使用Ubuntu16.04出現的問題：mysql: [Warning] Using a password on the command line interface can be insecure. ERROR 2002 (HY000): Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (2)，原因是因為丟失mysqld.sock檔案。

[email protected]:~$ mysql -uroot -pmysql
mysql: [Warning] Using a password on the command
 
 line interface can be insecure.
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

終端輸入mysql -uroot -h 127.0.0.1 -p

[email protected]:~$ mysql -uroot -h 127.0.0.1 -p 
Enter password: 
ERROR 2003 (HY000): Can't connect to MySQL server on '127.0.0.1' (111)
 

顯然，也沒有用。
進入，

cd /etc/mysql/mysql.conf.d

[email protected]:/etc/mysql/mysql.conf.d$ ls
mysqld.cnf  mysqld_safe_syslog.cnf
[email protected]:/etc/mysql/mysql.conf.d$ vim mysqld.cnf 

進入mysql.cnf檔案，如下：

然後儲存退出，並將這個目錄許可權修改一下：

/etc/mysql/mysql.conf.d$ sudo chmod 777 mysqld.cnf 

然後就啟動mysql 和mysqld 服務：

[email protected]:/etc/mysql/mysql.conf.d$ service mysql  restart
[email protected]:/etc/mysql/mysql.conf.d$ service mysqld restart

然而，mysqld啟動又出錯了，啟動失敗，憤怒啊！！！不用管它！

[email protected]:~$ service mysqld restart
Failed to restart mysqld.service: Unit mysqld.service not found.

進入目錄並檢視：

[email protected]:/var/run$ cd mysqld/
[email protected]:/var/run/mysqld$ ls
mysqld.sock  mysqld.sock.lock

然後使用當前的 mysqld.sock 測試一下：

[email protected]:/var/run/mysqld$ mysql -uroot -p -S /var/run/mysqld/mysqld.sock

此時，終於見到光明瞭。可以正常進入mysql資料庫。

[email protected]:/var/run/mysqld$ mysql -uroot -p -S /var/run/mysqld/mysqld.sock 
mysql: [Warning] World-writable config file '/etc/mysql/mysql.conf.d/mysqld.cnf' is ignored.
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.24-0ubuntu0.16.04.1 (Ubuntu)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> 

到此還不算完成！
建立軟連結：

[email protected]:~$ ln -s /var/run/mysqld/mysqld.sock /var/lib/mysql/mysql.sock

進入如下目錄：

[email protected]:~$ cd /var//run/mysqld/
[email protected]:/var/run/mysqld$ ls
mysqld.sock  mysqld.sock.lock

然後再將原來修改的 mysql.cnf 檔案改回來，

至此，算是完成了。
重新進入終端測試一下：

此時，成功搞定！今日什麼也沒有做，花了近一天的時間，才完成這個大bug的！！！