Resizing an UFS2 filesystem on FreeBSD 4.x

Resizing an UFS2 filesystem on FreeBSD 4.x is not as straightforward as on recent versions of FreeBSD since gpart appeared in 7.0, and GPT was not common yet. You have to use fdisk and disklabel instead.
This howto assumes that your system is installed on the first IDE drive (ad0) which is 20 GB in size. There is just one BSD slice (aka an MBR partition in DOS/Windows speak) that covers the whole disk (ad0s1). This slice contains 3 FreeBSD partitions (ad0s1a, ad0s1b, ad0s1d) plus one pseudo partition that covers the whole slice (ad0s1c). The former ones serve as root filesystem, swap device, and /var filesystem, respectively. You want to grow /var by 10 GB. You will need root privileges and access to the local console. The system will be rebooted three times.

• Backup your data
• Note your slice data:

  # fdisk ad0
  ******* Working on device /dev/ad0 *******
  parameters extracted from in-core disklabel are:
  cylinders=41610 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Figures below won't work with BIOS for partitions not in cyl 1
  parameters to be used for BIOS calculations are:
  cylinders=41610 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Media sector size is 512
  Warning: BIOS sector numbering starts with sector 1
  Information from DOS bootblock is:
  The data for partition 1 is:
  sysid 165,(FreeBSD/NetBSD/386BSD)
      start 63, size 41942817 (20479 Meg), flag 80 (active)
  	beg: cyl 0/ head 1/ sector 1;
  	end: cyl 1023/ head 15/ sector 63
  The data for partition 2 is:
  <UNUSED>
  The data for partition 3 is:
  <UNUSED>
  The data for partition 4 is:
  <UNUSED>
  

• As we will add 10 GB, the slice has to be resized to no more than 41942817 + 10 * 1024 * 1024 * 2 = 62914337 512-bytes sectors. Since it must end on a cylinder boundary, we must use the nearest multiple of 1008 (blocks per cylinder, as shown in the output of fdisk), which is 62914320 blocks
• Also, save the BSD partitions' geometry:

  # disklabel -r ad0
  # /dev/ad0c:
  type: ESDI
  disk: ad0s1
  label: 
  flags:
  bytes/sector: 512
  sectors/track: 63
  tracks/cylinder: 16
  sectors/cylinder: 1008
  cylinders: 41609
  sectors/unit: 41942817
  rpm: 3600
  interleave: 1
  trackskew: 0
  cylinderskew: 0
  headswitch: 0		# milliseconds
  track-to-track seek: 0	# milliseconds
  drivedata: 0 
  
  8 partitions:
  #        size   offset    fstype   [fsize bsize bps/cpg]
    a:  8388608        0    4.2BSD     2048 16384    89 	# (Cyl.    0 - 8322*)
    b:  4194304  8388608      swap                    	# (Cyl. 8322*- 12483*)
    c: 41942817        0    unused        0     0       	# (Cyl.    0 - 41609*)
    e: 29359905 12582912    4.2BSD     2048 16384    89 	# (Cyl. 12483*- 41609*)
  

• As we will resize the slice by 62914320 - 41942817 = 20971503 blocks, partition ad0s1e can be grown by the same amount, resulting in 29359905 + 20971503 = 50331408 blocks
• The pseudo partition ad0s1c has to cover the whole slice and will be resized to 62914320, likewise
• Shutdown the system and resize the underlying block device, e.g. the virtual harddisk
• After boot, verify that FreeBSD has detected the disk resize:

  # dmesg | grep ad0
  ad0: 30720MB <QEMU HARDDISK> [62415/16/63] at ata0-master BIOSPIO
  Mounting root from ufs:/dev/ad0s1a
  

• Resize the slice:

  # fdisk -u ad0
  ******* Working on device /dev/ad0 *******
  parameters extracted from in-core disklabel are:
  cylinders=62415 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Figures below won't work with BIOS for partitions not in cyl 1
  parameters to be used for BIOS calculations are:
  cylinders=62415 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Do you want to change our idea of what BIOS thinks ? [n] 
  Media sector size is 512
  Warning: BIOS sector numbering starts with sector 1
  Information from DOS bootblock is:
  The data for partition 1 is:
  sysid 165,(FreeBSD/NetBSD/386BSD)
      start 63, size 41942817 (20479 Meg), flag 80 (active)
  	beg: cyl 0/ head 1/ sector 1;
  	end: cyl 1023/ head 15/ sector 63
  Do you want to change it? [n] y
  Supply a decimal value for "sysid (165=FreeBSD)" [165] 
  Supply a decimal value for "start" [63] 
  Supply a decimal value for "size" [41942817] 62914320
  Explicitly specify beg/end address ? [n] 
  sysid 165,(FreeBSD/NetBSD/386BSD)
      start 63, size 62914320 (30719 Meg), flag 80 (active)
  	beg: cyl 0/ head 1/ sector 1;
  	end: cyl 975/ head 0/ sector 63
  Are we happy with this entry? [n] y
  The data for partition 2 is:
  <UNUSED>
  Do you want to change it? [n] 
  The data for partition 3 is:
  <UNUSED>
  Do you want to change it? [n] 
  The data for partition 4 is:
  <UNUSED>
  Do you want to change it? [n] 
  Partition 1 is marked active
  Do you want to change the active partition? [n] 
  
  We haven't changed the partition table yet.  This is your last chance.
  parameters extracted from in-core disklabel are:
  cylinders=62415 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Figures below won't work with BIOS for partitions not in cyl 1
  parameters to be used for BIOS calculations are:
  cylinders=62415 heads=16 sectors/track=63 (1008 blks/cyl)
  
  Information from DOS bootblock is:
  1: sysid 165,(FreeBSD/NetBSD/386BSD)
      start 63, size 62914320 (30719 Meg), flag 80 (active)
  	beg: cyl 0/ head 1/ sector 1;
  	end: cyl 975/ head 0/ sector 63
  2: <UNUSED>
  3: <UNUSED>
  4: <UNUSED>
  Should we write new partition table? [n] y
  

• Reboot the system
• After reboot, verify that the slice has been resized by checking the output of fdisk ad0 once again
• Now adjust the FreeBSD partitions:

  # disklabel -e -r ad0
  

• The vi editor will come up with the current partition scheme:

  # /dev/ad0c:
  type: ESDI
  disk: ad0s1
  label:
  flags:
  bytes/sector: 512
  sectors/track: 63
  tracks/cylinder: 16
  sectors/cylinder: 1008
  cylinders: 62415
  sectors/unit: 62914320
  rpm: 3600
  interleave: 1
  trackskew: 0
  cylinderskew: 0
  headswitch: 0           # milliseconds
  track-to-track seek: 0  # milliseconds
  drivedata: 0
  
  8 partitions:
  #        size   offset    fstype   [fsize bsize bps/cpg]
    a:  8388608        0    4.2BSD     2048 16384    89   # (Cyl.    0 - 8322*)
    b:  4194304  8388608      swap                        # (Cyl. 8322*- 12483*)
    c: 41942817        0    unused        0     0         # (Cyl.    0 - 41609*)
    e: 29359905 12582912    4.2BSD     2048 16384    89   # (Cyl. 12483*- 41609*)
  

• Change the partitions table to:

  #        size   offset    fstype   [fsize bsize bps/cpg]
    a:  8388608        0    4.2BSD     2048 16384    89   # (Cyl.    0 - 8322*)
    b:  4194304  8388608      swap                        # (Cyl. 8322*- 12483*)
    c: 62914320        0    unused        0     0         # (Cyl.    0 - 41609*)
    e: 50331408 12582912    4.2BSD     2048 16384    89   # (Cyl. 12483*- 41609*)
  

• Now reboot into single user mode: At the boot loader press any key except [Enter] within 10 seconds, then enter boot -s
• When asked for the shell, simply hit [Enter]
• First, run a filesystem check on /var:

  # fsck -f /dev/ad0s1e
  

• If no error was found, resize the filesystem:

  # growfs /dev/ad0s1e
  

  Enter Yes (case sensitive!) when asked if you did backup your data
• As a safety measure, run a filesystem check on /var once again:

  # fsck -f /dev/ad0s1e
  

• Exit single user mode and boot into multi user mode:

  # exit
  

• Log into the system and verify that /var has been resized:

  # df -h
  Filesystem    Size   Used  Avail Capacity  Mounted on
  /dev/ad0s1a   3.9G   271M   3.4G     7%    /
  /dev/ad0s1e    24G   354K    22G     0%    /var
  procfs        4.0K   4.0K     0B   100%    /proc