using ps aux
unbound 5197 0.0 1.3 22144 13424 ? Ss 11:51 0:10 /usr/sbin/unbound -d
Hence I used the command:
sudo chown unbound.unbound /mnt/dns_logs/unbound.log
to make sure the unbound user has access:
-rw-r--r-- 1 unbound unbound 2901 Apr 22 11:51 /mnt/dns_logs/unbound.log
Here is the configuration file:
server:
#If no logfile is specified, syslog is used
logfile: /mnt/dns_logs/unbound.log
verbosity: 2 (2 is working)
Thank you for all your help. 