Install Alpine in sys mode on local SSD.

• Download Alpine Linux x86_64: https://alpinelinux.org/downloads/
• dd image to USB drive
• Update APU2 BIOS if needed, connect via serial console.
• Boot APU2 from USB, F10, select USB drive
• At boot: press TAB

  Booting from Hard Disk...
  
  ISOLINUX 6.04 6.04-pre1 EHDD Copyright (C) 1994-2015 H. Peter Anvin et al
  boot: 
   vanilla
  boot: 

• Type the name, append console settings and press ENTER:

  vanilla console=ttyS0,115200

  <SNIP>
  
   * Creating user login records ... [ ok ]
   * Wiping /tmp directory ... [ ok ]
   * Setting hostname ... [ ok ]
   * Starting busybox syslog ... [ ok ]
   * Starting firstboot ... [ ok ]
  
  Welcome to Alpine Linux 3.9
  Kernel 4.19.18-0-vanilla on an x86_64 (/dev/ttyS0)
  
  localhost login: 

• Log in with root and no password.
• Run the setup-alpine script.
• Reboot with the same console 'trick' as above.
• Add a new user with adduser.
• Edit /etc/motd.
• Enable serial console access, edit /etc/update-extlinux.conf, then run update-extlinux
• reboot

• If u encounter a long delay at boot, it might be an entropy (randomness) problem, install haveged:

  apk add haveged
  rc-service haveged start
  rc-update add haveged default