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Install Sierra on usb from internal drive

Been trying to install Sierra on a usb in order to wipe the internal drive and reinstall from the usb.


The goal is to recover storage space taken up by a partition containing Mojave. (there are currently 2 partitions; Sierra and Mojave. I have been unable to remove Mojave via disk utility.)


I have tried to download Sierra from the app store without success. Screen informed me the app is damaged.


If there is an easier way to accomplish this please advise. Thank You.


Thus far I have:

  1. Backed up using TM
  2. Formatted the usb.

Mac mini, macOS 10.12

Posted on Mar 17, 2021 11:41 AM

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Question marked as Top-ranking reply

Posted on Mar 18, 2021 10:58 PM

The copy of Sierra is not damaged, try again, do not use the mac while it is downloading or any other devices that share

the same internet connection. Read this.

If you do have an operating system on your mac and it is functioning then you can download

Sierra using this method.

How to get old versions of macOS – Apple Support

Go to Download macOS and click on macOS Sierra 10.12

This downloads InstallOS.dmg to your Downloads folder.


The next section can only be done on a mac that is capable of running Sierra,

a mac that came preinstalled with an OS later than Sierra will refuse to do the next bit.


When downloaded open to get InstallOS.pkg, double-click on

that and an installation window will open, read and follow the prompts,

this does not install Sierra but uses the InstallOS.pkg to create the 

Install macOS Sierra.app which you will find in your Applications folder.


(If the installation window asks which disk you want to install to, you must pick 

the disk that you are booted to at the time. Not any internal or external disk that 

you want to eventually install Sierra on, that is for later.)


There is a problem with making a bootable USB installer with the Install macOS Sierra.app

where it returns an error Volumes/<USBname> is not a valid mount point. There is a workaround.


With Install macOS Sierra.app in your Applications folder open Terminal.


Paste in this command


sudo plutil -replace CFBundleShortVersionString -string "12.6.03" /Applications/Install\ macOS\ Sierra.app/Contents/Info.plist


press return

enter your password

press return


now paste in the createinstallmedia command for Sierra where MyVolume can be replaced with the name of your USB stick


If your USB name has more than one word separated by spaces you would need to type it in as

/The\ USB\ Name


sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app


press return 

follow the prompts


Having made the USB installer you need to boot to it.

Restart your mac while pressing the option/ alt key when you see the Startup Manager select the USB

and press Return.

When you boot to the USB you will see a Utilities panel click on Disk Utility and press Return.

Highlight the Disk not any of the indented Volumes then Click on Erase.

Give the Disk a name.

Format: Mac OS Extended (Journaled)

Scheme: GUID Partition Map

Click Erase.

When Done quit Disk Utility.


Your mac will now have one single partition.


Click on Install OS to install macOS Sierra.


Once installed you can then transfer back your data from the Time Machine Sierra back up you made earlier,

do not transfer anything from the Mojave partition back up.

Similar questions

15 replies
Question marked as Top-ranking reply

Mar 18, 2021 10:58 PM in response to novanut

The copy of Sierra is not damaged, try again, do not use the mac while it is downloading or any other devices that share

the same internet connection. Read this.

If you do have an operating system on your mac and it is functioning then you can download

Sierra using this method.

How to get old versions of macOS – Apple Support

Go to Download macOS and click on macOS Sierra 10.12

This downloads InstallOS.dmg to your Downloads folder.


The next section can only be done on a mac that is capable of running Sierra,

a mac that came preinstalled with an OS later than Sierra will refuse to do the next bit.


When downloaded open to get InstallOS.pkg, double-click on

that and an installation window will open, read and follow the prompts,

this does not install Sierra but uses the InstallOS.pkg to create the 

Install macOS Sierra.app which you will find in your Applications folder.


(If the installation window asks which disk you want to install to, you must pick 

the disk that you are booted to at the time. Not any internal or external disk that 

you want to eventually install Sierra on, that is for later.)


There is a problem with making a bootable USB installer with the Install macOS Sierra.app

where it returns an error Volumes/<USBname> is not a valid mount point. There is a workaround.


With Install macOS Sierra.app in your Applications folder open Terminal.


Paste in this command


sudo plutil -replace CFBundleShortVersionString -string "12.6.03" /Applications/Install\ macOS\ Sierra.app/Contents/Info.plist


press return

enter your password

press return


now paste in the createinstallmedia command for Sierra where MyVolume can be replaced with the name of your USB stick


If your USB name has more than one word separated by spaces you would need to type it in as

/The\ USB\ Name


sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app


press return 

follow the prompts


Having made the USB installer you need to boot to it.

Restart your mac while pressing the option/ alt key when you see the Startup Manager select the USB

and press Return.

When you boot to the USB you will see a Utilities panel click on Disk Utility and press Return.

Highlight the Disk not any of the indented Volumes then Click on Erase.

Give the Disk a name.

Format: Mac OS Extended (Journaled)

Scheme: GUID Partition Map

Click Erase.

When Done quit Disk Utility.


Your mac will now have one single partition.


Click on Install OS to install macOS Sierra.


Once installed you can then transfer back your data from the Time Machine Sierra back up you made earlier,

do not transfer anything from the Mojave partition back up.

Mar 19, 2021 10:56 AM in response to Eau Rouge

I haven't been this nervous since 1979; the date I got married.


Since last we chatted, I successfully downloaded Sierra to the USB, code name: Sierra, restarted holding down option, chose code name, chose disk utility. Here is where I got stuck (see above post on dense/stupid). Wasn't sure if the USB erased Mojave or not. Drank a pot of coffee first, used the bathroom numerous times and chose "install macOS Sierra". Tried to reread your instructions on, 1. my old mac pro (couldn't send a reply, probably due to its ((and my)) age) and 2. tried to send a reply on my iPad. Couldn't do that either. So I waited till Sierra was installed. When done I checked the status of Mojave and, surprise, it's gone! (at least I think so):

If so, please instruct how to transfer 'only' data from TM, not Mojave, that is, if you're not completely frustrated with me...


Thank you a million times...



Mar 19, 2021 8:16 AM in response to Eau Rouge

Sorry to be so dense/stupid but on the second paste:

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app

should I paste that first to a sticky to change the (myvolume) name to the usb's name? Tried just pasting it to terminal only to be told (volume/myvolume) is not a valid mount point.


Just for simplicity I named the flash drive: Sierra


Go ahead, I've been called dense/stupid lots of times...

Mar 19, 2021 8:37 AM in response to novanut

Well you can either change the name of the USB to MyVolume or if you paste the command into Terminal you can then

use the left arrow button to get the cursor to the end of MyVolume then use the backspace button to erase MyVolume then type in Sierra. Use the right arrow button to go to the end of the command and press return.


Or just paste the following in instead.


sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Sierra --applicationpath /Applications/Install\ macOS\ Sierra.app

Install Sierra on usb from internal drive

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