What is the Preboot volume on my internal disk?

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zhouchenh Author

Level 1

21 points

What is the Preboot volume on my internal disk?

I found a volume named Preboot by running "diskutil list" in Terminal. I have no idea about what it is.

I recently upgraded to macOS 10.13, and I never saw this volume before.

Here's what I got by running "diskutil list".

/dev/disk0 (internal):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme 500.3 GB disk0

1: EFI EFI 314.6 MB disk0s1

2: Apple_APFS Container disk1 499.3 GB disk0s2

/dev/disk1 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +499.3 GB disk1

Physical Store disk0s2

1: APFS Volume Macintosh HD 425.2 GB disk1s1

2: APFS Volume Preboot 21.1 MB disk1s2

3: APFS Volume Recovery 519.9 MB disk1s3

4: APFS Volume VM 2.1 GB disk1s4

MacBook Pro (15-inch, 2017), macOS High Sierra (10.13)

Posted on Oct 11, 2017 9:27 AM

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Answer 1

Best reply

x64uk

Level 4

1,524 points

Oct 11, 2017 5:13 PM in response to zhouchenh

When you have an encrypted boot volume, you receive a log-in screen before the main OS boots and you have to authenticate to that in order for the encryption key for the boot volume to be released.

The preboot partition contains the code which handles that login, and then as keg55 says, hands off to the main OS (after unlocking the disk of course).

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Answer 2

Oct 11, 2017 5:14 PM in response to zhouchenh

zhouchenh wrote:

I found a volume named Preboot by running "diskutil list" in Terminal. I have no idea about what it is.

I recently upgraded to macOS 10.13, and I never saw this volume before.

Everything looks normal and as it should for APFS with macOS High Sierra.

You can get a better sense of the apfs container via terminal, copy and paste:

diskutil apfs list

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Answer 3

keg55

Level 6

11,743 points

Oct 11, 2017 9:48 AM in response to zhouchenh

It's a component of the APFS file system and may do some pre-boot housekeeping and security tasks, then hand off to the main boot partition.

You might want to Google what the Preboot component does.

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