freebsd/usr.bin/mkuzip/mkuzip.8

.\"-
.\" Copyright (c) 2004-2016 Maxim Sobolev <sobomax@FreeBSD.org>
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.\" $FreeBSD$
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.Dd March 17, 2006
.Dt MKUZIP 8
.Os
.Sh NAME
.Nm mkuzip
.Nd compress disk image for use with
.Xr geom_uzip 4
class
.Sh SYNOPSIS
.Nm
.Op Fl v
.Op Fl o Ar outfile
.Op Fl s Ar cluster_size
.Op Fl j Ar compression_jobs
.Ar infile
.Sh DESCRIPTION
The
.Nm
utility compresses a disk image file so that the
.Xr 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
.Nm
utility
works in two phases:
.Bl -enum
.It
An
.Ar infile
image is split into clusters; each cluster is compressed using
.Xr zlib 3
or
.Xr lzma 3 .
.It
The resulting set of compressed clusters along with headers that allow
locating each individual cluster is written to the output file.
.El
.Pp
The options are:
.Bl -tag -width indent
.It Fl o Ar outfile
Name of the output file
.Ar outfile .
The default is to use the input name with the suffix
.Pa .uzip
for the
.Xr zlib 3
compression or
.Pa .ulzma
for the
.Xr lzma 3 .
.It Fl L
Use
.Xr lzma 3
compression algorithm instead of the default
.Xr zlib 3 .
The
.Xr lzma 3
provides noticeable better compression levels on the same data set
at the expense of much slower compression speed (10-20x) and somewhat slower
decompression (2-3x).
.It Fl s Ar cluster_size
Split the image into clusters of
.Ar cluster_size
bytes, 16384 bytes by default.
The
.Ar cluster_size
should be a multiple of 512 bytes.
.It Fl v
Display verbose messages.
.It Fl Z
Disable zero-blocks detection and elimination.
When this option is set, the
.Nm
would compress empty blocks (i.e. clusters that consist of only zero bytes)
just as it would any other block.
When the option is not set, the
.Nm
detects such blocks and skips them from the output.
Setting
.Fl Z
results is slight increase of compressed image size, typically less than 0.1%
of a final size of the compressed image.
.It Fl d
Enable de-duplication.
When the option is enabled the
.Nm
detects identical blocks in the input and replaces each subsequent occurence
of such block with pointer to the very first one in the output.
Setting this option results is moderate decrease of compressed image size,
typically around 3-5% of a final size of the compressed image.
.It Fl S
Print summary about the compression ratio as well as output
file size after file has been processed.
.It Fl j Ar compression_jobs
Specify the number of compression jobs that
.Nm
runs in parallel to speed up compression.
When option is not specified the number of jobs set to be equal
to the value of
.Va hw.ncpu
.Xr sysctl 8
variable.
.El
.Sh NOTES
The compression ratio largely depends on the cluster size used.
.\" The following two sentences are unclear: how can gzip(1) be
.\" used in a comparable fashion, and wouldn't a gzip-compressed
.\" image suffer from larger cluster sizes as well?
For large cluster sizes (16K and higher), typical compression ratios
are only 1-2% less than those achieved with
.Xr gzip 1 .
However, it should be kept in mind that larger cluster
sizes lead to higher overhead in the
.Xr geom_uzip 4
class, as the class has to decompress the whole cluster even if
only a few bytes from that cluster have to be read.
.Pp
The
.Nm
utility
inserts a short shell script at the beginning of the generated image,
which makes it possible to
.Dq run
the image just like any other shell script.
The script tries to load the
.Xr geom_uzip 4
class if it is not loaded, configure the image as an
.Xr md 4
disk device using
.Xr mdconfig 8 ,
and automatically mount it using
.Xr mount_cd9660 8
on the mount point provided as the first argument to the script.
.Pp
The de-duplication is a
.Fx
specific feature and while it does not require any changes to on-disk
compressed image format, however it did require some matching changes to the
.Xr geom_uzip 4
to handle resulting images correctly.
.Sh EXIT STATUS
.Ex -std
.Sh SEE ALSO
.Xr gzip 1 ,
.Xr xz 1 ,
.Xr lzma 3 ,
.Xr zlib 3 ,
.Xr geom 4 ,
.Xr geom_uzip 4 ,
.Xr md 4 ,
.Xr mdconfig 8 ,
.Xr mount_cd9660 8
.Sh AUTHORS
.An Maxim Sobolev Aq Mt sobomax@FreeBSD.org