I don’t use my local GlassFish much, so of course: I lost the admin password. Here’s a simple method to be able to log in again.
Start asadmin from the $GLASSFISH/bin folder.
domain1 not running
Command list-domains executed succesfully.
Next create a domain that does not exist yet. Supply an admin user and password that you can remember!
Enter the value for the domain_name operand> dummy
Enter admin user name [Enter to accept default "admin" / no password]> admin
Enter the admin password [Enter to accept default of no password]> ******
Enter the admin password again> ******
Using default port 4848 for Admin.
Using default port 8080 for HTTP Instance.
Domain dummy created.
Domain dummy admin port is 4848.
Domain dummy admin user is "admin".
Command create-domain executed successfully.
Now go to the config folder of domain dummy ($GLASSFISH/glassfish/domains/dummy/config). There is a file admin-keyfile. Copy this file to the config folder of your original domain, e.g. domain1 ($GLASSFISH/glassfish/domains/domain1/config). Make sure you make a backup of the original admin-keyfile first.
Confirm that you can log in as admin again. If so, you can safely delete the dummy-domain:
asadmin> delete-domain dummy
Domain dummy deleted.
Command delete-domain executed successfully.