I’ve done clean installs on many macs and I have never downloaded anything from the app store. All of my installers have come from internet – and most of the times I don’t install the newest macOS.
You can make a bootable USB disk with something like DiskMaker X, or you could put your mac into Target Disk mode (hold “T” while booting) and connect to another mac with firewire/thunderbolt cable, then run the installer from there.
You may be able to update to the newest – just be sure the software you need to run is compatible. All of our macos versions here can be made ‘bootable’. Not everyone wants to sign up to the App Store.
I use this to create my Linux bootable ISOs, can this program be utilized instead of DiskMaker X , since I already have it installed ? Also I grabbed the Mac OS X El Capitan 10.11.6 and it’s a .dmg file, when I try 123movies to use as an image in Etcher it says it can’t be used. Would DiskMaker X solve this issue or am I doing something wrong ?
Use the InstallESD.dmg as source (It’s located at the: OS X El Capitan 10.11.6 (15G31).dmg> Install OS X El Capitan.app> Contents> SharedSupport path)
That did the trick, thank you and all of you that contributed, now I am no longer worried at what might happen if I needed to reinstall my OS, one more question if I may, I now have a 16G SanDisk Ultra USB3, which is named “OS X Install ESD” when I plug it into my Macbook USB port and it displays the contents of the install medium, is this the correct result? If so then when in recovery I would plug this in and take it from there?