Fix macOS PKDownloadError error 8 (stalled installer)

Quick answer for advanced users

Run sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder in Terminal, then restart the App Store or Software Update. Still broken? Delete ~/Library/Caches/com.apple.appstore and /Library/Updates (after a backup).

Why this happens

PKDownloadError error 8 (sometimes shown as "The download failed. PKDownloadError error 8") appears when macOS can’t pull down packages from Apple’s CDN. I’ve seen it most often on Ventura and Monterey, especially after a VPN disconnect or switching Wi-Fi networks mid-download. The culprit is almost always a stale DNS cache or a stuck storedownloadd process holding on to a dead connection. Apple’s servers are usually fine — it’s your local network state that’s the problem.

This isn’t a hardware issue or a corrupted system file 99% of the time. Don’t bother reinstalling macOS or running First Aid on your disk for this. It’s a transient network handshake failure that needs a swift kick.

Step-by-step fix

Flush DNS and reset network services — Open Terminal and paste:
```
sudo dscacheutil -flushcache
sudo killall -HUP mDNSResponder
```
This clears the local DNS resolver cache. On macOS Ventura and later, you might also need to toggle Wi-Fi off/on in System Settings.
Kill the stalled download process — Run:
```
sudo killall storedownloadd
```
That process manages package downloads. If it’s hung, no new download will start. After killing it, the next update attempt will spawn a fresh one.
Clear download caches — Quit the App Store or System Settings. Then in Finder, hit Cmd+Shift+G and go to ~/Library/Caches/com.apple.appstore. Delete everything inside. Also check /Library/Updates (note: root-level Library, not user). Trash its contents too. You’ll need admin rights for the second path.
Switch to a wired connection — If you’re on Wi-Fi and the error persists, plug in Ethernet. Some corporate Wi-Fi portals or double NAT setups choke on large Apple downloads. I’ve seen this on UniFi and Cisco Meraki networks.
Retry the download — Open System Settings > General > Software Update (or App Store on older macOS). Click "Update Now" again. It should resume without error.

If the main fix doesn’t work

Sometimes the error masks a corrupted receipt file. Try this:

Delete installation receipts — In Terminal:
```
sudo rm -rf /System/Library/Receipts/InstallHistory.plist
```
This resets the update history. Don’t worry, it’s rebuilt on next update check. Backup first if paranoid.
Use the command-line installer — If you’re updating to a full OS version (e.g., Sonoma), download the installer from the App Store first, then run:
```
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/startosinstall --agreetolicense
```
This bypasses the GUI download handler entirely.
Check system clock — Wrong date/time breaks SSL certificate validation. Go to System Settings > General > Date & Time and toggle "Set time automatically" off and on. Then run sudo sntp -sS time.apple.com in Terminal.

Prevention tip

Before starting a big macOS download, restart your router and Mac to clear ARP tables and stale DNS. Also — don’t switch networks mid-download. If you’re on a VPN, disconnect it. Apple’s CDN uses Akamai, and VPNs sometimes route traffic through a bad edge node that drops the connection after a few seconds. I keep a wired backup for updates because Wi-Fi interference is still a common cause of this error.

One more thing: if you see PKDownloadError error 8 on a brand new Mac out of the box, your date is almost certainly wrong. Set it manually via Terminal with date MMDDhhmmYYYY before running setup.