Hey folks, I’ve dealt with this exact recovery server error multiple times when upgrading older macOS releases like Sierra to High Sierra. Let’s go through the tried-and-true fixes that have worked for me and the broader community:

1. Verify Your Network Connection #

• Start with the basics: ensure you’re on a stable Wi-Fi or (preferably) Ethernet connection. Flaky wireless can interrupt communication with Apple’s servers.
• Power cycle your router/modem—unplug it for 30 seconds, plug it back in, wait for it to fully restart, then reconnect your Mac.

2. Correct Your Mac’s Date & Time #

Apple’s recovery servers rely on accurate date/time settings for authentication, and this is one of the most common fixes:

• If you’re in your regular Sierra system: Open System Preferences > Date & Time, uncheck "Set date and time automatically", manually input the correct current date/time, then re-enable the automatic setting after a minute.
• If you’re in Recovery Mode: Open Terminal from the Utilities menu, run date mmddHHMMyyyy (replace with your actual date—e.g., date 100515002024 for October 5th, 3:00 PM 2024), then quit Terminal and retry the update.

3. Upgrade Directly from the App Store #

If you were trying to upgrade via Recovery Mode, switch to the regular system:

• Boot back into Sierra, open the App Store.
• Click your profile icon in the top right, go to the Purchased tab, find "macOS High Sierra", and download the installer.
• Run the installer from your desktop—this uses the App Store’s download servers instead of recovery servers, which often bypasses the error.

4. Reset PRAM/NVRAM (Intel Macs Only) #

This fixes low-level system glitches that might block server communication:

• Shut down your Mac, then turn it on and immediately hold Command + Option + P + R.
• Keep holding until you hear the startup chime twice, then release. Let your Mac boot normally, then try the update again.
• Note: Apple Silicon Macs don’t require this—just restart your Mac normally.

5. Create a Bootable High Sierra Installer #

If all other methods fail, a bootable installer is a reliable workaround:

1. On a working Mac (running Sierra or later), download the macOS High Sierra installer from the App Store’s Purchased tab.
2. Insert an 8GB+ USB drive (it will be erased), note its name from Finder.
3. Open Terminal and run this command (replace [USB_NAME] with your drive’s name):

   sudo /Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/[USB_NAME] --applicationpath /Applications/Install\ macOS\ High\ Sierra.app
   

4. Enter your admin password when prompted, wait for the installer to be created.
5. Plug the USB into your target Mac, restart it, hold the Option key, and select the bootable installer.
6. Follow the on-screen prompts to upgrade to High Sierra.

内容的提问来源于stack exchange，提问作者Sazzad Hissain Khan