When your Mac starts acting up, you’ll probably run through some common troubleshooting procedures, such as restarting it, running Disk Utility, and perhaps performing a Safe Boot. Your repair repertoire should also include a couple of additional procedures that can occasionally eliminate otherwise inscrutable problems–zapping the NVRAM and resetting the SMC.
The procedures here apply to Intel-based Macs. M-Series Macs don’t have a procedure for zapping the NVRAM, and they don’t have an SMC. For M1-Series Macs, try shutting down the computer, waiting for several seconds, and then boot it.
What is PRAM?
Back in the day, the standard list of quick fixes for random Mac ailments always included clearing the PRAM. The P in PRAM stood for "parameter" (the RAM was just RAM–random access memory), and it referred to a small amount of special, battery-backed memory in every Mac that stored information the computer needed before it loaded the operating system. If the values in this memory got out of whack for one reason or another, your Mac might not start up correctly or might exhibit any of numerous odd behaviors afterward. So you could press a key sequence at startup to reset (or "zap") the PRAM, returning it to default, factory values.
What is NVRAM?
NVRAM (non-volatile random-access memory) refers to a small amount of your Mac’s memory that stores certain settings in a location. NVRAM was previously referred to as the Parameter RAM or PRAM. NVRAM serves approximately the same purpose as PRAM, but instead of storing a dozen or more pieces of information, it now contains just a few: your selected startup disk, speaker volume, screen resolution, time zone, and–if your Mac has crashed recently–details of the last kernel panic.
NVRAM corruption is fairly uncommon, but if your Mac seems to take forever to figure out the correct boot disc, starts up with the wrong screen resolution, or suffers from weird audio problems (like there’s no sound whatsoever or the menu bar’s volume control is grayed out), a reset of the NVRAM might help–and it’s quick and harmless.
When should you reset NVRAM?
Resetting the NVRAM is a quick and easy way to troubleshoot your computer that is acting strangely. For example, reset the NVRAM or PRAM, when you experience one of these:
- Display problems. (e.g., Mac Brightness Not Working.
- Time zone or date problems.
- Wrong startup disk.
- Sound problems (e.g., Sound Volume is Too Low on Mac or Sound Not Working On Mac
- Shut down or startup problems (e.g., Mac Won’t Shut Down, or Slow Startup Times In macOS)
- Slow keyboard or similar issues. (e.g., Keyboard Lag on Mac)
- Mouse problems. (e.g., Mouse Cursor (Pointer) Disappears on Mac
Resetting NVRAM is also recommended as the final step before you sell, give away, or trade in an Intel-based Mac.
Is it safe to reset the NVRAM?
When you reset the NVRAM, your Mac will revert to factory default settings. So it’s safe in the sense it that it does not harm the Mac, but you might think of it as "unsafe" in that any customization you’ve done to the system settings may be lost. You may have to go back and reinstate some of those settings.
How reset NVRAM
M Mac (Apple silicon)
M Macs don’t have a procedure for resetting NVRAM. because you don’t need to reset the NVRAM or PRAM on Macs powered by Apple Silicon.
The NVRAM is also present on all Macs with Apple silicon. But the NVRAM works differently on these Macs. As stated above, you do not have to reset the NVRAM because your Mac automatically reset it when needed. Your Mac checks the NVRAM when your Mac is powered on and then reset it if it detects problems. Thus, if you want to reset the NVRAM on your Apple silicon Mac, simply shut it down completely, wait a few seconds, and then power up the Mac.
Intel Macs
To reset your NVRAM, you use exactly the same procedure you once used to reset PRAM.
- Turn off your Mac (Apple menu > Shut Down).
- Locate these four keys: Option, Command, P, and R. Do not press them yet.
- Turn on your Mac by pressing the power button and then immediately press and hold these four keys for about 20 seconds until:
- your Mac restarts and you hear the startup sound for a second time.
- you see the Apple logo disappears twice if you have a Mac with the Apple T2 Security Chip.
- Your Mac should start up normally.
If you hold down Command-Option-P-R at startup and you see nothing but a gray screen that doesn’t change for several minutes–no Apple logo, no progress bar, no second startup chime–don’t panic. The most likely cause is that your Mac isn’t registering the key presses due to wonkiness with a USB device. Disconnect all USB devices (except your keyboard, if it’s a wired keyboard), hold the power button down until the Mac shuts off completely, and then press it again and immediately hold down Command-Option-P-R.
If that doesn’t work and you’re using an external Bluetooth keyboard, try plugging in a USB keyboard instead. If you’re able to reset the NVRAM successfully with the wired keyboard, you can disconnect it and go back to your normal Bluetooth keyboard.
Terminal
More advanced users can try using the Terminal to reset to NVRAM, though if you’ve reached this option the problem is likely bigger than resetting NVRAM. And as with all Terminal commands, the usual caveats apply: You’re messing with macOS’s bash shell and could do irrevocable damage with the wrong keystroke. But if you’d like to try, you can type the following command into a new Terminal window:
nvram -c
After running the command, restart your Mac so the changes can take effect.
After the reset
After you reset the NVRAM or PRAM, some of your settings will be erased. You may want to go to System Settings to customize these settings:
- speaker volume,
- screen resolution,
- startup disk selection,
- and time zone information.
What is SMC?
The System Management Controller (SMC) is a subsystem that controls all power, light, and sensor functions for your Mac.
Note: You cannot reset the SMC on Macs with Apple silicon.
When should you reset the SMC?
There are a number of macOS problems that could be fixed by resetting the SMC. For example, if you are experiencing power or battery problems on your Mac (e.g., the battery is not charging,), you may want to reset the SMC. The followings are some of the signs you may see that may require you to reset it:
- Your Mac’s power button is not working, nothing happens when pressed.
- Your Mac sleeps or shuts down unexpectantly.
- The fans run constantly even though your Mac is not experiencing heavy use.
- Your Mac shows a black screen.
- Your Mac’s lights (such as status indicator, keyboard backlight, battery indicator lights) behave incorrectly.
- Your Mac is running extremely slow even though Activity Monitor does not show any unusual activity.
- Apps are not responding.
- Problems with external displays.
- Your MacBook is overheating.
Is it safe to reset the SMC?
It is safe to reset the SMC. You should check your Battery system preferences afterward to see if your customizations have been maintained.
How to reset the SMC
M-series Macs
M-series Macs don’t have a System Management Controller (SMC). The functions the SMC handled are now handled by the M chip itself. Postings on Apple’s forums suggest shutting down an M-series Mac completely and leaving it off for 30 seconds to perform something like an SMC reset. After 30 seconds, power on the Mac.
If your problems persist, you can try reinstalling the M-series Mac’s firmware. It’s a procedure that’s a little more complicated than what you might be used to. You need another Mac with the Apple Configurator 2 app installed, a USB-C cable that supports both power and data (used to connect the two Macs), and an internet connection.
Intel Macs
Apple says you shouldn’t reset the SMC without first trying other troubleshooting tasks, such as force-quitting problematic apps and restarting your Mac. However, Apple doesn’t mention any negative consequences of resetting the SMC, nor any way to determine for sure if the SMC is glitchy without resetting it and noticing that the problem went away. We’ve reset my Macs’ SMCs many times with no apparent ill effects, and on one occasion that did turn out to be the solution to a problem.
Before you can reset your SMC, you must shut down your Mac. After that, the procedure varies depending on the type of Mac you have.
MacBook models with the T2 chip
MacBook Air and MacBook Pro models introduced in 2018 or later include the T2 chip. Here’s how to reset:
- Turn off your Mac by choosing Shut Down from the Apple menu.
- Press and hold the following three keys: Control (on the left side), Option (Alt) (on the left side), Shift (on the right side).
- Keep holding these three keys for 7 seconds. Then while holding the keys, press and hold the power button.
- Now press and hold these 4 keys for an additional 7 seconds. Then release all keys.
- Wait a few seconds. And press the power button to turn on your Mac.
All Desktop Macs
These include iMac, iMac Pro, and Mac Pro models. Here is how:
- Turn off your Mac.
- Unplug its power cord.
- Wait 15 seconds.
- Now plug the power cable back in.
- Wait 5 seconds.
- Turn on your Mac by pressing the power button.
MacBook models with a non-removable battery
These models include all MacBook Air models, as well as MacBook and MacBook Pro models introduced in mid-2009 or later. The only exception is the 13-inch MacBook (Mid 2009). These models do not have the T2 chip. Here is how:
- Turn off your Mac.
- Press and hold these three keys: Shift (left side), Control (left side), Option (Alt) (left side).
- While holding these three keys, start pressing and holding the power key too.
- Keep pressing and holding these 4 keys for 10 seconds.
- Then release all 4 keys.
- Wait a few seconds. And press the power button to turn on your Mac as usual.
MacBook models with a removable battery
Is your battery removable? Just look at the bottom of your computer. Do you see some mechanism for removing the battery? If you have a MacBook and MacBook Pro model introduced in early 2009 or earlier or a 13-inch MacBook (Mid 2009), then your computer has a removable battery.
- Turn off your Mac.
- Remove its battery.
- Press and hold the power button for 5 seconds.
- Then reconnect the battery.
- Turn on your Mac by pressing the power button as usual.
Hopefully, now you reset the SMC, your issue is fixed.
Although neither of these procedures is a guaranteed cure, both of them can solve a number of odd problems, and are worth a few minutes of your time before hauling your Mac in to see the local Apple Genius.
Terminal
There is no Terminal command for resetting the SMC.