I have a MacBook Air that has suddenly stopped booting at all. I booted into recovery mode and see the harddrive fine in Disk Utility. The partition is there as well marked: Mac OS X Base System. I can verify this partition with Verify Disk. The disk verifies just fine and appears to be ok.

However when I go to set it as the startup disk (in Choose startup disk), it doesn't show. I get a blank list.

What gives? How can the disk be seen by Disk Utility but not Choose startup disk?

Other things attempted:

  • ⌥⌘RP to reset PRAM (reset the box)
  • Shift on boot for safe mode (did nothing)
  • What's the write status in disk utility of the HD? – jason May 19 '13 at 0:59
  • Did you do system updates or install anything (or do anything else, such as change partitioning, etc.) just before this happened? Try to remember everything between reboots when it worked and then didn't. – nerdwaller May 19 '13 at 0:59
  • @nerdwaller no installs or updates. Computer froze solid while surfing the net. Held the power button after it became clear it was not going to recover. Then the problem started. – Fresheyeball May 19 '13 at 1:12
  • @Jason how do I do that/what do you mean? – Fresheyeball May 19 '13 at 1:13
  • @Fresheyeball click on the hard drive (the one you boot from) and look at the bottom of disk utility where the info on the disk is listed. Here's a [link]picture(cosmicpi.zapto.org/pub/docs/Screen_Shoot.png) – jason May 19 '13 at 1:21

Mac OS X Base System is the volume for the recovery system. Disk Utility should normally also show the Macintosh HD volume and disks in the sidebar.

If the Macintosh HD volume or the disk it is on is shown in the sidebar, try repairing them. The Repair Disk button performs completely different operations depending on whether a disk or a volume is selected. If the disk is not shown in Disk Utility, it could be a hardware issue.

According to a related question, resetting the SMC might help.

If the disk with the Macintosh HD volume is shown in Disk Utility, you can try to back it up by pressing the New Image button and saving the dmg file to an external disk. You can try to do an upgrade install or reinstall OS X from the recovery partition:

  • If you don't erase the Macintosh HD volume, the Reinstall OS X option does an upgrade install, or it downloads an OS X installer and replaces system files with the default versions.
  • If your erase Macintosh HD from Disk Utility first, Reinstall OS X does a clean reinstall.

Related questions:

  • Yeah, I get it now. The partition (labeled in your example as Macintosh HD) was not on the list. It's like the mac completely forgot it had the partition at all. I ended up reformatting and reinstalling osx. Working fine now, but I don't feel good about it. – Fresheyeball May 19 '13 at 18:14

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