compress disk image for use with
utility compresses a disk image file so
that the geom_uzip(4)
class will be able to
decompress the resulting image at run-time. This allows for a significant
reduction of size of disk image at the expense of some CPU time required to
decompress the data each time it is read. The
utility works in two phases:
- An infile image is split
into clusters; each cluster is compressed using
- The resulting set of compressed clusters along with
headers that allow locating each individual cluster is written to the
The options are:
- Name of the output file
outfile. The default is to use the input
name with the suffix .uzip.
- Split the image into clusters of
cluster_size bytes, 16384 bytes by
default. The cluster_size should be a
multiple of 512 bytes.
- Display verbose messages.
The compression ratio largely depends on the cluster size used. For large
cluster sizes (16K and higher), typical compression ratios are only 1-2% less
than those achieved with gzip(1)
. However, it
should be kept in mind that larger cluster sizes lead to higher overhead in
class, as the class has to
decompress the whole cluster even if only a few bytes from that cluster have
to be read.
utility inserts a short shell script at
the beginning of the generated image, which makes it possible to
“run” the image just like any other shell script. The script
tries to load the geom_uzip(4)
class if it is not
loaded, configure the image as an md(4)
device using mdconfig(8)
, and automatically mount
it using mount_cd9660(8)
on the mount point
provided as the first argument to the script.
utility exits 0 on success,
and >0 if an error occurs.