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2011 iMac (A1312) – macOS install loops/fails on HDD & external SSD, Recovery broken – advice needed

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ryanjamesshaw

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Original poster
Title (use this):
2011 iMac (A1312) – macOS install loops/fails on HDD & external SSD, Recovery broken – advice needed

Post content (copy/paste):

Hi all,

I’m hoping for some expert guidance because I’ve hit a wall trying to get macOS back onto a 2011 iMac (A1312).

Machine details

  • iMac 27" Mid-2011 (A1312)
  • Original internal HDD (suspected failing)
  • External USB SSD available
  • SSD temporarily removed during some testing
  • Wired USB keyboard/mouse
What I’ve tried

  • Internet Recovery and local Recovery (10.11.4 and 10.13)
  • Clean installs of El Capitan and High Sierra
  • Date change in Terminal for certificate expiry (e.g. 2016)
  • Offline installs (no Wi-Fi connected)
  • Installing to:
    • Internal HDD (fails)
    • External USB SSD (also fails)
  • Bootable High Sierra USB created via multiple methods
Current symptoms

  • High Sierra installer starts but consistently fails near the end (often around “4 minutes remaining”) and reboots back to Utilities or installer loops.
  • El Capitan fails at “verifying / preparing installation”.
  • When booted from the High Sierra USB and trying to erase the internal HDD, Disk Utility reports:
    • “Could not mount disk after erase”
    • “File system formatter failed”
  • This makes me suspect the internal HDD is failing.
  • Installing to the external SSD still results in installer loops/errors.
  • Recovery environments seem unreliable / broken on this machine now.
What I’m trying to achieve

  • Ideally get any working macOS on this iMac (High Sierra preferred, El Capitan acceptable as a stepping stone).
  • Happy to:
    • Boot permanently from an external SSD, or
    • Replace the internal HDD with an SSD if that’s the only sane option.
  • I currently don’t have access to another Intel Mac, which makes creating a “known-good” installer harder.
Questions

  1. Is this a known issue on 2011 iMacs now (installer signing / firmware / recovery servers)?
  2. Is the failing internal HDD enough to explain installer loops even when targeting an external SSD?
  3. Is the only reliable path now:
    • Creating an installer from another Intel Mac, or
    • Using OpenCore Legacy Patcher even just to install stock High Sierra?
  4. Any confirmed workaround people here have used recently (2024/2025) to get macOS onto this model?
I’m comfortable with Terminal, hardware swaps, and patchers — I just want a path that actually works.

Thanks in advance to anyone who’s kept these machines alive.
 
When I installed an SSD in my 21.5" 2011 iMac several years ago, I had lots of problems doing a clean install to the drive. Didn't matter if I was using bootable installer or internet recovery. I don't know if the errors were exactly the same as yours, but what ultimately worked was to use the machine-specific install disks to put the factory OS on (10.6.6 in my case), then update to El Capitan using the software updater downloaded from Apple, then update again to High Sierra using the apple updater.

If you haven't tried installing from the machine-specific install DVD yet, I would give that a try.
 
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ryanjamesshaw said:
Title (use this):
2011 iMac (A1312) – macOS install loops/fails on HDD & external SSD, Recovery broken – advice needed

Post content (copy/paste):

Hi all,

I’m hoping for some expert guidance because I’ve hit a wall trying to get macOS back onto a 2011 iMac (A1312).

Machine details

  • iMac 27" Mid-2011 (A1312)
  • Original internal HDD (suspected failing)
  • External USB SSD available
  • SSD temporarily removed during some testing
  • Wired USB keyboard/mouse
What I’ve tried

  • Internet Recovery and local Recovery (10.11.4 and 10.13)
  • Clean installs of El Capitan and High Sierra
  • Date change in Terminal for certificate expiry (e.g. 2016)
  • Offline installs (no Wi-Fi connected)
  • Installing to:
    • Internal HDD (fails)
    • External USB SSD (also fails)
  • Bootable High Sierra USB created via multiple methods
Current symptoms

  • High Sierra installer starts but consistently fails near the end (often around “4 minutes remaining”) and reboots back to Utilities or installer loops.
  • El Capitan fails at “verifying / preparing installation”.
  • When booted from the High Sierra USB and trying to erase the internal HDD, Disk Utility reports:
    • “Could not mount disk after erase”
    • “File system formatter failed”
  • This makes me suspect the internal HDD is failing.
  • Installing to the external SSD still results in installer loops/errors.
  • Recovery environments seem unreliable / broken on this machine now.
What I’m trying to achieve

  • Ideally get any working macOS on this iMac (High Sierra preferred, El Capitan acceptable as a stepping stone).
  • Happy to:
    • Boot permanently from an external SSD, or
    • Replace the internal HDD with an SSD if that’s the only sane option.
  • I currently don’t have access to another Intel Mac, which makes creating a “known-good” installer harder.
Questions

  1. Is this a known issue on 2011 iMacs now (installer signing / firmware / recovery servers)?
  2. Is the failing internal HDD enough to explain installer loops even when targeting an external SSD?
  3. Is the onlyreliable path now:
    • Creating an installer from another Intel Mac, or
    • Using OpenCore Legacy Patcher even just to install stock High Sierra?
  4. Any confirmed workaround people here have used recently (2024/2025) to get macOS onto this model?
I’m comfortable with Terminal, hardware swaps, and patchers — I just want a path that actually works.

Thanks in advance to anyone who’s kept these machines alive.
Click to expand...
Hi ryanjamesshaw,
I have the 2011 12.2 which I purchased 3 years ago to update my slow 2007 24" core duo. I want to keep these old iMacs running to preserve functionality of Epson printer, Artixscan M1 and run Adobe CS5. As time passes getting OSX to run on these machines is hampered by Safari and icloud obsolescence which obstructs password verification amongst other issues.

Recently I have updated the drives and installed every OSX from Snow Leopard to High Sierra with many struggles,
so I can offer some possible help.

1. The 2011 iMac
From your analysis I would agree you must start with a new drive. Your external may be failing because the internal is faulty and that is the cause of all your difficulties. I installed a 2TB SATA Samsung Evo 870 which gives a real lift to speed at IOPS Read:565 Write:404. About 5x faster than HDD. The GPU, AMD 6970 on this computer is of dubious quality. If your screen has not yet failed you are fortunate in having a good GPU and upgrade can be justified. How much you wish to spend is up to you. Avoid iFixit and OWC as expensive and rely on Ali Express. There is nothing substandard in the tools etc. they sold to me.

This Ali Express toolkit is a bargain:
www.aliexpress.com

Bundle Deals 2.0

www.aliexpress.com www.aliexpress.com

With care you can easily install a new drive, HDD or USB. You need two suction cups:
https://www.aliexpress.com/item/1005006283586334.html?spm=a2g0o.productlist.main.8.4a7171c8t8LrUo&aem_p4p_detail=202602111945591944680562603750000124345&algo_pvid=24ac2786-b5c3-44d4-8a98-046540baa9cd&algo_exp_id=24ac2786-b5c3-44d4-8a98-046540baa9cd-7&pdp_ext_f={"order":"1138","eval":"1","fromPage":"search"}&pdp_npi=6@dis!AUD!3.69!3.68!!!17.91!17.86!@2101e2b617708679590534771eb0aa!12000036604197387!sea!AU!0!ABX!1!0!n_tag:-29910;d:b71d9286;m03_new_user:-29895;pisId:5000000200977695&curPageLogUid=YAjRcEyfJzA7&utparam-url=scene:search|query_from:|x_object_id:1005006283586334|_p_origin_prod:&search_p4p_id=202602111945591944680562603750000124345_2

This video shows the steps for upgrading:
www.ifixit.com

mid 2011 iMac Hard disk Replacement

if you have experianc with replacing drives on PC's this will be easy. If not, make sure to watch the video and there are some other things you...
www.ifixit.com www.ifixit.com

Very Important: Before dissembling iMac protect against static damaging power board by wearing silicon surgical gloves. While the iMac is apart, plug in power and observe the pilot lights on the Logic board.

This Manual is helpful: https://www.nodevice.com/service-manuals/pc/apple/imac-27-inch-mid-2011/620667#p47

2. OSX
I assume you want to get the latest OSX possible. This machine can access HighSierra via Internet Recovery. With OCLP I think it will run up to Sequoia.
So if you really want to use this slow but solid machine instead of buying a more recent computer, you will need to buy some tools and become a DIY technician. I found it worth the effort. Ultimately, do you wish to spend on upgrading costs or buy a later, faster computer with better interconnectivity speeds - again your decision.

3. Installation:
With a new drive installed, iMac Recovery will invite you to format drive and install High Sierra (original system), via Recovery and all should be sweetness and light.

Inform us of any problems.
 
Last edited:
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Just wanted to come back and say a proper thank you to everyone who helped.

After multiple installer failures, recovery issues, date certificate problems, disk erase errors, and more USB attempts than I care to admit, it’s finally up and running.

It turns out the machine isn’t a 2011 as I originally thought — it’s actually a Late 2009 iMac.

Specs:

  • 2.66GHz Intel Core i5
  • 16GB RAM
  • ATI Radeon 512MB
  • Now booting macOS High Sierra from an external SSD


High Sierra kept failing at around 4 minutes remaining with the familiar “application damaged” / install loop errors. After properly formatting and retrying several times, it eventually completed successfully. It now boots consistently into High Sierra. Restarts are a little slow, but completely stable.


Genuinely appreciate the help and patience here — without the advice in this thread I’d probably have given up on it.


Now I just need to figure out what I’m actually going to do with it… 😅
 
  • Like
Reactions: sahnert
ryanjamesshaw said:
Just wanted to come back and say a proper thank you to everyone who helped.

After multiple installer failures, recovery issues, date certificate problems, disk erase errors, and more USB attempts than I care to admit, it’s finally up and running.

It turns out the machine isn’t a 2011 as I originally thought — it’s actually a Late 2009 iMac.

Specs:

  • 2.66GHz Intel Core i5
  • 16GB RAM
  • ATI Radeon 512MB
  • Now booting macOS High Sierra from an external SSD


High Sierra kept failing at around 4 minutes remaining with the familiar “application damaged” / install loop errors. After properly formatting and retrying several times, it eventually completed successfully. It now boots consistently into High Sierra. Restarts are a little slow, but completely stable.


Genuinely appreciate the help and patience here — without the advice in this thread I’d probably have given up on it.


Now I just need to figure out what I’m actually going to do with it… 😅
Click to expand...

I have 2 iMac 2009 in my house.
One is in stock (various broken stuffs so I am not very keen to fix)
One is used by my son daily for web surfing, video watching. (Mac OS Monterey by OCLP, GPU upgraded to AMD Firepro M6100 4GB VRAM)

It's also good as an external display.
Video input port is miniDisplayPort.
 
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