When you have a raw disk image file, you may need to increase its size at some point. With dd, you can do this:
dd conv=notrunc oflag=append if=/dev/zero of=backups bs=1M count=1024
This will add 1GB of zero data to the image file ‘backups’. You can then use resize2fs on it to increase the file system size (that is, if you use ext2/3/4):
e2fsck (-f) backups resize2fs backups
However, if the disk image is a volume encrypted with cryptsetup + luks, first open it:
losetup /dev/loop/0 backups cryptsetup luksOpen /dev/loop/0 encrypted-backups
Then resize the encrypted volume:
cryptsetup resize encrypted-backups e2fsck (-f) /dev/mapper/encrypted-backups resize2fs /dev/mapper/encrypted-backups
And I know, I still have to add LVMs to my set of skills…
Hi,
thanks for the tips. However, if you use the dd as mentionned in the first line you are at risk depending on the version of dd you are using.
conv=notrunc should be added to the command line, otherwise the image file may be overwritten (the documentation for dd is not clear enough regarding this).
Someting like this:
dd conv=notrunc oflag=append conv=notrunc if=/dev/zero of=backups bs=1M count=1024
You can see a discussion concerning on debian bugtracker:
See bug #373736 at debian.org
Thanks!
I don’t get it. I need to specify it twice, once before oflag and after?
Oh… It seems I was totally blind 🙂 I didn’t see it was their already. Feel free to revert my comment and delete it forever 🙂
No reason to pollute the network and in particular the earth with all my bits of mistake.
Thanks,
Raphaël
I’ll do no such thing :). Your mention of that bug report is useful.
can we extend it online, if the file is mounted as loopback device. any idea or suggestion would be greatly appreciated
Good stuff!
I read somewhere else that truncate is the command to use, but I discovered that
df -h file.imgincorrectly reported the original size whilels -lh file.imgreported it correctly after using truncate.Next time I’ll use this dd command instead.
du strictly measures disk usage. If you have a sparse file, you can have a file that shows up in ls as 10 GB, and only take a few kB of actual disk space.