What is the reason for failing to connect to the database?

Database Apache Password

With Apache as a server, MySQL as a database, all with the root user, password: 123456. What is the reason for the failure to report a connection to the database?
It is normal for me to use SQLyog to view the database. User name and password yes. What's the reason?

Reply to discussion (solution)

./install_amp--username=root--password=123456
That's the start statement, what's the reason?

Recommended to post error messages for analysis

./install_amp--username=root--password=123456
What is it?

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