Help reinstalling OSX on old iMac 2009

[Grvsvg]

Hi guys, i have an issue i don't understand.

I got a iMac 2009 from a friend, with El Capitan installed, but HDD is broken, although i still can boot recovery (where SOS filesystem is failing). My goal is to reuse this computer, of course

I managed to open iMac, replaced HDD by SSD, attached old HDD to sata/USB converter, an boot on recovery (from USB, so). Yay ! Recovery seems ok ! I could even copy datas for my friend, as HDD is not encrypted.

From recovery, i use diskutil to erase SSD (so GPT and HFS+ are now on SSD), then i tryed reinstall from the recovery.
It asks me itunes account, with 2FA, no problem, as my friend provided this to me and accepted 2FA from his iphone.
It begins reinstalling (connect itunes, start downloading - i guess - an El Capitan DMG, do stuff, then reboot, and... i got an install error !

What / How can i fix that ? Tryed downloading ISO (was snow leopard) from internet, put it on USB key, boot but can't install.

Is there a way i could reinstall (even 2009 OS) from blank to my SSD ? Could i remove iTunes account (as i would put mine instead...) for a blank install ? Is there any unofficial ISO/DMG that could help me to get this ?

Thank you very much.

 

[Rod]

The normal process that a previous mac owner should observe is to sign out of all Apple accounts eg iTunes, App Store etc and using Recovery open Disk Utility and erase the HD. At this point depending on the OS you can Reinstall the MacOSX that came with the device.
Your problem is the El Capitan Operating System is still logged into his Apple Account. The (now external) HD needs to be erased and restored to pre owner state so that the Setup Wizard can can guide you through the process of setting up a new Apple account or logging in with an existing one.
This won't help you much though because the external is faulty.
To install a new copy of El Capitan onto a blank SSD you need a Bootable macOS Installer on an external drive (usually a USB thumb drive).
The catch is you need a working Mac computer to do this. Old versions of MacOSX installers are available online, you then need a free third party app to convert the installer into a bootable drive.
From there the process is simple; boot from the USB, use Disk Utility (on the USB) to erase, format and map the internal SSD then the installer to instal a "clean" copy of your chosen MacOSX.

 

[Grvsvg]

(...)

Thank you VM @Rod , now i have a few questions.
I have a Macbook Air (2016 or 2017), with latest macOS release i could install.
1) to download El Capitan installer, is there differents versions that i must choose to be compatible with iMac 2009 (A1225) ? Or can i DL the basic one ?
2) i heard of Transmac to make DMG to USB thumb, perhaps i miss a point to do this on macOS ? This is what you mean when you talk about "free 3rd app" ? Perhaps you have better software to do this ?
3) by doing this, the new install will no longer be bind to my friend's account ? Notice i can ask him for unlocking 2FA no problem, but if i can avoid, this is better

Thank you a lot, i'm a Mac noob as i'm using my MBA mainly to compile iOS stuff, so not very experienced with deep system maintenance (but, jeez, that iMac is insanely beautiful).

 

[Rod]

I take it you mean that you could use your 2016-2017 MBA to download the software you need.

1. No there is only one version of the MacOSX installer for each version. Once installed it may be possible to upgrade to a later Mac OSX but I believe your iMac came originally with Mac OSX 10.5 (Leopard) and can be updated only as far as MacOSX El Capitan 10.11.
Downloads are available by link to the App Store here; How to get old versions of macOS
Once downloaded Quit it if it tries to launch and leave it in your Applications folder.

2. Transmac will not do what you need in this case. I suggest after you have your MacOSX El Capitan Installer downloaded successfully you download Instal Disk Creator (Third Party App) from MacDaddy io. (its free) here; MacDaddy - Easy to use but powerful software. Made to high standards.

3.You will need a small USB thumb drive of about 20-25Gb for the creation of a bootable installer. Be aware it will be completely erased by the creation of a bootable installer on it.
Launch Instal Disk Creator, it should find your copy of MacOSX El Capitan Installer and picture it in its little window at the top. Plug in your USB drive if you haven't already and select it in the destination/target menu.

If/once you have done all that you will be able to boot your iMac from the USB Thumb Drive by holding the Option Key at Startup.

Now comes the fun part. You need to open Disk Utility on the USB drive and Erase, Format and map the internal SSD. Pretty simple it's all done on one window.

Gotta make dinner now, 1830 where I am. Get back to me if you have any questions on the process so far.

 

[Rod]

PS. When you get to erasing your SSD do it at the media level. That is in Disk Utility in the left column you need to erase the top item. It will have a proprietary name like Toshiba 500Gb SSD.
Having done that you need to create a Partition on the drive, just one unless you want to complicate your life, it’s best to call it Macintosh HD.
The Partition needs to be formatted Mac OS Extended (Journalled)
Mapping needs to be GUID.

 

[ferrarr]

Once downloaded Quit it if it tries to launch and leave it in your Applications folder.

Those older versions of OS X/macOS download as a dmg file. The Article you linked states:

Safari will download the following older installers as a disk image named InstallOS.dmg or InstallMacOSX.dmg. Open the disk image, then open the .pkg installer inside the disk image. It will install an app named Install [Version Name]. Open that app from your Applications folder to start installing the operating system.

Here's how Apple recommends making a bootable 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. These steps are primarily for system administrators and other experienced users who are familiar with entering commands in Terminal.

support.apple.com

 

[Grvsvg]

@Rod omw downloading install disk creator and El Capitan DMG. More feedback when it is over, but i warmly tahnk you for your help.

Edit; everything was fine. Many thanks !!!

 

[Rod]

As ferrarr has mentioned El Capitan will be in the form of a dmg. (Disk Image) but opening it will simply place the El Capitan Installer in your Applications folder as per my previous post.
Booting your device from the USB drive may require you to plug it in and hold the Option/alt key while starting up your iMac. As your SSD is blank its possible the iMac will just boot from the USB but just to be sure use the hold down Option/alt key until you see the Apple logo just in case.