这种错误一般是 mysql 服务器异常关机导致的，解决方案如下：
# Ubuntu
sudo service mysql stop sudo usermod -d /var/lib/mysql/ mysql sudo service mysql start
# CentOS sudo systemctl stop mysql.service sudo usermod -d /var/lib/mysql/ mysql sudo systemctl start mysql.service
mysql 启动失败：su: warning: cannot change directory to /nonexistent: No such file or directory
原文：https://www.cnblogs.com/cnwcl/p/13805643.html