Traccar server not starting

When I run traccar using default config (using H2 storage), it runs.
But when I switch to mysql, it crashes. Seconds after issuing sudo /opt/traccar/bin/traccar start,
It will log

Starting traccar...
Waiting for traccar......
running: PID:27320

and in tracker.log:

2017-03-20 16:22:12  INFO: Operating system name: Linux version: 3.13.0-92-generic architecture: amd64
2017-03-20 16:22:12  INFO: Java runtime name: OpenJDK 64-Bit Server VM vendor: Oracle Corporation version: 24.111-b01
2017-03-20 16:22:12  INFO: Memory limit heap: 1776mb non-heap: 214mb
2017-03-20 16:22:12  INFO: Character encoding: UTF-8 charset: UTF-8
2017-03-20 16:22:12  INFO: Version: 3.7-SNAPSHOT

But it wont start. When I issue:
sudo /opt/traccar/bin/traccar status
It says tracar is not running.

This is my traccar.xml:

<entry key='database.driver'>com.mysql.jdbc.Driver</entry>
<entry key='database.url'>jdbc:mysql://127.0.0.1:3306/traccar_db?allowMultiQueries=true&autoReconnect=true&useUnicode=yes&characterEncoding=UTF-8&sessionVariables=sql-mode=''
<entry key='database.user'>[my username]</entry>
<entry key='database.password'>[my password]</entry>

I forgot to check the wrapper.log. It's complaining about duplicate keys.

So, have you figured out the problem or do you have any more questions?