fdisk
fdisk(8) is a disk partitioning utility. It is called when installing OpenBSD to change the default partition layout of the disk. It can also be called manually after installation when you want to add a new disk.
WARNING: BE CAREFUL! fdisk can cause irreversible data loss. We recommend you backup your files before attempting to run these commands. You should also double check every command to make sure you have made no typos or mistakes. A single typo could destroy your data forever!
NOTE: This guide is no substitute for reading the OpenBSD FAQ. In particular, you may want to read the section on Disk Setup.
Whole Disk for OpenBSD
If you want to set aside an entire disk for OpenBSD, it's relatively easy. First, find the correct disk using dmesg:
$ dmesg | grep -E '(wd|sd)[0-9]' sd0 at scsibus1 targ 0 lun 0: <VirtIO, Block Device, > sd0: 20480MB, 512 bytes/sector, 41943040 sectors sd1 at scsibus2 targ 0 lun 0: <VirtIO, Block Device, > sd1: 256000MB, 512 bytes/sector, 524288000 sectors root on sd0a (5f6d0b5c9f65249d.a) swap on sd0b dump on sd0b
NOTE: On OpenBSD, there are two disk drivers: wd and sd. wd is an IDE-like disk, and sd is a SCSI-like disk (including USB disks). Here, I have two SCSI-like disks.
In this case, the disk I want to add is sd1, a [[Vmctl/Disk|new
disk]] for additional storage. Here is the simple way to create fdisk partitions (Master Boot Record partitions):
$ doas fdisk -iy sd1
I can then proceed to use disklabel, followed by newfs.
Interactive fdisk
Instead of running the above command, it is possible to edit the fdisk partitions interactively:
$ doas fdisk -e sd1 Enter 'help' for information
Type help to get help, manual to read the fdisk man page, and print to view the partitions:
sd1: 1> help
help Command help list
manual Show entire OpenBSD man page for fdisk
reinit Re-initialize loaded MBR (to defaults)
setpid Set the identifier of a given table entry
disk Edit current drive stats
edit Edit given table entry
flag Flag given table entry as bootable
update Update machine code in loaded MBR
select Select extended partition table entry MBR
swap Swap two partition entries
print Print loaded MBR partition table
write Write loaded MBR to disk
exit Exit edit of current MBR, without saving changes
quit Quit edit of current MBR, saving current changes
abort Abort program without saving current changes
sd1: 1> print
Disk: sd1 geometry: 66837/255/63 [1073741824 Sectors]
Offset: 0 Signature: 0x0
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: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused
This disk sd1 is completely blank, so it is probably safe to edit the fdisk partitions and format the disk.
WARNING: If the disk already has existing partitions, double check to make sure you are not wiping out important data!
First, let's reinit. This should automatically create an fdisk partition on the last partition, partition 3, for OpenBSD and use all available space. It will also initialize this as the boot block.
sd1: 1> reinit
Disk: sd1 geometry: 66837/255/63 [1073741824 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 - 66836 254 63 [ 64: 1073736341 ] OpenBSD
Use 'write' to update disk.
Notice that the Signature changes from 0x0 to 0xAA55, and partition #3 is now set to id A6 (the OpenBSD partition type).
This can also be done manually by using the edit command on partition 3:
sd1: 1> edit 3
Starting Ending LBA Info:
#: id C H S - C H S [ start: size ]
-------------------------------------------------------------------------------
3: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused
Partition id ('0' to disable) [01 - FF]: [0] (? for help) A6
Do you wish to edit in CHS mode? [n] y
BIOS Starting cylinder [0 - 66836]: [0]
BIOS Starting head [0 - 254]: [1]
BIOS Starting sector [1 - 63]: [2]
BIOS Ending cylinder [0 - 66836]: [0] 66836
BIOS Ending head [0 - 254]: [0] 254
BIOS Ending sector [1 - 63]: [1] 63
We need to edit in Cylinder-Head-Sector (CHS) mode. To use the full space of the disk, you will want to choose the lowest numbers in the range for the starting cylinder, head, and sector; and the highest possible numbers for the ending cylinder, head, and sector.
We now write to disk:
sd1*: 1> write Writing MBR at offset 0.
We'll print G to see everything in gigabytes:
sd1: 1> print G
Disk: sd1 geometry: 66837/255/63 [1073741824 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: 0G] unused
1: 00 0 0 0 - 0 0 0 [ 0: 0G] unused
2: 00 0 0 0 - 0 0 0 [ 0: 0G] unused
*3: A6 0 1 2 - 66836 254 63 [ 64: 512G] OpenBSD
If everything looks good,
sd1: 1> quit