Resetting an Apple portable's System Management Controller (SMC)

The System Management Controller is an integrated circuit (computer chip) that is on the logic board of the computer. As the name implies, it is responsible for power management of the computer. It controls backlighting, hard disk spin down, sleep and wake, some charging aspects, trackpad control, and some input/output as it relates to the computer sleeping.

Over time, the settings in the System Management Controller may become unusable, which can result in operational anomalies with the computer. Examples include not turning on, not waking from sleep, not charging the battery, or not recognizing the AC Adapter, among others.

Resetting the SMC is not intended for resolution of a stall or situation in which the computer is unresponsive. An SMC reset should not be necessary except as a last resort in cases where a hardware failure of the power management system is suspected. Performing an SMC reset returns the hardware, including NVRAM (Non-Volatile Random Access Memory), to default settings and forces the computer to shut down.

For most situations, a restart is sufficient. If the computer has stopped responding, try each one of these steps, one by one. Test in between steps to see if it has worked. If one step works, don't worry about the next, as you're up and running! Only go on to reset the SMC if you've tried all of the steps listed here and the computer still isn't working.

1. Force Quit (Option-Command-Escape)
2. Restart (Control-Command-Power)
3. Force Shut Down (press the power button for 10 seconds)

Only perform an SMC reset on the computer if none of the above steps resolved the situation. If this is the case, see below for instructions on locating the reset button or key combination for your model of computer. If your computer is earlier than the models listed here, see "Resetting PowerBook and iBook Power Management Unit (PMU)" or "PowerBook: Resetting Power Management Unit (PMU)".

MacBook, MacBook Pro

1. If the computer is on, turn it off.
2. Disconnect the AC Adapter and remove the computer's battery.
3. Press and hold down the power button for 5 seconds and then release the button.
4. Reconnect the battery and AC Adapter.
5. Press the Power button to restart the computer.

MacBook Air

1. If the MacBook Air is on, turn it off.
2. Connect the power adaptor to a working power source.
3. On the MacBook Air keyboard, press (left) Shift-Control-Option along with the power button once.
   Note: You must use the keys on the left side of the MacBook Air keyboard.
4. Wait 5 seconds and press the power button to start the MacBook Air.

Apple recommends only performing an SMC reset when the MacBook Air has been properly shutdown. This prevents issues from occurring to the file system.

While the power adaptor does not need to be connected to reset the SMC, it may be necessary in situations where the battery needs charging, or the MacBook Air has been without power for an extended period of time.