cacti的错误 

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FATAL: Cannot connect to MySQL server on 'localhost'. Please make sure you have specified a valid MySQL database name in 'include/config.php'

1.查看config.php下，是否配置正确

        查看cactiusr的host是否有localhost 权限

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mysql -ucactiuser -h localhost -p

        查看登录是否成功 ，如果登录正常则排除

2.MYSQL权限问题

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SQL>GRANT ALL ON cacti.* TO cactiuser@localhost IDENTIFIED BY 'somepassword';

3.当mysql中的所有配置和cacti的config.php都正确，却还是出现该错误时，那就是mysql套接字的原因了~

        cacti会自动的去查找/var/lib/mysql/mysql.sock 该套接字，但是如果是源码安装的mysql，未指定套接字位置时，套接字的位置为/tmp/mysql.sock，由于cacti未找到/var/lib/mysql/mysql.sock，所以显示的是“Cannot connect to MySQL server on ‘localhost’”

        解决：做一个/tmp/mysql.sock到/var/lib/mysql/mysql.sock的软连接

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ln -s  /tmp/mysql.sock  /var/lib/mysql/mysql.sock