Factory reset iMac can't get Yosemite back on

"Factory reset iMac can't get Yosemite back on: [...]Is there a way that I can get the Yosemite .dmg file onto the external and open Yosemite with disk utility on the external hd? Do I have to use terminal to make the thumb drive bootable?"

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Yosemite Bootable Installer:

Apple no longer supports Bootable Installers for Yosemite. See your option here: Create a Bootable Installer for macOS - Apple Support

Crumurtronz Said:

"Factory reset iMac can't get Yosemite back on"

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Thank you for the screenshot.

About this Error:

A. Non-Encryption is the Culprit:

This is not a secure site, because it does not start with https. https is encryption. All of Apple's site are of encryption. So, I am wondering if it is a glitch in Apple's site. Yosemites is quite olde and obsolete, and indeed, it is shown here: Use Apple Products on Enterprise Betworks - Apple Support

B. So, contact Appel Support:

Ask apple exactly what is occurring here. It may be a glitch that they need to fix.

Apple Contact Us Info:

• Contact Us - Choose Locations
• Proceed from there as Necessary
• NOTE: Due to the Coronavirus Pandemic, calls are taking a bit linger to get through. And, that makes sense, because many are at home working out-of-the-house or are taking classes over-the-web, this they have more time on their hands to contact Apple Support. So, it might take a bit to get through to Apple Support. But, just stay on the line, and someone will be with yo

Crumurtronz Said:

"Factory reset iMac can't get Yosemite back on"

-------

Thank you for the screenshot.

About this Error:

A. Non-Encryption is the Culprit:

This is not a secure site, because it does not start with https. https is encryption. All of Apple's site are of encryption. So, I am wondering if it is a glitch in Apple's site. Yosemites is quite olde and obsolete, and indeed, it is shown here: Use Apple Products on Enterprise Betworks - Apple Support

B. So, Contact Apple Support:

Ask apple exactly what is occurring here. It may be a glitch that they need to fix.

Apple Contact Us Info:

• Contact Us - Choose Locations
• Proceed from there as Necessary
• NOTE: Due to the Coronavirus Pandemic, calls are taking a bit linger to get through. And, that makes sense, because many are at home working out-of-the-house or are taking classes over-the-web, this they have more time on their hands to contact Apple Support. So, it might take a bit to get through to Apple Support. But, just stay on the line, and someone will be with yo

Crumurtronz Said:

"I was just wondering if I can have the 2009 iMac always boot to the external.[...]"

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Default Mac Startup Disk:

1. Go here: Change your Mac Startup Disk - Apple Support
2. Scroll to: Set a default startup disk

IMPORTANT: Be certain you select a network startup volume and not a network install image.

So, if an available option, back Up your Mac First:  Be certain you Create a Time Machine Backup of your Mac, so that way you can have something to restore your Mac from, should anything go wrong with the reconfiguration.

It takes a little bit of getting Used to. So, find a few videos on YouTube pertaining to this.

Crumurtronz Said:

"Factory reset iMac can't get Yosemite back on: I make the usb thumb drive with Yosemite.dmg bootable. It will then be able to install the system on the internal or external hd?“

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No. Because is not officially an application. So, trash that. It’s more of an iso image file (in relevance to a CD installer). So, trash that. And avoid getting USB Bootable Installers secondhand (ie off of eBay), as someone may install junk on it.

Crumurtronz Said:

"I opened the .dmg file and went through the process but did not install. Seen the Yosemite installer in the apps folder. Tried the terminal but that was a no go. I downloaded a program and it did what terminal does and all went well. Thanks for your help."

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Obtaining an Installer:

What program did you download to get this to work? Where did you get this program?