https://www.raspberrypi.org/documentation/configuration/config-txt/README.md

After Linux has booted, you can view the current active settings using the following commands:

  vcgencmd get_config <config>: this displays a specific config value, e.g.  vcgencmd get_config arm_freq.

  vcgencmd get_config int: this lists all the integer config options that are set (non-zero).

  vcgencmd get_config str: this lists all the string config options that are set (non-null).

Note that there are a few config settings that cannot be retrieved using  vcgencmd.


see http://elinux.org/RPiconfig