Multiple entries similar to the following are found in /var/log/samba4/smbd.log:
Loading new DNS update grant rules
[2020/06/25 15:53:50.796282, 0] ../../lib/util/util_runcmd.c:327(samba_runcmd_io_handler)
/usr/sbin/rndc: Failed to exec child - No such file or directory
[2020/06/25 15:53:50.801204, 0] ../../source4/dsdb/dns/dns_update.c:91(dnsupdate_rndc_done)
../../source4/dsdb/dns/dns_update.c:90: Failed rndc update - NT_STATUS_UNSUCCESSFUL
[2020/06/25 15:54:50.811383, 2] ../../source4/dsdb/dns/dns_update.c:270(dnsupdate_rebuild)
These occur every 10 minutes or so. The AD DC is configured to use the internal dns. There are no bind packages installed on that host.
The problem is that these errors are swamping the log file. There are so many entries relating to this one issue that noticing that something else needs attention is seriously impaired.
This code is removed in 4.12.
Using the 'rndc command = /bin/true' option in 4.10 and 4.11
should avoid the messages