Preseed the Debian Installer

0. Introduction

   With a preseed file, we can skip installation steps and even fully automate the installation. We started with creating a preseed file.

1. Create a Preseed File

   You can find the example preseed file for current Debian stable here. The preseed file below will skip the user creation step in setup and set the root password to 123456.

   d-i passwd/root-login boolean true
   d-i passwd/make-user boolean false
   d-i passwd/root-password password 123456
   d-i passwd/root-password-again password 123456

2. Adding the Preseed File to initrd

   Debian installer supports both netboot installation and CD installation.

   1. Network Boot

      If you are using netboot installation, you only need to uncompress initrd.gz, then prepend the preseed file, and recompress it.

      gunzip initrd.gz
      echo /path/to/the/preseed/file | cpio -H newc -o -A -F initrd
      gzip initrd

   2. CD

      If you are using CD installation, you will need to install utility tools first.

      apt install genisoimage libarchive-tools

      Next, we want to extract the initrd from ISO.

      mkdir isofiles
      bsdtar -C isofiles -xf /path/to/the/iso/file.iso
      # If you are using amd64 architecture:
      chmod +w -R isofiles/install.amd/ && cd isofiles/install.amd/
      # If you are using i386 architecture:
      chmod +w -R isofiles/install.386/ && cd isofiles/install.386/

      Then we want to add the preseed file to the initrd.

      gunzip initrd.gz
      echo /path/to/the/preseed/file | cpio -H newc -o -A -F initrd
      gzip initrd && chmod -w -R ./ && cd ..

      Last, we need to regenerate md5sum.txt and create a new ISO.

      chmod +w md5sum.txt
      find -follow -type f ! -name md5sum.txt -print0 | xargs -0 md5sum > md5sum.txt
      chmod -w md5sum.txt
      cd ..
      
      genisoimage -r -J -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot -boot-load-size 4 -boot-info-table -o /path/to/the/output/file.iso isofiles