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macrumors newbie
Original poster
May 17, 2017
Help please! I have iMac 2011, get it last year from craigslist with El Capitan on that moment. Upgraded to Sierra recently. Then decided to erase disk and reinstall. But now I cannot because it shows that disk is locked.

Here are details.

1. I restarted iMac

2. No keys need to be pressed/hold - it goes directly to macOS Utilities with a 4 options: Restore from Time Machine Backup (I don't have backup), Reinstall macOS, Get Help Online, Disk Utility

3. I select Reinstall macOS, then Continue

4. Opens window macOS Sierra, where I click Continue

5. After clicking Agree with license agreement it goes to next window

6. Here under macOS Sierra I see label "Select the disk where you want to install macOS" and 2 disk icons: OS X Base System (499 GB) and Recovery
HD (650 MB). BTW, sometimes after restarting second disk Recovery HD doesn't appear here

7. When click on OS X Base System disk icon, it shows warning :"This disk is locked."

8. If click on next icon with Recovery HD, it just shows what arrow with no label

9. Anyway, Install -> button never gets enabled

10. The only way too get out of this installation screen is to restart iMac

11. After restarting and getting macOS Utilities, I go to Disk Utility

12. Screen shows one Internal disk: ST3.....Media, when expand, shows disk icon OS X Base System

13. If OS X Base System is selected, only first tab "First Aid" is enabled on Disk Utility, rest - Partition, Erase, Restore Unmount - are disabled. If running first aid, no errors shown up

14. If disk ST3..... Media is selected, it enables also second tab Partition

15 . From here you cannot click add(+) because it's disabled..

Any help will be gratefully appreciated


macrumors Penryn
Feb 20, 2009
Get a USB flash drive, 16gb or larger.

Create a bootable installer on the flash drive using either:
1. Install disk creator
2. Diskmaker X
3. The terminal

Boot from the installer flash drive.

Re-initialize the internal drive (so you start "from scratch")

Install onto the re-initialized drive.
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