You're close, but your problem is you have both instances pointing at the master. What you want is one instance updating the master every second, and the second instance reading the slave every second.

Also note it does not need to run on the actual database servers at all, it uses a regular mysql client connection. I run mine from my cacti server. Here's my sanitized /etc/rc.local for an example:

/usr/bin/mk-heartbeat -D maatkit -u maatkit -paardvark --update -h sql-master.fake.net --daemonize
/usr/bin/mk-heartbeat -D maatkit -u maatkit -paardvark -h sql-slave.fake.net --monitor --file /tmp/sql-slave.heartbeat --daemonize

1

you can use maatkit's mk-heartbeat

2

you can look at result of

show slave status;

run on sql slave but Seconds_Behind_Master is disturbingly inaccurate at times.

3

you can hack your own solution, similar to mine - i use it both for nagios monitoring and for feeding munin charts showing 'seconds behind master'.

on master server i have simple cron job:

* * * * * root /usr/local/bin/repltest

where repltest is:

#!/bin/bash
start=`date +%s`
d=0
while [ $d -lt 60 ] ; do
        echo "update repl_test set t= NOW(); " |mysql --defaults-file=/etc/mysql/debian.cnf repl_test
        sleep 3
        d=$(( `date +%s` - $start ))
done

on the slave i monitor value returned by:

echo "select UNIX_TIMESTAMP(NOW())-UNIX_TIMESTAMP(t) from repl_test" |  mysql --defaults-file=/etc/mysql/debian.cnf -N repl_test

local time on all servers is synchronized via ntp.

repl_test db contains:

CREATE TABLE IF NOT EXISTS `repl_test` (`t` datetime NOT NULL) ENGINE=MyISAM DEFAULT CHARSET=utf8;
INSERT INTO `repl_test` (`t`) VALUES(NOW());

if you run replication - i suggest you also set up mk-table-checksum to compare content of your sql servers from time to time.