Unexpected Default User in MySQL Client: Investigation and Resolution

Scenario Description

During local testing, the author observed that invoking the MySQL client via a Unix socket without specifying a user logged in as zhenxing instead of the expected root user, resulting in an "Access denied" error.

Initial Observations

Running mysql -S /data/mysql/3306/data/mysqld.sock -p displayed the error, and mysql --help|egrep "user|host|port" confirmed that the default user reported by the client was zhenxing.

Configuration File Investigation

The usual suspect, /etc/my.cnf, was examined and correctly set user=root. Subsequent checks of other typical locations ( /etc/mysql/my.cnf, /usr/local/mysql/etc/my.cnf, /data/mysql/3306/base/my.cnf, ~/.my.cnf) all returned "file not found" or contained no relevant settings.

Determining the Read Order

## 查看mysql客户端读取配置文件的顺序<br/>mysql --verbose --help|grep my.cnf<br/>order of preference, my.cnf, $MYSQL_TCP_PORT, /etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf /data/mysql/3306/base/my.cnf ~/.my.cnf

All listed files were excluded, yet the default user remained zhenxing.

Using --no-defaults

Even with --no-defaults, the client still reported user=zhenxing:

# mysql --no-defaults --help|egrep "user|host|port"<br/>host 127.0.0.1<br/>port 3306<br/>user zhenxing

Running mysql --print-defaults showed that the client would have been started with arguments including --user=zhenxing, indicating an extra source of configuration.

System Call Tracing

Using strace revealed the client attempts to stat several files; the only existing file beyond the standard list was /root/.mylogin.cnf:

stat("/root/.mylogin.cnf", {st_mode=S_IFREG|0600, st_size=336, ...}) = 0

Inspecting .mylogin.cnf

The file is generated by mysql_config_editor and stores encrypted login‑path credentials. Displaying its contents:

# mysql_config_editor print --all<br/>[client]<br/>user = "zhenxing"<br/>password = *****<br/>host = "127.0.0.1"<br/>port = 3306

This explains why the client defaults to zhenxing even when other option files are absent or when --no-defaults is used.

Conclusion

The MySQL client reads configuration in the order shown by mysql --verbose --help|grep my.cnf, but it also always reads the login‑path file .mylogin.cnf. This file overrides other settings, and its values are applied even with --no-defaults, providing a safer way to store passwords. The unexpected default user in the author's environment was caused by a previous test that populated .mylogin.cnf with the zhenxing credentials.