login.core found

While logged in to ttyv1 as root moving files between datasets, the web UI went offline. After reboot, the web UI showed an alert,

The following system core files were found: login.core. Please create a ticket at https://jira.ixsystems.com/ and attach the relevant core files along with a system debug. Once the core files have been archived and attached to the ticket, they may be removed by running the following command in shell: 'rm /var/db/system/cores/*'.
2021-03-01 12:19:40 (America/New_York)

login.core attached.