Troubleshooting MySQL Remote Connection Failure Caused by skip_networking Configuration

Author: Zhang Hao, DBA, mainly responsible for MySQL fault handling and DMP product support.

1 Background

A client’s testing colleague deployed MySQL 8.0 locally and added several variables to the configuration file; after restarting the database, remote connections to the database failed.

2 Investigation

1 Check Database Process Status

[root@hao-3 ~]# ps -ef|grep mysqld |grep 8888
actiont+ 25825     1  0 02:10 ?        00:00:01 /opt/mysql/base/8.0.28/bin/mysqld --defaults-file=/opt/mysql/etc/8888/my.cnf --daemonize --pid-file=/opt/mysql/data/8888/mysqld.pid --user=actiontech-mysql --socket=/opt/mysql/data/8888/mysqld.sock --port=8888

2 Check Service TCP Connection Status

Use the netstat command to view the TCP connections of the database service; the output is empty.

[root@hao-3 ~]# ps -ef|grep mysqld|grep 8888
actiont+ 25825     1  0 02:10 ?        00:00:05 /opt/mysql/base/8.0.28/bin/mysqld --defaults-file=/opt/mysql/etc/8888/my.cnf --daemonize --pid-file=/opt/mysql/data/8888/mysqld.pid --user=actiontech-mysql --socket=/opt/mysql/data/8888/mysqld.sock --port=8888
[root@hao-3 ~]# netstat  -lantup |grep 25825       // view process
[root@hao-3 ~]#
[root@hao-3 ~]# netstat  -lantup |grep 8888        // view port
[root@hao-3 ~]#

3 Check Database Port

The database port query returns 0.

[root@hao-3 ~]# /opt/mysql/base/8.0.28/bin/mysql -uroot -p1 -S /opt/mysql/data/8888/mysqld.sock
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 8.0.28 MySQL Community Server - GPL
...
mysql> show variables like 'port';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| port          | 0     |
+---------------+-------+
1 row in set (0.00 sec)

4 Check Configuration File

The client’s configuration contains the skip_networking variable, which disables TCP/IP connections.

mysql> show variables like '%networking%';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| skip_networking | ON    |
+-----------------+-------+
1 row in set (0.00 sec)

[root@hao-3 ~]# grep skip /opt/mysql/etc/8888/my.cnf
skip_external_locking = 1
skip_name_resolve = 1
skip_replica_start = 1
skip_networking=on

5 Official Documentation Explanation

skip_networking controls whether MySQL allows TCP/IP connections; it is disabled by default. When enabled, MySQL only accepts local connections and rejects any TCP/IP connections.

Note that when the --skip-grant-tables option is set, skip_networking is also enabled by default, thereby disabling all remote connections.

3 Conclusion

The skip_networking variable should be configured according to business needs: it is strongly recommended for MySQL instances that only need local access, but for most databases that require remote access it should remain disabled (default). The variable cannot be changed dynamically; it requires editing the configuration file and restarting the MySQL service.

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