Civilians should create a bootable installer on a USB thumb drive, of course:  <a href="https:&#x2F;&#x2F;support.apple.com&#x2F;en-us&#x2F;HT201372" rel="nofollow">https:&#x2F;&#x2F;support.apple.com&#x2F;en-us&#x2F;HT201372</a><p>And I&#x27;m only being slightly facetious.<p>The ability of modern hardware to download install an OS directly from firmware is a truly great and useful modern innovation, but it leaves a lot of unanswered questions: What if my network is bad? What if this used hardware is stolen?  What if I don&#x27;t have an account?  What if Apple goes bankrupt?<p>USB&#x2F;SD&#x2F;DVD installers do not require network access nor any sort of account&#x2F;purchase verification, and can be created (relatively) easily and officially from downloaded installers.  I have bootable disk images for every OS X installer since OS X Mavericks and I highly recommend it.<p>I&#x27;ll include a USB installer whenever I sell an old laptop.  It costs me next to nothing and gives the buyer some reassurance that they&#x27;re not buying a brick.  And if I decide to hang on to a piece of hardware, I have some assurance that I&#x27;ll be able to use it 10 years from now.