In the end, I dived into the Ubiquity source code used in Ubuntu 20.04 and it seems that developers have removed such features like pkgsel/include. Ubuntu documentation is silent about that. Also, I confirmed that preseed/late_command is not fired. The only thing working is ubiquity/success_command. I don't know if it was like that from the very beginning, but success_command is run with sh -c "commands here", which from my testing means that you are not able to run scripts inside ubiquity/success_command. After really long tinkering around, my final (working) solution is using cron to create a command after reboot, which will wait for Internet access (by checking 8.8.8.8):

ubiquity ubiquity/success_command string 

    mkdir -p /mnt/floppy; 

    mount -t vfat /dev/fd0 /mnt/floppy; 

    cp /mnt/floppy/sudoers /target/etc/sudoers.d/99_engineer; 

    chmod 440 /target/etc/sudoers.d/99_engineer; 

    mkdir -p /target/root; 

    cp /mnt/floppy/firstboot.sh /target/root/firstboot.sh; 

    chmod 750 /target/root/firstboot.sh; 

    echo '@reboot root bash /root/firstboot.sh >> /var/log/firstboot.log 2>&1' >> /target/etc/crontab;

Note that I have also used here floppy_files from Packer - this is why I can use /dev/fd0.

sudoers file:

engineer ALL=(ALL) NOPASSWD:ALL

firstboot.sh file:

#!/bin/bash



echo "Waiting for Internet ..."

while ! timeout 0.2 ping -c 1 -n 8.8.8.8 &> /dev/null

do

    printf "%c" "."

done

echo "OK"



# Instal SSH Server

apt-get -y update

apt-get -y install openssh-server



# Remove from crontab

sed -i '/firstboot/d' /etc/crontab

Btw, huge minus for all people responsible for removing pkgsel/include and other changes, which are documented everywhere and currently does not work in automatic-ubiquity, and which allowed in an easy manner to install extra stuff needed.