$ sudo apt-get remove mpg123 

Uninstall mpg123 including dependent package

If you would like to remove mpg123 and it's dependent packages which are no longer needed from Ubuntu,

$ sudo apt-get remove --auto-remove mpg123 

Use Purging mpg123

If you use with purge options to mpg123 package all the configuration and dependent packages will be removed.

$ sudo apt-get purge mpg123 

If you use purge options along with auto remove, will be removed everything regarding the package, It's really useful when you want to reinstall again.

$ sudo apt-get purge --auto-remove mpg123 

See Also,