Apple has long offered two versions of the same HFS+ partition formatting scheme used to create a filesystem for a Mac-mountable volume: “Mac OS Extended (Journaled)” and “Mac OS Extended (Case-sensitive, Journaled)”. With the addition of APFS formatting, that flavor is also available in case sensitive and insensitive versions. What a difference that “case-sensitive” makes!
Case-sensitive filesystems can allow multiple files to have the same human-readable name using different capitalization.
Blue dolphin.pdf and
blue dolphin.pdf and
bLuE dOlPhIn.PDF are all considered different items to a case-sensitive filesystem. With the opposite, a case-insensitive filesystem, the default option for macOS in HFS+ and APFS, those files can’t co-exist: They’re all effectively the same name with a different appearance.
In olden Unix days, case-sensitivity made sense in some contexts, and Apple offered a case-sensitive version of HFS+ for compatibility’s sake for those people who required it.
However, some Mac software—notably that made by Adobe and Valve—balks at case sensitivity. I’ve heard from and read of people who accidentally chose “case-sensitive” when setting up a drive, not realizing what they were getting themselves into. They’d like to shift off that into the more standard case-insensitive format.
While there was software in the past that could convert a case-sensitive partition to a case-insensitive one in place without copying the data off, the firm that made that software has shut down. (Coriolis Systems was a long-time Mac developer, and they
generously made all their software free on closing. However, the last supported version of macOS is 10.13. Because this involves filesystem-level changes, I would not use this software with 10.14 Mojave or later.)
Instead, you have to make a clone, reformat your partition, and copy the data back. For a startup volume:
Clone the drive that has case-sensitive formatting to another volume using Disk Utility, SuperDuper, or Carbon Copy Cloner. (You could use Time Machine, but it’s an inefficient way to restore an entire disk except in a pinch.)
Make sure you have a separate, complete backup in case the one created in step 1 fails.
Restart your Mac, and then hold down Command-R before the Apple logo appears to bring up macOS Recovery.
Click Disk Utility in the list of options that appears.
Select the internal drive or boot partition in the list at left.
Reformat it using a case-insensitive option.
Right-click it and select Restore.
From the Restore From popup menu, select your clone. If it’s a disk image, click the Image button to find it on a mounted drive.
Click Restore and be prepared to wait a long while!
When the restoration is complete, exit Disk Utility and select > Startup Disk.
Select the drive to which you restored your clone, and then click Restart.
If you’re copying an external or non-boot volume, you can omit steps 3 and 4 above and launch Disk Utility from your Mac in the Applications > Utilities folder.
By the way, you have of course noted that OS X and macOS have always retained the capitalization you use in names as you type it in or a program names it. That’s because the system is case preserving: It honors capitalization, but any variation in lower- and upper-case is ignored in finding a file or overwriting it.
This Mac 911 article is in response to a question submitted by Macworld reader Sebastian.
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