My mac is always quite hot and the fans are often at full speed even with moderate activity. Also, when I plug in the external monitor, the computer becomes very sluggish and kernel_task starts taking insane amounts of CPU.

So it looks like I need a SMC reset.

My question is: what does it entail? Will I lose some settings/configurations? Do I need to back up some data? Is there any risk that the system will not work properly after the reset? As weird as it sounds, I did not see these questions ever addressed anywhere the reset was mentioned online.

This is my working computer, so it would be very inconvenient if I somehow disabled it.

  • 1
    kernel_task is running artificially high to try make your machine cool itself down... hence the high fan activity. – Tetsujin Aug 15 '16 at 8:38

Will I lose some settings/configurations? No.

Do I need to back up some data? Well, you should always have backup of important data. When it comes to SMC reset it does not touch your storage/hard drive. So no data should be affected.

Is there any risk that the system will not work properly after the reset? There is a very slight risk. In 99,9999% of all times, if the computer are working perfectly and has no hardware issues the computer till work 100% properly after SMC reset. However there has been cases where the SMC reset fries the logic board, although, those cases had shown other hardware symptoms.

The SMC is responsible for these and other low-level functions:

  1. Responding to presses of the power button
  2. Responding to the display lid opening and closing on portable Macs
  3. Battery management
  4. Thermal management
  5. The SMS (Sudden Motion Sensor)
  6. Ambient light sensing
  7. Keyboard backlighting
  8. Status indicator light (SIL) management
  9. Battery status indicator lights
  10. Selecting an external (instead of internal) video source for some iMac displays
  • 2
    Where do you get that stat from? What cases have you seen that an SMC reset "fries" a logic board? – Allan Aug 15 '16 at 12:28
  • 1
    The stats are taken from thin air and based on personal experience, i have fried logic boards during SMC reset. They where semi working before the reset and afterwards where totally dead or showed very little signs of operation. Those where logic boards with a pre exciting problems such as video issues, liquid damage or corrupt firmware. However on healthy hardware it poses no danger. – Niklas Aug 16 '16 at 18:50
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    For the record, an SMC simply cannot fry a logic board as a reset only clears the values that the Systems Management Controller has in it's registers. As you have already alluded, if your logic board goes south after an SMC reset, rest assured you that your logic board was in the process of failing already. – Allan Aug 16 '16 at 20:21
  • Apple has included official guide on resetting SMC for end-users which implies that resetting SMC is a user-safe option (otherwise they would explicitly mention that you need to bring the MacBook to authorized center). – Alexander K. Sep 29 '20 at 19:50

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