killmode is useless in this context, and BatchMode is actually made
for this...

howto/cumin.md

@@ -82,9 +82,7 @@ Description=Setup port forward to puppetdb
 After=network.target
 
 [Service]
-ExecStart=/usr/bin/ssh -nNT -o ExitOnForwardFailure=yes -L 8080:localhost:8080 puppetdb-01.torproject.org
-KillMode=mixed
-
+ExecStart=/usr/bin/ssh -nNT -o ExitOnForwardFailure=yes -o BatchMode=yes -L 8080:localhost:8080 puppetdb-01.torproject.org
 ```
 
 With this in place, make sure that systemd has loaded this unit file: