Re­in­stall macOS if start-up vol­ume erased

Glenn Fleish­man shows how to re­cover a deleted start-up disk

Macworld - - Contents -

There are a cou­ple of op­tions with an erased par­ti­tion. Be­cause Re­cov­ery didn’t work, the fastest way to in­stall fresh is to make or bor­row a macOS in­staller on a USB flash drive or a disk drive. We have in­struc­tions for mak­ing a bootable in­staller with macOS Sierra (as well as archived ver­sions for sev­eral pre­vi­ous re­leases). You need at least an 8GB flash drive. The fol­low­ing ar­ti­cle in­cludes in­struc­tions on ob­tain­ing the in­staller, which might in­volve you hav­ing to use some­one’s else Mac to down­load it, if you don’t have a re­place­ment Mac on hand yet.

But if you can’t get ac­cess to another Mac or the nec­es­sary drive, it’s still pos­si­ble to use a dif­fer­ent Re­cov­ery mode on all re­cent Macs, dat­ing back to 2010. Nor­mally, you can start up a Mac while hold­ing down Com­mand-R to boot into what Ap­ple now calls macOS Re­cov­ery. That al­lows you to run Disk Util­ity, re­in­stall or wipe and in­stall the sys­tem, ac­cess Ter­mi­nal for com­mand-line func­tions, and so on. In that mode, when you choose to re­in­stall with­out eras­ing the drive, my rec­ol­lec­tion is that Re­cov­ery looks for the cur­rent OS sys­tem in­staller on your start-up disk in the Ap­pli­ca­tions folder, and uses that.

Fail­ing find­ing it, Re­cov­ery down­loads the cur­rently in­stalled ver­sion of macOS (or OS X), which is about 5GB. When com­plete, it in­stalls it and re­boots, and places the in­staller in the Ap­pli­ca­tions folder.

How­ever, there’s another op­tion: macOS Re­cov­ery over the In­ter­net, which re­quires ei­ther a Mac model

re­leased in 2012 or later, or most 2010 and 2011 mod­els with a firmware up­grade ap­plied. There, the Mac reaches out over a Wi-Fi or eth­er­net con­nec­tion to down­load the rel­a­tively mod­est Re­cov­ery soft­ware, which then boot­straps the down­load of the full macOS in­staller. Ap­ple says In­ter­net-based Re­cov­ery should hap­pen au­to­mat­i­cally on sup­ported mod­els, and you should see a spin­ning globe when that mode is in­voked while the down­load oc­curs. How­ever, if you have nor­mal Re­cov­ery in­stalled and it re­fuses to in­stall macOS for some rea­son, you can man­u­ally in­voke In­ter­net Re­cov­ery.

While Com­mand-R at start-up al­ways in­stalls what­ever the most re­cent ver­sion you in­stalled on your Mac, hold­ing down Com­mand-Alt-R brings down the very lat­est com­pat­i­ble ver­sion that can be in­stalled. Ap­ple also of­fers Shift-Com­mand-Alt-R, which in­stalls the ver­sion of OS X or macOS with which your com­puter shipped, or the next old­est com­pat­i­ble sys­tem still avail­able for down­load.

(Ap­ple just changed this be­hav­iour with 10.12.4, but if you’re us­ing In­ter­net Re­cov­ery for a clean in­stall on an erased drive, the new be­hav­iour should be ac­tive as it will be pulled from the ver­sion of Re­cov­ery that’s boot­strapped from Ap­ple’s servers. The pre-10.12.4 op­tion is sim­ply Com­mand-Alt-R, but it acts like the new Shift-Com­mand-Alt-R, in­stalling the shipped op­er­at­ing sys­tem or the old­est com­pat­i­ble ver­sion.)

Ap­ple rec­om­mends the Com­mand-Alt-R op­tion as the only safe way to re­in­stall a Mac with El Cap­i­tan or ear­lier ver­sions of macOS if you want to be sure your Ap­ple ID doesn’t per­sist even af­ter era­sure.

Re­cov­ery lets you in­stall onto an erased par­ti­tion, but only if Re­cov­ery wasn’t erased, too

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