降级：关机以后怎么做Downgrade: what to do after shutting down

你已经用 StayPut 做好了启动 U 盘、备份好了这台 Mac。下面每一步做完就勾一下，不会走丢。 You’ve made the USB startup disk with StayPut and backed up this Mac. Tick each step as you go so you don’t lose your place.

这会抹掉整台 Mac。开始前确认：Time Machine 备份已经做完；Mac 接上了电源；知道 Wi‑Fi 密码和 Apple 账户密码（抹掉后激活要用）。 This erases the whole Mac. Before you start: the Time Machine backup has finished; the Mac is on power; you know your Wi-Fi password and Apple Account password (needed to activate the Mac after erasing).

  1. 关机Shut down

    U 盘保持插着，最好直接插在 Mac 上，不要经过扩展坞。点左上角苹果菜单 →“关机”，等屏幕完全黑掉。 Keep the USB drive plugged in, directly into the Mac if you can (not through a hub). Choose Apple menu › Shut Down and wait until the screen is completely black.

  2. 进入启动选项Open startup options

    按住电源键不要松手，直到屏幕上出现“正在载入启动选项”，再松开。MacBook 的电源键是键盘右上角触控 ID 那个键；Mac mini 的电源按钮在机身底部靠后的角上；iMac、Mac Studio 的在背面。 Press and hold the power button until you see “Loading startup options”. Then let go. On a MacBook it’s the Touch ID key at the top right of the keyboard; on a Mac mini it’s on the bottom near the back corner; on an iMac or Mac Studio it’s on the back.

    看到的是一排磁盘图标，右边有一个齿轮“选项”。You’ll see a row of disk icons and a gear labelled Options.

  3. 选 U 盘启动Start from the USB drive

    点“Install macOS …”（黄色的 U 盘图标），再点下面的“继续”。如果让你选一个用户、输密码，就选你平时登录的那个账户，输它的密码。 Click “Install macOS …” (the yellow USB drive icon), then Continue. If it asks you to pick a user and enter a password, pick the account you normally log in with.

  4. 打开磁盘工具Open Disk Utility

    会出现一个列着几个选项的窗口（安装 macOS、磁盘工具……）。选“磁盘工具”，点“继续”。 A window with a few options appears (Install macOS, Disk Utility…). Select Disk Utility and click Continue.

  5. 抹掉这台 MacErase the Mac

    在左边“内置”下面选“Macintosh HD”，点上面的“抹掉”。名称保持“Macintosh HD”，格式选“APFS”，然后点“抹掉宗卷组”（没有这个按钮就点“抹掉”）。如果要你输 Apple 账户，输你自己的。 In the sidebar under Internal, select “Macintosh HD” and click Erase at the top. Keep the name “Macintosh HD”, choose APFS, then click “Erase Volume Group” (or Erase if that button isn’t there). If it asks for an Apple Account, use your own.

    选错盘会抹掉别的东西：认准“内置”下面的 Macintosh HD，不是 U 盘，也不是备份盘。Pick the right disk: Macintosh HD under Internal, not the USB drive and not your backup disk.

  6. 激活Activate

    抹掉后可能出现“激活 Mac”：连上 Wi‑Fi，按提示用 Apple 账户激活。完成后点“退出到恢复实用工具”。 You may see “Activate Mac”. Join Wi-Fi and sign in with your Apple Account as asked. When it’s done, click “Exit to Recovery Utilities”.

  7. 安装旧版本Install the older macOS

    退出磁盘工具（左上角“磁盘工具”菜单 →“退出”）。回到选项窗口，选“安装 macOS …”（你做 U 盘时选的那个版本），点“继续”，同意条款，选“Macintosh HD”，点“继续”。 Quit Disk Utility (Disk Utility menu › Quit). Back in the options window, choose “Install macOS …” (the version you put on the USB drive) and Continue, agree, choose “Macintosh HD” and Continue.

    大约 30–60 分钟，中间会重启几次，屏幕黑一会儿是正常的。别拔 U 盘，别合上屏幕。It takes about 30–60 minutes and restarts a few times; a black screen for a while is normal. Don’t unplug the USB drive or close the lid.

  8. 把文件拿回来Bring your files back

    装好后会出现开机设置。到“迁移助理”那一步，选“从 Mac、Time Machine 备份或启动磁盘”，插上备份盘，选最近的那份备份。 When the setup screens appear, at Migration Assistant choose “From a Mac, Time Machine backup or startup disk”, plug in your backup disk and pick the latest backup.

    迁移助理说这份备份用不了？用更新的 macOS 做的备份可能会被拒绝。先跳过、把设置做完，然后打开访达，在左边点备份盘，依次打开最近的那份备份 →“Macintosh HD - 数据”→“用户”→ 你的名字，把“文稿”“桌面”“图片”等文件夹拖回来。App 从 App Store 或官网重新安装。Migration Assistant says it can’t use the backup? A backup made on a newer macOS may be refused. Skip it and finish setting up, then open Finder, click the backup disk in the sidebar, open the latest backup › Macintosh HD - Data › Users › your name, and drag Documents, Desktop, Pictures and your other folders back. Reinstall your apps from the App Store or their websites.

    当时跳过了也没关系：以后在“应用程序 → 实用工具”里打开“迁移助理”。都搬完后可以再装一次 StayPut，把这台 Mac 锁定在这个版本。Skipped it? Open Migration Assistant later from Applications › Utilities. Afterwards, reinstall StayPut and lock this Mac to this version.