Follow these steps if a Mac running macOS High Sierra 10.13 stops at the startup screen that shows the Apple logo with a progress bar, and verbose mode shows a repeating message of "Too many corpses being created."
To use verbose mode, hold down Command-V immediately after pressing the power button to turn on your Mac, or immediately after your Mac begins to restart. If verbose mode shows the repeating "Too many corpses being created" message, you can allow the Mac to start up by moving a cache file:
Restart your Mac and hold down Command-R to start up from macOS Recovery.
If the startup drive has FileVault turned on, open Disk Utility and proceed with the next step. If FileVault is off, skip to step 5.
Select the startup drive and click Mount in the Disk Utility toolbar. When prompted, select a login name and enter the password. Then click Unlock to mount the startup drive.
Quit Disk Utility.
Choose Utilities > Terminal from the menu bar.
Type this command in Terminal: cd /Volumes/Macintosh\ HD/var/db/caches/opendirectory/ Modify the command to reflect the name of the startup volume if it's not Macintosh HD. Remember to use an escape character \ before each white space in the command path.
Type this command in Terminal: mv ./mbr_cache ./mbr_cache-old The mv Terminal command is safer than the rm command. Errant white space in an rm command can destroy the user's data.
Choose Apple () menu > Restart.
The first startup after running these commands takes longer than usual as the cache is recreated. Subsequent startups will take the normal amount of time.