A license key must be obtained to make the FreeSurfer tools operational. Obtaining a license is free and comes in the form of a license.txt file. Once you obtain the license.txt key file, copy it to your FreeSurfer installation directory (i.e. the top-level directory, usually called "freesurfer"). This is also the location defined by the $FREESURFER_HOME environment variable, which is described later in the setup and configuration section.
Follow this link to obtain a license key that enables your copy of Freesurfer.
Note: Registering for the license key does not enable one to post messages to the Freesurfer mailing list. To post to the list, you must subscribe to the list by following this link.