my entire HD is now "Mac OS X Base System":

enter image description here

ps: Mac OS X Base System is Disk0s2

I cant delete this partition to install Mac OS X; I already try the terminal, but message reply "you cannot erase the boot disk".

Does anyone have any idea how can I fix this?


Probably your pMBR/GPT got corrupted or the Base System is somehow mapped falsely. Usually the first partition (EFI) and the last partition (Recovery HD) aren't visible. Additionally a freshly erased disk0s2 ususally contains ~200 MB and not 1.4 GB (which is "by accident" the uncompressed size of a Base System).

The best thing is to completly erase the internal disk by whether:

  1. Booting to Internet Recovery Mode by hitting altcmdR immediately after the start chime, repartitionung the internal HDD to one partition and installing a new system.


  1. Attaching a thumb drive and installing a fresh system there. After rebooting from the thumb drive, repartition the internal HDD and install a fresh system to the internal disk.

In both cases the invisible EFI partition will be build automatically as well as the Recovery HD while installing a new system.

| improve this answer | |

There is nothing to delete here.

You are currently using 1.5 Gig and you have 497 Gig free.

Just install the new OS X.

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  • The base system is locked, I cant install. – DHEKU Mar 30 '15 at 14:01
  • Locked by whom ? – Ruskes Mar 30 '15 at 16:30

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