Resizing a macOS VM’s APFS boot drive to use all available disk space

A while back, I wrote a post on how to resize the boot drive of an existing virtual machine. However, that guidance only applies to a boot drive that uses HFS+ for its filesystem.

Now that Apple File System (APFS) is available and the default file system on macOS High Sierra, a different procedure must be used in order to resize the APFS-formatted boot drive of an existing virtual machine. For more details, see below the jump.

For an APFS boot drive, you need to do two things:

1. Identify the appropriate APFS container:

APFS containers act as storage pools for APFS volumes. APFS volumes are what act as the mounted filesystem, where you store your files, directories, metadata, etc. When you grow the APFS container, the APFS volumes will likewise get additional space.

To identify the container for the boot volume, use the diskutil command shown below:

/usr/sbin/diskutil info / | awk '/Part of Whole/ {print $4}'

2. Once the appropriate APFS container has been identified, use the diskutil command shown below to resize the container with all available disk space.

Note: You can specify a size of zero (0) to grow the targeted container using all unallocated drive space.

/usr/sbin/diskutil apfs resizeContainer /dev/apfs_container_id_goes_here 0

In this example, I have a VM where my APFS-formatted boot drive is using 42.7 GBs of space, but the VM disk has 85.9 GBs of available space.

Assuming that the command above gave us disk1 as a result, the command shown below can be used to resize the boot drive’s APFS container with all available disk space.

/usr/sbin/diskutil apfs resizeContainer /dev/disk1 0

Once the container resizing has completed, the OS should now recognize and be able to use the newly-allocated space.

I’ve updated an existing script to identify if a boot drive is running HFS+ or APFS, then run the appropriate diskutil commands for that filesystem. It is available below and on my GitHub repo:

https://github.com/rtrouton/rtrouton_scripts/tree/master/rtrouton_scripts/resize_vm_boot_partition

This script is also available as a payload-free package on my GitHub repo, available for download from the payload_free_package directory available from the link above.

	#!/bin/bash
	# This script is designed for use with virtual machines which
	# need to resize their boot volumes. The script checks the boot
	# volume using the diskutil info command and detects if the boot
	# volume is using HFS+ or APFS for the boot volume's filesystem.
	#
	# If the boot volume is using HFS+ for its filesystem, the
	# diskutil resize command is used to assign the boot volume
	# all available free space.
	#
	# If the boot volume is using APFS for its filesystem, the
	# diskutil info command is used again to get the appropriate
	# APFS container ID. Once the container ID is available, the
	# diskutil apfs resizeContainer command is used to assign the
	# boot volume's host container all available free space.
	ERROR=0
	boot_filesystem_check=$(/usr/sbin/diskutil info / | awk '/Type \(Bundle\)/ {print $3}')
	if [[ "$boot_filesystem_check" = "hfs" ]]; then
	# Use the diskutil resize command to assign
	# all available free space on the drive to
	# the HFS+ boot volume.
	/usr/sbin/diskutil resizeVolume / R
	elif [[ "$boot_filesystem_check" = "apfs" ]]; then
	# Get APFS container ID on boot drive
	apfs_container_id=$(/usr/sbin/diskutil info / | awk '/Part of Whole/ {print $4}')
	# Use the diskutil apfs resizeContainer to
	# assign all available free space on the
	# drive to the APFS boot volume.
	/usr/sbin/diskutil apfs resizeContainer /dev/"$apfs_container_id" 0
	else
	echo "Filesystem detected: $boot_filesystem_check"
	echo "Unknown filesystem on boot drive."
	echo "Exiting with error."
	ERROR=1
	fi
	exit $ERROR

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resize_vm_boot_partition.sh

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