mysql 安装，创建用户

sudo apt install mysql-client-core-5.7

问题1：

        ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock'

   That error means the file /var/run/mysqld/mysqld.sock doesn't exists, if you didn't install mysql-server, then the file would not exist. So in that case, install it with

sudo apt-get install mysql-server

But if the mysql-server is already installed and is running, then you need to check the config files.

The config files are:

/etc/my.cnf
/etc/mysql/my.cnf
/var/lib/mysql/my.cnf

In /etc/my.cnf, the socket file config may be /tmp/mysql.sock and in /etc/mysql/my.cnf the socket file config may be /var/run/mysqld/mysqld.sock. So, remove or rename /etc/mysql/my.cnf, let mysql use /etc/my.cnf, then the problem may solved.