How to install Mountain Lion on an external drive or in a VM

To reproduce a bug, reported from my customer, I have to test my software under Mac OS X 10.8.5. Mountain Lion.

OS X 10.11.6 El Capitan is running my the development machine.
I have

  • the “OS X Mountain Lion”
  • an external USB drive
  • Virtual box

What I have tried:
Double Click the “OS X Mountain Lion” and get the message, that this version of the program “OS X Installation” ist to old and couldn’t be started.
With this action OS X Mountain Lion should be installed on an external USB drive. This was my first choice.

Open the Installation app within the process to create Virtual Machine with Virtual box. Virtual Box needs a dmg file. The use of a virtual machine was my second choice.

What can I do to get a running Mountain Lion installation?

Can’t you just drag the installer in the window when it asks for a OS disk?

its been a while… but can’t you plug in the external drive
boot from the install disk (you have to hold down a few keys during boot process… google it)
and choose the external drive as the destination?

this way the OSX on your main drive, and its contents are never even touched (nor are they booted)

then you can removed the install disk, reboot the system the same as above, and choose between new and old OSX

You should be able to install in VirtualBox. Inside the Install OS X Mountain Lion app package, you will find the installation disk as InstallESD.dmg within /Contents/SharedSupport.

Copy it outside the app, so it becomes accessible.

Create a new Virtual Box VM for Mountain Lion, then in Settings, disk storage, select the CD (empty), click on the small cd image on the right, and choose InstallESD.dmg. Click OK.

Start the VM. Login is verbose, don’t freak, and wait until you get to the screen where you select the language, then follow the prompts.

Use the disk utility to format the virtual hard drive, then click “Reinstall OS X” and select you virtual HD.

@Christian Schmitz : I only have “VirtualBox”. The InstallerApp doesn’t work. At the moment I’m a step further. In the package of the installer there is a InstallESD.dmg in the SharedSupport folder. When I use this wit VirtualBox the installation starts, the language could be selected, the apple terms could be accepted and then I could choose a drive to install, but there is only an empty dialog.

@Dave S : When I restart Mac OS X and hold the Option key down, than a Bootmanager appears. With this Bootmanager, I can than start an OS from an external drive. What I want to to ist to install Mountain Lion on this external drive.

@Michel Bujardet : Thanks Michel. Like described above, there is an empty dialog for selecting the installation volume and only the Back button is available. The Install button is greyed.

Any idea how to deal with it?

You need to format the virtual hard drive before that with Disk Utility, before your select Reinstall OS X.

Here is a guide for installing on external drive OSX on External

When did you download Mountain Lion? Due to an expired certificate older versions can’t be installed and you need to download a fresh installer.

Thanks Brian,

but this solution seems only to work, if a newer OS should be installed. In my case an older OS system should be installed and when the installer starts, it prevents the installation because a newer OS is already there.

Hello Markus, thanks for your suggestion. It’s an older one from 2012. At this level of the installation process there is no problem with the certificate.

Did you run disk utility to format the VM’s Hard disk?

Hi Jim,

thanks, that is the solution. I haven’t done it before. The following thread contains the solution in steps:

It is installing now.

Some time ago I cloned my OSX 10.6 to a external drive and it worked great.

Not sure if this will be an option for you but just wanted to throw it out there OSX Disk Utility


[quote=280689:@Torsten Gaidies]Hi Jim,

thanks, that is the solution. I haven’t done it before. The following thread contains the solution in steps:

It is installing now.[/quote]

That is just what I kept telling you above since my first post how to …

Off topic. Thanks - that worked for me to set up an El Capitan virtual machine via my Virtualbox Yosemite from a .dmg. Sweet.

There may be a different explanation: your MacBook Pro is too young and therefore Mountain Lion cannot be installed on it.

To be sure, check the Mountain Lion release date and compare it to your MacBook Pro version (year / early, mid, late of that year).

Actually you should run into problems with that one soon enough. I would download a newer version.