Advices on automating installation for Debian 11

Question

I'm currently trying to automate Debian 11 template creation through Packer for Nutanix environment and need some advices about preseeding/automating Debian installation.

First of all, after reading this bible https://www.debian.org/releases/stable/amd64/apbs02.fr.html I went into using preseed.cfg file. I started with the preseed.cfg file provided by Debian then adapt some stuff to fit my needs. Finally, I validate the syntax using debconf-set-selections -c preseed.cfg command => everything is fine.

Now, i saw there's 3 differents ways to use preseed.cfg :

• through initrd : seems quite difficult to me and didn't find an easy tutorial/documentation
• through network : not an option at this moment due to some firewall restriction
• through file : seems the easiest and best option at the moment

When Packer starts the VM creation, it loads debian ISO as a CD-ROM in 1st position, and an empty virtual disk in the second position. I tell packer to load my preseed.cfg scripts as a cd-rom, so from an hypervisor perspective, a second cd-rom drive is mounted in the 3rd position.

BUT, in this case, VM boot on ISO (cd-rom 1st position), it doesn't mount the second cd-rom drive that have the preseed.cfg file and i can't access it unless I go to the debian console then mount the 2nd drive.

I saw a forum about uploading preseed.cfg into my original debian.iso folder and modifying the /isolinux/txt.cfg file like this (and then recreates the iso with OSCDIMG) :

label install
    menu label ^Install
    kernel /install.amd/vmlinuz
    append vga=788 initrd=/install.amd/initrd.gz preseed/file=/cdrom/preseed/preseed.cfg --- quiet

My question is : is it fair to act like this ? is there something i missed or something easier to make it work easily ?

EDIT : i tried the initrd method, the only remaining thing is that i have to manually select Automated Install. How to get rid of this action ?

EDIT2: 02-01-2023

• i tried 2 more different things, 1st having this line in isolinux/txt.cfg append auto=true priority=critical vga=788 initrd=/install.amd/initrd.gz preseed/file=/cdrom/preseed.cfg --- quiet => NOK, it still boot on boot menu (but ok if i select automated install manually, so it means preseed.cfg works pretty well)
• and 2nd, test with prompt 1 timeout 1 in isolinux.cfg => goes directly to select language manually...

EDIT3: 03-01-2023 here's the preseed.cfg i use :

# SETUP AUTO MODE
d-i auto-install/enable boolean true
d-i debconf/priority select critical
# LANGUAGE & KEYMAP
d-i debian-installer/locale string fr_FR
d-i keyboard-configuration/xkb-keymap select fr(latin9)
# NETWORK
d-i netcfg/choose_interface select auto
d-i netcfg/get_hostname string template-debian-11-x64
d-i netcfg/get_domain string my_domain.net
d-i netcfg/hostname string template-debian-11-x64
# MIRRORS
d-i mirror/http/hostname string  http://deb.debian.org/debian/ 
d-i mirror/http/hostname string http://security.debian.org/debian-security 
# ACCOUNTS
d-i passwd/root-password password mypassword!
d-i passwd/root-password-again password mypassword!
d-i passwd/user-fullname string user
d-i passwd/username string user
d-i passwd/user-password password mypassword!
d-i passwd/user-password-again password mypassword!
d-i passwd/user-uid string 1010
d-i passwd/user-default-groups string si audio cdrom video
# LVM PART
d-i partman-auto/disk string /dev/sda
d-i partman-auto/method string lvm
d-i partman-auto-lvm/guided_size string 95%
d-i partman-lvm/device_remove_lvm boolean true
d-i partman-md/device_remove_md boolean true
d-i partman-lvm/confirm boolean true
d-i partman-lvm/confirm_nooverwrite boolean true
d-i partman-auto/choose_recipe select multi
d-i partman-partitioning/confirm_write_new_label boolean true
d-i partman/choose_partition select finish
d-i partman/confirm boolean true
d-i partman/confirm_nooverwrite boolean true
#APT
d-i apt-setup/cdrom/set-first boolean false
tasksel tasksel/first multiselect standard, ssh-server
# GRUB
d-i grub-installer/bootdev string /dev/sda
d-i grub-installer/only_debian boolean true
d-i grub-installer/with_other_os boolean true
#FINAL
d-i finish-install/reboot_in_progress note

Thanks a lot

Gael

Answer 1

Use a boot_command in Packer, which will send keypresses to the VM and, basically, type things into it. What it'll "type" is up to you. This goes to the packer file (I named it base.pkr.hcl):

...
variable "preseed_file" {
  type    = string
  default = "base.preseed"
}
...
source "qemu" "qemu" {
  ...
  boot_command = [
    "<wait><wait><wait><esc><wait><wait><wait>",
    "/install.amd/vmlinuz ",
    "initrd=/install.amd/initrd.gz ",
    "auto=true ",
    "debian-installer/locale=ru_RU.UTF-8 ",
    "keyboard-configuration/xkb-keymap=ru ",
    "keyboard-configuration/optionscode=grp:caps_toggle,lv3:ralt_switch,compose:rctrl,grp_led:scroll ",
    "url=http://{{ .HTTPIP }}:{{ .HTTPPort }}/preseed.cfg ",
    "hostname=${var.vm_name} ",
    "domain=${var.domain} ",
    "interface=auto ",
    "vga=788 noprompt quiet --<enter>"
  ]
  http_content         = { "/preseed.cfg" = templatefile(var.preseed_file, { var = var }) }
  ...
}
...

This way, packer will both serve the preseed file to the VM via HTTP and effectively override the boot options that are built into ISO with ones that you supply within packer file. No need to do any changes to ISO.

---

I am using Qemu; this is a copy of what I end up with when I did that half of a year ago. It looks like Nutanix builder doesn't have this boot_command; however, you can try to build the system using e.g. Qemu or Virtualbox and then use it with Nutanix. I just don't know.

Answer 2

Regarding your first question, I don't think there's any easier way to enable automated install for debian installer in terms of passing the preseed file to it. Mounting a second image could be a good idea for your specific need, but AFAIK debian installer does not respect a second media for its preseed and there are no workarounds that I know of (FYI, ubuntu's subiquity installer does support such input).

To achieve a "no-hands" install, I'll explain 2 things that should be taken care of.

Debian installer config (preseed)

To make the debian installer go fully automatic, you'll need this in your preseed file:

d-i debconf/priority select critical

This will simply tell debian installer not to ask questions it can find an answer to. In addition to that, you need to enable the auto mode with d-i auto-install/enable boolean true, but ignore this for now (I'll talk about auto mode in the next part). From auto mode doc:

The auto kernel parameter is an alias for auto-install/enable and setting it to true delays the locale and keyboard questions until after there has been a chance to preseed them, while priority is an alias for debconf/priority and setting it to critical stops any questions with a lower priority from being asked.

P.S. You can pass some the question/answers as kernel parameters with key=value format, where key is an alias. That requires changing boot parameters. See the full list: aliases useful with preseeding

Bootloader config

In addition to installer configuration, we need to make some changes to the bootloader too. For isolinux bootloader to work in an unattended install scenario, I make these 2 changes to its config files inside the iso:

1. Set auto mode via a kernel parameter.
2. Tell isolinux auto-select the default entry in the menu.

First change is done by adding auto=true to the append line of the default menu entry. For debian 11, I found "Graphical install" to be the default entry. Since the config for this entry is read from isolinux/gtk.cfg, this change should be applied in that file. e.g. you can change your example bootloader config append line to "append auto=true vga=...".

Second goal is achieved by changing timeout 0 to timeout 1 in isolinux/isolinux.cfg (see this).

Note 1: The auto=true kernel parameter is the alias for d-i auto-install/enable boolean true preseed config. It turned out that it should be enabled by kernel parameters for some reasons. Putting its equivalent in preseed file still ends up in language selection prompt waiting for user's input (maybe by the time that the preseed file is read by debian installer it's too late to enable the auto mode?).

Note 2: You don't need prompt 1 in isolinux config. It will probably do the opposite of what you want, which is preventing automatic selection of default entry (see the last line of this section).

Note 3: Changing bootloader config requires modifications in iso contents (and thus an iso rebuild).

Note 4: The isolinux bootloader is commonly used for BIOS (legacy) systems. In UEFI systems, you need to configure GRUB instead.