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I'm having the following problem.

When I try to boot my MacBook Pro 13" mid 2009 with "El Capitan" installed from my internal HD, a prohibition sign appears on the screen and eventually my mac turns off. I have an external HD with El Capitan installed and it boots nicely. When I try to repair the volume on Disk Utility I get the following message

enter image description here

I can use the terminal to force unmount the volume and then repair it. But after that, when trying to repair it again I get the same mistake, and also the HD still won't boot. I have discarded a defective SATA cable and a corrupted HD since I'm able to copy files from the HD to my bootable HD without problem, so I'm guessing this issue is software related.

Any help would be most welcome.

Update: When I use first aid on the main drive I get the following message:

enter image description here

Even after doing that, the partition won't boot or unmount for repair.

Luis Vera
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  • Is it an SSD or an HDD? What is the S.M.A.R.T status? – NoahL Apr 11 '17 at 21:11
  • @NoahL It is an HDD, I don't know how to look for the S.M.A.R.T status? – Luis Vera Apr 11 '17 at 21:13
  • Select the disk (where it says "ST1000LM014-1E...") and look in the bottom left corner of the information grid – NoahL Apr 11 '17 at 21:14
  • @NoahL It says: Verified – Luis Vera Apr 11 '17 at 21:16
  • Try running first aid on the entire disk instead of just the partition – NoahL Apr 11 '17 at 21:16
  • @NoahL Ok, Updated question with added picture of first aid on disk and explanation. – Luis Vera Apr 11 '17 at 21:20
  • If you don't mind waiting a bit for the installation, is there any reason not to install the OS from the bootable flash drive you have? – NoahL Apr 11 '17 at 21:22
  • @NoahL Not at all, the thing is that I already did that one time, and after a week or two, the problem returned. So I want to know what might be the cause of it. I have an external enclosure and the HD still won't work with it. But I'm puzzled, since I can copy files from it to my external HD without problem. – Luis Vera Apr 11 '17 at 21:26
  • @NoahL When I change permissions (from read only to read&write) I get error code -50, I'm able to copy files from it but not to copy files to it (also get error -50). – Luis Vera Apr 11 '17 at 21:29
  • See this answer. A prohibitory sign means your install is corrupted. No amount of repairing permissions is going to fix corruption. It's like giving you a new set of keys to a building that was just gutted by a fire... How and why it got corrupted is another matter - your drive could be failing. See this answer to find out if drive failure is the case. – Allan Apr 11 '17 at 21:42
  • In case you wanted a second opinion, I totally agree with @Allan on this, not only with his comment above but with his answers (linked to in his comment). If it was me I'd replace the internal drive. – Monomeeth Apr 12 '17 at 00:01
  • @Monomeeth than you both for your comments. I will certainly replace my HD, I cannot trust this one. Nevertheless, I would like to know for sure that the problem lies on it. I am going to reformat it and reinstall Mac OS. If it works, can I be sure that the problem isn't the HD? Or how can I make sure? – Luis Vera Apr 12 '17 at 00:32
  • @LuisVera - You said in your question that you are able to boot off an external drive. Do so, then install and run Disk Drill (the diagnostic tools are free). It will do an in depth scan of your drive - much "deeper" than what the SMART status provides. – Allan Apr 12 '17 at 10:34
  • @Allan thank you! I did reformat my HD and reinstalled Mac OS and it is working (i'm currently booted on in), but I will still look at Disk Drill for any Hard Drive failure – Luis Vera Apr 12 '17 at 20:03

1 Answers1

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I'm assuming that the partition Backup OS X on your external drive is a bootable partition.

Turn on the Mac and hold down the option key. This will show you all the bootable partitions that the Mac can find. If the partition Internal HD in your internal drive does not show up then EFI has not discovered the required files for a boot partition and the OS on it can be considered damaged and should be replaced.

From what you describe I suspect some sort of damage to the low level formatting of the partition.

At this point I would boot from another partition and use Carbon Copy Cloner or a similar tool to backup the damaged partition and then erase and reformat the entire drive before installing a new System or a known good backup.

Tony Williams
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  • When you "clone a damaged partition" you clone the damage. Your best bet is to backup and if necessary, data recovery. – Allan Apr 12 '17 at 10:36
  • @allan - You certainly do, but a backup will probably do the same thing. Note I didn't recommend using the clone, merely making one before nuking the drive and starting again. The clone gives him the chance of recovering any files he may require. – Tony Williams Apr 13 '17 at 11:24