It was apparmor in my case. Try add the following to /usr/share/zentyal/stubs/dns/apparmor-named.local.mas:
/usr/lib/x86_64-linux-gnu/ldb/modules/ldb/** rm,
also alter 'Access to kerberos keytab' to '/var/lib/samba/private/dns.keytab rk,'.
There are other modules namely, mysqld ejabberdctl, complaining at boot time.
For mysqld add the following to /usr/share/zentyal/stubs/dns/apparmor-mysqld.local.mas:
/sys/devices/system/node/** r,
@{PROC}/@{pid}/status r,
For ejabberdctl:
profile su {
/run/samba/winbindd/pipe rw,
}
to /etc/apparmor.d/local/usr.sbin.ejabberdctl