falstaff – yet another tech blog

This short tutorial shows how to resize a ext4 root filesystem online. Most people use gparted from a recovery system for this task, and I also recommend that for if you are not familiar with the tools used in this guide. Also, make sure you have a backup of the data (I did this myself on a system I just installed, so I would not mind if anything goes wrong). Generally this is not different from doing a manual MBR/fdisk resize, except that we need to treat the unique partition GUID specially since we should maintain it (for boot loaders/boot managers).

So, here is how I resized my ext4 root partition (sda2) using gdisk and resize2fs:

1. gdisk /dev/sda
2. Print information (i<enter>2)

   Partition GUID code: 0FC63DAF-8483-4772-8E79-3D69D8477DE4 (Linux filesystem)
   Partition unique GUID: 7FAC4BC8-6186-4CDF-B6CA-EB73D7C942D1
   First sector: 206848 (at 101.0 MiB)
   Last sector: 109051903 (at 52.0 GiB)
   Partition size: 108845056 sectors (51.9 GiB)
   Attribute flags: 0000000000000000
   Partition name: ''

3. Delete the partition (d<enter>2<enter>)

   Command (? for help): d
   Partition number (1-4): 2

4. Recreate a new, large partition (n<enter>2<enter>….)
   on my setup, gdisk guessed the right first sector. The end sector was also guessed right, since I wanted to fill it up all remaining space

   Command (? for help): n
   Partition number (2-128, default 2): 
   First sector (34-500118158, default = 206848) or {+-}size{KMGTP}: 
   Last sector (206848-336072703, default = 336072703) or {+-}size{KMGTP}: 
   Current type is 'Linux filesystem'
   Hex code or GUID (L to show codes, Enter = 8300): 
   Changed type of partition to 'Linux filesystem'

5. Now copy the old Partition unique GUID to the new partition (x<enter>c<enter>2<enter>)

   Expert command (? for help): c
   Partition number (1-4): 2
   Enter the partition's new unique GUID ('R' to randomize): 7FAC4BC8-6186-4CDF-B6CA-EB73D7C942D1
   New GUID is 7FAC4BC8-6186-4CDF-B6CA-EB73D7C942D1

6. At this point one can verify everything again, after pressing w (to safe the partition), your data might be lost if you did not do this carefully… Just be warned 🙂
7. Reread your block device partition (sudo blockdev –rereadpt /dev/sda)
   Note: This did not work for me, so I had to reboot the system once. However, I still could resize online afterwards, so no big down-time and no external recovery media required 🙂
8. sudo resize2fs /dev/sda2

   resize2fs 1.42.8 (20-Jun-2013)
   Filesystem at /dev/sda2 is mounted on /; on-line resizing required
   old_desc_blocks = 4, new_desc_blocks = 11
   The filesystem on /dev/sda2 is now 41983232 blocks long.