Question

Below is the result of the query select host, user from mysql.user from a fresh installed MySQL 5.

+-----------+------------------+
| host      | user             |
+-----------+------------------+
| 127.0.0.1 | root             |
| localhost | debian-sys-maint |
| localhost | root             |
| ubuntu    | root             |
+-----------+------------------+

127.0.0.1, localhost, and ubuntu all point to the same machine, which is the local host. I can’t find any difference after removing the rows with the seemingly duplicate host/user pairs from the table.

What’s the difference between these? Can I safely remove the other two?

Answer 1

From the manual:

When you install MySQL, the grant tables are populated with an initial
set of accounts. The names and access privileges for these accounts
are described in Section 2.10.3, “Securing the Initial MySQL
Accounts”, which also discusses how to assign passwords to them.

And:

Some accounts have the user name root. These are superuser accounts
that have all privileges and can do anything. The initial root account
passwords are empty, so anyone can connect to the MySQL server as root
without a password and be granted all privileges.

On Unix, each root account permits connections from the local
host. Connections can be made by specifying a host name of localhost
or the actual host name or IP address.

However, I can’t find any rationale for this. There’s nothing elsewhere in the manual that suggests that this is required for any particular reason, but presumably it’s to cover all the bases for request verification. There may be some instances where one originating local connection uses one account whilst others require use alternatives; I guess it was decided that ensuring local root access will always work, no matter what the edge case, was a good thing.