Change to single partition AFTER installation

You can change OpenBSD to run using a single partition after doing a default installation. You might rightly ask why on earth you would want to do this, after all the FAQ “encourages users to split their disk into a number of partitions”. Well it’s great if you have a large disk and in a secure implementation but what if you just want to run on a single partition to make better use of the disk or virtual disk space.

Requirements and disclaimer

  • Don’t do this if you’re at all interested in security and reliability!
  • You need to be reasonably adept at using OpenBSD already, not new user friendly.
  • You will need a second disk or a virtual disk to accomplish this.
  • Definitely practise on a virtual machine BEFORE attempting this for real.
  • Don’t blame me if you lose absolutely everything, make sure you have a backup.
  • Remember that your data will be on the second disk if something does go wrong.


Basic Steps

  • Determine current disk and layout (df -h, note whether wd0 or sd0?)
  • Shutdown halt -p
  • Attach second disk
  • Power on
  • Determine new disk name sysctl hw.disknames is it wd1 or sd0 etc?
  • Write MBR to new disk fdisk -iy wd1
  • Create partition on new disk disklabel -E wd1, a a, w, q
  • Create file system on new disk newfs wd1a
  • Mount second disk mount /dev/wd1a /mnt
  • What data to copy second disk (df -h to get a list of what to copy)
  • Make directories of each top level mount point of source disk, /mnt/home, /mnt/usr, /mnt/var etc
  • Copy all the data to the second disk:
    cd /home && tar cf – . | (cd /mnt/home && tar xpf – )
    cd /usr && tar cf – . | (cd /mnt/usr && tar xpf – )
    cd /var && tar cf – . | (cd /mnt/var && tar xpf – )
  • Don’t worry about socket errors
  • Backup then edit fstab, add wxallowed to root mount point and remove all mounts after c
  • Reboot using /bsd.rd at the loading screen and select (S)hell when prompted
  • Make devices cd /dev; sh MAKEDEV wd0 wd1
  • Resize main disk disklabel -E wd0, p, make note of size of b partition
  • Remove partitions b and above, grow a with m and recreate swap
  • Grow the a partition growfs wd0a then fsck /dev/wd0a
    mount /dev/wd1a /mnt and /dev/wd0a /mnt2
  • Map keyboard layout (/mnt2/sbin/wsconsctl keyboard.encoding=uk)
  • Restore data using tar
    cd /mnt && tar cf – . | (cd /mnt2 && tar xpf – )
  • Shutdown and remove second disk halt -p
  • Power on