How to find out the location of currently used MySQL configuration file in linux

The information you want can be found by running

mysql --help

or

mysqld --help --verbose

I tried this command on my machine:

mysql --help | grep "Default options" -A 1

And it printed out:

Default options are read from the following files in the given order:
/etc/my.cnf /usr/local/etc/my.cnf ~/.my.cnf

See if that works for you.