Looking for some help please.

I am preparing my 2014 MacBook for a trade in. I followed the instructions that Apple sent but failed on the 'turn FileVault off' stage. I did this, but my prediction now is that at some point during the process my battery went flat as everything I'm reading implies that my disc is still encrypted.

I booted up into recovery mode to complete the Erase Hard drive and reinstall MacOS process. Using Disc Utility I then erased the top disc it showed me - 251 GB Apple SSD SM0256F Media.

I then went to erase the 2nd disc it showed Mac OS X Base System (which shows 1.15GB used) However I am unable to erase this in Disc Recovery. In the Erase tab the 'erase free space' / security options / erase buttons are all greyed out.

How can I erase this disc? Presumably this is what I need to reinstall MacOS as currently when I try to run reinstallation from disc recovery no disc shows in the installation dialog

Thanks so much

1 Answer 1


The Base System (& the potential 20 or so tiny volumes you may be able to see below that) are part of your current Recovery session. You cannot erase them - nor do you need to. They are ephemeral & will disappear once you again boot to a normal OS.

You install your new OS to the main drive, once it has been erased.

  • Unfortunately when I go to install the OS no disc shows up as a place to install. The base system seems to contains all my data as it only has 1gb free rather than the full disc.
    – trixiek
    Dec 25, 2020 at 18:32
  • When you initially erased the SSD, precisely what format did you use? Also, what version of macOS is Internet recovery offering?
    – Tetsujin
    Dec 26, 2020 at 8:39
  • As per the instructions on my trade in sheet I believe I did APFS, Internet Recovery is trying to install 10.8 Mountain Lion. The main drive is showing itself as Not Mounted. The base system is showing Format Mac OS Extended, 10k+ folders, used 1.15gb, available 38mb. Thank you!
    – trixiek
    Dec 29, 2020 at 15:55
  • Mountain Lion cannot see APFS at all; it has no idea what it is. You will need to reformat the entire internal drive GUID/HFS+ (mac os extended, journaled) Leave the Base System alone, that's your temporary structure used for recovery.
    – Tetsujin
    Dec 29, 2020 at 15:58
  • 1
    All sorted. Thank you so much for saving the day Tetsujin!
    – trixiek
    Dec 30, 2020 at 22:28

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .