[This section is still work in progress]
It would appear that in the new Mojave App Store, older purchased OS Installers no longer appear.
Testing the El Capitan installer which has a published URL it will appear in the App Store, but if requested to download no longer says 'not valid for this Mac' it now says 'The requested version of macOS is not available'.
Some further testing is required - contributions welcome - to see if other OS versions are similarly removed. We may need direct links for these, which I don't have at present.
For OS X versions from Lion up to El Capitan.
The simplest way - if available to you - is to use your Purchase History on the App Store.
If you have ever previously installed any OS X version, it will still be available to you from that list. This should include any public beta versions too.
The version available from that list will always be the latest version of its type - i.e. 10.7.5, 10.8.6... 10.11.6
Image heavily modified to show only OS versions.
Note, it will say Download or Install depending on whether or not you have the Installer file saved locally - even on a non-boot drive.
For OS versions since Sierra.
Sierra itself has now vanished from everybody's Purchase History. However, Apple are keeping Sierra fully available, even though High Sierra is out. No Apple ID is required.
If the version you are trying to download is older than the Mac you are attempting to download it to - the Store will not allow the download.
[looking for workarounds to this part - edits welcome - I can't test this as the newest Mac I have is a 2012 Mac Pro]
Potential workarounds, need testing -
How to re-download Lion from Mountain Lion
If you are trying to update an older machine running Snow Leopard or Lion, then you can get a special version of El Capitan from the App Store
This version of El Capitan is for users running OS X Snow Leopard or
OS X Lion who would like to upgrade to macOS High Sierra. If you are
running Snow Leopard or Lion and would like to upgrade to High Sierra,
you need to install El Capitan first. This version of El Capitan can
also be installed on computers that are not compatible with High
Note that last sentence... this version will not install on any machine that is not currently on Snow Leopard or Lion, if the machine is capable of running High Sierra.
That leaves it as quite a specific resource & not a general 'get out of jail free card' for anyone wanting El Capitan.
If you need to reinstall from Recovery, & were previously running Sierra 10.12.4 or higher, there are now 3 options available.
Hold the appropriate key combo at the boot chimes...
- Cmd ⌘ R
reinstall the latest macOS that was installed on your Mac, without upgrading to a later version
- Opt ⌥ Cmd ⌘ R
upgrade to the latest macOS that is compatible with your Mac
- Shift ⇧ Opt ⌥ Cmd ⌘ R
reinstall the macOS that came with your Mac, or the version nearest to it that is still available.
The first 2 options are available to any Mac newer than Lion, approximately 2009.
There is also the option of creating a bootable USB of the Recovery Disk, using this Apple tool - Apple KB: OS X: About Recovery Disk Assistant
Should you have access to an older point release of any OS, 10.11.0 etc & wish to upgrade, then you can download Combo Updaters from Apple that contain everything necessary to go straight to the latest point release in a single step, e.g. 10.11.6
Google is good at finding these, as the top hit if you just search
combo update 10.11 etc but here are links to a few
El Capitan 10.11.6
High Sierra 10.13.6
If you need to create a bootable USB to install from
How do I make a bootable USB flash drive on a Mac?
How do I create a Mac bootable USB drive using Windows?
If none of these methods are available to you, you have two options
Find a friend who can access the download [recommended]
Find a torrent/sharing site [not recommended]
There is no 'legitimate' way to download macOS from anything other than a Mac. It requires the Apple App store.
Note: You can not use a Time Machine backup to revert to an OS which is older than the OS of the latest backup on that Time Machine drive.
This means that to preserve your ability to ever restore to an earlier backup & OS with your Time Machine backup, you must swap out that Time Machine drive before upgrading the OS. This is because once the Time Machine drive sees the new OS, there's no going back to the older OS using it. You can still pick data out from the Time Machine manually, but cannot use it to restore to the older OS.