InstantVM notes (Devuan Chimaera)

I run quite a few Virtual Machines hosted on my own hardware (generally multi-core AMD servers with 32 Gbytes RAM), running KVM / QEMU.

Many years ago a colleague and I created some scripts to make the creation of a new VM easier than it normally is (without using a GUI), but this still leaves you with a blank VM pointing at some installation CD image, which you then need to use to create the working VM.

Setting up a Devuan machine like this can easily take half an hour or so.

I wanted something faster, which would create a server installed and running the way I like it, so I decided to create a disk partition image which can be copied into a blank VM, and when booted, does a few things like set up its network, assign its hostname, and automatically expand the root filesystem to fit whatever size partition you asked for.

The result allows me to create a new VM in under 2 minutes (time is dependent on the hosting hardware, Internet connection speed, and how many packages have been updated since you created the template).

I created templates for Devuan Ascii and Beowulf, but I didn't keep proper notes on the process at the time, therefore these notes are being written as I go through the same procedure to create a Chimaera template. I expect I'll need them again in around a couple of years, once Daedalus has been released.

These notes were written in July 2022, and sure enough in October 2023 I've adapted them for Daedalus. It took me until February 2026 to get round to adapting them again for Excalibur.

1. Create a 2Gbyte partition Chimaera VM and go through the standard Devuan installation process, but do not re-start the server at the end
   • Use DHCP networking on eth0
   • Set the hostname to (literally) MyHostNameGoesHere
   • Leave the domain name blank
   • The root password, the first user and its password, will be replicated on every VM created from this image
   • Select Manual partitioning
     • Create vda1 of as large a size as possible, but leave around 1-2Mbyte free (yes, megabytes) for vda2 - try 2145900KB as the size for vda1
       • Make vda1 an ext4 partition for /
       • Set vda2 to "do not use"
     • Create vdb1 as swap
   • For a 2 Gbyte root FS, the package selector won't offer a desktop environment, but "SSH server" should be selected by default - this is exactly what you want for a server
   • When the installer wants to restart the machine, pause the Grub menu and then just shut down the VM
2. Use ddrescue or similar to take a copy of the resultant disk image, just in case something goes horribly wrong with the next few steps and you need to start again - this saves you going through the entire Devuan installation process again
3. Use kpartx to mount the (as yet never-booted-up) root partition and preserve the pristine /var/log directory, copy some files to be unpacked later, and then adjust some configuration files:

   kpartx -a /dev/LVM/VMname
   mount /dev/mapper/LVM-VMname1 /mnt
   rsync -Pav fs.tgz /mnt/
   cd /mnt
   rsync -Pav var/log/ var/log.pristine
   rm -f etc/apt/sources.list etc/apt/sources.list~
   sed -i "s/export PATH/export PATH\nexport HISTSIZE=10000\nexport HISTFILESIZE=10000\nexport HISTCONTROL=none\nexport HISTTIMEFORMAT=\"%F %T \"\nexport QUOTING_STYLE=literal/" etc/profile
   sed -i "s/#PermitRootLogin prohibit-password/PermitRootLogin yes/; s/PubkeyAuthentication yes/PubkeyAuthentication yes\nPubkeyAcceptedKeyTypes=+ssh-dss/" etc/ssh/sshd_config
   sed -i "s/HashKnownHosts yes/HashKnownHosts no/" etc/ssh/ssh_config
   sed -i "s/sulogin/sulogin -t 30/" etc/init.d/checkfs.sh
   sed -i "s/#kernel.printk = 3 4 1 3/kernel.printk = 3 4 1 3/" etc/sysctl.conf
   sed -i "s/:root:/:MyHostNameGoesHere:/" etc/passwd
   umount /mnt
   dd if=/dev/zero of=/dev/mapper/LVM-VMname2
   kpartx -d /dev/LVM/VMname

   • Note: The fs.tgz file contains:

     etc/apt/apt.conf.d/42norecommendationsplease
     etc/apt/apt.conf.d/42nosuggestionsplease
     etc/apt/sources.list.d/Devuan-Chimaera.list
     etc/boot.d/firstboot
     etc/cron.midnight/
     etc/cron.midnight/.placeholder
     etc/cron.minutely/
     etc/cron.minutely/.placeholder
     etc/cron.yearly/
     etc/cron.yearly/.placeholder
     etc/cron.daily/backup
     etc/crontab
     etc/fstab
     etc/network/interfaces
     etc/timezone
     etc/rsyslog.d/default.conf
     etc/rsyslog.d/central.conf
     home/youruser/.ssh/authorized_keys
     root/.ssh/authorized_keys
     root/.ssh/backup.id_rsa
     root/.ssh/backup.id_rsa.pub
     root/.ssh/known_hosts

4. Start the VM and run the following commands on it:

   tune2fs -L rootfs /dev/vda1
   ln -fs /usr/share/zoneinfo/Europe/Berlin /etc/localtime
   cd /
   tar -xvf fs.tgz
   rm -f fs.tgz
   apt-get install -y aptitude
   aptitude install -y less ntp rsync vim
   aptitude purge -y nano vim-tiny
   echo 'syntax off' >>~/.vimrc
   [ -e /etc/default/su ] || echo ALWAYS_SET_PATH=yes >/etc/default/su
   cat /etc/default/su | grep -q ALWAYS_SET_PATH || echo ALWAYS_SET_PATH=yes >>/etc/default/su
   aptitude install -y parted acpi{d,-support-base} sendmail s-nail dnsutils
   echo 'RESUME=LABEL=swap' >/etc/initramfs-tools/conf.d/resume
   update-initramfs -k all -u

5. Shut down the server

You now have a VM server image which can be ddrescue'd over the top of a blank VM partition (2 Gbytes or bigger), and when booted, will be a usable VM in under 2 minutes, using the NewInstantVM script.

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After using this procedure for some years, two significant aspects have come to light:

1. the template is not kept up to date with new package releases, and therefore the time to set up a machine gets longer and longer as time goes by, since the base template gets more and more out of date, with more updates needing to be applied when each machine gets created
2. some package upgrades present an on-screen prompt (eg: "press q to quit" after displaying changelogs) and not only is this invisible if you don't happen to have connected to the VM console during the upgrade process, but it's actually impossible to quit from the display - none of q, Escape, Ctrl/C or anything else I have tried will exit from the changelog and continue with the upgrade process.

I think that setting DEBIAN_FRONTEND=noninteractive prior to the upgrade process might resolve the latter.