The current understanding seems to indicate that "all SSD" machines will have at least their main/root file system converted to APFS on the install of High Sierra.

That means HFS+ is still a viable boot file system (as it was during testing the beta on an external rotational drive). I want to keep HFS+ for now.

How do I force a full default install, including Recovery HD, onto an "all SSD" MacBook Pro that keeps HFS+ as the only file system?

  • Why not use the new APFS file system if your Macbook has an SSD? Mine upgraded fine and the new APFS file system does seem a lot faster for me. – MitchellK Oct 15 '17 at 14:02
  • Backwards compatibility, cross-platform compatibility, .0-avoidance, let others beta-test it, conflicting benchmark infos so far. Documentation for APFS still quite underwhelming. Zaphod plays it safe. – LangLangC Oct 15 '17 at 14:07
  • Understood :) new file systems can be troublesome, lucky to report no issue discovered (yet) with APFS but it's still early days. – MitchellK Oct 15 '17 at 14:08
  • @MitchellK : a few security weaknesses, a few migration problems, basic problem with any irreversible conversion. – daniel Azuelos Apr 29 at 21:06
up vote 10 down vote accepted

It should work by exiting any High Sierra installer GUI and starting the install from the command line:

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

Further install options can be obtained by using the --usage argument:

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.
--volume, path to the target volume.


Sources report that the command (in the Beta version) doesn't do anything on the first execution but on the second.

  • Are there filed reports back now that it's not officially beta anymore? And what about using this option from a bootable stick (createinstallmedia)? – LangLangC Oct 6 '17 at 13:19

Read here how to do it with ....startosinstall.... https://derflounder.wordpress.com/2017/09/26/using-the-macos-high-sierra-os-installers-startosinstall-tool-to-avoid-apfs-conversion/ an easy solution, from a very experienced source.

  • Nice mention in the article of the undocumented –nointeraction flag "to automate the installation process from the command line without additional requiring actions by the logged-in user". – Alex Ixeras Oct 15 '17 at 10:37

One method to prevent an automatic conversion when installing High Sierra is to redirect the install onto an external drive first.
(Or a traditional HDD on larger desktop machines and laptops that were modified to have these drives in addition to SSDs.)

From the external drive this installation can then be cloned back to the main internal boot drive (preferably after the boot drive is erased). Once the clone is back on an SSD the filesystem will stay at HFSplus.

If the goal of the whole procedure is a "clean install" anyway then this is less of a detour as it may seem. It might be actually faster in this way, if the options involve a slow USB-stick you have to prepare for this with createinstallmedia and then install from there vs. first installing onto a very fast external drive. [That same possible advantage may be desired when someone wants multiple machines to upgrade to High Sierra. See update2 below]

No external drives will currently be converted to APFS when installing macOS 10.13.

No-one really knows for how long this principle will hold true but currently this is the case for both kinds of drives: rotational magnetic and solid state drives.

Since this is met with so much opinion, others suggest:

Safest way to upgrade to macOS High Sierra without APFS

The way that I strongly suggest doing this is the safest and easiest. Safest because if something goes awry, the upgrade can be dropped without changing what you already have:

  1. Clone the boot drive to any spare external drive.
  2. Boot off the spare/clone.
  3. Upgrade the spare/clone. The updater will leave the file system alone—it won’t be converted to APFS.
  4. Boot off the now updated spare/clone. Check things out and verify that things are working to your satisfaction—and don’t rush this. Make sure everything is acting right and that everything you normally do is OK as well.
  5. Satisfied? Clone the now updated external to the original boot drive.
  6. Boot from the original boot drive (now updated).

By doing it this way, there is no change to the existing boot drive until you explicitly choose to clone back over it with the updated system.


Please note that a "clean install" is different from the in-place upgrade now often preferred by users: a clean install means that previous programs, settings and data should be erased (via formatting) before the new installation is cloned back and therefore have to be restored afterwards either manually or with Migration Assistant.
While a clone of a fresh install may be performed similar like an upgrade – just on top of whatever is on your boot drive – this method is not advisable. Formatting the internal boot drive before cloning back the new and fresh install ensures that the internal drive is in just the same "really fresh install" condition that is the primary goal of performing a "clean install".


Update2: Upgrading multiple machines in this way is not recommended by Apple anymore, since firmware updates are now rolled into the installer. Unless we figure out how the firmware updates are to be applied manually. Although this issue seems to be more pressing with APFS installations than with HFS+ as outlined in the question.

The clone route outlined above is currently only recommendable for upgrading a single machine (where a firmware upgrade will take place) or re-installing the operating system on machines that had the firmware updates coming with and in High Sierra already applied.

  • There is absolutely no need whatsoever to have to go through such rigamarole when a clean install can be done, from a USB Installer created from the Install macOS High Sierra.app, using e.g. .../startosinstall --converttoapfs NO from the booted USB drive. – user3439894 Oct 6 '17 at 15:59
  • 100% correct for "no need". It is an option. And "Install to stick" or "createinstallmedia" both take some time. That's meant with "less of a detour". – LangLangC Oct 6 '17 at 16:02
  • Might be worth mentioning that cloning will delete the content of the main HD and all applications/user files/etc need to restored from backup afterwards. – nohillside Oct 6 '17 at 19:21
  • 1
    @user3439894 Unfortunately when you send the command the Installation begins. It doesn't modify the installer and then you can put it on USB. There must be a method to create the USB and then from within the installer set the flag for APFS conversion – Chriz74 Oct 9 '17 at 15:26
  • @Chriz74, FYI I did a clean install by downloading the 'Install macOS High Sierra.app' from the App Store, created a USB Installer using info in Apple's ht201372 document, then booted using the USB Installer. From there, I erased and repartition the SSD in Disk Utility, using HFS+, then in Terminal started the install keeping the HFS+ filesystem on the SSD. AFAIK There is no setup config file that you can set to keep HFS+ when starting the install from the GUI. Would having that be nice, sure, but it's no big deal to start the install from the command line if you don't want to convert to APFS! – user3439894 Oct 9 '17 at 16:02

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