/ i had to reset my login password on the pi-hole, over ssh, via:
$ sudo pihole setpassword
before i was able to actually log in. It seems the update clobbered the password.
Next, after logging in, i visited the DNS settings under System > Settings > DNS. Here, my custom DNS setting was gone, so it seems the update clobbered this, too. I re-added the
127.0.0.1#5335
entry to the "Custom DNS Servers" box at the bottom of the page (note that the interface seems to have changed here; i no longer see four boxes for custom DNS settings in the web interface; only one large box at the bottom of the page).
Once set, i logged back into the router and changed my DNS settings back to allow the pi-hole to do all DNS resolution. Things now seem to be working again.
Conclusion & Questions
I hope this helps others who may run across this issue. Follow-up comments from more knowledgeable users would be most welcome, as, while things are /working/ again, it feels a hack—for example, why do i need to kill lighttpd [edit: this is part of the update process to v6 for most users; see below]? Is this clobbering a one-time thing, or is there a deeper problem? Etc.
Thanks!
Edit: Additional Info
So, part of the issue is that i was unaware that this was a major update;
$ pihole -up
doesn't provide much warning. Others may wish to see the release notes here:
https://discourse.pi-hole.net/t/introducing-pi-hole-v6/75863
In particular:
Since i update over ssh, i, of course, never saw this dialog box. I suspect many others will have missed this note, too. To disable lighttpd permanently:
$ sudo systemctl lighttpd disable
I hope this additional context is helpful.