Resizing an UFS2 filesystem on FreeBSD

As stated previously, resizing a FreeBSD filesystem (read: UFS2) might by a bit tricky. At least on FreeBSD 9.2 this isn't true anymore. To resize a UFS filesystem:

• Backup your data
• Resize the underlying block device, e.g. the virtual harddisk
• Rescan all SCSI/SAS/SATA buses:

  $ camcontrol rescan all
  

• List all block devices:

  $ gpart show

  If this doesn't show the correct size for the resized device, then reboot. During reboot ignore any warnings about invalid GPT headers
• Fix the invalid GPT header (replace ada0 by your actual block device):

  $ gpart recover ada0

• Allow write access to GEOM providers:

  $ sysctl -w kern.geom.debugflags=16

• Resize the third partition (again, replace 3 and ada0):

  $ gpart resize -i 3 ada0

• Resize the filesystem:

  $ growfs ada0p3

  Enter Yes (case-sensitive!) when asked
• Disallow write access to GEOM providers (just as a security measure):

  $ sysctl -w kern.geom.debugflags=0

This even works for a mounted root filesystem.