com.apple.DiskManagement.disenter error: why your drive will not mount, and the order to try fixes

You plug in a drive, it shows up greyed out in Disk Utility, and clicking Mount gives Could not mount. (com.apple.DiskManagement.disenter error 49218.) or a similar number. The drive is detected, so the cable and port are fine. Something is stopping macOS from attaching the file system.

The number changes from Mac to Mac and from drive to drive. Do not spend long trying to decode it: the steps below are the same whatever it says, and they are in order from harmless to drastic.

1. Check whether a disk check is holding it

When a drive is unplugged without being ejected, macOS runs a file system check the next time it is connected. On large exFAT drives that check can run for a very long time, and while it runs the drive cannot be mounted. This is the most common cause, and the one that loses nothing.

ps aux | grep -i '[f]sck'

If you see fsck_exfat, fsck_hfs or fsck_apfs with your disk's identifier, the check is running. You have two choices: wait for it, which is the safer one, or stop it and mount the drive.

sudo pkill -f fsck
diskutil list external          # find the identifier, e.g. disk4s2
diskutil mount disk4s2

2. Mount it from Terminal and read the real message

Disk Utility hides the detail. diskutil sometimes says more, and log shows what the system tried.

diskutil mount disk4s2
log show --last 5m --predicate 'process == "diskarbitrationd"' | tail -40

3. Run First Aid

In Disk Utility, choose View, Show All Devices, select the volume, then First Aid. If it fails, our guide to Disk Utility First Aid failing covers what the failure messages mean.

4. Check the format is one this Mac can read

5. Only then, think about erasing

Erasing makes the drive mount again, but it removes everything on it. If the data matters and steps 1 to 3 did not work, stop here and recover it first. If the drive does not appear at all, that is a different problem: see external drive not showing up.

To avoid the error next time, eject drives before unplugging them. That one habit prevents most of the stuck checks that cause it.