Disk label conventions

  • a: root of the system (on a boot disk)
  • b: swap of the system (on a boot disk)
  • c: whole OBSD partition
  • i: points to the first MBR partition on the disk

Formatting a USB drive to be a keydisk

Instructions assume usb drive has been assigned sd1 during boot. See dmesg. Also, you might have to create the node:

cd /dev && sh MAKEDEV sd1

First, create the MBR:

# fdisk -iy sd1
# disklabel sd1

Then, create partitions as needed on the drive. I suggest making a big MSDOS partition to still be able to use the key (beware untrusted machines), and an OpenBSD partition at the end to store the keys.

In our example, the disk has 15.133.248 sectors of 512 bytes available. That’s roughly 8Gb. We’ll devote 11Mo at the end of the disk to the keys. We’ll need around 22.000 sectors to do that.

The MBR will already contain 1 big OpenBSD partition spanning the whole disk. We need to resize it.

# fdisk -e sd1
> edit 3

-- move partition to offset 15133248 - 22000 = 15111248
-- use all remaining space, i.e. 22000 sectors
-- Also, create the MSDOS partition at the beginning
-- Feel free to leave unused space for further things

> edit 1
-- Set size to 4g

-- Write and quit
> w
> q

Now we need to create the labels on the OBSD partition.

# disklabel -E sd1

-- Get some info on the drive
-- At this point, labels c and i should already exist
> p

-- Create the label a for the keydisk
> a a
offset: default
size: 2000
FS type: RAID

> w
> q

Reset a FDE disk

If you’re trying to setup a disk with bioctl that was already encrypted, the command will fail. You need to detach the disk first.

That may require a sh MAKEDEV command as well.

Careful, this will possibly delete other data on your disk.

# bioctl -d sd3
# dd if=/dev/zero of=/dev/rsc0c bs=10m count=1

Format a USB HDD for use with dump(8)

  1. Plug the disk in, and find out what /dev/sd* device it’s attached to with dmesg. You should see something like this:
umass0 at uhub0 port 5 configuration 1 interface 0 "ASMedia AS2115" rev 3.00/0.01 addr 2
umass0: using SCSI over Bulk-Only
scsibus2 at umass0: 2 targets, initiator 0
sd1 at scsibus2 targ 1 lun 0: <ASMT, 2115, 0> SCSI4 0/direct fixed serial.174c1153000000000000
sd1: 476940MB, 512 bytes/sector, 976773168 sectors

From here on, the disk will be referred to as sd1. Adjust the commands according to your setup.

  1. Prepare an MBR sector on the disk
# fdisk -iy sd1

If you still have the default MBR template, your disk will be one big OpenBSD partition. Check this with fdisk

# fdisk sd1
Disk: sd1       geometry: 60801/255/63 [976773168 Sectors]
Offset: 0       Signature: 0xAA55
            Starting         Ending         LBA Info:
 #: id      C   H   S -      C   H   S [       start:        size ]
 0: 00      0   0   0 -      0   0   0 [           0:           0 ] unused
 1: 00      0   0   0 -      0   0   0 [           0:           0 ] unused
 2: 00      0   0   0 -      0   0   0 [           0:           0 ] unused
*3: A6      0   1   2 -  60800 254  63 [          64:   976768001 ] OpenBSD

Then follow the instructions at to encrypt the disk as needed.

Mount an encrypted backup disk

Create the mount directory if it doesn’t exist yet.

# mkdir -p /mnt/encrypted_removable

Mount the drive. Note the distinction between the physical drive, and the encrypted drive.

# bioctl -c C -l sd1a softraid0
> passphrase

Now the software encrypted disk should be ready to be mounted.

# mount /dev/sd3i /mnt/encrypted_removable


mount: invalid argument

If you just created the partition and the label, did you also run newfs? See