How to find slave's IP address and user name from Master server?

On the master server:

SELECT * FROM information_schema.PROCESSLIST AS p WHERE p.COMMAND = 'Binlog Dump';

This shows all connected slaves, their ipaddresses, user, and even how long they have been connected since they last connected as slaves.

There is an interesting way to report all registered slaves connect to the master.

The command is called SHOW SLAVE HOSTS;

This will not directly show the IP of the slaves but you can configure the master and slaves to do so in a unique way.

With MySQL 5.5, just run SHOW SLAVE HOSTS; and you just get something like this:

MySQL> show slave hosts;
+-----------+------+------+-----------+
| Server_id | Host | Port | Master_id |
+-----------+------+------+-----------+
| 106451148 |      | 3306 | 106451130 |
+-----------+------+------+-----------+
1 row in set (0.00 sec)

MySQL> show variables like 'server_id';
+---------------+-----------+
| Variable_name | Value     |
+---------------+-----------+
| server_id     | 106451130 |
+---------------+-----------+
1 row in set (0.00 sec)

As shown
column 1 is the Slave's server-id
column 2 is the Slave's name as specfied in report-host variable (blank by default)
column 3 is the Slave's port number connecting to master
column 4 is the Slave's Master server-id (run this from the Master)

With versions MySQL 5.1 and back, you get this by default:

MySQL> show slave hosts;
Empty set (0.01 sec)

MySQL>

You can assign a hostname to each slave by adding this to the slave's /etc/my.cnf

report-host=MySQLSlave_10.1.2.3

Restart mysql and hopefully the name will appear as you typed it in /etc/my.cnf
If the periods are not acceptable, make them dashes like this:

report-host=MySQLSlave_10-1-2-3

Then do the following

1. SHOW SLAVE HOSTS;
2. Use the PHP explode function, delimiting by underscore character, and take the second element of the array
3. Use the PHP function str_replace, replacing dash (-) with period (.)

And WA LA, you have an IP address

Log into mysql and execute SHOW FULL PROCESSLIST. You will get slaves IP addresses.

I'd try logging into mysql and looking at the global variables:

mysql -u [dbuser] -p -e "show global variables";