Sorry to answer myself, but it may be usefull for others... Knoppix uses any swap partition it finds. Since /dev/hda2 was swap (which doesn't show in mount, of course), the device was busy. swapoff /UNIONFS/dev/hda2 did release the drive. I partitioned with sfdisk, but fdisk -l /dev/hda is consistent.
-- Jorge Almeida -- gentoo-user@gentoo.org mailing list
