Preparing Debian ISO image with remote installation over SSH

debian_ssh_install_iso.md

Preparation of ISO Image

1. Create working directory:

   mkdir debinst
   

2. Download netinstall image:

   (cd debinst && curl -OL https://cdimage.debian.org/debian-cd/current/amd64/iso-cd/debian-11.4.0-amd64-netinst.iso)
   

3. Prepare debinst/preseed.cfg with following content:

   # prevent questions for network configuration
   d-i netcfg/get_hostname string debian
   d-i netcfg/get_domain string local
   
   # activating of remote installation over SSH
   d-i anna/choose_modules string network-console
   d-i network-console/password           password installer
   d-i network-console/password-again     password installer
   
   # netcfg will choose an interface that has link if possible. This makes it
   # skip displaying a list if there is more than one interface.
   d-i netcfg/choose_interface            select auto
   

4. Run docker container to prepare new ISO:

   docker run --rm -it -v $PWD/debinst:/mnt/debinst debian bash
   

   (Note: The following commands are assumed to be executed inside the container.)

5. Install required packages:

   apt update && apt install -y --no-install-recommends xorriso isolinux cpio nano
   

6. Create temp directory for ISO image:

   export ISO_FILES="$(mktemp -d)"
   

7. Extract original installation image to temp directory:

   xorriso -osirrox on -indev /mnt/debinst/debian-*-amd64-netinst.iso -extract / $ISO_FILES
   

8. Extract initrd.gz:

   gunzip $ISO_FILES/install.amd/initrd.gz
   

9. Add preseed.cfg to initrd:

   (cd /mnt/debinst && echo preseed.cfg | cpio -H newc -o -A -F $ISO_FILES/install.amd/initrd)
   

10. gzip back initrd:

    gzip $ISO_FILES/install.amd/initrd
    

11. Recalculate md5 sum:

    (cd $ISO_FILES; md5sum `find -follow -type f` > md5sum.txt)
    

12. Modify $ISO_FILES/boot/grub/grub.cfg:

    nano $ISO_FILES/boot/grub/grub.cfg
    

    1. Add menu timeout to the top of file:

       set timeout=10
       

    2. Insert new menu entry for automatic install before all current entries:

       menuentry --hotkey=r 'Remote install' {
           set background_color=black
           linux    /install.amd/vmlinuz auto=true vga=788 --- quiet
           initrd   /install.amd/initrd.gz
       }
       

13. Make new ISO image:

    xorriso -as mkisofs -o /mnt/debinst/debian-preseed.iso -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 $ISO_FILES
    

14. Exit docker container:

    exit
    

15. Flash ISO image to external drive:

    sudo dd if=./debinst/debian-preseed.iso of=/dev/disk2 bs=1m
    

16. Plug flash drive into target machine and boot from it.

17. Check DHCP server for IP address of target machine and connect to installator via SSH:

    ssh installer@target
    

    (Note: Use the password from preseed.cfg to authenticate.)

Inspired by

• https://github.com/paullockaby/preseed/blob/main/build
• https://itdraft.ru/2019/12/17/avtomaticheskaya-ustanovka-debian-pri-pomoshhi-preseed/
• https://unix.stackexchange.com/questions/43012/remote-accessible-live-distribution-aka-live-cd
• https://sleeplessbeastie.eu/2015/10/12/how-to-install-debian-remotely/
• https://www.debian.org/releases/bullseye/example-preseed.txt