fixing an unmounted exfat drive on macos

In case you ever forget to eject your external hard drive after a time machine backup and in case you are also using a partitioned drive with exfat but then it goes unmounted/missing, here is how to fix it.

What I saw after unplugging and plugging the drive back in, is only the TIMEMACHINE icon on my desktop, not the normal EXFAT and TIMEMACHINE like below:

I opened my terminal and ran:

sudo diskutil list

Entered my password and saw something like:

Ran:

sudo fsck_exfat /dev/disk2

But saw:

fsck_exfat: Opened /dev/rdisk2 read-only
** Checking volume.
** Checking main boot region.
   Main boot region is invalid.  Trying alternate boot region.
** Checking alternate boot region.
   Alternate boot region is invalid.
** The volume  could not be verified completely.

In hindsight, I think I was supposed to use the actual identifier for exfat, so I maybe should have ran:

sudo fsck_exfat disk2s2

What I tried instead was go into Disk Utility , at the time I only saw TIMEMACHINE, so I clicked on it so I can perform First Aid on it:

Before the disk utility even finished first aid, my EXFAT appeared again and mounted, I was able to access my files.

Beware First Aid on TIMEMACHINE may take a while, at least 30–40 minutes.