Cannot connect to MySQL with JDBC - Connection Timeout - Ubuntu 9.04

Question

I am running Ubuntu and am ultimately trying to connect Tomcat to my MySQL database using JDBC.

It has worked previously but after a reboot the instance now fails to connect.

• Both Tomcat 6 and MySQL 5.0.75 are on the same machine
• Connection string: jdbc:mysql:///localhost:3306
• I can connect to MySQL on the command line using the mysql command
• The my.cnf file is pretty standard (Available on request) has bind address: 127.0.0.1
• I cannot Telnet to the MySQL port despite netstat saying MySQL is listening
• I have one IpTables rule to forward 80 -> 8080 and no firewall I'm aware of.

I'm pretty new to this and I'm not sure what else to test. I don't know whether I should be looking in etc/interfaces and if I did what to look for. It's weird because it used to work but after a reboot it's down so I must have changed something.... :).

I realise a timeout indicates the server is not responding and I assume it's because the request isn't actually getting through. I installed MySQL via apt-get and Tomcat manually.

MySqld processes

root@88:/var/log/mysql#  ps -ef | grep mysqld
root     21753     1  0 May27 ?        00:00:00 /bin/sh /usr/bin/mysqld_safe
mysql    21792 21753  0 May27 ?        00:00:00 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql --user=mysql --pid-file=/var/run/mysqld/mysqld.pid --skip-external-locking --port=3306 --socket=/var/run/mysqld/mysqld.sock
root     21793 21753  0 May27 ?        00:00:00 logger -p daemon.err -t mysqld_safe -i -t mysqld
root     21888 13676  0 11:23 pts/1    00:00:00 grep mysqld

Netstat

root@88:/var/log/mysql# netstat -lnp | grep mysql
tcp        0      0 0.0.0.0:3306            0.0.0.0:*               LISTEN      21792/mysqld
unix  2      [ ACC ]     STREAM     LISTENING     1926205077 21792/mysqld        /var/run/mysqld/mysqld.sock

Toy Connection Class

root@88:~# cat TestConnect/TestConnection.java

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class TestConnection {

  public static void main(String args[]) throws Exception {
    Connection con = null;

    try {
      Class.forName("com.mysql.jdbc.Driver").newInstance();
      System.out.println("Got driver");
      con = DriverManager.getConnection(
                "jdbc:mysql:///localhost:3306",
                "uname", "pass");
      System.out.println("Got connection");

      if(!con.isClosed())
        System.out.println("Successfully connected to " +
          "MySQL server using TCP/IP...");

    } finally {
        if(con != null)
          con.close();
    }
  }
}

Toy Connection Class Output

Note: This is the same error I get from Tomcat.

root@88:~/TestConnect# java -cp mysql-connector-java-5.1.12-bin.jar:. TestConnection
Got driver
                Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 1 milliseconds ago. The driver has not received any packets from the server.
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
        at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122)            
        at TestConnection.main(TestConnection.java:14)
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
        at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
        at com.mysql.jdbc.Util.handleNewInstance(Util.java:409)
        at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1122)
        at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:344)
        at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2181)
        ... 12 more
Caused by: java.net.ConnectException: Connection timed out
        at java.net.PlainSocketImpl.socketConnect(Native Method)
        ... 13 more

Telnet Output

root@88:~/TestConnect# telnet localhost 3306
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection timed out

Answer 1

Netstat shows that MySQL is indeed listening on port 3306 on all local addresses. Since telnet cannot connect to 127.0.0.1 there is a firewall that stops your you - try running sudo ufw default allow to effectivly disable it, or sudo ufw allow 3306 and see if it makes any changes.

Answer 2

What does your /etc/hosts file look like? Do you have an entry like the following?

127.0.0.1   localhost

Can you try to telnet:

telnet 127.0.0.1 3306 or telnet 127.0.0.1:3306

or JDBC connect to:

jdbc:mysql://127.0.0.1:3306

Answer 3

The connection string ought to be

jdbc:mysql://localhost:3306

instead of

jdbc:mysql:///localhost:3306

Also on unix/linux, by default the client/server communication is done via the unix socket file and not via tcp/ip. Hence you are not able to telnet to port 3306 on your local machine.

Answer 4

Were you always using the same signature for the getConnection method, or is that one of the things you changed before it stopped working? (The '///' in the string suggestions it was a recent addition.)

If this is new code, you might try the following connection string:

String dbUrl = "jdbc:mysql://localhost:3306/[db]?user=[user]&password=[password]"; Connection conn = DriverManager.getConnection(dbUrl);

This is the example format on the mysql.com documentation page:

http://dev.mysql.com/doc/refman/5.0/es/connector-j-usagenotes-basic.html