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.

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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