The proper way to perform maintenance on your machine is to wait until all active contracts have expired or the machine is vacant.
For unplanned or unscheduled maintenance, use this schedule maint command. That will notify the client that you have to take the machine down and that they should save their work.
You can specify a date, duration, reason and category for the maintenance.Example: vastai schedule maint 8207 —sdate 1677562671 —duration 0.5 —maintenance_category “power”