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I have a MacBook with OS X on one partition, a few other partitions and a Bootcamp Windows 7 on another partition.

Right now, I can boot into Windows but I cant boot into OS X. I am typing this while using Windows as the host OS.

When I boot into OS X I get the prohibited sign, and boot into OS X via Safe Mode, I see hfs_mountroot failed: 5 cannot mount root, errno = 19

At first glance this seems to be an I/O issue, that my harddrive is dying or something, but the Windows partition works flawlessly.

So something has happened to the boot on that OS X partition. Other places on the net say the drive is done and that I need to image it or that I need the OSX startup disc but even then its a gamble. But I disagree since it is clearly that one partition that is having some issues with its boot protocol and not the entire hard drive.

To further illustrate my point, my Windows 7 has MacDrive installed, and I can browse all the files on my OS X HFS+ partitions!

With that in mind, is there anything I can do to get my OS X boot partition to work again? Thank you!

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Same problem with me. Mac OS Mountain Lion running on Machintosh HD partition. Suddenly one evening safari crashed and on reboot it was incredibly slow. It then stopped booting at all, giving me the "no" symbol. Various disk repairs and permissions repairs later (successful ones) it got worse. Refusing to boot at all and giving me the same error as above in safe mode: hfs_mountroot failed: 5 cannot mount root, errno = 19 It must be something wrong with the Mac partition as I have Windows 7 running smoothly on the other partition. Also, worth noting - the mac recovery partition also fails to bo –  user35597 Nov 28 '12 at 23:04
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2 Answers 2

What you may be able to try is running the fsck command in Single User Mode. As soon as you press the power button on your computer, press and hold Command+S until a terminal interface appears. When you see this: root:$ or something similar, type fsck -f and press enter. This will start a file system check which will most likely solve your problems. When it is finished, type reboot and press enter.

For my own curiosity, can you perhaps take a picture of the results? I'd be curious to see what it finds.

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I would boot from the OS X start up disc that came with your machine as a first step. From there you can launch Disk Utility and run "Verify Disk." Although it may not be a hardware issue, this is a good, safe place to start your diagnostic workflow from, since it does not involve any wipe or reinstall of your root OS. If Disk Utility reports that the disk is damaged, it may be able to fix the problem. See if that gives you any clarification or resolves your problem before anything else.
Good luck!

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