Using the macOS High Sierra OS installer’s startosinstall tool to avoid APFS conversion

As part of the upgrade process to macOS High Sierra, Apple has stated that certain drives will be converted from using the HFS+ filesystem to Apple’s new default filesystem, APFS. The conversion criteria is shown below:

For those Mac admins who don’t necessarily want to convert yet, there is a way to configure the macOS High Sierra OS installer to skip the APFS conversion. For more details, please see below the jump.

Apple includes a command line tool named startosinstall as part of the macOS High Sierra OS installer application, inside Install macOS High Sierra.app/Contents/Resources.

This tool has several options, including a –converttoapfs option which allows control over the APFS conversion process.

	computername:~ username$ "/path/to/Install macOS High Sierra.app/Contents/Resources/startosinstall" –usage
	Usage: startosinstall
	Arguments
	–applicationpath, a path to copy of the OS installer application to start the install with.
	–license, prints the user license agreement only.
	–agreetolicense, agree to license the license you printed with –license.
	–rebootdelay, how long to delay the reboot at the end of preparing. This delay is in seconds and has a maximum of 300 (5 minutes).
	–pidtosignal, Specify a PID to which to send SIGUSR1 upon completion of the prepare phase. To bypass "rebootdelay" send SIGUSR1 back to startosinstall.
	–converttoapfs, specify either YES or NO on if you wish to convert to APFS.
	–installpackage, the path of a package to install after the OS installation is complete; this option can be specified multiple times.
	–usage, prints this message.
	Example: startosinstall –converttoapfs YES
	computername:~ username$

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To run an automated upgrade to macOS High Sierra, where the APFS conversion is skipped, please run the command shown below with root privileges:

/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --applicationpath /Applications/Install\ macOS\ High\ Sierra.app --agreetolicense --converttoapfs NO --nointeraction

Note: The –nointeraction flag is an undocumented option to automate the installation process from the command line without additional requiring actions by the logged-in user.

To show what the process looks like when upgrading from macOS Sierra, please see below for a video.

Note: This video has been edited to artificially reduce the amount of time the upgrade process takes to run. Run time of the pre-edited video was 19 minutes 38 seconds.