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I have an old iMac with the specs below.
I want to install the most recent OS available for this machine.
I want erase all existing data and accounts on the machine.
I do not have admin access.
I have an apple id, not associated with this machine.

If Yosemite 10.10.5 is the most recent that can be installed on this machine, then I want to erase all existing data and accounts on the machine.

What can I do?

Available: 158.72 GB (158,723,710,976 bytes)
Capacity: 999.35 GB (999,345,127,424 bytes)
Mount Point: /
File System: Journaled HFS+
Writable: Yes
Ignore Ownership: No
BSD Name: disk0s2
Volume UUID: 94E5A9F7-B5AC-35BA-8B5C-D3973289C5F4
Physical Drive:
Media Name: ST31000528ASQ Media
Medium Type: Rotational
Protocol: SATA
Internal: Yes
Partition Map Type: GPT (GUID Partition Table)
S.M.A.R.T. Status: Verified

screenshot

harddisk

Edit: I've now done this:

Download El Capitan file InstallMacOSX.dmg to hard drive
Dbl-click on this file.
It opens folder that shows InstallMacOSX.pkg
Dbl-click on this file.
It opens dialog Install OS X
Click through a few times, then it says Install time remaining: about 2 minutes
Then after a couple of minutes it shows a message:
The installation was successful. The software was installed

I restarted the machine and ran installer. Now running OS X El Capitan 10.11.6

Then did all the above again with Sierra. Now running macOS Sierra 10.12.6

Now I go to the High Sierra page and attempt to install it and I see this error:

HIGH SIERRA

2 Answers 2

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According to everyman.com, the latest version of macOS for your Mac is High Sierra. There is this previous Ask Different question regarding gaining Administrator access: I don't have administrator account on my mac. You should be able to get High Sierra from the Apple website How to get old versions of macOS. There is also this previous Ask Different question: How can I download an older version of OS X/macOS?. One option, for a clean install of High Sierra, would be to create a bootable installer, boot from the installer, erase the internal drive and install macOS.

Example of Downloading High Sierra

Note: All updates available from the App Store application must be downloaded and installed before proceeding.

Open Safari and enter the URL https://support.apple.com/en-us/HT211683, as shown below.

The webpage shown below should appear.

Scroll down until you see the link "macOS High Sierra", as shown below.

After selecting the link labeled "macOS High Sierra", the App Store application should open and the following should appear.

Note: If the following does not appear, then all updates available from the App Store application where not downloaded and installed as required.

app store

At this point you should be able to select Get to start the download of the Install macOS High Sierra application.

Note: If the Install macOS High Sierra application opens, then quit the application.

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  • I have downloaded macOSUpdCombo10.13.6.dmg and put it on a USB drive. However, the instructions to create a bootable installer require the admin password, which I do not have. Jan 10 at 15:59
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    Al: Why did you download the macOSUpdCombo10.13.6.dmg file? I ask, because I do not see where you would need this file. In other words, this file first requires High Sierra to be already installed. If you install High Sierra, then you should get macOS 10.13.6. Are you still using Yosemite? If so, have you tried to get Administrator access by using any of the answers to the question: "I don't have administrator account on my mac"? Jan 10 at 16:44
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    No part of the answer mentions downloading a combo updater. A combo updater is of no use to you whatsoever until you have that OS 10.13 on your Mac already. It will not upgrade any earlier OS.
    – Tetsujin
    Jan 10 at 17:55
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    You cannot create install media from any updater. I don't know where you found either of those, but it wasn't from any of the links in the answer. You also need to read the creation command line more carefully. Mount points are at /Volumes/volumename
    – Tetsujin
    Jan 10 at 18:59
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    Al, I updated my answer with an explanation of how to download the High Sierra Installer. I now realize Apple may have made some recent changes that may require additional modifications to my answer. However, I will not be able to make any modifications unless you first comment on any problems you find with my answer. Jan 11 at 22:42
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Given the age of this machine, consider dropping in a SATA-based SSD rather than the spinning drive it likely still has. Doesn't have to be be new - I put a 64 GB SSD in a 2007 imac successfully.

This will give you a completely blank disk to start from, and it will be a virgin install by definition. Also, its a decent speed boost and also helps with virtual memory speed.

Later you can connect your old drive via a USB-SATA adapter and read in any files you still want, then format it.

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    @AlLelopath a SSD would be more for increased speed than capacity. It likely needs a 3.5" SATA drive, so a 2.5" in an adapter should work, make less heat, and work faster. I'd not spend a lot of money on an 11 year old machine.
    – Criggie
    Jan 11 at 2:15
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    I understand that speed is the reason for the SSD but while I'm at it, I figure I might as well go for 2TB. So this is a 2.5 SATA SSD, This will work, yes? What is the adapter that you speak of? Jan 11 at 3:53
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    By adapter, I mean a cheap metal bracket that can screw to the outside of the 2.5" drive to give the dimensions of a 3.5" drive. Something like pbtech.co.nz/product/ADPKIN2439105/… and it should cost very little. Its just folded metal or plastic, with some screw holes. A separate question is whether your mac can see and use a 2TB drive, and whether it can boot off a 2 TB drive (two related but different questions)
    – Criggie
    Jan 11 at 8:07
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    Note that both 2007 and 2009 iMacs only have a 3 Gb/s SATA interface. To get full use in terms of speed from a SATA SSD, the interface needs to be 6 Gb/s, which did not occur for iMacs until the 2011 model year. See this everymac website for a storage interface listing by iMac model. Jan 11 at 8:27
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    @Tetsujin: What you say is true, but I am nonetheless appreciative of this "answer" and may end up going this route. Jan 11 at 14:42

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