pdns-server fails to start - can't find an exiting file

[Brownowl]

Hi folks,

I suspect this plea for help is more appropriate for the mailing list, but I've sent two emails in the last few days and they seem to have fallen into a black hole. And yes, I still have a valid account and email on the list.

Anyway, I hope this isn't too far out of bounds, and I would really appreciate some help with this please. It's probably something simple, but I just can't see it however hard I look.

I've been using pdns happily with mysql and a tinydns backend for several years now on a couple of Ubuntu machines. These now need to be replaced, so I've installed all I need on a new one. However, I have a problem getting pdns to run, and I'm really struggling to work out what's causing the problem.

I get the following messages on startup:

pdns_server[262519]: Failed to open cdb database file
'/var/tmp/data.cdb': No such file or directory

pdns_server[262519]: Fatal error: Failed to open cdb database file
'/var/tmp/data.cdb': No such file or directory

systemd[1]: pdns.service: Main process exited, code=exited, status=1/FAILURE

systemd[1]: pdns.service: Failed with result 'exit-code'.
systemd[1]: Failed to start PowerDNS Authoritative Server.

However, the file concerned is very much there!

# ls -al /var/tmp/data.cdb
-rw-r--r-- 1 root root 56678 Dec 15 10:55 /var/tmp/data.cdb

ls -al /var
drwxrwxrwt 11 root   root   4096 Dec 15 12:49 tmp

I've tried chmod 777 and chown pdns:pdns to no avail. I've set logging
to debug, but there are no clues there either. It has exactly the same
permissions and ownership as on the old machines.

The setup script I followed is the one I wrote when I installed it on
the older machines, and I've checked and re-checked the config files,
which as far as I can see are identical, but I'm stumped.

I'm sure I'm missing something simple, but however hard I look and use
Google I can't see it. So I'd really appreciate some help please.

New platform is Ubuntu Server 22.04.3 LTS and pdns-server version is
4.8.3 including tinydns and mysql backends).

In case it's relevant, the old machines are Ubuntu Server 20.04.6 LTS
and pdns version 4.2.1-1build2

Many thanks, Laurie.

[rgacogne]

I'm pretty sure this is because we set PrivateTmp in our systemd unit file, for security reasons: https://www.freedesktop.org/software/systemd/man/latest/systemd.exec.html#PrivateTmp=

That means PowerDNS doesn't see the global /tmp and /var/tmp/ directories but their own private ones. I would suggest moving your cdb file to a different location. If you cannot do that, you can set PrivateTmp=false via systemctl edit --full pdns.

[Brownowl]

Many, many thanks. That was exactly it! Completely news to me, and I can't imagine I would ever have found that on my own!

Thanks again - this can be marked as solved. Yay!

Cheers, Laurie.

PS. Still no success getting an email into the mailing list.

[Habbie]

PS. Still no success getting an email into the mailing list.

I see why. I just sent you an email :)