Boot failure High Sierra imac 2011 mid

Hi BD Aqua,

thanks for your mail. Unfortunately after the new installation this only worked for 2 reboots. I have found another way. This now seems to have worked.

1)Restart your Mac and hold down Command-R to start up from macOS Recovery.

2)If the startup drive has FileVault turned on, open Disk Utility and proceed with the next step. If FileVault is off, skip to step 4.

3)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.

4)Choose Utilities > Terminal from the menu bar.

5)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.)

6)Press Return.

7)Type this command in Terminal:

mv ./mbr_cache ./mbr_cache-old

8)Press Return.

9)Quit Terminal.

10)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.