Mysql 3306 error

In mysql, Can’t connect to MySQL server on localhost error occurs when mysql is unable to connect to localhost due to the connection issue with mysql or a database configuration issue with mysql. You may see an error Can’t connect to MySQL server on ‘127.0.0.1’ when you connect to ip and unable to connect to localhost 3306. You can’t connect to mysql server on localhost or ip 127.0.0.1 (3306) because either the mysql server may not be started or it may not be running, or the network connection to the mysql server is not established, or the mysql server port is different.

Some times, the application can’t connect to local mysql server or mysql could not connect server may not be running or mysql unable to connect to localhost:3306. The application can’t connect to mysql server on ‘localhost:3306’.

If you are trying to access mysql server from a remote server, the error message “Can’t connect to MySQL server on ‘ localhost ‘” may be displayed in the application. This error occurs if the application is unable to connect to mysql server due to a variety of reasons. In this post, we will see the error message “Can’t connect to MySQL server on ‘ localhost ‘” and how to fix this error.

The error message indicates that there is a problem when connecting to mysql from the calling application. If you identify a connectivity issue, the error message will be fixed.

Can't connect to MySQL server on 'localhost'
Can't connect to local MySQL server through socket '/tmp/mysql.sock'

Root Cause

The error is shown in the application because the application was unable to connect to the mysql server. There could be a number of reasons. This issue is caused by a network failure.

The network failure could be on mysql server side or on the connecting application side. The other reason is that the mysql server is not running on the server. Mysql may be shut down manually, or mysql may not be running on the server machine due to some error.

Solution 1

If the database is running on the local machine, run the ping command with localhost. If the database is running on the remote server, ping the ip of the database server. In this way, we can validate the database server is alive or shutdown or network issue. If the ping does not respond, check that the server is switched on. Check that the network cable is connected correctly.

For local machine

$> ping 127.0.0.1

For remote server

$> ping <ip of the remote server>

$> ping 172.168.1.3

Solution 2

Check that mysql is running or not in the database server. The mysql server may be switched off or stopped due to some critical error. try to restart the mysql server. Check the following command to check whether the mysql server is running or not.

$> netstat -ln | grep mysql

fcc1dd9a70716e73 stream      0      0 fcc1dd9a734eb92b                0                0                0 /tmp/mysqlx.sock
fcc1dd9a707174b3 stream      0      0 fcc1dd9a732f1f7b                0                0                0 /tmp/mysql.sock

The command above shows the network status of the mysql command. The command below will show whether or not the mysql port is listening. The default port number is 3306.

$> netstat -ln | grep 3306

tcp4       0      0  127.0.0.1.3306         127.0.0.1.53815        ESTABLISHED
tcp4       0      0  127.0.0.1.53815        127.0.0.1.3306         ESTABLISHED
tcp4       0      0  127.0.0.1.3306         127.0.0.1.53814        ESTABLISHED
tcp4       0      0  127.0.0.1.53814        127.0.0.1.3306         ESTABLISHED

If the above two commands do not return the expected result, check whether the mysql process is running or not using the following command.

$> ps -ax | grep mysql
  113 ??         4:47.15 /usr/local/mysql/bin/mysqld --user=_mysql --basedir=/usr/local/mysql  ... ... ... ... ... ... ... ... --early-plugin-load=keyring_file=keyring_file.so

Solution 3

If mysql is running, check the status of mysql service. If the server appears to be running. Stop the server and restart the service again. If mysql server is hung due to issues such as memory issues, the network issue will be resolved. Use the command below to check the service

$> sudo server mysql status

$> sudo server mysql stop

$> sudo server mysql start

$> sudo /etc/init.d/mysqld status

$> sudo /etc/init.d/mysqld stop

$> sudo /etc/init.d/mysqld start

Solution 4

The mysql server is running without error. Network issues have been resolved and no network issues have been identified. Now connect to mysql server using mysql command. You can also check using the telnet command

$> telnet 172.168.1.3 3306

$> mysql -u root -p -h <host name/ip>

if the port is different from the default port 3306

$> mysql -u root -p -h <host name/ip> -P <port>

Solution 5

If the above command is working successfully and you still see error in mysql. Check out my.cnf file. My.cnf file contains all configurations of mysql. Run the command below to find the location of my.cnf file,

$> mysql --help | grep my.cnf

or just run 

$> mysql --help

Open my.cnf file and search for the word bind-address. If there is an existing change as below. If it doesn’t exist, add the line below.

to refer the localhost 
bind-address = 127.0.0.1

to refer for any address
bind-address = 0.0.0.0

Solution 6

If all of the above steps are checked and configured, restart the mysql server. All changes will be updated and start with a new configuration. If there is an error in the configuration, mysql will throw an error and will not start the server. Run the command below to check and restart mysql server

$> sudo server mysql status

$> sudo server mysql stop

$> sudo server mysql start

Solution 7

Start the mysql server with install and initialize option and check the mysql server is running or not. if you are using windows, run the mysql server as admin.

C:Program FilesMySQLMySQL Serverbin>mysqld --install

C:Program FilesMySQLMySQL Serverbin>mysqld --initialize

Solution 8

If you are using windows operating system and mysql database is installed newly, then use “MySQL Installer – Community” from the menu to reconfigure. select “mysql server” in the product tab and click the “reconfigure” in the “Quick Action” tab. This will reconfigure the mysql database.

Server Not Running in Specified Location

If the error you get is something like:

mysql -uname -p
ERROR 2002 (HY000): Can't connect to local MySQL server through 
  socket '/var/run/mysqld/mysqld.sock' (2 "No such file or directory")

or

mysql -uname -p --port=3307 --protocol=tcp
ERROR 2003 (HY000): Can't connect to MySQL server on  'localhost' 
  (111 "Connection refused")

the server is either not running, or not running on the specified port, socket or pipe. Make sure you are using the correct host, port, pipe, socket and protocol options, or alternatively, see Getting, Installing and Upgrading MariaDB, Starting and Stopping MariaDB or Troubleshooting Installation Issues.

The socket file can be in a non-standard path. In this case, the socket option is probably written in the my.cnf file. Check that its value is identical in the [mysqld] and [client] sections; if not, the client will look for a socket in a wrong place.

If unsure where the Unix socket file is running, it’s possible to find this out, for example:

netstat -ln | grep mysqld
unix  2      [ ACC ]     STREAM     LISTENING     33209505 /var/run/mysqld/mysqld.sock

Unable to Connect from a Remote Location

Usually, the MariaDB server does not by default accept connections from a remote client or connecting with tcp and a hostname and has to be configured to permit these.

(/my/maria-10.4) ./client/mysql --host=myhost --protocol=tcp --port=3306 test
ERROR 2002 (HY000): Can't connect to MySQL server on 'myhost' (115)
(/my/maria-10.4) telnet myhost 3306
Trying 192.168.0.11...
telnet: connect to address 192.168.0.11: Connection refused
(/my/maria-10.4) perror 115
OS error code 115:  Operation now in progress

To solve this, see Configuring MariaDB for Remote Client Access

Authentication Problems

Note that from MariaDB 10.4.3, the unix_socket authentication plugin is enabled by default on Unix-like systems. This uses operating system credentials when connecting to MariaDB via the local Unix socket file. See unix_socket authentication plugin for instructions on connecting and on switching to password-based authentication as well as Authentication from MariaDB 10.4 for an overview of the MariaDB 10.4 changes..

Authentication is granted to a particular username/host combination. user1'@'localhost', for example, is not the same as user1'@'166.78.144.191'. See the GRANT article for details on granting permissions.

Passwords are hashed with PASSWORD function. If you have set a password with the SET PASSWORD statement, the PASSWORD function must be used at the same time. For example, SET PASSWORD FOR 'bob'@'%.loc.gov' = PASSWORD('newpass') rather than just SET PASSWORD FOR 'bob'@'%.loc.gov' = 'newpass';

Problems Exporting Query Results

If you can run regular queries, but get an authentication error when running the SELECT … INTO OUTFILE, SELECT … INTO DUMPFILE or LOAD DATA INFILE statements, you do not have permission to write files to the server. This requires the FILE privilege. See the GRANT article.

Access to the Server, but not to a Database

If you can connect to the server, but not to a database, for example:

USE test;
ERROR 1044 (42000): Access denied for user 'ian'@'localhost' to database 'test'

or can connect to a particular database, but not another, for example
mysql -u name db1 works but not mysql -u name db2, you have not been granted permission for the particular database. See the GRANT article.

Option Files and Environment Variables

It’s possible that option files or environment variables may be providing incorrect connection parameters. Check the values provided in any option files read by the client you are using (see mysqld Configuration Files and Groups and the documentation for the particular client you’re using — see Clients and Utilities).

Option files can usually be suppressed with no-defaults option, for example:

mysqlimport --no-defaults ...

Unable to Connect to a Running Server / Lost root Password

If you are unable to connect to a server, for example because you have lost the root password, you can start the server without using the privilege tables by running the --skip-grant-tables option, which gives users full access to all tables. You can then run FLUSH PRIVILEGES to resume using the grant tables, followed by SET PASSWORD to change the password for an account.

localhost and %

You may have created a user with something like:

CREATE USER melisa identified by 'password';

This creates a user with the ‘%’ wildcard host.

select user,host from mysql.user where user='melisa';
+--------+------+
| user   | host |
+--------+------+
| melisa | %    |
+--------+------+

However, you may still be failing to login from localhost. Some setups create anonymous users, including localhost. So the following records exist in the user table:

select user,host from mysql.user where user='melisa' or user='';
+--------+-----------+
| user   | host      |
+--------+-----------+
| melisa | %         |
|        | localhost |
+--------+-----------+

Since you are connecting from localhost, the anonymous credentials, rather than those for the ‘melisa’ user, are used. The solution is either to add a new user specific to localhost, or to remove the anonymous localhost user.

See Also

• CREATE USER
• GRANT
• Authentication from MariaDB 10.4
• Authentication from MariaDB 10 4 video tutorial