Catalina Clean install - why no USB on Startup Disks?

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Level 3

561 points

Catalina Clean install - why no USB on Startup Disks?

I followed instructions to create a bootable USB with Catalina in order to do clean install.

I did not have option to select that USB in Preferences - Startup disk. Started nevertheless to restart and hold Command-R to no avail.

Restarted this time with Alt key pressed, then saw my SSD, a greyed out macOS Catalina (with some 22 GB available - which made sense as my USB was 32GB before creating the startup disk.

Guess the SSD was destination disk. Went through all installation, it's done - but everything is still there (stuff on desktop, Documents folder content, and all 3 profiles... So obviously, I have NOT done a clean install...

In the first place, why I could not see the USB in Startup disks (in Preferences) ? That would have meant, I guess, I would have really started from it (I most likely started from the Install macOS Catalina file which was on the computer ??...

It's not my first time to do a clean install (done it with several other releases in the past). Creating the USB bootable seemed to take the time I have experienced in the past, whether for Mojave, High-Sierra and others....

Posted on Oct 12, 2019 4:11 PM

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Answer 1

Top-ranking reply

fuzzymo

Level 4

2,054 points

Oct 18, 2019 6:59 PM in response to lanstrad1

I believe you are saying that your bootable install USB drive does not work. The USB (32GB) drive media has to be formatted as macOS Extended (Journaled) with a GUID Partition Map scheme (not a Master Boot Record scheme). Most USB flash drives come new out of the package with a Master Boot Record scheme. To format the drive open Disk Utility. Click on "View". Then select "Show All Devices". Select your 32GB drive media in the Disk Utility sidebar, not the volume below it. Click on "Erase". In the dropdown select Format: MacOS Extended (Journaled), Scheme: GUID Partition Map. Click on the "Erase" button in the dropdown.

Now use your instructions to create a bootable USB installer. Once the bootable installer is successfully created, it should show up in System Preferences/ Startup Disk.

How to create a bootable installer for macOS - Apple Support

How to erase a disk for Mac - Apple Support

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Answer 2

callaway

Level 3

526 points

Oct 17, 2019 3:31 PM in response to lanstrad1

Insert your bootable USB with Catalina, then restart and hold the Option key.

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Answer 3

fuzzymo

Level 4

2,054 points

Oct 19, 2019 4:01 AM in response to lanstrad1

You have to click on "View", "Show All Devices". Open Disk Utility. Select your USB 32GB drive media, not the volume on the USB drive indented below it to see these options. In my screenshots I am using a Sandisk Cruzer Switch Media.

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Answer 4

fuzzymo

Level 4

2,054 points

Oct 19, 2019 6:26 AM in response to lanstrad1

If you run the installer while it is still in the Applications Folder, it will disappear and be deleted from the Applications Folder when the install is finished. You will have to download the installer again if you wish to use it to make a bootable installer.

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Answer 5

lanstrad1 Author

Level 3

561 points

Oct 17, 2019 6:31 PM in response to callaway

Been there, done that twice. Still : everything is present (apps, docs, everything...)

Should I first reformat the SSD then restart and proceed ?

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Answer 6

lanstrad1 Author

Level 3

561 points

Oct 17, 2019 2:55 PM in response to lanstrad1

Ok let me rephrase...

I'm trying to follow this, after creating a USB installer (bootable). See my comments in BOLD:

Go to System Preferences
Сlick Startup disk and choose the installer you just created. === Whether the USB is connected or not, I DON NOT see it...
Restart your Mac and hold down Command-R to boot into recovery mode.
Take your bootable USB and connect it to your Mac. === How the **** would I see the USB if it was not connected yet !!?? However, even seeing ''something'' which seems to have 32GB but is greyed out, install does not erase anything !

When the macOS Utilities screen appears, follow these steps:

Select Reinstall a new copy of macOS. === See previous comment
Click Continue, then click Continue again when the next window appears.
Agree to the terms and conditions, then select your Mac’s internal drive.
Click Install.

I end up with an update on previous install, nothing clean here !

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Answer 7

dialabrain

Level 10

137,081 points

Oct 19, 2019 4:36 AM in response to lanstrad1

lanstrad1 wrote:

How do you do this ? I restart with cmd+R and enter disk utility, but can’t see such an option, would you do this with usb connected ? Connect it after?

I take it you have a new Mac.

See: About Secure Boot - Apple Support

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Answer 8

lanstrad1 Author

Level 3

561 points

Oct 19, 2019 2:38 PM in response to James Dempsey

Indeed: creating a bootable installee disk on usb thumb for purpose of installing Catalina on the Mac it’s plugged to, and clean install of course (with need to selectively reinstall everything and bring back data.

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Answer 9

lanstrad1 Author

Level 3

561 points

Oct 18, 2019 6:23 PM in response to James Dempsey

How do you do this ? I restart with cmd+R and enter disk utility, but can’t see such an option, would you do this with usb connected ? Connect it after?

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Answer 10

lanstrad1 Author

Level 3

561 points

Oct 19, 2019 6:05 AM in response to dialabrain

Nope. MBP mid-2012

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Answer 11

Oct 18, 2019 3:52 AM in response to lanstrad1

Catalina has some new security feature that prevents it from installing onto/booting from external drives that don't already have an OS installed by default. You can get around that by booting into Recovery Mode and using the Disk Utility to change the security settings to allow this.

I had to do this just to install Catalina onto a USB-connected external hard drive.

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Answer 12

lanstrad1 Author

Level 3

561 points

Oct 19, 2019 6:14 AM in response to fuzzymo

Ok that worked (to erase and select GUID Partition - with the view all). Now need to see if clean install will work :)

I might just decide to wait a few more updates now before doing the clean install. Don't know why but the installer disappeared from my Application folder (after I ''installed'' it over - thinking I was ''clean installing'' from the USB ... And it appears that download got really long after a week...

Thank you very much fuzzymo for that important detail.

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Answer 13

Oct 19, 2019 8:04 AM in response to lanstrad1

Wait, are you trying to actually INSTALL Catalina on a USB thumb drive for the purpose of using it from the thumb drive, or simply creating a BOOTABLE INSTALLER disk on the USB thumb drive for the purpose of using it to install on the Mac it's plugged in to? Because those are two different things.

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Answer 14

lanstrad1 Author

Level 3

561 points

Oct 18, 2019 8:55 PM in response to fuzzymo

I see no such thing as “Master Boot Record” or GUID Partition Map.... Erased my usb stick but can’t see these options. It’s MacOs Extended Journaled.

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Catalina Clean install - why no USB on Startup Disks?

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