Powering off a desktop system may interfere with some operations that involve that machine. This section presents some guidelines to take into account before deciding when to use system Power Management features on a desktop machine.
If you suspend your system for three days or longer, and your machine has a local mail spool, you may fail to receive items of mail that have been bounced back to the sender.
Mail aliases on a machine are not available to other users while that machine is suspended. If the machine is suspended long enough (typically three days), messages sent to an alias on that machine are bounced back to the sender.
The Suspend-Resume feature may have an impact on a networked application. A networked program may fail if it is not resilient when a peer system is suspended and does not respond to network traffic.
One example of this is when you run an Xhosted application from one system and display it on another system. If the Power Management software suspends the latter system, the application software may fail.
The Power Management software is not supported on SunATM(TM) devices. The ATM protocol is connection oriented, which means calls must be established between two endpoints (such as workstations) before data can be transferred. Each end of the call must maintain the connection actively, so neither end of an ATM connection can use the Power Management software to suspend and, later, resume the connection.
When a system resumes, cron jobs scheduled to run during the time the system was suspended with the Power Management software are handled in the following way:
The first cron job (the one scheduled to run earliest during the time the system was suspended) is started as soon as the system resumes.
The second and subsequent cron jobs that might have run during the time the system was suspended are not run at all.
Normally, the cron command identifies the next job to run and calculates the interval to wait until it is time to run that job. When a system resumes, the cron command calculates the interval until the first job has expired; then this already-queued cron job is run. The cron process then rechecks its queue of jobs. It only considers jobs whose execution time has not yet passed, so any additional jobs whose run time fell during the time the system was suspended are not run.
The Power Management software is active by default on sun4u systems (such as the Sun Ultra 1). Accordingly, the Power Management system for those machines evaluates each automatic power-cycle request that occurs due to the system being idle. If an evaluation determines that the thermal shock of power cycling on a particular occasion would decrease hardware reliability, then that power-cycle request is deferred.
Despite this feature, you can choose to turn off a sun4u system manually at any time. This checking feature is intended as a brake on the hardware being subjected to an excessive number of automatic power-cycle requests.