OS initial setup

Removing snap package

Free resources (computing, memory and storage) since I am not going to use snap package manager.

• Step 1. List snap packages installed

  sudo snap list
  

  The output will something like

  sudo snap list
  Name    Version   Rev    Tracking       Publisher   Notes
  core18  20210611  2074   latest/stable  canonical✓  base
  lxd     4.0.7     21029  4.0/stable/…   canonical✓  -
  snapd   2.51.1    12398  latest/stable  canonical✓  snapd
  

• Step 2. Remove snap packages with command snap remove <package>

  snap remove lxd && snap remove core18 && snap remove snapd
  

• Step 3. Remove snapd package

  sudo apt purge snapd
  

  Remove packages not required

  sudo apt autoremove
  

Raspberry PI specific configuration

Installing Fake RTC clock

Raspberry PI does not have by default a RTC (real-time clock) keeping the time when the Raspberry PI is off. A RTC module can be added to each RaspberryPI but we won’t do it here since we will use NTP to keep time in sync.

Even when NTP is used to synchronize the time and date, when it boots takes as current-time the time of the first-installation and it could cause problems in boot time when the OS detect that a mount point was created in the future and ask for manual execution of fscsk

As a side effect the NTP synchronizatio will also take longer since NTP adjust the time in small steps.

For solving this fake-hwclock package need to be installed. fake-hwclock keeps track of the current time in a file and it load the latest time stored in boot time.

Installing Utility scripts

Raspberry PI OS contains several specific utilities such as vcgencmd that are also available in Ubuntu 20.04 through the package libraspberrypi-bin

sudo apt install libraspberrypi-bi

Two scripts, using vcgencmd command for checking temperature and throttling status of Raspberry Pi, can be deployed on each Raspberry Pi (in /usr/local/bin directory)

pi_temp for getting Raspeberry Pi temperature pi_throttling for getting the throttling status

Boths scripts can be executed remotely with Ansible:

ansible -i inventory.yml -b -m shell -a "pi_temp" raspberrypi
    
ansible -i inventory.yml -b -m shell -a "pi_throttling" raspberrypi

Change default GPU Memory Split

The Raspberry PI allocates part of the RAM memory to the GPU (76 MB of the available RAM)

Since the Raspberry PIs in the cluster are configured as a headless server, without monitorm and using the server Ubuntu distribution (not desktop GUI) Rasberry PI reserved GPU Memory can be set to lowest possible (16M).

• Step 1. Edit /boot/firmware/config.txt file, adding at the end:

  gpu_mem=16
  

• Step 2. Reboot the Raspberry Pi

  sudo reboot
  

Enabling VXLAN module (Ubuntu 22.04)

VXLAN support is not present in kernel since Ubuntu 21.04. It makes K3S fail to run. See more details in K3S issue

Starting with Ubuntu 21.10, vxlan support on Raspberry Pi has been moved into a separate kernel module, that need to be manually installed. See specific Raspberry PI K3S specific installation requirements. Further details in this Ubuntu bug: “VXLAN support is not present in kernel - Ubuntu 21.10 on Raspberry Pi 4 (64bit)”

sudo apt install linux-modules-extra-raspi & reboot