How and when to reset your Mac’s PRAM and SMC

There are times when your Mac (s aapl) will just start misbehaving. Video settings getting reset, fans start running at full speed, keyboard lights don’t come on when they should.  This is most likely to happen following a hardware upgrade, extended power outage or even a major software upgrade (like Lion). In those cases, sometimes you need to reset your Mac’s parameter random access memory (PRAM) or system management controller (SMC) to get things running smoothly again.

Try this first

There are some good best practices to perform before running off and resetting your Mac at the first sign of strange behavior. This isn’t a step-by-step list; try each and all of the below separately when you’re having trouble:

  • Quit (Command+Q) or even Force Quit (Command+Option+Esc) any and all running applications.
  • Log off and then log back on to any and all logged on user accounts.
  • Put the Mac to sleep and wake it up again.
  • Restart the Mac.
  • Shut down and unplug the Mac (and remove any battery if you have access) for at least thirty seconds before powering back on.

You may even have to press and hold the power button several seconds in extreme cases when your Mac is truly not responding or refuses to shut down and power off. But if you have tried all of this to no avail, then perhaps you do need to either reset your PRAM or your SMC.

Parameter random access memory

PRAM is used by OS X to store certain information that the system can access quickly. Macs will store settings like which startup drive to boot from, various display and video settings, startup speaker volume and even the DVD’s region settings. If you feel that you need to reset your Mac’s PRAM because of the issues you’re having, do the following:

  1. Turn off your Mac. Don’t worry about disconnecting the power or removing the battery.
  2. Turn on your Mac and hold down the Command, Option, P, and R keys all at the same time (all four keys).
  3. Keep holding down all four keys until you hear the startup sound for a second time.

If you do not hear the startup sound twice, then you most likely have not reset the PRAM.  If you find that your Mac is not retaining the information that is stored in PRAM when you perform a shutdown, then it might be time to replace your Mac’s main logic board battery.  This is sometimes referred to as the PRAM or Clock Battery. I hardly ever fully shut down and power off any of my Macs, and have yet to replace this battery on any Mac I have owned, so that should only be the culprit in very extreme cases.

System management controller

The SMC is an Intel-only (s intc) feature.  There are so many symptoms that can potentially be solved by resetting the SMC that you’d think you would need to do this sort of reset all of the time. These include fans running out of control, lights not displaying correctly, the Mac does not sleep or wake properly, and just generally poor performance and high CPU cycles for no good reason. There are three ways to reset your SMC, based on what sort of Intel-based Mac you have:
Portable Macs with removable batteries

  1. Shut down the Mac, unplug and remove the battery.
  2. Press and hold the power button for five seconds before releasing.
  3. Replace the battery (just put it back in), plug in the Mac and turn it back on.

Portable Macs without removable batteries

  • Shut down the Mac.
  • Ensure that the Mac is plugged into a power source.
  • While the Mac is turned off, press and hold the Shift, Control and Option keys, as well as the Power button.
  • Release all four keys at the same time (note: the Mac should not power on when performing this task).
  • Press the power button to turn the Mac back on.

Desktop Mac Pros, iMacs and Mac minis

  • Shut down and unplug the Mac.
  • Keep the Mac unplugged for at least fifteen seconds.
  • Plug the Mac back in and do not turn it back on for at least five seconds.
  • Press the power button to turn the Mac back on.

This shouldn’t be considered a routine operation, like fixing file permissions in Disk Utility. It’s just something to keep in mind as a possible last resort solution to weird behaviors that your Mac starts to develop, which can often happen when you perform upgrades like installing OS X Lion, especially on older hardware.