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Change to single partition post install

Posted on: 13 Jan 2024

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

Just because it can be done doesn't mean it should be done.

• 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.

References

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