Q: Bootable for All Mac OS X's

This procedure works for all the Mac OS X's. It is easier to type the command if you change the name of the installer file in the /Applications folder. Download the Mac OS installer. Currently, you can only get Sierra, Mac OS 10.12. The others are now gone.

Put that or a copy into the /Applications folder and use underscores where the spaces are (instead of Install macos Sierra.app, use Install_macos_Sierra.app) This makes typing the command easier. If you leave spaces, then you must type them in with a backslash in front of the space (as shown in the commands supplied by Apple.) That's because UNIX allows spaces in command names but only IF you literalize them with a backslash in front of the space. The Installer is usually deletes by itself when it installs onto a Mac, so you will have to have a copy around anyway. This is what you get when you run it to create a Sierra Bootable Flash Drive (below named SierraInstaller, which get changed by the procedure to Install macos Sierra!)

(All on 1 line in the Terminal app): (It will ask for the system password)[ I have exagerated spaces between the different items of the command to ensure you recognize the need for a space where you might see 2!]

[yourname]$ sudo  /Applications/Install_macos_Sierra.app/Contents/Resources/createinstallmedia   --volume /Volumes/SierraInstaller   --applicationpath  /Applications/Install_macos_Sierra.app

Ready to start.

To continue we need to erase the disk at /Volumes/SierraInstaller.

If you wish to continue type (Y) then press return: y

Erasing Disk: 0%... 10%... 20%... 30%...100%...

Copying installer files to disk...

Copy complete.

Making disk bootable...

Copying boot files...

Copy complete.

Done.

To USE the bootable disk:

1) Attach the bootable flash drive (Which if you look, has been re-named from

"SierraInstaller" to "Install macOS Sierra"

2) Reboot and hold 'Option' down after the startup gong. It should boot from the flash drive