See https://docs.sonarqube.org/display/SONAR/Documentation for current functionality
SonarQube 5.6 requires Java 8
Usage of external authentication and authorization system
If you are using an external authentication and authorization system (LDAP, Active Directory, Crowd, ...) for which you had to configure a realm in the "conf/sonar.properties" file, please make sure that you follow the "Upgrading" guide carefully. don't forget to copy the related SonarQube plugin and its related configuration in "conf/sonar.properties" (including "sonar.security.realm" and "sonar.security.localUsers" if present) into the new SonarQube instance otherwise you will be locked out after migration.