Transparent decompression (-z option) is available on Linux kernels using kernel version 2.4.14 or 2.4.9-ac14 or later. You also need the zisofs-tools package, containing the mkzftree utility, to create the compressed files; this package is available at: ftp://ftp.kernel.org/pub/linux/utils/fs/zisofs/ The mkzftree utility can also be used to read compressed CD-ROMs on systems which do not support transparent decompression. The use of a separate utility allows compression to be controlled on a per-file basis. A file which is not compressed can be read on any system. Transparent decompression is implemented as an extension to Rock Ridge, so Rock Ridge needs to be enabled (-R or -r options.)