Mounting the EFI Boot Partition on Mac OS X

terminalHere’s the answer to another reader request…

According to WIkipedia, “On Apple–Intel architecture Macintosh computers, the EFI partition is initially blank and not used for booting. However, the EFI partition is used as a staging area for firmware updates.”  When people look to create non-standard boot environments or attempt to build a hackintosh, the first step is often mounting and modifying the EFI boot partition.  Before you read any further, take note: altering your EFI boot partition is not supported by Apple and The Mac Admin takes no responsibility if you render your computer(s) unbootable by mounting and modifying this partition.

To mount an EFI boot partition, follow these steps:

1. Discover the volume identifier for your EFI boot partition.

Run this command:

diskutil list

The output should look something like this:

/dev/disk0
 #: TYPE                     NAME          SIZE       IDENTIFIER
 0: GUID_partition_scheme                  *251.0 GB  disk0
 1: EFI                                    209.7 MB   disk0s1
 2: Apple_HFS                Macintosh HD  250.1 GB   disk0s2
 3: Apple_Boot               Recovery HD   650.0 MB   disk0s3

 

In this case, the volume identifier of the EFI partition is disk0s1

2. Create a mount point.

A mount point is a directory where a non-booted volume is mounted.  On Mac OS X, mount points are typically created in /Volumes.  We can create a directory called efi within /Volumes by running the following command:

mkdir /Volumes/efi

 

3. Mount the EFI partition at the efi mount point.

Run the command:

sudo mount -t msdos /dev/disk0s1 /Volumes/efi

 

That’s it.  Your EFI volume will be mounted.  Modify it at your own risk.