| /var Itself is Probably Mounted Although your errors message refers only to "some partitions" being mounted, I suspect that the one really causing the problem is /var itself. I would not expect that you'd be able to alter the partition size of a partition that is mounted.
If your disk has spare, unused partitions, paehaps you can mount up an empty one someplace, copy the existing /var into it, change your /etc/fstab (or equivalent?) to mount this new partition as /var, and reboot. Then the "real" /var will not be mounted, and you may be able to alter the partition size.
if there are no free partitions, maybe you can insert a 2nd disk and use a partition on it for a temporary /var. |