"Previous shutdown cause: -20"

Hello Tran Thien Duy,

We understand that you want to know what does -20 error refer to as well as the Previous shutdown cause: 1 mean. We're happy to help!

Let's try an SMC reset. 

How to reset the SMC of your Mac

You may also want to try an NVRAM reset. 

Reset NVRAM or PRAM on your Mac

If you're still experiencing the issue after performing the above tasks, then let's try Safe Mode. 

How to use safe mode on your Mac

Let us know if that worked for you.

Thank you for using Apple Support Communities.

Take care!

Tran Thien Duy,

As a side note, if you are getting Shutdown Cause 1 consistently, I would:

1. Check to make sure your power adapter is fully seated in both the wall and in your device.
2. If you reseat the connector (MagSafe, USB-C, power cable) and the issue persists, I would purchase/seek out a replacement, genuine Apple power adapter (third party power adapters can cause problems due to not being made to the exact OEM specifications).
3. If the issue persists after replacing the adapter, then that means that something in your computer is not able to fully read the power adapter, that changes dramatically based on what device you are dealing with. I would contact Apple Support for additional help if that is the case.

Good luck!

I have this same issue and none of these work. As far as I can tell, iMac Pro's don't seem to start up in Safe Mode in any straightforward way. This issue happens randomly every few days. The computer starts up and says that it was a kernel panic caused by BridgeOS and the ridiculous T2 chip. The reports to Apple are ignored because this has been a couple of years and there is no solution or bug fix. The only resolution is to restart the computer every day which makes it impossible to run anything that might take a couple of days to finish.

Hey Tran Thien Duy!

Since no one else seems to be answering your specific question directly, let me see what I can do.

Shutdown Cause 1 is a software code for "power adapter disconnected". That should not be taken as hard truth because shutdown codes have been remapped and indicate different things overtime from what I understand. Additionally, more codes are added while others are removed. So, here is a full list of all of the codes I have been able to piece together over the years (I know there are some codes I am missing) :

Software Codes

	1            Power adapter disconnected
	3            Dirty Shutdown/Sleep resulting from forced restart or shutdown
	5            Clean Shutdown/Sleep initiated by the user
	6            Undocumented, system initiated
	9            Undocumented, system initiated

Intermediate Codes

	0            Sudden loss of power or SafeSleep initiated by system

Hardware Codes

	-3           Multiple temperature sensors too high
	-60          Bad master directory block, serious disk error
	-61          Unresponsive app resulting in forced shutdown
	-62          Unresponsive app resulting in forced shutdown
	-64          Kernel panic, probably due to Firmware issue
	-71          Memory too hot
	-74          Battery too hot
	-75          MagSafe power adaptor communication problem
	-78          Incorrect input current from power adapter
	-79          Incorrect current from battery
	-86          Proximity temperature (heatsink, etc) too high
	-95          Proximity temperature (heatsink, etc) too high
	-100         Power supply too hot
	-101         Display too hot
	-103         Battery voltage too low
	-104         Unknown battery fault
	-127         SMC/PMU forced shutdown for another cause
	-128         Unknown, possibly battery at the end of its life, but can also occur when the SMC initiates an automatic restart following a kernel panic; or last reason was not logged

If anyone has additional codes they are willing to share, please comment or send me a PM 👍🏻

Hope that helps,

Patrick

Hey Tran Thien Duy,

Thanks for replying back!

The next step would be to contact Apple Support directly for further help on this issue.

Contact Apple Support

Have a great day!