how to prepare a bootable usb disk from "InstallESD.dmg"

If you use pkgutil to expand the InstallMacOSX.pkg it opens to three items, the Distribution file, InstallMacOSX.pkg and Resources. You can alter the Distribution file to ignore the supported platform check, see below.

Creating the Install OS X El Capitan.app on a mac that came with a newer OS than El Capitan.

Download the InstallMacOSX.dmg from Section 4 of How To Upgrade To El Capitan

Double-click to open InstallMacOSX.dmg to Install MacOSX.pkg.

Drag InstallMacOSX.pkg to the Desktop.

Open Terminal, enter the text

pkgutil --expand <drag the InstallMacOSX.pkg here> ~/Desktop/Expanded

A folder will be created on the Desktop after a while with the contents of the .pkg file.

In there you will see an item called Distribution, Control-click on that and select Open With

go to Other and select Text Edit.

When the file opens scroll down to the section that reads,

function isSupportedPlatform(){

type in at the end return true; so it now reads as,

function isSupportedPlatform(){return true;

Now click Save and close the document.

Go back to Terminal and enter the text,

pkgutil --flatten <drag the Expanded folder here> ~/Desktop/InstallElCapitan.pkg

press Return, after several minutes, be patient, (check to see if the prompt has returned to Terminal) a new package will be created on the Desktop.

When created double-click on that and an installation window will open where you will now convert the 

new InstallElCapitan.pkg to the Install OS X El Capitan.app which will be placed in your Applications folder.

You can now create a bootable USB using the install app and createinstallmedia,

Create A Bootable USB

If you have the time I would be grateful if you could give this a trial, it works here on my mac, but I would like confirmation from yourself or any others reading this that the procedure works on macs that came with macOS Sierra or newer pre-installed. Oh and tell me if my description of the procedure is easy to follow and understand..

Recently certificates for older install apps for certain macOS's expired meaning they could no longer be installed.

If you are using an old bootable USB installer you created a while ago then that is the error message you will see.

One thing you can do as a workaround is to change the Date & Time of the mac to a date in 2018 for example.

The installer should now work, when the installation has finished you can change the Date & Time back to today.

Apple did release updated installer files at the end of October, you can get El Capitan here, 

How to upgrade to OS X El Capitan – Apple Support

At Section 4 download InstallMacOSX.dmg. When that has downloaded open it and you will get InstallMacOSX.pkg.

Double-click on that and an installation window will open, this will convert InstallMacOSX.pkg to the

Install OS X El Capitan.app which will be in your Application folder.

Use the Install OS X El Capitan.app to create a new bootable USB installer, How to create a bootable installer for macOS – Apple Support

Please note you can only convert the InstallMacOSX.pkg to the Install OS X El Capitan.app on a mac that can install El Capitan.

Therefore if your mac came with macOS Sierra, macOS High Sierra, macOS Mojave or macOS Catalina pre installed you will not be able to convert the InstallMacOSX.pkg to the Install OS X El Capitan.app.

Eau Rouge wrote:

Please note you can only convert the InstallMacOSX.pkg to the Install OS X El Capitan.app on a mac that can install El Capitan.

Therefore if your mac came with macOS Sierra, macOS High Sierra, macOS Mojave or macOS Catalina pre installed you will not be able to convert the InstallMacOSX.pkg to the Install OS X El Capitan.app.

You can extract the contents using the command line and "pkgutil". I think the command is something like:

pkgutil  --expand  <path-to-InstallMacOSX.pkg>   "/Applications"

If this does not work, then you may need to add a non-existent folder name to the destination location such as "/Applications/ElCapitan". I've used several different extraction tools recently and I'm providing this from memory since I'm not at my Mac right now.



Ah-ha! I was starting to wonder about you, Eau Rouge, as your replies in at least two other (now-locked) threads from Nov. and Dec. last year on the same exact topic were, well, lacking, lol. This post of yours here is the actual, full-detail, working answer for those using Mojave and Catalina (whether it came with the Mac or was upgraded to same -say on a 2016 laptop- later...😉).

Anyway, I can also confirm that this worked using a 2018 MBPro (started with the "InstallMacOSX.dmg" for El Capitan) for a mid-2007 iMac to set the latter up for a (non-networked, aka, offline - since these macOSes are totally EOL) project, and I had to max out its OS to get the old specialty software on it (was left at Mavericks and in the garage for some years until now). Thanks much, Eau Rouge!

UPDATE: While this allows createinstallmedia to work and claim to succeed, the resulting USB drive seems to not boot this 2007 iMac, but that may be the iMac or the USB drive (Disk Utility in Mavericks' Recovery Mode sees the drive and it looks good otherwise), so YMMV? *sigh*