Install, reinstall and erase macOS

A Mac on the bench carries three questions: can it be mended without losing the user’s files, is it going to someone else, and does it start at all? Those answers pick one of five paths, and only two of them erase the disk. A reinstall from macOS RecoverymacOS Recovery: The small macOS kept on a Mac for repairs. From it you can reinstall macOS, restore a Time Machine backup, repair or erase the disk in Disk Utility, reset a forgotten login password and open Terminal. replaces the system files and leaves every account and document in place. Erase All Content and Settings wipes a Mac for its next owner in one pass, on macOS Monterey 12 or later with Apple silicon or the T2 chip. An older Mac is erased in Disk Utility and then reinstalled. A Mac that shows nothing at all is revived, or as a last resort restored, from a second Mac over a USB-C cable.

You will read a Mac’s version and chip from a recorded session, step through a reinstall that keeps the data, work a handover in the order that protects files, check Activation Lock before anything is erased, and apply one rule order to nine support calls.

Which Mac is this, and which macOS does it run?

Three facts belong in the ticket before anyone touches a menu: the installed version of macOS, whether the Mac runs on Apple silicon or an Intel processor, and whether a backup exists. The first two take one read-only session on the Mac itself:

from session import run

# The three facts to write into the ticket before any reinstall: which macOS is installed (name, version and build),
# whether the Mac runs on Apple silicon (arm64) or an Intel processor, and the kernel the installed system boots.
# Every command here only reads the system; nothing is installed, erased or changed.
run("""
sw_vers
uname -m
sysctl -n hw.optional.arm64
uname -s -r
""")

$ sw_vers
ProductName:		macOS
ProductVersion:		26.7.1
BuildVersion:		25G241
$ uname -m
arm64
$ sysctl -n hw.optional.arm64
1
$ uname -s -r
Darwin 25.6.0

sw_vers names the system, its version and its build, which is the number Apple’s release notes use. uname -m prints the processor family: arm64 means Apple siliconApple silicon: Apple's own processors for the Mac, reported as arm64 by uname -m. Such a Mac starts macOS Recovery from its power button, and its firmware can be revived or restored from a second Mac., and x86_64 means an Intel processor. sysctl -n hw.optional.arm64 is the same answer as a flag: it prints 1 on Apple silicon and nothing at all on an Intel Mac. The Mac in the session runs macOS 26.7.1, build 25G241, on Apple silicon with the Darwin 25.6.0 kernel.

The chip decides three things later in this lesson: which keys start Recovery, whether the Mac has the one-click erase feature, and whether its firmware can be revived from another Mac. So it is worth one command, not a guess from the case or the model name.

The installed version matters for a second reason. Apple’s security releases page lists the latest macOS as 27.0.1 and publishes security updates for three versions at a time: macOS Golden Gate 27, macOS Tahoe 26 and macOS Sequoia 15. The Mac in the session, on 26.7.1, is one major version behind the current one and still inside that window. A reinstall from Recovery gives you back the version that is installed, not the newest one, so moving a Mac to a newer major version is a separate job: see updates, patches and drivers.

The third fact has no command behind it: ask the user. The Time Machine menu in the menu bar shows when the last backup finished, and a Mac whose answer is “never” changes the order of the whole job, because the safe steps come before the useful ones. On a Mac with FileVault turned on, the login password is also the only way into the data, so a user who cannot remember it is a very different ticket from one whose Mac merely boots to a grey screen.

macOS Recovery starts differently on each chip

Recovery is a small macOS stored on the Mac itself, with the tools that cannot run while the ordinary system is running: Reinstall macOS, Restore From Time Machine, and Disk Utility for repairing or erasing the startup disk, with other utilities such as Terminal in the menu bar at the top of the screen.

Getting into it is where most tickets stall, because the two chips need different actions. On a Mac with Apple silicon, shut the Mac down, then press and hold the power button until the screen says “Loading startup options”; release it, click Options, then Continue. On an Intel Mac, press and release the power button and immediately hold Command-R until a logo or a spinning globe appears. If macOS will not shut down first, hold the power button for up to 10 seconds until the Mac turns off.

Two more prompts follow on both chips: which volume to recover, usually Macintosh HD, and a user whose login password you know. Step through the whole path, from a cold Mac to a system that starts again with its files untouched:

The step that catches people out is the password prompt. Recovery wants a login password of an account on this Mac, not an Apple Account password. When nobody has it, the work becomes a password reset: Apple’s instructions are to click “Forgot all passwords?” at that prompt, then prove ownership with a recovery key or the Apple Account previously used with the Mac. Do that only on a Mac your organisation or the user in front of you owns, and record who authorised it.

An Intel Mac has one extra route. If its built-in Recovery is damaged, it falls back to Internet Recovery, shown as a spinning globe, and two key combinations force that on purpose: Option-Command-R and Shift-Option-Command-R. Each also changes which version of macOS the reinstall offers, so they are worth knowing when a Mac must land on a particular version. A warning symbol on the globe, or a numbered error such as -2001F, points at the network rather than the Mac.

Three habits save the second visit on an Intel Mac. Use the built-in keyboard of a laptop rather than an external one, because the keys have to be read before macOS loads; with an external keyboard, wait a few seconds after pressing the power button and prefer a wired one made for a Mac. Attach Ethernet, or pick a network from the Wi-Fi menu, when Internet Recovery asks for one. And if the Mac has been set to start from Windows with Boot Camp, set it back to starting from macOS before trying the key combination at all, because the firmware is looking at the other disk.

A reinstall from Recovery keeps every file

Reinstall macOS writes a fresh copy of the operating system over the one on the disk. Accounts, documents, settings and installed apps stay where they are, which is why it is the first thing to try when a Mac boots to a grey screen, loses its login window, or behaves as though system files are damaged. It is not a cure for everything: it will not recover a forgotten password, repair a failing disk, or remove a configuration profile pushed by a management service.

The table is also the warning: because a reinstall leaves the data, it does nothing to prepare a Mac for a new owner. That is a different path, two sections down.

Back up first anyway, whenever the disk can still be read. Time Machine is built in, and Apple’s guidance is a backup disk with at least twice the storage of the Mac, used for backups only: a 1 TB Mac wants a 2 TB disk. Its schedule is hourly backups for the past 24 hours, daily backups for the past month and weekly backups for every month before that, with the oldest deleted when the disk fills. Run First Aid in Disk Utility before the install as well, as the figure above shows: a reinstall onto a disk with errors spends an hour writing files that may not survive.

One tool belongs in this section rather than the next. A bootable installer on a USB drive, made with createinstallmedia, is not needed to upgrade or reinstall macOS at all; Apple describes it for the cases where the usual methods fail, or where several Macs must be installed without downloading the installer each time. A 32 GB flash drive is more than enough, and it is erased in the making.

Erase All Content and Settings is the handover tool

When a Mac goes to a new owner, a colleague or a trade-in, the job is the opposite of a reinstall: the system should stay and everything personal should go. Erase All Content and Settings does that in one pass from inside macOS. Apple’s conditions are exact: macOS Monterey 12 or later, on a Mac with Apple silicon or the Apple T2 Security Chip. Everything older takes the manual route below.

The button lives in System Settings: click General in the sidebar, scroll down on the right, click Transfer or Reset, then Erase All Content and Settings. On macOS Monterey 12 itself the same feature sits in the System Preferences menu. The Mac then asks for two different passwords, and the order surprises people: first the login password of an administrator of this Mac, then the Apple Account password, because the erase signs the Mac out of Apple services. If a message offers to sign back in to iCloud, Apple’s instruction is to ignore it and continue.

Follow the whole handover, including where the files are saved and where an older Mac turns off the main road:

Two conditions in the figure are easy to miss. On a Mac with Apple silicon running macOS 26 or later, Apple asks you to check Repair Assistant for an unfinished repair first, because a part moved from another Mac can still be tied to its old owner’s Apple Account. And if the Mac reports that other volumes must be erased first, Windows was probably installed with Boot Camp: remove it and its partition with Boot Camp before erasing.

What makes this path quick is that the installed macOS stays: there is no download and no installer, so a handover takes minutes rather than the hour a reinstall needs on a slow line. The Mac restarts into the setup assistant, and for a Mac you are passing on, Apple’s advice is not to work through it. Hold the power button until the Mac turns off, and the next owner gets the first screen, exactly as a new Mac does.

The manual route for an older Mac is six steps rather than one: sign out of iCloud and then iMessage, unpair or rename Bluetooth accessories that carry someone’s name, start from Recovery, erase the disk in Disk Utility, reinstall macOS, press Command-Q at the setup assistant, and on an Intel Mac reset NVRAM so that settings kept outside the disk go too. In Disk Utility that erase is of the whole APFSAPFS: Apple File System, the format macOS installs onto from macOS 10.13 on. Apple lists strong encryption, space sharing and snapshots among its features. More in “Operating systems, editions and support dates” volume group, not one volume of it, or the Mac is left with orphaned data volumes.

Activation Lock decides whether a Mac can be set up

Activation LockActivation Lock: A Mac feature that follows Find My: while it is on, the owner's Apple Account password or the device passcode is required before anyone can turn Find My off, erase the Mac, or reactivate and use it. is the reason a second-hand Mac sometimes cannot be used at all. Turning on Find My enables it, and from then on the owner’s Apple Account password or the device passcode is required before anyone can turn off Find My, erase the Mac, or reactivate and use it. Apple’s requirements for the feature are a Mac with Apple silicon or the T2 chip, macOS Catalina 10.15 or later, the default security policy (Full Security, or Secure Boot with external media disallowed on a T2 Mac), and two-factor authentication on the Apple Account.

The owner clears it themselves, in one of two ways. On a Mac they can sign in to: System Settings, their name, iCloud, See All, then Find My Mac, turned off with their Apple Account password. On a Mac that is offline, lost or already in someone else’s hands: sign in at iCloud.com/find, select the Mac and click Remove. A Mac managed by an organisation is different again: the device management service that enrolled it clears the lock, which is why company Macs should be enrolled before they are handed to staff rather than after.

The second column is a support boundary, not a puzzle to solve. There is no legitimate technician’s trick for a Mac locked to another person’s Apple Account, and treating one as a challenge wastes hours and risks handling stolen property. Apple’s own route is an Activation Lock support request with proof of purchase, and that is where such a ticket goes.

One more case looks like a lock and is not quite one. A Mac repaired with a part taken from another Mac can carry a part still tied to that Mac’s owner, which is why Apple asks owners of Apple silicon Macs on macOS Tahoe 26 or later to check Repair Assistant for an unfinished repair before erasing or passing the Mac on. A workshop that swaps parts between machines, as a school or a repair bench does, should record which part went where, because the Mac will ask about it later.

A Mac with no sign of life needs a second Mac

Rarely, a Mac with Apple silicon or the T2 chip loses the firmware that starts it. Apple names the symptoms: an exclamation point in a circle, a blank screen that nothing else explains, a status light showing the firmware recovery pattern, or an installation that fails for no other reason. A power cut during a macOS installation is one documented cause, and no key combination on the Mac itself can fix it, because the part that reads the keys is the part that is broken.

The repair is done by a second Mac. It can be any model on macOS 14 or later, online, with around 32 GB of storage available for what it downloads, and the two Macs are joined by a USB-C to USB-C cable that carries data as well as charge. A Thunderbolt 3 cable will not do, the cable must go straight into both Macs rather than through a hub, and on the affected Mac it must be in the DFU port with nothing in its other USB ports. Both Macs stay on power throughout.

The order in that figure is the whole point. Reviving rewrites the firmware and the recovery system and leaves the disk alone; Apple’s page says to try it first because it is faster and it does not erase the Mac. Restoring puts the Mac back to factory settings, which erases everything on it, and is for a Mac that reviving could not bring back. One of them is a repair, the other is a repair plus a data-loss conversation, so they are never offered to a user as interchangeable.

Two practical details save callbacks. The proof that DFU modeDFU mode: Device firmware update mode: the state in which a Mac's firmware can be rewritten by a second Mac over a USB-C cable. The Mac's own screen stays blank and the second Mac shows a DFU window in the Finder. worked is a DFU window in the Finder of the second Mac, showing “Mac” in the sidebar and “Mac DFU Mode” on the right; if it does not appear, Apple’s first suggestions are the Finder’s sidebar setting for devices, then the timing of the key presses, then a different cable. And on a managed network the second Mac needs to reach Apple’s network, 17.0.0.0/8, so a proxy, firewall or VPN that blocks it will stop a revive halfway.

Getting into DFU mode is also the step people practise least, and it differs by shape of Mac. A laptop is held at Control, Option, Shift and the power button together on its own built-in keyboard, with the timings Apple gives for Apple silicon and for T2 Macs. A desktop needs no keys at all: unplug it from power, hold the power button, and keep holding while you plug the power back in. Both keep the cable in the DFU port and every other USB port empty, which is worth checking twice before deciding that the Mac is beyond a revive.

One rule order for nine calls

Each path above is simple on its own. The skill is picking one in the first minutes of a call, from what the user can tell you. This program holds nine calls as data, applies the conditions of Apple’s articles in a fixed order, and prints the path and a short reason code for each:

"""Picks the path for nine Mac calls: reinstall, erase, reset a password, or revive the firmware from another Mac.

The conditions are Apple's own (support articles 102518, 102541, 102664 and 108900). The first rule that matches a
call wins, so the order in recommend() is the order a technician works in: what is not ours to change, then a Mac
that will not start at all, then the disk, then whether the Mac is being handed on, and only then the everyday
reinstall that keeps the data.
"""

CALLS = [
    {
        "name": "Lab iMac: login password unknown",
        "chip": "apple-silicon", "macos": 26, "starts": "desktop", "disk": "healthy",
        "purpose": "keep-user", "lock": "ours", "tried_revive": False, "blocked": "login-password",
    },
    {
        "name": "Finance iMac: First Aid reports errors",
        "chip": "t2", "macos": 15, "starts": "desktop", "disk": "errors",
        "purpose": "keep-user", "lock": "ours", "tried_revive": False, "blocked": None,
    },
    {
        "name": "MacBook Pro: system files damaged",
        "chip": "apple-silicon", "macos": 26, "starts": "recovery-only", "disk": "healthy",
        "purpose": "keep-user", "lock": "ours", "tried_revive": False, "blocked": None,
    },
    {
        "name": "MacBook Air: handed to a new joiner",
        "chip": "apple-silicon", "macos": 26, "starts": "desktop", "disk": "healthy",
        "purpose": "hand-on", "lock": "ours", "tried_revive": False, "blocked": None,
    },
    {
        "name": "Intel MacBook Air, no T2: being sold",
        "chip": "intel", "macos": 12, "starts": "desktop", "disk": "healthy",
        "purpose": "hand-on", "lock": "ours", "tried_revive": False, "blocked": None,
    },
    {
        "name": "Intel iMac: flashing question mark",
        "chip": "intel", "macos": 15, "starts": "recovery-only", "disk": "not-found",
        "purpose": "keep-user", "lock": "ours", "tried_revive": False, "blocked": None,
    },
    {
        "name": "Used Mac: another owner's Apple Account",
        "chip": "apple-silicon", "macos": 15, "starts": "desktop", "disk": "healthy",
        "purpose": "keep-user", "lock": "other-apple-account", "tried_revive": False, "blocked": None,
    },
    {
        "name": "Managed MacBook Air: a leaver's lock",
        "chip": "apple-silicon", "macos": 26, "starts": "desktop", "disk": "healthy",
        "purpose": "hand-on", "lock": "managed", "tried_revive": False, "blocked": None,
    },
    {
        "name": "Power cut in an update: dead screen",
        "chip": "apple-silicon", "macos": 26, "starts": "no", "disk": "healthy",
        "purpose": "keep-user", "lock": "ours", "tried_revive": False, "blocked": None,
    },
]

# What each path does to what is on the disk, so a ticket can say it before the work starts.
ERASES = {
    "erase-all-content-and-settings",
    "erase-then-reinstall",
    "restore-firmware-in-dfu",
}


def erase_all_ready(call):
    """True when the Mac meets Apple's conditions for Erase All Content and Settings (article 102664)."""
    return call["macos"] >= 12 and call["chip"] in ("apple-silicon", "t2")


def recommend(call):
    """Return the path to take for one call, and the short reason code that explains it."""
    if call["lock"] == "other-apple-account":
        return "stop-and-reach-the-owner", "LOCK-NOT-OURS"
    if call["lock"] == "managed":
        return "clear-lock-in-device-management", "LOCK-MANAGED"
    if call["starts"] == "no":
        if call["tried_revive"]:
            return "restore-firmware-in-dfu", "REVIVE-DID-NOT-HELP"
        return "revive-firmware-in-dfu", "FIRMWARE-REVIVE-FIRST"
    if call["disk"] == "not-found":
        return "check-disk-in-recovery", "NO-STARTUP-DISK"
    if call["disk"] == "errors":
        return "first-aid-then-back-up", "DISK-ERRORS-FIRST"
    if call["purpose"] == "hand-on":
        if erase_all_ready(call):
            return "erase-all-content-and-settings", "ERASE-FEATURE-READY"
        return "erase-then-reinstall", "NO-ERASE-FEATURE"
    if call["blocked"] == "login-password":
        return "reset-password-in-recovery", "PASSWORD-ONLY"
    return "reinstall-over-the-data", "KEEP-THE-DATA"


print(f"{'Call':39} {'Path':31} Reason")
print("-" * 92)
for call in CALLS:
    path, reason = recommend(call)
    print(f"{call['name']:39} {path:31} {reason}")

erasing = [c["name"] for c in CALLS if recommend(c)[0] in ERASES]
print()
print(f"Erases the disk: {len(erasing)} of {len(CALLS)} calls; the other {len(CALLS) - len(erasing)} leave it as it is.")
for name in erasing:
    print(f"  back up first: {name}")

print()
print("The new joiner's MacBook Air, with one field changed:")
handover = CALLS[3]
for chip, macos in (("apple-silicon", 26), ("t2", 12), ("intel", 12), ("apple-silicon", 11)):
    other = dict(handover, chip=chip, macos=macos)
    path, reason = recommend(other)
    print(f"  {chip:13} macOS {macos:>2}  ->  {path:31} {reason}")

print()
revived = dict(CALLS[8], tried_revive=True)
print("The dead screen, after a revive that did not finish:", " / ".join(recommend(revived)))
print("Keeping the data is the last rule: every other path is a rule that matched before it.")

Call                                    Path                            Reason
--------------------------------------------------------------------------------------------
Lab iMac: login password unknown        reset-password-in-recovery      PASSWORD-ONLY
Finance iMac: First Aid reports errors  first-aid-then-back-up          DISK-ERRORS-FIRST
MacBook Pro: system files damaged       reinstall-over-the-data         KEEP-THE-DATA
MacBook Air: handed to a new joiner     erase-all-content-and-settings  ERASE-FEATURE-READY
Intel MacBook Air, no T2: being sold    erase-then-reinstall            NO-ERASE-FEATURE
Intel iMac: flashing question mark      check-disk-in-recovery          NO-STARTUP-DISK
Used Mac: another owner's Apple Account stop-and-reach-the-owner        LOCK-NOT-OURS
Managed MacBook Air: a leaver's lock    clear-lock-in-device-management LOCK-MANAGED
Power cut in an update: dead screen     revive-firmware-in-dfu          FIRMWARE-REVIVE-FIRST

Erases the disk: 2 of 9 calls; the other 7 leave it as it is.
  back up first: MacBook Air: handed to a new joiner
  back up first: Intel MacBook Air, no T2: being sold

The new joiner's MacBook Air, with one field changed:
  apple-silicon macOS 26  ->  erase-all-content-and-settings  ERASE-FEATURE-READY
  t2            macOS 12  ->  erase-all-content-and-settings  ERASE-FEATURE-READY
  intel         macOS 12  ->  erase-then-reinstall            NO-ERASE-FEATURE
  apple-silicon macOS 11  ->  erase-then-reinstall            NO-ERASE-FEATURE

The dead screen, after a revive that did not finish: restore-firmware-in-dfu / REVIVE-DID-NOT-HELP
Keeping the data is the last rule: every other path is a rule that matched before it.

Read the order of the rules in recommend() rather than the list of paths: what we have no right to change comes first, then a Mac that will not start, then the disk, then whether the Mac is being handed on, and the reinstall that keeps the data is the default at the end. Two of the nine calls erase the disk, so two tickets need a backup before any work starts and seven do not.

Three rows show why the order is not cosmetic. The lab iMac whose login password nobody knows comes out as PASSWORD-ONLY, not as an erase, because its disk is healthy and its data is wanted: the fix is a reset in Recovery, and erasing would be an expensive way to avoid asking for proof of ownership. The finance iMac answers DISK-ERRORS-FIRST even though the user asked for a reinstall, because the disk rule sits above every rule that writes to it. And the managed MacBook Air returns LOCK-MANAGED rather than a handover erase, which sends the technician to the device management service rather than to System Settings.

The reason codes are what belongs in the ticket. A path says what you will do; a code says which condition decided it, so the next person can agree or disagree with the decision instead of guessing at it. NO-ERASE-FEATURE records that a chip and a version were both checked. FIRMWARE-REVIVE-FIRST records that the Mac showed no sign of life and that nobody has given up on the data yet.

The block near the end of the output changes one field of the new joiner’s MacBook Air at a time, and the answer flips between ERASE-FEATURE-READY and NO-ERASE-FEATURE exactly where Apple’s conditions say it should: an Apple silicon or T2 Mac on macOS 12 or later gets the one-pass erase, an Intel Mac without T2 and a Mac on macOS 11 do not. The same three questions drive this table, which rules paths out as you answer them:

Practise: the path for three calls

Write the decision for the three calls that matter most on a help desk: a Mac being handed on, a Mac that will not start, and a Mac locked to someone else’s Apple Account. The sample tests check each rule, including the one that refuses a value it does not recognise instead of erasing a Mac by accident.

Write the rules in the order the prompt gives them and return as soon as one matches. That order is the lesson’s whole argument in four lines of code: an impossible job is recognised before a destructive one, a destructive one before a safe one, and the safe reinstall is what is left when nothing else applies. Then take the self-check, which asks about the conditions, the two password prompts and the paths from both figures.

def recovery_path(call):
    """Return the path for one call: a reinstall, an erase, or a firmware revive or restore."""
    return "reinstall-over-the-data"

from recovery_path import recovery_path

OURS = {"chip": "apple-silicon", "macos": 26, "starts": "desktop", "purpose": "keep-user", "lock": "ours", "tried_revive": False}


def test_hand_on_a_mac_that_can_erase_itself():
    """sends a modern Mac being handed on to Erase All Content and Settings"""
    call = dict(OURS, purpose="hand-on")
    assert recovery_path(call) == "erase-all-content-and-settings"
    assert recovery_path(dict(call, chip="t2", macos=12)) == "erase-all-content-and-settings"


def test_hand_on_an_older_mac():
    """erases an older Mac from Recovery instead, then reinstalls"""
    call = dict(OURS, purpose="hand-on", chip="intel", macos=12)
    assert recovery_path(call) == "erase-then-reinstall"
    assert recovery_path(dict(call, chip="apple-silicon", macos=11)) == "erase-then-reinstall"


def test_a_mac_that_will_not_start():
    """revives the firmware first, and only restores after a revive that did not finish"""
    dead = dict(OURS, starts="no")
    assert recovery_path(dead) == "revive-firmware-in-dfu"
    assert recovery_path(dict(dead, tried_revive=True)) == "restore-firmware-in-dfu"


def test_a_lock_that_is_not_ours():
    """stops at a Mac locked to another person's Apple Account, whatever else the call says"""
    assert recovery_path(dict(OURS, lock="other-apple-account")) == "stop-and-reach-the-owner"
    assert recovery_path(dict(OURS, lock="other-apple-account", purpose="hand-on")) == "stop-and-reach-the-owner"


def test_everything_else_keeps_the_data():
    """falls back to the reinstall that leaves the files in place"""
    assert recovery_path(OURS) == "reinstall-over-the-data"
    assert recovery_path(dict(OURS, chip="intel", macos=15)) == "reinstall-over-the-data"


def test_an_unknown_purpose_is_refused():
    """refuses a purpose it does not know instead of guessing"""
    try:
        recovery_path(dict(OURS, purpose="wipe-it"))
    except ValueError:
        return
    raise AssertionError("recovery_path with purpose 'wipe-it' should raise ValueError")

Interview questions

Warm-up (fresher): how do you start macOS Recovery, and what does the Mac ask for once it is there?

It depends on the chip, so read that first. On a Mac with Apple silicon, shut it down, hold the power button until “Loading startup options” appears, release it and click Options, then Continue. On an Intel Mac, press and release the power button and immediately hold Command-R until a logo or spinning globe appears. Recovery then asks which volume to recover, usually Macintosh HD, and for a user whose login password you know; that is a macOS login password, not an Apple Account password. If no one has it, the ticket turns into a password reset through “Forgot all passwords?”, which needs a recovery key or the Apple Account previously used with the Mac. Once in, Recovery offers Reinstall macOS, Restore From Time Machine and Disk Utility, with other utilities such as Terminal in the menu bar.

Warm-up (fresher to 2-5 years): a user wants their Mac “reset”. Which two very different jobs could that mean?

Ask what should survive. If the Mac stays with them and software is broken, the job is Reinstall macOS from Recovery: it replaces the system files and keeps accounts, documents, apps and settings, so nothing has to be restored afterwards. If the Mac is going to someone else, the job is Erase All Content and Settings from System Settings, which removes data, apps and settings, signs the Mac out of Apple services and leaves it at the setup assistant with the installed macOS still in place. The first needs no backup to be safe, though you take one anyway; the second is irreversible, so files are backed up or transferred before it starts. Confusing them either loses a day restoring files, or hands the next owner the last person’s data.

Two harder calls follow: a returned Mac nobody can activate, and a Mac that died mid-update with unsaved work on it. Write down the one thing you would check first, then see whether the model answer starts there:

Key takeaways

• Read the installed version with sw_vers and the chip with uname -m before anything else, because the chip decides the Recovery keys, the one-pass erase and whether firmware can be revived from a second Mac.
• Recovery starts by holding the power button on Apple silicon and with Command-R on Intel, and it asks for a macOS login password, which turns a forgotten-password call into a reset through “Forgot all passwords?”.
• Reinstall macOS replaces the system files and keeps every account, document and setting, so it is the first fix for damaged software and the wrong tool for a handover.
• Erase All Content and Settings needs macOS Monterey 12 or later on an Apple silicon or T2 Mac, asks for the login password and then the Apple Account password, and leaves the Mac at the setup assistant with no download needed.
• Activation Lock requires the owner’s Apple Account password or passcode before anyone can turn off Find My, erase or reactivate a Mac, so a Mac locked to someone else goes back to its owner or to Apple’s support request, never to a workaround.
• A Mac that shows no sign of life is revived from a second Mac on macOS 14 or later over a USB-C data cable in DFU mode, and only restored, which erases it, when reviving fails.