When the shutdown command is shutting down a system, the process creates an /etc/nologin file. This file displays a message indicating that the system is being shut down and that logins are not possible. Alternately, a superuser can separately create and manage this /etc/nologin file.
This type of shutdown does not block the superuser from logging in. Starting in this release, the following additional users are not blocked when the nologin file is present on the system:
Users assigned with the root role
Users assigned with the solaris.system.maintenance authorization
For further information, see the nologin (4) and shutdown (1M) man pages.