Extend a partition on an OpenBSD system

Posted on May 1, 2024

Table of contents:

This post is a method to extend the last partition of the disk layout (usually) to use all the available disk space on an OpenBSD system.

Extending the root partition

The root partition cannot be extended on a live system. The system must be restarted on a ramdisk.

With a graphical output/serial console redirection

Reboot on the installation ramdisk, on the boot prompt, enter boot bsd.rd

>> OpenBSD/amd64 BOOT 3.67
boot> boot bsd.rd

Open a shell

Welcome to the OpenBSD/amd64 7.6 installation program.
(I)nstall, (U)pgrade, (A)utoinstall or (S)hell? S
#

Create the /dev/rsd0* devices

# cd /dev/
# sh MAKEDEV sd0

Skip to the next section Extend the disklabel partition layout, then Resize the filesystem with growfs and reboot.

Headless mode (should work)

Here, we will automate the previous section and gather all our luck.

Create a custom ramdisk, start from /bsd.rd and replace the .profile with this one.

Extract the ramdisk from /bsd.rd

# gunzip -k -S "" -o /root/bsd.rd /bsd.rd
# rdsetroot -x       /root/bsd.rd /root/ramdisk

Mount the ramdisk

# vnconfig vnd0 /root/ramdisk
# mkdir /root/ramdisk.d
# mount -o nodev,nosuid,noexec /dev/vnd0a /root/ramdisk.d

Replace the .profile file

# install -m 644 -o root -g wheel -- dot.profile /root/ramdisk.d/.profile"

Unmount the ramdisk

# umount /dev/vnd0a
# vnconfig -u vnd0

Create a new ramdisk file /bsd.gf

# rdsetroot /root/bsd.rd /root/ramdisk
# gzip -k -S "" -o /bsd.gf /root/bsd.rd

Boot on the patched ramdisk

# echo boot hd0a:/bsd.gf >> /mnt/boot.conf

reboot

Extend the disklabel partition layout

Read the disk layout with disklabel

# disklabel -h sd0
# /dev/rsd0c:
type: SCSI
disk: SCSI disk
label: Block Device
duid: caebcd6353c3b714
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 255
sectors/cylinder: 16065
cylinders: 13054
total sectors: 209715200 # total bytes: 102400.0M
boundstart: 64
boundend: 41943040

16 partitions:
#                size           offset  fstype [fsize bsize   cpg]
  a:           150.0M               64  4.2BSD   2048 16384  2400 # /
  b:           256.0M           307264    swap                    # none
  c:        102400.0M                0  unused
  d:          1981.7M           831552  4.2BSD   2048 16384 12960 # /usr
  e:           833.1M          4890048  4.2BSD   2048 16384 12960 # /tmp
  f:          1238.8M          6596256  4.2BSD   2048 16384 12960 # /var
  g:           651.4M          9133344  4.2BSD   2048 16384 10339 # /usr/X11R6
  h:          1915.4M         10467424  4.2BSD   2048 16384 12960 # /usr/local
  i:          2226.3M         14390144  4.2BSD   2048 16384 12960 # /usr/src
  j:          5476.5M         18949536  4.2BSD   2048 16384 12960 # /usr/obj
  k:          5750.8M         30165504  4.2BSD   2048 16384 12960 # /home

We can resize the last partition (here sd0k, mounted on /home), the max size in sectors is equal to total sectors (209715200) - offset (30165504). If you are performing this operation on the live system, unmount the partition.

# umount /home
# disklabel -e sd0

This command will open the vi text editor, edit the line for /home, change the size to the value calculated before, and save.

# /dev/rsd0c:
type: SCSI
disk: SCSI disk
label: Block Device
duid: caebcd6353c3b714
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 255
sectors/cylinder: 16065
cylinders: 13054
total sectors: 209715200
boundstart: 64
boundend: 41943040

16 partitions:
#                size           offset  fstype [fsize bsize   cpg]
  a:           307200               64  4.2BSD   2048 16384  2400 # /
  b:           524288           307264    swap                    # none
  c:        209715200                0  unused
  d:          4058496           831552  4.2BSD   2048 16384 12960 # /usr
  e:          1706208          4890048  4.2BSD   2048 16384 12960 # /tmp
  f:          2537088          6596256  4.2BSD   2048 16384 12960 # /var
  g:          1334080          9133344  4.2BSD   2048 16384 10339 # /usr/X11R6
  h:          3922720         10467424  4.2BSD   2048 16384 12960 # /usr/local
  i:          4559392         14390144  4.2BSD   2048 16384 12960 # /usr/src
  j:         11215968         18949536  4.2BSD   2048 16384 12960 # /usr/obj
  k:         179549696        30165504  4.2BSD   2048 16384 12960 # /home

# Notes:
# Up to 16 partitions are valid, named from 'a' to 'p'.  Partition 'a' is
# your root filesystem, 'b' is your swap, and 'c' should cover your whole
# disk. Any other partition is free for any use.  'size' and 'offset' are
# in 512-byte blocks. fstype should be '4.2BSD', 'swap', or 'none' or some
# other values.  fsize/bsize/cpg should typically be '2048 16384 16' for a
# 4.2BSD filesystem (or '512 4096 16' except on alpha, sun4, ...)

After saving, the partition size is updated:

# disklabel -h sd0
# /dev/rsd0c:
type: SCSI
disk: SCSI disk
label: Block Device
duid: caebcd6353c3b714
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 255
sectors/cylinder: 16065
cylinders: 13054
total sectors: 209715200 # total bytes: 102400.0M
boundstart: 64
boundend: 41943040

16 partitions:
#                size           offset  fstype [fsize bsize   cpg]
  a:           150.0M               64  4.2BSD   2048 16384  2400 # /
  b:           256.0M           307264    swap                    # none
  c:        102400.0M                0  unused
  d:          1981.7M           831552  4.2BSD   2048 16384 12960 # /usr
  e:           833.1M          4890048  4.2BSD   2048 16384 12960 # /tmp
  f:          1238.8M          6596256  4.2BSD   2048 16384 12960 # /var
  g:           651.4M          9133344  4.2BSD   2048 16384 10339 # /usr/X11R6
  h:          1915.4M         10467424  4.2BSD   2048 16384 12960 # /usr/local
  i:          2226.3M         14390144  4.2BSD   2048 16384 12960 # /usr/src
  j:          5476.5M         18949536  4.2BSD   2048 16384 12960 # /usr/obj
  k:         87670.8M         30165504  4.2BSD   2048 16384 12960 # /home

Resize the filesystem with `growfs`

# growfs /dev/sd0k
We strongly recommend you to make a backup before growing the Filesystem

 Did you backup your data (Yes/No) ? Yes
new filesystem size is: 44887424 frags
Warning: 390656 sector(s) cannot be allocated.
growfs: 87480.0MB (179159040 sectors) block size 16384, fragment size 2048
        using 432 cylinder groups of 202.50MB, 12960 blks, 25920 inodes.
super-block backups (for fsck -b #) at:
 12027040, 12441760, 12856480, 13271200, 13685920, 14100640, 14515360, 14930080, 15344800, 15759520, 16174240, 16588960, 17003680, 17418400, 17833120,
 ...
 174597280, 175012000, 175426720, 175841440, 176256160, 176670880, 177085600, 177500320, 177915040, 178329760, 178744480

Check the filesystem and remount it

# fsck_ffs -f /dev/sd0k
** /dev/rsd0k
** Last Mounted on /home
** Phase 1 - Check Blocks and Sizes
** Phase 2 - Check Pathnames
** Phase 3 - Check Connectivity
** Phase 4 - Check Reference Counts
** Phase 5 - Check Cyl groups
11 files, 11 used, 43383113 free (17 frags, 5422887 blocks, 0.0% fragmentation)

MARK FILE SYSTEM CLEAN? [Fyn?] y


***** FILE SYSTEM WAS MODIFIED *****

Mount the partition and verify its new size.

# mount /home
# df -h /home
Filesystem     Size    Used   Avail Capacity  Mounted on
/dev/sd0k     82.7G   22.0K   78.6G     1%    /home