Make a unattended installation of Ubuntu server image

In this post we see how I investigated to find the target preseed file matches my requirement. This post shows the step-by-step commands in summary.

Firstly let's fetch the iso contents from the original iso image.

$ sudo mount -o loop ~/Desktop/images/ubuntu-16.04.1-server-amd64.iso ./160401-base-iso/
mount: /dev/loop6 is write-protected, mounting read-only
$ cp -rT ./160401-base-iso/ ./160401-target-iso/
$ sudo umount ~/Desktop/images/ubuntu-16.04.1-server-amd64.iso

Then let's tweak isolinux, which is used to boot the system at the very first time, a bit:

$ chmod u+w 160401-target-iso/isolinux/txt.cfg
$ vi 160401-target-iso/isolinux/txt.cfg

You may want to use the txt.cfg directly from here https://gist.github.com/tai271828/cbe426c158c68ae8f51a18b0ad26af52#file-txt-cfg

and

default install
label install
  menu label ^Install Ubuntu Server
  kernel /install/vmlinuz
  append  file=/cdrom/preseed/unattended-ubuntu-server.seed vga=788 initrd=/install/initrd.gz quiet languagechooser/language-name=English debian-installer/locale=en_US keyboard-configuration/layoutcode=us ---

You may also want to use the isolinux.cfg here as well https://gist.github.com/tai271828/cbe426c158c68ae8f51a18b0ad26af52#file-isolinux-cfg

$ chmod u+w 160401-target-iso/isolinux/isolinux.cfg
$ vi 160401-target-iso/isolinux/isolinux.cfg

set timeout as 1 (or any positive integer. 0 means waiting forever)

Lastly let's put the preseed, unattended-ubuntu-server.seed

,  pointed by txt.cfg. Please check the details of the preseed file here: https://gist.github.com/tai271828/cbe426c158c68ae8f51a18b0ad26af52#file-unattended-ubuntu-server-seed

Everything is ready! Let's generate the iso. Under the target iso folder

sudo mkisofs -r -V "UBUNTU160401" -cache-inodes -J -l -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o ~/Desktop/images/ubuntu-16.04.1-server-amd64-autoinstall.iso .

The above steps are wrapped up here https://gist.github.com/tai271828/cbe426c158c68ae8f51a18b0ad26af52#file-prepare-image-sh Tweak it to match your file hierarchy.

PS Ubuntu server by default has no tty7 (used for X to provide GUI conventionally) and use tty1.

What is Next...

The final product is an iso. You could boot it from virt-manager easily by using it as a virtual CD-ROM disk. However, in the modern world, we use live USB much more often now. To make a bootable live USB of this iso, you may achieve the goal by

sudo isohybrid ubuntu-16.04.1-server-amd64-autoinstall.iso
sudo dd bs=4M if=./ubuntu-16.04.1-server-amd64-autoinstall.iso of=/dev/sdX conv=fdatasync

How and why isohubrid works you could refer to my another blog post in Chinese http://zh-tw-tai271828.blogspot.tw/2017/07/hack-iso-usb-isohybrid.html

To investigation process to make a unattended installation of Ubuntu server image

If you are trying to find a step-by-step solution post, this post is NOT for you. Please go to here to have a step-by-step solution http://tai271828.blogspot.tw/2018/04/make-unattended-installation-of-ubuntu.html .


The longevous and respectable installer, debian-installer (d-i), provides powerful feature to customize and automate your installation by preseed, which is a configuration file to answer the questions of the installation prompt. The core question is: how do I know which question regarding which prompt, and what answer is acceptable or understandable by d-i?


If you check the d-i manual to try to answer the above question, you will find (1) the document enlists basic question-answers grouping by features (2) the groups collect basic description and may not elaborate the details for each question-answer item (3) you may customize your installation but you don't find the question-answer matches your requirement.

To overcome the lack of information, I did

(1) (default, RTFM ;) ) check the manual.[1]
(2) search example preseed file developed by others. google or check others' open source projects.
(3) find a workable benchmark. (debconf-get-selections is a useful and promising solution)


Regarding (1), I read the manual in this way very often: (a) confirm my goal ("What question I want to solve? Describe it in technical action item words.") (b) imagine what the solution may look like. What the design of the solution may be. (c) find the possible design from the manual (d) if nothing was found, skim the sub-titles of the  manual, and go back to (a)(b)(c). Read the document line-by-line is the final action which may or may not be considered to adapt.

Regarding (2), google may be useful (google "unattended ubuntu server preseed github", for example) or NOT. Targeting on open source projects and have a look of their source is more efficient in my experience, especially the project is still a working and alive project.

Regarding (3), this skill is also suggested by Effective Debugging: 66 Specific Ways to Debug Software and Systems: Item 5 Find the Difference between a Known good System and a Failing One [2]. To create the benchmark of a good system (with working answers to the questions), debconf-get-selections is a tool to dump the contents of the debconf database[3], which contains the question-answers in your system. You may want to append --installer when using debconf-get-selection to fetch the question-answers of installation stage.

A usual way looks like this:

1. Prepare a working system installed manually and answered all prompted as your wish. VM may be a good choice.
2. Login the working system. Dump the question-answers by debconf-get-selections --installer
3. Compare the question-answers or find possible question-answers against to the prompt you want to bypass automatically.

This is a bit trial-and-error flow. Setup an easy flow to repeat will be helpful very much. 

[1] Usually Appendix B. is recommended https://www.debian.org/releases/stable/amd64/apb.html.en

[2] https://books.google.com.tw/books?id=Fa6JDAAAQBAJ&pg=PT125&lpg=PT125&dq=effective+debugging+titles&source=bl&ots=moKocciySF&sig=HuoF5Dl3mJBoGf84YUXix-Hk5ic&hl=en&sa=X&ved=2ahUKEwjFwajc3c3aAhXNNpQKHa6dDocQ6AEwA3oECAAQSQ#v=onepage&q=effective%20debugging%20titles&f=false

[3] By default there is not debconf-get-selections, you may need to install it by "apt-get install debconf-utils" to get it.

Use grub to boot the target kernel after reboot

The key concept is that grub.cfg is the final product. The grub behavior will be performed according to grub.cfg (and the environment variables used by it). Thus please try to control everything with the tools of grub first. Let the tools control grub.cfg and environment variables for you.

Firstly, enable the default value is mutable: change the default value from 0 to be saved.

$ sudo vi /etc/default/grub
GRUB_DEFAULT=0

to be

GRUB_DEFAULT=0

and then give it a default value (0 here). The number "0" is the grub entry number. It could be 0, 1, 2, ...etc. depends on the order and number of your entries.

$ sudo grub-set-default 0

Update the grub.cfg and make all change effective.

$ sudo update-grub

Now your grub entries are ready to be selected. For example, select the 6th entry of a sub-menu (order number 1)

$ sudo grub-reboot "1>6"

And then reboot

$ sudo reboot

By the way titles should also work according to its GNU manual. https://www.gnu.org/software/grub/manual/grub/html_node/Simple-configuration.html

Previously it was documented the way to use entry title. While this still works it’s not recommended since titles often contain unstable device names and may be translated