To be completely clear, changing the service type to "forking" will tell systemd that the process will daemonize itself, and removing the "-f" will tell bind9 to daemonize itself. Bind9 will daemonize itself _when it is ready_. Thus, you will even see configuration errors that you would otherwise miss if if they would occur several seconds after startup.
diff -rupN a/lib/systemd/system/bind9.service b/lib/systemd/system/bind9.service --- a/lib/systemd/system/bind9.service 2018-03-23 00:09:58.000000000 +0100 +++ b/lib/systemd/system/bind9.service 2018-06-04 23:11:36.504356488 +0200 @@ -6,8 +6,10 @@ Wants=nss-lookup.target Before=nss-lookup.target [Service] +Type=forking +PIDFile=/run/named/named.pid EnvironmentFile=/etc/default/bind9 -ExecStart=/usr/sbin/named -f $OPTIONS +ExecStart=/usr/sbin/named $OPTIONS ExecReload=/usr/sbin/rndc reload ExecStop=/usr/sbin/rndc stop
