Solving a communications link failure with JDBC and MySQL

Question

I m trying to connect to the local MySQL server but I keep getting an error   Here is the code   public class Connect        public static void main String   args            Connection conn   null           try               String userName    myUsername               String password    myPassword                String url    jdbc mysql   localhost 3306 myDatabaseName               Class forName  com mysql jdbc Driver   newInstance                conn   DriverManager getConnection url  userName  password               System out println  Database connection established              catch  Exception e                System err println  Cannot connect to database server                System err println e getMessage                 e printStackTrace              finally               if  conn    null                    try                       conn close                        System out println  Database Connection Terminated                      catch  Exception e                                       and the errors    Cannot connect to database server 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  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 411          at com mysql jdbc SQLError createCommunicationsException SQLError java 1116          at com mysql jdbc MysqlIO  lt init gt  MysqlIO java 344          at com mysql jdbc ConnectionImpl coreConnect ConnectionImpl java 2333          at com mysql jdbc ConnectionImpl connectOneTryOnly ConnectionImpl java 2370          at com mysql jdbc ConnectionImpl createNewIO ConnectionImpl java 2154          at com mysql jdbc ConnectionImpl  lt init gt  ConnectionImpl java 792          at com mysql jdbc JDBC4Connection  lt init gt  JDBC4Connection java 47          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 411          at com mysql jdbc ConnectionImpl getInstance ConnectionImpl java 381          at com mysql jdbc NonRegisteringDriver connect NonRegisteringDriver java 305          at java sql DriverManager getConnection DriverManager java 582          at java sql DriverManager getConnection DriverManager java 185          at Connect main Connect java 16      Caused by  java net ConnectException  Connection refused         at java net PlainSocketImpl socketConnect Native Method          at java net PlainSocketImpl doConnect PlainSocketImpl java 351          at java net PlainSocketImpl connectToAddress PlainSocketImpl java 213          at java net PlainSocketImpl connect PlainSocketImpl java 200          at java net SocksSocketImpl connect SocksSocketImpl java 366          at java net Socket connect Socket java 529          at java net Socket connect Socket java 478          at java net Socket  lt init gt  Socket java 375          at java net Socket  lt init gt  Socket java 218          at com mysql jdbc StandardSocketFactory connect StandardSocketFactory java 257          at com mysql jdbc MysqlIO  lt init gt  MysqlIO java 294              15 more   I ve set the classpath  made sure my cnf had the skip network option commented out    java version is 1 2 0 26  64 bit  mysql 5 5 14 mysql connector 5 1 17  I made sure that the user had access to my database

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I know this is an old thread but I have tried numerous things and fixed my issue using the following means..

I'm developing a cross platform app on Windows but to be used on Linux and Windows servers.

A MySQL database called "jtm" installed on both systems. For some reason, in my code I had the database name as "JTM". On Windows it worked fine, in fact on several Windows systems it flew along.

On Ubuntu I got the error above time and time again. I tested it out with the correct case in the code "jtm" and it works a treat.

Linux is obviously a lot less forgiving about case sensitivity (rightly so), whereas Windows makes allowances.

I feel a bit daft now but check everything. The error message is not the best but it does seem fixable if you persevere and get things right.

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If you are using local emulator  you have to use IP address 10 0 2 2 instead of localhost to access to your local MySQL server

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I ve just faced the same problem  It happened because the MySQL Daemon was binded to the IP of the machine  which is required to make connection with an user that has permission to connect  your machine  In this case  the user should have permission to connect USER NAME MACHINE NAME OR IP  I wanted remote access to my machine so I changed in my cnf from  bind-address   MY IP ADDRESS   To  bind-address   0 0 0 0   Which will allow an user from localhost AND even outside  in my case  to connect to the instance  Both below permissions will work if you bind the MySQL to 0 0 0 0   USER NAME MACHINE NAME OR IP  USER NAME localhost

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In my case    Change the remote machine mysql configuration  at  etc mysql my cnf  change  bind-address   127 0 0 1 to   bind-address   127 0 0 1 On the remote machine  change mysql user permissions with GRANT ALL PRIVILEGES ON     TO  user      IDENTIFIED BY  password   IMPORTANT  restart mysql on the remote machine  sudo  etc init d mysql restart

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I found the solution  since MySQL need the Localhost in-order to work   go to  etc network interfaces file and make sure you have the localhost configuration set there   auto lo iface lo inet loopback   NOW RESTART the Networking subsystem and the MySQL Services   sudo  etc init d networking restart  sudo  etc init d mysql restart  Try it now

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It happens  in my case  when there is not enough memory for MySQL  A restart fixes it  but if that s the case consider a nachine with more memory  or limit the memory taken by jvms

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It is majorly because of weak connection between mysql client and remote mysql server   In my case it is because of flaky VPN connection

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The resolution provided by Soheil was successful in my case   To clarify  the only change I needed to make was with MySQL s server configuration   bind-address     INSERT-IP-HERE     I am using an external MySQL server for my application  It is a basic Debian 7 5 installation with MySQL Server 5 5 - default configuration   IMPORTANT      Always backup the original of any configuration files you may modify  Always take care when elevated as super user    File   etc mysql my cnf   Line  bind-address          192 168 0 103  127 0 0 1   Restart your MySQL Server service    usr sbin service mysql restart   As you can see  I simply provided the network IP of the server and commented out the default entry  Please note that simply copy and paste my solution will not work for you  unless by some miracle our hosts share the same IP   Thanks   Soheil

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As the detailed answer above says  this error can be caused by many things   I had this problem too   My setup was Mac OSX 10 8  using a Vagrant managed VirtualBox VM of Ubuntu 12 04  with MySQL 5 5 34   I had correctly setup port forwarding in the Vagrant config file   I could telnet to the MySQL instance both from my Mac and from within the VM   So I knew the MySQL daemon was running and reachable   But when I tried to connect over JDBC  I got the  Communications link failure  error    In my case  the problem was solved by editing the  etc mysql my cnf file   Specifically  I commented out the   bind-address 127 0 0 1  line

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Go to Windows services in the control panel and start the MySQL service  For me it worked  When I was doing a Java EE project I got this error  Communication link failure   I restarted my system and then it worked    After that I again got the same error even after restarting my system  Then I tried to open the MySQL command line console and login with root  even then it gave me an error    Finally when I started the MySQL service from Windows services  it worked

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I faced this problem also   As Soheil suggested   I went to php ini file at the  path C  windows php ini   then I revised port number in this  file    it is on the line mysqli default port              So I  changed it in my java app as it s in the php ini file now it works fine with me

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In phpstorm   vagrant autoReconnect driver option helped

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For Windows  - Goto start menu write    MySqlserver Instance Configuration Wizard  and reconfigure your mysql server instance  Hope it will solve your problem

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I have had the same problem in two of my programs  My error was this   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    I spent several days to solve this problem  I have tested many approaches that have been mentioned in different web sites  but non of them worked  Finally I changed my code and found out what was the problem  I ll try to tell you about different approaches and sum them up here   While I was seeking the internet to find the solution for this error  I figured out that there are many solutions that worked for at least one person  but others say that it doesn t work for them  why there are many approaches to this error  It seems this error can occur generally when there is a problem in connecting to the server  Maybe the problem is because of the wrong query string or too many connections to the database   So I suggest you to try all the solutions one by one and don t give up   Here are the solutions that I found on the internet and for each of them  there is at least on person who his problem has been solved with that solution   Tip  For the solutions that you need to change the MySQL settings  you can refer to the following files    Linux   etc mysql my cnf or  etc my cnf  depending on the Linux distribution and MySQL package used  Windows  C   ProgramData   MySQL MySQL Server 5 6 my ini  Notice it s ProgramData  not Program Files    Here are the solutions    changing  bind-address  attribute   Uncomment  bind-address  attribute or change it to one of the following IPs   bind-address  127 0 0 1   or  bind-address  0 0 0 0    commenting out  skip-networking    If there is a  skip-networking  line in your MySQL config file  make it comment by adding     sign at the beginning of that line    change  wait timeout  and  interactive timeout    Add these lines to the MySQL config file   wait timeout   number  interactive timeout   number  connect timeout   number   Make sure Java isn t translating  localhost  to     1  instead of  127 0 0 1     Since MySQL recognizes 127 0 0 1  IPv4  but not    1  IPv6   This could be avoided by using one of two approaches   Option  1  In the connection string use 127 0 0 1 instead of localhost to avoid localhost being translated to    1  Option  2  Run java with the option -Djava net preferIPv4Stack true to force java to use IPv4 instead of IPv6  On Linux  this could also be achieved by running  or placing it inside  etc profile   export  JAVA OPTIONS  -Djava net preferIPv4Stack true     check Operating System proxy settings  firewalls and anti-virus programs   Make sure the Firewall  or Anti-virus software isn t blocking MySQL service   Stop iptables temporarily on linux  If iptables are misconfigured they may allow tcp packets to be sent to mysql port  but block tcp packets from coming back on the same connection     Redhat enterprise and CentOS systemctl stop iptables service   Other linux distros service iptables stop   Stop anti-virus software on Windows    change connection string   Check your query string  your connection string should be some thing like this   dbName    my database   dbUserName    root   dbPassword       String connectionString    jdbc mysql   localhost     dbName     user     dbUserName     amp password     dbPassword     amp useUnicode true amp characterEncoding UTF-8     Make sure you don t have spaces in your string  All the connection string should be continues without any space characters   Try to replace  localhost  with the loopback address 127 0 0 1  Also try to add port number to your connection string  like   String connectionString    jdbc mysql   localhost 3306 my database user root amp password Pass amp useUnicode true amp characterEncoding UTF-8     Usually default port for MySQL is 3306   Don t forget to change username and password to the username and password of your MySQL server    update your JDK driver library file test different JDK and JREs  like JDK 6 and 7  don t change max allowed packet    max allowed packet  is a variable in MySQL config file that indicates the maximum packet size  not the maximum number of packets  So it will not help to solve this error    change tomcat security   change TOMCAT6 SECURITY yes to TOMCAT6 SECURITY no   use validationQuery property   use validationQuery  select now    to make sure each query has responses   AutoReconnect   Add this code to your connection string    amp autoReconnect true amp failOverReadOnly false amp maxReconnects 10     Although non of these solutions worked for me  I suggest you to try them  Because there are some people who solved their problem with following these steps   But what solved my problem   My problem was that I had many SELECTs on database  Each time I was creating a connection and then closing it  Although I was closing the connection every time  but the system faced with many connections and gave me that error  What I did was that I defined my connection variable as a public  or private  variable for whole class and initialized it in the constructor  Then every time I just used that connection  It solved my problem and also increased my speed dramatically   Conclusion  There is no simple and unique way to solve this problem  I suggest you to think about your own situation and choose above solutions  If you take this error at the beginning of the program and you are not able to connect to the database at all  you might have problem in your connection string  But If you take this error after several successful interaction to the database  the problem might be with number of connections and you may think about changing  wait timeout  and other MySQL settings or rewrite your code how that reduce number of connections

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In my case it was an idle timeout  that caused the connection to be dropped on the server  The connection was kept open  but not used for a long period of time  Then a client restart works  while I believe a reconnect will work as well   A not bad solution is to have a daemon service to ping the connection from time to time

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After years having the same issue and no permanent solution this is whats solved it for the past 3 weeks  which is a record in terms of error free operation   set global wait timeout 3600  set global interactive timeout 230400   Don t forget to make this permanent if it works for you

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I was experiencing similar problem and the solution for my case was    changing bind-address   0 0 0 0 from 127 0 0 1 changing url s localhost to localhost 3306   the thing i felt is we should never give up  i tried every options from this post and from other forums as well   happy it works  saurab

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I just restarted MySQL  following a tip from here  https   stackoverflow com a 14238800  and it solved the issue  I had the same issue on MacOS  10 10 2  and MySql  5 6 21  installed via homebrew  The confusing thing was that one of my apps connected to the database fine and the other did not  After trying many things on the app that threw the exception com mysql jdbc CommunicationsException as suggested by the accepted answer of this question to no avail  I was surprised that restarting MySQL worked  The cause of my issue might have been the following as suggested in the answer in the aforementioned link   Are you using connection pool   If yes  then try to restart the server  Probably few of the connections in your connection pool are in closed state

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For me the solution was to change in the conf file of mysql server the parameter bind-address  127 0 0 1  or bind-address  x x x x  to bind-address  0 0 0 0   Thanks

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In case you are having problem with a set of Docker containers  then make sure that you do not only EXPOSE the port 3306  but as well map the port from outside the container -p 3306 3306  For docker-compose yml   version   2   services      mdb          image  mariadb 10 1         ports              -  3306 3306

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If you are using hibernate  this error can be caused for keeping open a Session object more time than wait timeout  I ve documented a case in here for those who are interested

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Had the same  Removing port helped in my case  so I left it as jdbc mysql   localhost

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In my case  I am a noob   I was testing Servlet that make database connection with MySQL and one of the Exception is the one mentioned above   It made my head swing for some seconds but I came to realize that it was because I have not started my MySQL server in localhost  After starting the server  the problem was fixed   So  check whether MySQL server is running properly

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Setting the bind-address to the server s network IP instead of the localhost default  and setting privileges on my user worked for me   my cnf   bind-address   192 168 123 456   MySql Console   GRANT ALL PRIVILEGES ON dbname   to username     IDENTIFIED BY  password

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If you are using MAMP PRO  the easy fix  which I really wish I had realized before I started searching the internet for days trying to figure this out  Its really this simple     You just have to click  Allow Network Access to MySQL  from the MAMP MySQL tab    Really  thats it   Oh  and you MIGHT have to still change your bind address to either 0 0 0 0 or 127 0 0 1 like outlined in the posts above  but clicking that box alone will probably solve your problems if you are a MAMP user

[java] Solving a "communications link failure" with JDBC and MySQL

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