Take a Pi Image

We update our Pi image every 4-6 months to keep install times speedy. As part of an install, we update the Pi to make sure it has all the latest security patches, and the longer it’s been since we updated the image, the longer that update takes. The following is the process we follow to take an image.

Getting started

Download the lastest lite Raspbian image from the Raspberry Pi Foundation and flash it onto an SD card. Before inserting the SD card into a Pi, it’s helpful to create a file called ssh in the boot partition so that you can SSH into the Pi once it’s plugged in. Once that’s done, insert the SD card into the Pi, plug in a network cable, and insert the power cable to turn the Pi on.

Once the Pi is powered on, you’ll be able to SSH into the Pi using the IP address that is printed a few lines above the login line. The default username is pi and the default password is raspberry.

OS Setup

Most of these commmands require being root to run them. It’s easiest to just become the root user by running sudo su when you start a new section.

Update the OS

touch /boot/ssh (1)
timedatectl set-timezone "America/Denver" (2)

date -s "$(wget -qSO- --max-redirect=0 google.com 2>&1 | grep Date: | cut -d' ' -f5-8)Z" (3)

apt update
apt -y upgrade
apt -y install vim
apt -y autoremove
apt -y autoclean

vim /etc/default/keyboard (4)

passwd pi (5)
usermod -aG sudo pi

vim /home/pi/.ssh/authorized_keys (6)

reboot
1 Make sure SSH stays enabled
2 Set the timezone to the appropriate timezone for yourself
3 This command updates the default time
4 Change XKBLAYOUT to us
5 Change the default password to whatever password you want
6 Copy any public ssh keys into this folder so that they can log into the pi without the password

Docker

First, install the docker engine.

curl -fsSL https://get.docker.com | sh
usermod -aG docker pi

systemctl enable docker
reboot

Then install docker-compose using pip.

apt update
apt -y install python3 python3-pip libffi-dev
pip3 install docker-compose

reboot

Other programs

We are currently using salt to manage our Pi’s. We will install salt as well as the programs required to get the UI started.

wget -O - https://repo.saltstack.com/apt/debian/9/armhf/archive/2018.3.2/SALTSTACK-GPG-KEY.pub | sudo apt-key add -
echo "deb http://repo.saltstack.com/apt/debian/9/armhf/archive/2018.3.2 stretch main" > /etc/apt/sources.list.d/saltstack.list

apt update
apt install -y xserver-xorg xinit i3 chromium-browser tmux imagemagick x11-apps dnsmasq salt-minion ntpdate htop
apt -y upgrade
apt -y autoremove
apt -y autoclean

reboot

Pi Setup Service

We have a service to help provision new Pi’s. This service that we enable in the image pulls that service down and starts it.

mkdir /byu
curl https://raw.githubusercontent.com/byuoitav/flight-deck/master/image/pi-setup.service > /byu/pi-setup.service
curl https://raw.githubusercontent.com/byuoitav/flight-deck/master/image/pi-setup.sh > /byu/pi-setup.sh
chmod +x /byu/pi-setup.sh

systemctl daemon-reload
systemctl enable /byu/pi-setup.service

Final steps

To keep the image as small as possible, clear the commmand history.

history -c
shutdown -h now

Create a new image

Now that we have an SD card with the OS in the state we want it, we need to create an image based on that state. To start, plug the SD card into your computer.

Copying the image from an SD card will require the same amount of storage as the size of the SD card. For example, a 32GB SD card will require at least 32GB of free space.

Take the image

Once the SD card is plugged into your computer, use lsblk to figure out where the SD card is mounted.

sudo dd if=/dev/sdb of=/path/to/clone.img (1)
1 Replace /dev/sdb with the mount location of the SD card, and the of= to the location you want the image to go

Shrink image

Right now, the image matches the size of the SD card; A lot of that space is wasted. Pi Shrink is a script that will cut out that useless space.

Always be careful downloading and running scripts, especially as sudo. 
curl https://raw.githubusercontent.com/Drewsif/PiShrink/master/pishrink.sh > pishrink.sh
chmod +x pishrink.sh
sudo ./pishrink.sh /path/to/clone.img /path/to/shrunk-image.img (1)
1 Replace /path/to/ with the appropriate locations

If you need to make small changes to the image after you have already taken it:

  1. Get the start blocks with fdisk -l /path/to/shrunk-image.img. The output will look like:

    Disk byuav-2019-08-21.img: 3.56 GiB, 3809141248 bytes, 7439729 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xfd9cf439

Device                Boot  Start     End Sectors  Size Id Type
byuav-2019-08-21.img1        8192  532480  524289  256M  c W95 FAT32 (LBA)
byuav-2019-08-21.img2      540672 7439728 6899057  3.3G 83 Linux

  2. Create directories in /mnt to mount each block to (i.e., mkdir /mnt/piroot)

  3. Mount the block(s) you want to modify, using the start sector from above. In this case, to mount the second block to /mnt/piroot, I would use this command:

    mount -v -o offset=$((512*540672)) -t ext4 byuav-2019-08-21.img `/mnt/piroot`

  4. Modify the images files however you need by adding/modifying/deleting files from /mnt/piroot

  5. Unmount the block(s)

    umount /mnt/piroot

Compress image

To have the smallest image size, use gzip to compress the shrunk image before sharing it.

gzip -k -9 /path/to/shrunk-image.img