creating a bootable USB drive - problems

Ok the thing you are not getting is that you have to develop the InstallMacOSX.dmg

to eventually get the Install OS X El Capitan.app in your Applications folder.

There are three steps, download InstallMacOSX.dmg,

open that to get InstallMacOSX.pkg, you then open that and it will

create the Install OS X El Capitan.app.

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

El Capitan using this method. Read all the instructions especially the bold text.

Use well known brand of USB stick 8GBs or over in size.

How to get old versions of macOS – Apple Support

Go to Download OS and click on OS X El Capitan 10.11

this downloads InstallMacOSX.dmg to your Downloads folder.

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

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

When downloaded open to InstallMacOSX.pkg, double-click on

that and an installation window will open, this does not install El Capitan

but converts the InstallMacOSX.pkg to the Install OS X El Capitan.app which 

you will find in your Applications folder, it should be 6.2GBs in size.

(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 El Capitan on, that is for later.)

To start the installation of El Capitan double click on the Install OS X El Capitan.app.

Create a bootable USB installer disk using the Install OS X El Capitan.app in the Applications 

folder and the createinstallmedia command in the Terminal app. 

Read the instructions here,

How to create a bootable installer for macOS – Apple Support

sudo /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ OS\ X\ El\ Capitan.app

Since El Capitan is really old and many third party apps are no longer updated or available you may want to consider installing Linux on the laptop. The Linux OS will be much more current & up to date and also allow the use of the common web browsers such as Firefox, Google Chrome, and Vivaldi. Plus Linux includes the free open source office suite LibreOffice. Zoom can also be installed as well if remote classes are expected.

Linux Mint or one of the Ubuntu flavors such as Kubuntu or Ubuntu MATE are good choices as they should easily install on this laptop and just work (they are all free). Plus they can work with minimal memory (4GB is best, but it may be fine with just 2GB of RAM). You can easily test it out by booting the Linux USB installer which should include an option to boot into a Live demo mode. Of course it will be extremely slow running from a USB stick. Installation to the internal drive will perform much better. Linux is a great way to greatly extend the useful life of an older computer.

You can create a bootable Linux installer or Live USB stick by using the downloaded Linux .iso file as a source for Etcher. Option Boot the Linux USB drive and select the orange icon labeled "EFI".

David Graeme-Baker wrote:

Oh yes Linux. !

Please remember that I want to give my laptop to a young student for online study, I think loading Linux onto it, whilst providing him/her an interesting educational challenge, would not give immediate access via one of the most user friendly and accepted operating systems.

It depends on what technologies the school is using for online classes. Many schools are using Chromebooks which are pretty much a special variation of Linux which puts everything into the Chrome browser. As I mentioned in the other post Zoom which is used by many schools is supported on Linux as are the common web browsers. It would be a good idea to check with the school to verify what technology and apps are required for online learning. You may find Linux will be just fine.

As for "one of the most user friendly ... operating systems", I really don't consider macOS to qualify anymore. I have the scars to prove it.

Yes and if you had read my post you would have noticed this paragraph in bold lettering.

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

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

That rules out your 2018 mac mini. And therefore would rule in your MacPro.

Told you all that three days ago.