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linux:distribution:debian:debian-9-preseed-uefi-encrypted-lvm

Preseed Debian 9 – UEFI with Encrypted LVM

I had a difficult time finding good, easy to digest info online on how to do preseed a Debian install with Encrypted LVM. There’s a couple of blog posts, the Debian Wiki and some Serverfault/StackOverflow questions that led the way for me to accomplish this. (the helpful links are at the bottom of this post.)


The Goal

Here’s a breakdown of what I was hoping to accomplish by preseeding the Debian install. Users

I disable the root account which installs sudo and adds the created user to the sudo group. The preseed.cfg is configured to do that as well.

It is set to create a user and assign them a temporary password “insecure“. Then, at first login the password expires and asks for a new password. I feel doing it that way makes it safer for me to put the config online in a git repo. I could always change it before adding it to the ISO.

There is also an option of creating an encrypted hash of the password to put in the config file. If you want to do that you can install whois and use the mkpasswd utility.

[[email protected]]$ mkpasswd -m sha-512 -S $(pwgen -ns 16 1) insecure
Password: $6$CLWf73UuuEggHhWL$53WWmQF5Oe7WTtUU/Fz0f2ierBXVqzt8YQD1rfVRdcTm8MplzIOABBIDtXWzP0fpWI9F.RmeR4Kt.Lfk6irAv1

If you decide to take that route, make sure to edit the bottom of the preseed.cfg to remove the code that expires the weak password.


Networking

As it sits in the git gist, DHCP is used to assign the IP and hostname.

I’ll configure it to assign a static IP and hostname during the networking section of the install before adding it to the ISO.


Partitioning

I wanted to be able to re-create a UEFI Debian install that also has Encrypted LVM partitions.

Over the past few months I’ve been experimenting with different partition layouts and here is where I settled (for now):

Unencrypted

~550M – /boot/efi
~250M – /boot

Encrypted LVM

~15G – /
~120G – /home
~32G – Swap
~4G – /tmp
~10G – /var

Rest of the disk on standby for future use.

If you don’t need any special partitioning, it is a lot easier to select one of the default options. (atomic, home, or multi) Just make sure to change the line to use it and comment out the custom recipe.

d-i partman-auto/choose_recipe select multi

See the gist at the bottom of the page for an example of custom partition layouts.


Packages

When manually installing Debian on my Gaming Desktop with i3wm, I usually only select Standard System Utilities and SSH-Server at the software installation prompt.

I needed to add non-free and contrib to the etc/apt/sources.list for installing nvidia-drivers and steam.

Adding the i386 architecture for installing Steam and a few other packages that require it was also a priority.

I figured that getting a jump on installing a desktop environment, utilities and drivers, etc. would be pretty awesome. I configured it to install vim and xorg.

Feel free to add more packages to the following line:

d-i pkgsel/include string openssh-server build-essential vim git

I also had success adding packages to the bottom of the file like so:

d-i preseed/late_command string apt-install figlet fortune-mod;

Not sure if one method is preferred to the other..


Using the preseed.cfg

Network

You can place the preseed.cfg file on a web server of some sort and point the installer at it.

You can point the installer to a gist or file in a repository, or host it on a webserver.

If you have another computer on the same network, you can create a python server in the directory like so:

[[email protected]:preseed]$ ls
preseed.cfg
[[email protected]:preseed]$ python3 -m http.server
Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...

The file in that directory and will be available at “http://xx.xx.xx.xx:8000/preseed.cfg

After starting the installer, the network should be auto configured with DHCP. If you want to change the hostname from the default of ‘debian’ once it’s done, you can Alt+F2 and edit /etc/hostname with nano. Then Alt+F1 back to the installer, select Advanced Options > Automated Install and it will continue from there.


ISO

Adding it to the ISO is easy to do as well.

I used the following packages to complete these steps:

  • xorriso
  • isolinux
  • zip
  • unzip

Steps

  • Download the debian iso
  • Rename it to debian.iso
  • Make a directory to hold the extracted iso:
    mkdir isofiles
  • Extract ISO to the isofiles directory:
    xorriso -osirrox on -indev debian.iso -extract / isofiles
  • Add write permissions to initrd:
    chmod +w isofiles/install.amd/
  • Unzip initrd:
    gunzip isofiles/install.amd/initrd.gz
  • Add preseed to the initrd:
    echo preseed.cfg | cpio -H newc -o -A -F isofiles/install.amd/initrd
  • Re-zip initrd:
    gzip isofiles/install.amd/initrd
  • Remove write abilities of initrd:
    chmod -w -R isofiles/install.amd
  • Enter isofiles directory:
    cd isofiles
  • Generate new md5sum.txt:
    md5sum `find -follow -type f` > md5sum.txt
  • Move back a directory:
    cd ..
  • Generate new iso:
    [[email protected]]$ xorriso -as mkisofs \
    -isohybrid-mbr /usr/lib/ISOLINUX/isohdpfx.bin \
    -c isolinux/boot.cat \
    -b isolinux/isolinux.bin \
    -no-emul-boot \
    -boot-load-size 4 \
    -boot-info-table \
    -eltorito-alt-boot \
    -e boot/grub/efi.img \
    -no-emul-boot \
    -isohybrid-gpt-basdat \
    -o preseed-debian.iso \
    isofiles/

Script it!

After doing that a couple of times when making changes, it got a little old. I figured why not create a bash script to handle most of it for me? You can check it out at my git repo.

Install using the ISO

Take the generated iso (preseed-debian.iso if you’re using the commands from above) and write it to a USB jump drive or upload it to Proxmox.

Boot the computer/VM from it and at the menu, select Advanced Options > Automated Install.

Wait a few seconds and it should start the installation process!


Final Thoughts

There is still a small amount of human interaction necessary to install, but it sure beats doing the whole thing manually!

We still have to:

  • Tell the installer to use automated install
  • Enter password for encryption (can be preseeded)
  • Interrupt writing random data if you want (can be preseeded)

Now I won’t be so hesitant to do things that may mess up my install since it’s much easier to re-install Debian. All I’ll have to do is run the preseeded iso then pull my dotfiles and stow them. Things can be back up and running in no time!


linux/distribution/debian/debian-9-preseed-uefi-encrypted-lvm.txt · Last modified: 2020/03/17 18:47 by chuck