Installing Debian is easy enough – but what if you have no physical access to the target machine or it has no screen or keyboard? Stock images require at least a few local key strokes before you can continue the installation, remotely...
This little tool will remaster a stock Debian image for 100% remote installation via ssh or serial console.
# Edit the configuration variables
make config
# download the latest Debian netinst image for `ARCH`
make download
# Adapt preseed.cfg
edit preseed.cfg
# Build image
make image
# Write image to usb stick
make usb
I wanted to install Debian on a server remotely – i.e. without keyboard access or the chance to peek at a physical screen. I found plenty of information on the net but none of the tutorials really worked for me. Some included preseeding the image but failed to automatically start the installation without a key press, others seemed to customize a zillion things but ended up getting stuck in some error message or other. The problem with ssh remote installation with stock images is that they still require some initial human interaction to select the desired menu option and some basic setup before the network is configured. That makes the whole point of remote installation moot...
So I read my way through lots of tutorials and put together a slim working solution – at least working for me. So here is my minimal and lazy solution to Debian headless installation image building. I mostly documented it for myself but maybe it's useful for someone out there.
My main intent was to connect to the ssh-server of the Debian installer. Another possible route for headless installation is via serial console. That can either be a physical RS-232 cable or a virtual serial port provided by a remote management module/software such as HPEs iLO or something similar.
The Makefile we use here to implement all functionality intentionally lacks
some of the typical Make magic: Targets don't track dependencies so you will
have to rebuild everything, whenever you change something. So please make clean, first. Yes – a full build will cost you a valuable six seconds every
time. Use them to worship code simplicity.
I didn't have much luck with booting i386 images via UEFI – neither the stock Debian images nor the remastered ones. But maybe it's just my particular machine/BIOS...
This tool was developed and tested on Debian LINUX. While all major LINUX
distributions are likely to offer the necessary pieces of software, there may
be some non-obvious differences. Accordingly, I recommend to run this on a
Debian system. If you don't have one, you may try a VM or container running
Debian. One difference that I am aware of is that many distributions use
either genisoimage or mkisofs and make one of them a symbolic link to the
other. In this particular case, they are not interchangeable – genisoimage
is required.
To install all necessary tools run:
make install-depends
Edit Makevars and set the variables to match your situation. You can use
make config
to do so. This should work on most Debian-based systems. If it doesn't, just edit
the Makevars file with your preferred text editor.
At the very minimum you need to set the following variables:
SOURCE: the name of your stock Debian ISO image file.
TARGET the name of the remastered ISO image.
ARCH indicates the target processor architecture – amd64 or i386 (other
architectures are not supported). This variable is used to identify the
installation folder in the image (install.amd) and to determine which
image to download.
USBDEV is the device file that represents your usb stick. The latter is
needed for make usb and make FAT. Be extra careful to set USBDEV
correctly! If you set it incorrectly, you may overwrite your system disk!
LABEL is the CD volume label. It must be ≤ 32 chars in length.
While the main goal of this project was to allow installation via ssh, a serial
console is an alternative in some cases.
The following default config for the serial console device should work most of the time:
CONSOLE = ttyS0,115200n8
When the serial console is active, all output is redirected to the serial interface and you will not see boot messages or the installer on a connected screen after that point. Accordingly, normal local installation will not work. If you want your image to allow local installation (i.e. non-headless), instead, you may set
CONSOLE = tty0
You can just download the latest Debian netinst image with
make download
If this is not the image you want to start with, just download/provide one yourself and save it in the folder where this Makefile lives.
In any case, make sure to set the SOURCE variable in the config file (make config) to match the image name.
Preseeding is Debian's method of automatically answering some or all of the configuration questions you usually have to answer during the installation process.
You must provide a preseed.cfg file for headless installation!
The included preseed.cfg file configures the bare minimum to get past the
installer questions so that network and ssh can be launched. Please edit the
file – at least change the password...
If the minimal file does not cover all your needs, get a full template
make example-preseed.cfg
mv example-preseed.cfg preseed.cfg
and modify it to your needs. For comprehensive information on preseeding, study this:
https://www.debian.org/releases/stable/amd64/apb.en.html
or
https://www.debian.org/releases/stable/i386/apb.en.html
make clean
make image
For experts, only! If you know what you are doing, you can now enter the tmp
folder and add packages, edit files etc. You can find some information on what
you can do here. But you
don't need to manually follow the steps for re-creating md5 sums and assembling
the image.
To pack your changes into the image just run the last steps manually, again:
make md5sums
make iso
This step is optional but may save you a lot of trouble later.
make qemu-bios
make qemu-uefi
This will fire up a QEMU session booting your new image.
You can follow the boot process in the emulator and eventually connect to the installer like this:
ssh installer@localhost -p22222
Or via serial console:
telnet localhost 33333
So you can test-drive the installation before trying it on a real server. The
default password is r00tme – please change it in the preseeding file.
Alternatively, you can configure passwordless login via ssh key file – there
is example code in the preseed.cfg. For this to work, you need to provide the
key file from a local web server. In pinch, this may be all you need:
python3 -m http.server
And here a little screenshot of what that looks like in qemu. The two bottom panels show the local screen (left) and the serial console (right):
If you still have a cdrom drive, use your favorite ISO burner to write the image to cd. I can't find my old usb-cd drive and prefer using a usb stick, anyway:
Insert a USB stick and find out its device file
lsblk
Double check, that USBDEV is set correctly in Makevars.
Caution: The next two steps will write to the device configured in the
USBDEV. If you failed to set that correctly, you will overwrite whatever disk
happens to be associated with that device!
Write the image to the stick:
make usb
Add a FAT partition to the stick:
make FAT
This may be useful if you need to add custom firmware files or anything else you would like to use during installation.
Insert the USB stick (or CD) in the target system and power it up. Wait a few minutes for the installer to boot and bring up the network. Find out the IP address of the machine (e.g. from the router/DHCP server). Alternatively, configure static IP in the preseed file. Once the system is up you should be able to ping it. Now log in and complete the installation remotely:
ssh installer@yourmachine
The default password is r00tme; it can (and should!) be configured in the
preseeding file. Alternatively, you can configure passwordless login via ssh
key file – there is example code in the preseed.cfg. For this to work, you
need to provide the key file from a local web server.
NOTE: The included minimal preseed.cfg assumes that you are connected via
LAN cable (as a server should be). If you want to/must use a WIFI connection you
need to configure this.
If the serial interface was configured correctly, you should be able to connect
through a terminal program (cu, minicom, etc.) via serial interface. E.g.
cu -l /dev/ttyUSB0 -s 115200
or
screen /dev/ttyUSB0 115200
Where /dev/ttyUSB0 is the serial interface on your local computer which is
connected to the server.
In the case of a virtual serial interface in iLO (or similar), please refer to the manufacturers instructions on how to connect to it.
Just because it took me a while to realize: The Debian remote-installer uses
screen to provide multiple virtual consoles. You can switch between them with
CTRL-a TAB. See man screen for more information.
If you found a bug or have an idea for improvements, feel free to open an issue and describe the fix or feature you have in mind. Please don't submit a pull request without discussing it, first.