Expanding a LUKS encrypted disk image

ශාකුන්තල | Shaakunthala, , , , , , ,

Yesterday I wrote about How to create an encrypted LUKS disk image.

Today I wanted to experiment more with it. I wanted to try resizing a LUKS volume, and after one failed attempt I found a way. If you still have the disk image of yesterday’s example, just follow me. 🙂

  1. Safety first! Unmount, luksClose and then backup your image file. 
    sudo umount /dev/mapper/myluksvol1 && sudo cryptsetup luksClose myluksvol1
cp /home/shaakunthala/luksvolume1 /home/shaakunthala/luksvolume1.bak
  2. Now, make more room in the container. 
    dd if=/dev/zero of=/home/shaakunthala/luksvolume1 bs=1M count=1024 oflag=append conv=notrunc

    Yesterday we created a 512 MB disk image, now let’s add one more gigabyte. Conv and oflag options tell dd not to overwrite or truncate the image but append zero data.

  3. Open the encrypted volume. 
    sudo cryptsetup luksOpen /home/shaakunthala/luksvolume1 myluksvol1
  4. Repair ext4 file system to make sure it’s clean and then resize to claim ‘unallocated’ 1 GB. 
    sudo fsck -fvy /dev/mapper/myluksvol1
sudo resize2fs /dev/mapper/myluksvol1
sudo fsck -fvy /dev/mapper/myluksvol1 # One last sanity check
  5. Now, if there are no errors the filesystem has successfully grown to the maximum available size of the encrypted partition. 
    sudo mount /dev/mapper/myluksvol1 /mnt
df -h /mnt

I’m still experimenting this and next thing I would like to try out on my own is how to shrink a LUKS encrypted disk image.

Expanding a LUKS encrypted disk image

3 thoughts on “Expanding a LUKS encrypted disk image”

  1. kdk says:

    Thank you for your posts on LUKS encryption. Very useful! Not overloaded with unnecessary information.

    Reply
  3. jidec says:

    On point 4, use instead:
    cryptsetup resize myluksvol1

    Then mount the luks disk:
    mount /dev/mapper/myluksvol1 /mnt

    and resize the FS hosted by the luks disk: (ext4 in your case):
    resize2fs /dev/mapper/myluksvol1 (not sure about the syntax of this command)
    or for XFS:
    xfs_growfs /dev/mapper/myluksvol1

    Job done.

    Reply

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