After trying to disable kerberos via the UI the following message is seen in the ambari-server logs and the service fails to start.
...INFO [main] KerberosChecker:57 - Checking Ambari Server Kerberos credentials.
WARN [main] KerberosChecker:81 - /etc/security/keytabs/ambari.server.keytab doesn't exist
ERROR [main] KerberosChecker:115 - Configuration Error - either doNotPrompt should be false or at least one of useTicketCache, useKeyTab, tryFirstPass and useFirstPass should be true
Ensure the following is set: kerberos.check.jaas.configuration=false
Further disable kerberos for ambari server by removing: