El Capitan! Come back!

[stinkhorn9]

Sorry for the staggering levels of ineptitude that will come to light here.

I have my mum's unwanted iMac (late 2015), which came with El Capitan installed. I wiped it ready for use - and without being aware, doing so involved upgrading it to Big Sur. All good. Later, I thought downgrading it back might make it a speedier machine, so I somehow managed to downgrade it back to El Capitan - which did prove quicker. It was never my main machine though, so I decided to sell it, given how much use it was getting. So I upgraded it to Monterey; utterly failed to sell it - and so now want to downgrade it back to El Capitan because Monterey is painfully slow on it.

But: the installers I've downloaded from Apple for El Capitan - and Mojave - are both 'too old' to run when Monterey is the installed OS - while the Big Sur installer can't be used either because Monterey is newer than it (duh). I fear that I've permanently hobbled the machine by putting Monterey on it (it doesn't handle it very well) and there's no way back!

Any advice? Assume I'm an utter novice...

 

[velocityg4]

Make a USB installer. Then boot off it, wipe the drive in Disk Utility and start over. I would go with at least High Sierra or Catalina. So, you can run current software easily enough. You just need to download the installer then make use Terminal. I couldn't say if there'll be issues with this in Monterey creating an old installer.

Create a bootable installer for macOS - Apple Support

You can use a USB flash drive or other secondary volume as a startup disk from which to install the Mac operating system.

support.apple.com

Although if you add a USB 3.0 SSD and clone your boot drive to it. Then use it for booting. Your iMac should be plenty snappy in Monterey.

 

[stinkhorn9]

Make a USB installer. Then boot off it, wipe the drive in Disk Utility and start over. I would go with at least High Sierra or Catalina. So, you can run current software easily enough. You just need to download the installer then make use Terminal. I couldn't say if there'll be issues with this in Monterey creating an old installer.

Create a bootable installer for macOS - Apple Support

You can use a USB flash drive or other secondary volume as a startup disk from which to install the Mac operating system.

support.apple.com

Although if you add a USB 3.0 SSD and clone your boot drive to it. Then use it for booting. Your iMac should be plenty snappy in Monterey.

Thank you So I've formatted a USB drive and am currently downloading the OS installer. But do I just drag it onto the USB drive? How does installing it from that differ from installing it from the very computer it's connected to?

 

[Nermal]

But do I just drag it onto the USB drive?

No. You follow the instructions in the linked article to run the "createinstallmedia" tool.

 

[velocityg4]

Thank you So I've formatted a USB drive and am currently downloading the OS installer. But do I just drag it onto the USB drive? How does installing it from that differ from installing it from the very computer it's connected to?

The install USB is basically a light version of macOS. With a few utilities for managing your disks, OS and install. So, you don't have to worry about compatibility of the install program in the download with your current macOS version.

As @Nermal said. Follow the instructions.

 

[stinkhorn9]

The install USB is basically a light version of macOS. With a few utilities for managing your disks, OS and install. So, you don't have to worry about compatibility of the install program in the download with your current macOS version.

As @Nermal said. Follow the instructions.

OK, so I've got as far as getting the install app in my Applications folder, entering the command in Terminal, then entering my password - but the reply is '[/Applications/Install OS X El Capitan.a does not appear to be a valid OS installer application.'

I can't see that I've strayed from the createinstallmedia instructions thus far...

 

[stinkhorn9]

OK, so I've got as far as getting the install app in my Applications folder, entering the command in Terminal, then entering my password - but the reply is '[/Applications/Install OS X El Capitan.a does not appear to be a valid OS installer application.'

I can't see that I've strayed from the createinstallmedia instructions thus far...

Update: the Apple URL I originally used to get the Terminal command had en-us in it: I changed it to en-gb, and am now making progress.

 

[stinkhorn9]

Update: the Apple URL I originally used to get the Terminal command had en-us in it: I changed it to en-gb, and am now making progress.

OK! I'm at the point where I need to select the disk where I want to install OS X - but the only disk available to select is the USB drive I'm trying to boot from. Can't get any further... Can anyone help?

 

[stinkhorn9]

OK! I'm at the point where I need to select the disk where I want to install OS X - but the only disk available to select is the USB drive I'm trying to boot from. Can't get any further... Can anyone help?

Don't worry (if anyone's still reading this ) - I'm getting historical help from Apple support forums re: Disk Utility/partitioning, etc - and I think I've cracked it. Thanks Velocity and Nermal for your input!

 

[Rimmsi]

Internet recovery not working?

 

[stinkhorn9]

Internet recovery not working?

I didn't even know that was a thing! It's up and running El Capitan now though - thanks.