Mount swapfile when booting from external storage (see: https://discussionsjapan.apple.com/thread/110201665 )

01-install.sh.example

#!/bin/bash

sudo mv com.example.mountswap.plist /Library/LaunchAgents
sudo chown root:wheel /Library/LaunchAgents/com.example.mountswap.plist
sudo launchctl load com.example.mountswap.plist 

com.example.mountswap.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>com.example.mountswap</string>
    <key>ProgramArguments</key>
    <array>
      <string>diskutil</string>
      <string>mount</string>
      <string>-mountPoint</string>
      <string>/private/var/vm</string>
      <string>disk3s4</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
  </dict>
</plist>