What is the default username and password for SonarQube?
username: admin
password: admin
http://docs.sonarqube.org/display/SONAR/Authentication#Authentication-AdminCredentialsDefaultAdminCredentials
If you are like me and have installed Sonarqube 6.4 using jdk 9 / jre 9 the login will always fail. This is due to the fact that java 9 is not supported. Please change the java version to 8 that is supported.
You can also point to a different java version in the conf/wrapper.conf file:
wrapper.java.command=/some/path/to/proper/jdk8
Valid jdk/jre options are found here: https://docs.sonarqube.org/display/SONAR/Requirements