[nsd-users] Repeated crashes of NSD, without a clear explanation

[Stephane Bortzmeyer]

For now one week, one machine has NSD crashing after a few hours of
running, corrupting nsd.db.

The log (verbosity 4) says:

Jan 06 20:31:30 ada nsd[1974]: process 1975 exited with status 9
Jan 06 20:31:30 ada nsd[1974]: [2020-01-06 19:31:30.892] nsd[1974]: error: process 1975 exited with status 9
Jan 06 20:31:30 ada nsd[1974]: rmdir /tmp/nsd-xfr-1974 failed: Directory not empty
Jan 06 20:31:30 ada nsd[1974]: [2020-01-06 19:31:30.909] nsd[1974]: warning: rmdir /tmp/nsd-xfr-1974 failed: Directory not empty
Jan 06 20:31:31 ada nsd[2195]: nsd starting (NSD 4.1.26)
Jan 06 20:31:31 ada nsd[2195]: [2020-01-06 19:31:31.418] nsd[2195]: notice: nsd starting (NSD 4.1.26)
Jan 06 20:31:31 ada nsd[2195]: setup SSL certificates
Jan 06 20:31:31 ada nsd[2195]: [2020-01-06 19:31:31.421] nsd[2195]: info: setup SSL certificates
Jan 06 20:31:31 ada nsd[2196]: /var/lib/nsd/nsd.db: not cleanly closed 0
Jan 06 20:31:31 ada nsd[2195]: [2020-01-06 19:31:31.798] nsd[2196]: warning: /var/lib/nsd/nsd.db: not cleanly closed 0
Jan 06 20:31:31 ada nsd[2195]: [2020-01-06 19:31:31.798] nsd[2196]: warning: can not use /var/lib/nsd/nsd.db, will create anew

And then NSD stops. I have to start it manually, making it work for a
few more hours.

This machine worked fine, with the same set of zones, for several
years (yes, of course, software was upgraded, but another Debian,
machine, same version and same NSD, and almost same set of zones, has
no problem).

Debian "stable" 10.2, Linux kernel 4.19.0, NSD 4.1.26. As I said, a
very similar machine works fine.

% ls -alt /var/lib/nsd
total 552
-rw-------  1 nsd  nsd  589824 Jan  6 20:33 nsd.db
-rw-r--r--  1 nsd  nsd    6605 Jan  6 20:31 xfrd.state
drwxr-xr-x  2 nsd  nsd    4096 Jan  6 20:31 .
drwxr-xr-x 70 root root   4096 Jan  6 20:18 ..

Deleting all /var/lib/nsd and starting from a fresh directory changes
nothing.

What can I investigate?