Invoked with the boot or reboot subcommands, it writes a new BOOT_TIME entry. This is designed to be invoked at system bootstrap before any login services are started. login-update-utmpx creates the files for the login log and the active login table if they do not already exist. The entry can be later read with who -b or last reboot .

Invoked with the shutdown subcommand, it writes a new SHUTDOWN_TIME entry. This is designed to be invoked at system shutdown after all login services have been stopped. The entry can be later read with last reboot . (On Linux operating systems, which do not have SHUTDOWN_TIME, the entry is a fake RUN_LVL entry that can be later read with who -r .)