Debian "preseed" System Installer

Tip

If you want to bootstrap Ubuntu systems, you can look at my Ubuntu autoinstall setup.

This is a script for building a new installer for Debian "trixie" using a technique called a "preseeding". By using a "preseed" script we tell the installer the answer to a lot of routine questions to give ourselves a standard environment for new hosts. The script in this repository does the following:

• Creates a "paul" user with an SSH authorized_keys file and a known good environment.
• Prompts you for a disk configuration but chooses xfs instead of ext4 for the primary disk partition.
• Enables "security" and "updates" repositories but does not enable backports, sources or automatic updates.
• Fixes the systemd timesync configuration.
• Fixes the /etc/resolv.conf file.
• Installs standard system utilities and an SSH server.
• Installs some additional basic, common software.

When using the installer there are still several questions that you must answer. These include:

• If there are multiple active interfaces you must choose one.
• What IP address and host name to use for this new host.
• Which disk to use for the installation. WARNING! This disk will be erased.
• Which disk will receive the master boot record.

Otherwise this will create an entirely automated installation.

How To Use This Script

Follow these steps to run this script:

1. Get on a Debian host!
2. Download an netinstall image from the Debian website.
3. Clone this repository.
4. Install these libraries: apt-get install -y --no-install-recommends xorriso isolinux pwgen
5. Run the build script: ./build /path/to/debian-13.x.x-amd64-netinst.iso /path/to/preseed-debian-13.x.x-amd64-netinst.iso
6. Use the new ISO file to build your host.

Note that the preseed.cfg file has no password for logging in as the "paul" user. You can set a password or just use SSH keys. You can change the password by following these steps:

1. Put the new password in a text file. Call it something like "newpassword.txt".
2. Generate the new password: cat newpassword.txt | mkpasswd -s -m sha-512 -S "$(pwgen -ns 16 1)"
3. Place that new password in the preseed.cfg file.
4. Remove newpassword.txt and definitely do not put it into source control.

Using the "preseed" ISO

Use this ISO just like you would any other install ISO. A preseeded ISO file can build baremetal systems or virtual machines. It is only useful for on-premise instances and is not useful for cloud instances.

Building a USB Boot Disk on macOS

It's pretty simple:

1. Run diskutil list to find the thumb drive. It'll be labeled something like "/dev/disk6 (external, physical)"
2. Run diskutil unmount /dev/disk6 or whatever the disk is called, to unmount any volume that it might already have.
3. Run sudo dd if=mydebian.iso of=/dev/disk6 bs=1M to erase the disk and install the ISO.

Your thumb drive is now bootable.

Building a USB Boot Disk on Linux

I'm also always having to look this up so here are the steps.

1. Attach the USB disk. Use lsblk to see what the device label is that the USB disk has received.
2. Write the ISO file to your USB disk: sudo dd bs=4M if=preseed.iso of=/dev/XXX conv=fdatasync

More Information

These links are where I got most of the information for building this preseed script.

• https://wiki.debian.org/DebianInstaller/Preseed
• https://wiki.debian.org/DebianInstaller/Preseed/EditIso
• https://github.com/pin/debian-vm-install
• https://www.debian.org/releases/squeeze/example-preseed.txt
• https://serverfault.com/questions/722021/preseeding-debian-install-efi
• https://github.com/dsgnr/ubuntu-16.04-unattended-install/blob/master/preseed.cfg