@f1ee7a25 You reinstalling from the installer on the recovery partition, from an external drive, or from internet recovery? 

 @531f5a72 Recovery partition on the computer itself. WiFi is connected. 

 @f1ee7a25  Try starting up with Option-Cmd-R, and see what Internet Recovery gives you. It might be failing because the old installer on your recovery partition isn't signed any longer. 

 @531f5a72 thank you - will try that next! 

 @531f5a72 Internet recovery doesn't seem to be working either, I think the hard drive may be failing (although it does boot, this could explain why it was dumped!) 

 @f1ee7a25 What does Disk Utility say? Maybe boot recovery mode again and do a check. 

 @531f5a72 disk utility gives a clean bill of health - but I don’t believe it! 

 @f1ee7a25 What’s the error code the install is throwing again? 

 @531f5a72 There’s no error code I can see. Does this every time at -399 seconds:

https://files.mastodon.social/media_attachments/files/111/186/477/478/299/932/original/988c3b1cb668379a.png 

 @f1ee7a25 Okay, so it’s in the setup stage, hasn’t properly started replacing files yet, and it isn’t throwing an error code. Tell you what, boot recovery mode and rePARTITION and reformat the drive, then try an install again. I feel like there’s something locked or corrupted or something that’s making the installer fail when it begins trying to manipulate files on the drive. 

 @531f5a72 I'm trying re-setting the parameter RAM next, then will look at partitioning. (My attempts to make a bootable Sierra install USB pen drive have failed also.) 

 @f1ee7a25 Yeah, with the later versions of macOS, you need to install a full environment to an external hard drive and then boot the target machine from that, then install to the internal drive from an downloaded installer on the external. Lots of problems trying to just do it from a pen drive. 

 @531f5a72 Ah that's interesting - bit of pain but I might give that a go. Partitioning in half didn't work - one half gave same errors as before, other half gives odd App Store type download failure errors. I wonder if there are TWO issues going on here, faulty drive AND something with certificates. 

 @f1ee7a25 I'm wondering whether it might be bad piece of RAM, or possibly a mainboard issue.You could try installing Ubuntu on it, see whether their hardware diags report anything. Linux tends to be more transparent than macOS about what state the hardware is in. 

 @531f5a72 Oh that's a thought! Thank you, I'll have one more crack at installing MacOS from an external drive then look at that. 

 @f1ee7a25  Don't forget, be booted from the external to install. 

 @531f5a72 Roger! 

 @f1ee7a25 if it's failing at the end - after the file copy process is complete - i'm guessing that it's the drive itself that's failing, which is the most common thing on the 2011's (almost all with the same trashy 1TB seagoat). iirc, os x does some heavy cleanup at the end of the process which might be hitting some bad sectors on the hdd.

if it was an old (out of date, signature expired) installer, it would have failed at the start of the install instead.

mercifully, these use zero glue on the glass bezel - just magnets, and replacing the hdd is a 20 minute job! 

 @5ad750c8 Ah - that's interesting, thank you. I did run Disk Utility which came up as ok. But disk failure sounds very plausible. 

 Not expecting this to work, but as local and internet Sierra recovery options aren't working, I've got it to boot off a Snow Leopard install DVD. Here goes nothing. Very slowly...

https://files.mastodon.social/media_attachments/files/111/184/593/248/406/839/original/5ff582705e0ce42c.jpeg 

 ...as expected...

https://files.mastodon.social/media_attachments/files/111/184/659/678/161/665/original/fc69d9ddada0b04a.jpeg 

 I wonder if this is relevant. Resetting the NVRAM may be worth a try?

https://files.mastodon.social/media_attachments/files/111/186/292/405/887/134/original/f1e11599c5ffa4b3.png 

 Parameter RAM reset didn't make any difference. Tried partitioning the disk, one fails as before, the other has given two new error messages so far. WiFi is connected, it's impossible to run the installer without internet.

https://files.mastodon.social/media_attachments/files/111/187/208/401/598/853/original/46a45a93ea46e634.jpeg

https://files.mastodon.social/media_attachments/files/111/187/208/973/282/492/original/eb22b52d900aea99.jpeg 

 @f1ee7a25 

Try a live Linux session from a USB key and do an analysis from there?

I'm sure you can work what is going on with the disk and partitioning in a live sess. 

 @fcdb09df The issues feel very Mac-specific to me, I'm not sure even if I could boot it to Linux it would help. Disks all need to be in Mac format. 

 @f1ee7a25 @fcdb09df Do you have a spare external drive? You can boot it from a good copy of MacOS that was prepared on another machine. 

 @eb057e21 Good thought, I'll see if I can find a spare external disk drive and see if I can install the OS to that, reboot off it and use that to prepare a new install on the internal drive 

 @f1ee7a25 How many swears so far? 

 @7e2b7c22 Well new error messages has to be progress, right? 

 Found an old Firewire drive at the back of a drawer - will this faulty iMac let me install Sierra on to it, since it won't let me install it on the internal drive?

https://files.mastodon.social/media_attachments/files/111/190/005/729/934/778/original/dcd00fd9afb9cd83.jpeg 

 Will it heck as like. This iMac is cursed. I am starting to see why someone left it out for the refuse collection.

https://files.mastodon.social/media_attachments/files/111/190/096/059/848/602/original/97b8f2ca217cd6d6.jpeg 

 @f1ee7a25 anything in this? https://www.reddit.com/r/MacOS/comments/1030a4g/need_help_with_this_an_error_occurred_while/ 

 @f1ee7a25 Quick diagnostic: when you chose 'About this Mac' do you get a big spinning pentangle that can't be force-quit? And is there a kind of acrid blue smoke from the rear air vents? 

 @4d809b9a and the last install just failed with -666 seconds remaining…