'\" t
.\"
.\" Author: Lasse Collin
.\"
.\" This file has been put into the public domain.
.\" You can do whatever you want with this file.
.\"
.TH XZ 1 "2009-08-27" "Tukaani" "XZ Utils"
.SH NAME
xz, unxz, xzcat, lzma, unlzma, lzcat \- Compress or decompress .xz and .lzma files
.SH SYNOPSIS
.B xz
.RI [ option ]...
.RI [ file ]...
.PP
.B unxz
is equivalent to
.BR "xz \-\-decompress" .
.br
.B xzcat
is equivalent to
.BR "xz \-\-decompress \-\-stdout" .
.br
.B lzma
is equivalent to
.BR "xz \-\-format=lzma" .
.br
.B unlzma
is equivalent to
.BR "xz \-\-format=lzma \-\-decompress" .
.br
.B lzcat
is equivalent to
.BR "xz \-\-format=lzma \-\-decompress \-\-stdout" .
.PP
When writing scripts that need to decompress files, it is recommended to
always use the name
.B xz
with appropriate arguments
.RB ( "xz \-d"
or
.BR "xz \-dc" )
instead of the names
.B unxz
and
.BR xzcat.
.SH DESCRIPTION
.B xz
is a general-purpose data compression tool with command line syntax similar to
.BR gzip (1)
and
.BR bzip2 (1).
The native file format is the
.B .xz
format, but also the legacy
.B .lzma
format and raw compressed streams with no container format headers
are supported.
.PP
.B xz
compresses or decompresses each
.I file
according to the selected operation mode.
If no
.I files
are given or
.I file
is
.BR \- ,
.B xz
reads from standard input and writes the processed data to standard output.
.B xz
will refuse (display an error and skip the
.IR file )
to write compressed data to standard output if it is a terminal. Similarly,
.B xz
will refuse to read compressed data from standard input if it is a terminal.
.PP
Unless
.B \-\-stdout
is specified,
.I files
other than
.B \-
are written to a new file whose name is derived from the source
.I file
name:
.IP \(bu 3
When compressing, the suffix of the target file format
.RB ( .xz
or
.BR .lzma )
is appended to the source filename to get the target filename.
.IP \(bu 3
When decompressing, the
.B .xz
or
.B .lzma
suffix is removed from the filename to get the target filename.
.B xz
also recognizes the suffixes
.B .txz
and
.BR .tlz ,
and replaces them with the
.B .tar
suffix.
.PP
If the target file already exists, an error is displayed and the
.I file
is skipped.
.PP
Unless writing to standard output,
.B xz
will display a warning and skip the
.I file
if any of the following applies:
.IP \(bu 3
.I File
is not a regular file. Symbolic links are not followed, thus they
are never considered to be regular files.
.IP \(bu 3
.I File
has more than one hardlink.
.IP \(bu 3
.I File
has setuid, setgid, or sticky bit set.
.IP \(bu 3
The operation mode is set to compress, and the
.I file
already has a suffix of the target file format
.RB ( .xz
or
.B .txz
when compressing to the
.B .xz
format, and
.B .lzma
or
.B .tlz
when compressing to the
.B .lzma
format).
.IP \(bu 3
The operation mode is set to decompress, and the
.I file
doesn't have a suffix of any of the supported file formats
.RB ( .xz ,
.BR .txz ,
.BR .lzma ,
or
.BR .tlz ).
.PP
After successfully compressing or decompressing the
.IR file ,
.B xz
copies the owner, group, permissions, access time, and modification time
from the source
.I file
to the target file. If copying the group fails, the permissions are modified
so that the target file doesn't become accessible to users who didn't have
permission to access the source
.IR file .
.B xz
doesn't support copying other metadata like access control lists
or extended attributes yet.
.PP
Once the target file has been successfully closed, the source
.I file
is removed unless
.B \-\-keep
was specified. The source
.I file
is never removed if the output is written to standard output.
.PP
Sending
.B SIGINFO
or
.B SIGUSR1
to the
.B xz
process makes it print progress information to standard error.
This has only limited use since when standard error is a terminal, using
.B \-\-verbose
will display an automatically updating progress indicator.
.SS "Memory usage"
The memory usage of
.B xz
varies from a few hundred kilobytes to several gigabytes depending on
the compression settings. The settings used when compressing a file
affect also the memory usage of the decompressor. Typically the decompressor
needs only 5\ % to 20\ % of the amount of RAM that the compressor needed when
creating the file. Still, the worst-case memory usage of the decompressor
is several gigabytes.
.PP
To prevent uncomfortable surprises caused by huge memory usage,
.B xz
has a built-in memory usage limiter. The default limit is 40 % of total
physical RAM. While operating systems provide ways to limit the memory usage
of processes, relying on it wasn't deemed to be flexible enough.
.PP
When compressing, if the selected compression settings exceed the memory
usage limit, the settings are automatically adjusted downwards and a notice
about this is displayed. As an exception, if the memory usage limit is
exceeded when compressing with
.BR \-\-format=raw ,
an error is displayed and
.B xz
will exit with exit status
.BR 1 .
.PP
If source
.I file
cannot be decompressed without exceeding the memory usage limit, an error
message is displayed and the file is skipped. Note that compressed files
may contain many blocks, which may have been compressed with different
settings. Typically all blocks will have roughly the same memory requirements,
but it is possible that a block later in the file will exceed the memory usage
limit, and an error about too low memory usage limit gets displayed after some
data has already been decompressed.
.PP
The absolute value of the active memory usage limit can be seen near
the bottom of the output of
.BR \-\-long\-help .
The default limit can be overriden with
\fB\-\-memory=\fIlimit\fR.
.SH OPTIONS
.SS "Integer suffixes and special values"
In most places where an integer argument is expected, an optional suffix
is supported to easily indicate large integers. There must be no space
between the integer and the suffix.
.TP
.BR k " or " kB
The integer is multiplied by 1,000 (10^3). For example,
.B "5k"
or
.B "5kB"
equals
.BR "5000" .
.TP
.BR Ki " or " KiB
The integer is multiplied by 1,024 (2^10).
.TP
.BR M " or " MB
The integer is multiplied by 1,000,000 (10^6).
.TP
.BR Mi " or " MiB
The integer is multiplied by 1,048,576 (2^20).
.TP
.BR G " or " GB
The integer is multiplied by 1,000,000,000 (10^9).
.TP
.BR Gi " or " GiB
The integer is multiplied by 1,073,741,824 (2^30).
.PP
A special value
.B max
can be used to indicate the maximum integer value supported by the option.
.SS "Operation mode"
If multiple operation mode options are given, the last one takes effect.
.TP
.BR \-z ", " \-\-compress
Compress. This is the default operation mode when no operation mode option
is specified, and no other operation mode is implied from the command name
(for example,
.B unxz
implies
.BR \-\-decompress ).
.TP
.BR \-d ", " \-\-decompress ", " \-\-uncompress
Decompress.
.TP
.BR \-t ", " \-\-test
Test the integrity of compressed
.IR files .
No files are created or removed. This option is equivalent to
.B "\-\-decompress \-\-stdout"
except that the decompressed data is discarded instead of being
written to standard output.
.TP
.BR \-l ", " \-\-list
View information about the compressed files. No uncompressed output is
produced, and no files are created or removed. In list mode, the program
cannot read the compressed data from standard input or from other
unseekable sources.
.IP
.B "This feature has not been implemented yet."
.SS "Operation modifiers"
.TP
.BR \-k ", " \-\-keep
Keep (don't delete) the input files.
.TP
.BR \-f ", " \-\-force
This option has several effects:
.RS
.IP \(bu 3
If the target file already exists, delete it before compressing or
decompressing.
.IP \(bu 3
Compress or decompress even if the input is not a regular file,
has more than one hardlink, or has setuid, setgid, or sticky bit set.
The setuid, setgid, and sticky bits are not copied to the target file.
.IP \(bu 3
If combined with
.B \-\-decompress
.BR \-\-stdout
and
.B xz
doesn't recognize the type of the source file,
.B xz
will copy the source file as is to standard output. This allows using
.B xzcat
.B \--force
like
.BR cat (1)
for files that have not been compressed with
.BR xz .
Note that in future,
.B xz
might support new compressed file formats, which may make
.B xz
decompress more types of files instead of copying them as is to
standard output.
.BI \-\-format= format
can be used to restrict
.B xz
to decompress only a single file format.
.IP \(bu 3
Allow writing compressed data to a terminal, and reading compressed data
from a terminal.
.RE
.TP
.BR \-c ", " \-\-stdout ", " \-\-to-stdout
Write the compressed or decompressed data to standard output instead of
a file. This implies
.BR \-\-keep .
.TP
\fB\-S\fR \fI.suf\fR, \fB\-\-suffix=\fI.suf
When compressing, use
.I .suf
as the suffix for the target file instead of
.B .xz
or
.BR .lzma .
If not writing to standard output and the source file already has the suffix
.IR .suf ,
a warning is displayed and the file is skipped.
.IP
When decompressing, recognize also files with the suffix
.I .suf
in addition to files with the
.BR .xz ,
.BR .txz ,
.BR .lzma ,
or
.B .tlz
suffix. If the source file has the suffix
.IR .suf ,
the suffix is removed to get the target filename.
.IP
When compressing or decompressing raw streams
.RB ( \-\-format=raw ),
the suffix must always be specified unless writing to standard output,
because there is no default suffix for raw streams.
.TP
\fB\-\-files\fR[\fB=\fIfile\fR]
Read the filenames to process from
.IR file ;
if
.I file
is omitted, filenames are read from standard input. Filenames must be
terminated with the newline character. If filenames are given also as
command line arguments, they are processed before the filenames read from
.IR file .
.TP
\fB\-\-files0\fR[\fB=\fIfile\fR]
This is identical to \fB\-\-files\fR[\fB=\fIfile\fR] except that the
filenames must be terminated with the null character.
.SS "Basic file format and compression options"
.TP
\fB\-F\fR \fIformat\fR, \fB\-\-format=\fIformat
Specify the file format to compress or decompress:
.RS
.IP \(bu 3
.BR auto :
This is the default. When compressing,
.B auto
is equivalent to
.BR xz .
When decompressing, the format of the input file is autodetected. Note that
raw streams (created with
.BR \-\-format=raw )
cannot be autodetected.
.IP \(bu 3
.BR xz :
Compress to the
.B .xz
file format, or accept only
.B .xz
files when decompressing.
.IP \(bu 3
.B lzma
or
.BR alone :
Compress to the legacy
.B .lzma
file format, or accept only
.B .lzma
files when decompressing. The alternative name
.B alone
is provided for backwards compatibility with LZMA Utils.
.IP \(bu 3
.BR raw :
Compress or uncompress a raw stream (no headers). This is meant for advanced
users only. To decode raw streams, you need to set not only
.B \-\-format=raw
but also specify the filter chain, which would normally be stored in the
container format headers.
.RE
.TP
\fB\-C\fR \fIcheck\fR, \fB\-\-check=\fIcheck
Specify the type of the integrity check, which is calculated from the
uncompressed data. This option has an effect only when compressing into the
.B .xz
format; the
.B .lzma
format doesn't support integrity checks.
The integrity check (if any) is verified when the
.B .xz
file is decompressed.
.IP
Supported
.I check
types:
.RS
.IP \(bu 3
.BR none :
Don't calculate an integrity check at all. This is usually a bad idea. This
can be useful when integrity of the data is verified by other means anyway.
.IP \(bu 3
.BR crc32 :
Calculate CRC32 using the polynomial from IEEE-802.3 (Ethernet).
.IP \(bu 3
.BR crc64 :
Calculate CRC64 using the polynomial from ECMA-182. This is the default, since
it is slightly better than CRC32 at detecting damaged files and the speed
difference is negligible.
.IP \(bu 3
.BR sha256 :
Calculate SHA-256. This is somewhat slower than CRC32 and CRC64.
.RE
.IP
Integrity of the
.B .xz
headers is always verified with CRC32. It is not possible to change or
disable it.
.TP
.BR \-0 " ... " \-9
Select compression preset. If a preset level is specified multiple times,
the last one takes effect.
.IP
The compression preset levels can be categorised roughly into three
categories:
.RS
.IP "\fB\-0\fR ... \fB\-2"
Fast presets with relatively low memory usage.
.B \-1
and
.B \-2
should give compression speed and ratios comparable to
.B "bzip2 \-1"
and
.BR "bzip2 \-9" ,
respectively.
Currently
.B \-0
is not very good (not much faster than
.B \-1
but much worse compression). In future,
.B \-0
may be indicate some fast algorithm instead of LZMA2.
.IP "\fB\-3\fR ... \fB\-5"
Good compression ratio with low to medium memory usage.
These are significantly slower than levels 0\-2.
.IP "\fB\-6\fR ... \fB\-9"
Excellent compression with medium to high memory usage. These are also
slower than the lower preset levels. The default is
.BR \-6 .
Unless you want to maximize the compression ratio, you probably don't want
a higher preset level than
.B \-7
due to speed and memory usage.
.RE
.IP
The exact compression settings (filter chain) used by each preset may
vary between
.B xz
versions. The settings may also vary between files being compressed, if
.B xz
determines that modified settings will probably give better compression
ratio without significantly affecting compression time or memory usage.
.IP
Because the settings may vary, the memory usage may vary too. The following
table lists the maximum memory usage of each preset level, which won't be
exceeded even in future versions of
.BR xz .
.IP
.B "FIXME: The table below is just a rough idea."
.RS
.RS
.TS
tab(;);
c c c
n n n.
Preset;Compression;Decompression
\-0;6 MiB;1 MiB
\-1;6 MiB;1 MiB
\-2;10 MiB;1 MiB
\-3;20 MiB;2 MiB
\-4;30 MiB;3 MiB
\-5;60 MiB;6 MiB
\-6;100 MiB;10 MiB
\-7;200 MiB;20 MiB
\-8;400 MiB;40 MiB
\-9;800 MiB;80 MiB
.TE
.RE
.RE
.IP
When compressing,
.B xz
automatically adjusts the compression settings downwards if
the memory usage limit would be exceeded, so it is safe to specify
a high preset level even on systems that don't have lots of RAM.
.TP
.BR \-\-fast " and " \-\-best
These are somewhat misleading aliases for
.B \-0
and
.BR \-9 ,
respectively.
These are provided only for backwards compatibility with LZMA Utils.
Avoid using these options.
.IP
Especially the name of
.B \-\-best
is misleading, because the definition of best depends on the input data,
and that usually people don't want the very best compression ratio anyway,
because it would be very slow.
.TP
.BR \-e ", " \-\-extreme
Modify the compression preset (\fB\-0\fR ... \fB\-9\fR) so that a little bit
better compression ratio can be achieved without increasing memory usage
of the compressor or decompressor (exception: compressor memory usage may
increase a little with presets \fB\-0\fR ... \fB\-2\fR). The downside is that
the compression time will increase dramatically (it can easily double).
.TP
\fB\-M\fR \fIlimit\fR, \fB\-\-memory=\fIlimit
Set the memory usage limit. If this option is specied multiple times,
the last one takes effect. The
.I limit
can be specified in multiple ways:
.RS
.IP \(bu 3
The
.I limit
can be an absolute value in bytes. Using an integer suffix like
.B MiB
can be useful. Example:
.B "\-\-memory=80MiB"
.IP \(bu 3
The
.I limit
can be specified as a percentage of physical RAM. Example:
.B "\-\-memory=70%"
.IP \(bu 3
The
.I limit
can be reset back to its default value (currently 40 % of physical RAM)
by setting it to
.BR 0 .
.IP \(bu 3
The memory usage limiting can be effectively disabled by setting
.I limit
to
.BR max .
This isn't recommended. It's usually better to use, for example,
.BR \-\-memory=90% .
.RE
.IP
The current
.I limit
can be seen near the bottom of the output of the
.B \-\-long-help
option.
.TP
\fB\-T\fR \fIthreads\fR, \fB\-\-threads=\fIthreads
Specify the maximum number of worker threads to use. The default is
the number of available CPU cores. You can see the current value of
.I threads
near the end of the output of the
.B \-\-long\-help
option.
.IP
The actual number of worker threads can be less than
.I threads
if using more threads would exceed the memory usage limit.
In addition to CPU-intensive worker threads,
.B xz
may use a few auxiliary threads, which don't use a lot of CPU time.
.IP
.B "Multithreaded compression and decompression are not implemented yet,"
.B "so this option has no effect for now."
.SS Custom compressor filter chains
A custom filter chain allows specifying the compression settings in detail
instead of relying on the settings associated to the preset levels.
When a custom filter chain is specified, the compression preset level options
(\fB\-0\fR ... \fB\-9\fR and \fB\-\-extreme\fR) are silently ignored.
.PP
A filter chain is comparable to piping on the UN*X command line.
When compressing, the uncompressed input goes to the first filter, whose
output goes to the next filter (if any). The output of the last filter
gets written to the compressed file. The maximum number of filters in
the chain is four, but typically a filter chain has only one or two filters.
.PP
Many filters have limitations where they can be in the filter chain:
some filters can work only as the last filter in the chain, some only
as a non-last filter, and some work in any position in the chain. Depending
on the filter, this limitation is either inherent to the filter design or
exists to prevent security issues.
.PP
A custom filter chain is specified by using one or more filter options in
the order they are wanted in the filter chain. That is, the order of filter
options is significant! When decoding raw streams
.RB ( \-\-format=raw ),
the filter chain is specified in the same order as it was specified when
compressing.
.PP
Filters take filter-specific
.I options
as a comma-separated list. Extra commas in
.I options
are ignored. Every option has a default value, so you need to
specify only those you want to change.
.TP
\fB\-\-lzma1\fR[\fB=\fIoptions\fR], \fB\-\-lzma2\fR[\fB=\fIoptions\fR]
Add LZMA1 or LZMA2 filter to the filter chain. These filter can be used
only as the last filter in the chain.
.IP
LZMA1 is a legacy filter, which is supported almost solely due to the legacy
.B .lzma
file format, which supports only LZMA1. LZMA2 is an updated
version of LZMA1 to fix some practical issues of LZMA1. The
.B .xz
format uses LZMA2, and doesn't support LZMA1 at all. Compression speed and
ratios of LZMA1 and LZMA2 are practically the same.
.IP
LZMA1 and LZMA2 share the same set of
.IR options :
.RS
.TP
.BI preset= preset
Reset all LZMA1 or LZMA2
.I options
to
.IR preset .
.I Preset
consist of an integer, which may be followed by single-letter preset
modifiers. The integer can be from
.B 0
to
.BR 9 ,
matching the command line options \fB\-0\fR ... \fB\-9\fR.
The only supported modifier is currently
.BR e ,
which matches
.BR \-\-extreme .
.IP
The default
.I preset
is
.BR 6 ,
from which the default values for the rest of the LZMA1 or LZMA2
.I options
are taken.
.TP
.BI dict= size
Dictionary (history buffer) size indicates how many bytes of the recently
processed uncompressed data is kept in memory. One method to reduce size of
the uncompressed data is to store distance-length pairs, which
indicate what data to repeat from the dictionary buffer. The bigger
the dictionary, the better the compression ratio usually is,
but dictionaries bigger than the uncompressed data are waste of RAM.
.IP
Typical dictionary size is from 64 KiB to 64 MiB. The minimum is 4 KiB.
The maximum for compression is currently 1.5 GiB. The decompressor already
supports dictionaries up to one byte less than 4 GiB, which is the
maximum for LZMA1 and LZMA2 stream formats.
.IP
Dictionary size has the biggest effect on compression ratio.
Dictionary size and match finder together determine the memory usage of
the LZMA1 or LZMA2 encoder. The same dictionary size is required
for decompressing that was used when compressing, thus the memory usage of
the decoder is determined by the dictionary size used when compressing.
.TP
.BI lc= lc
Specify the number of literal context bits. The minimum is
.B 0
and the maximum is
.BR 4 ;
the default is
.BR 3 .
In addition, the sum of
.I lc
and
.I lp
must not exceed
.BR 4 .
.TP
.BI lp= lp
Specify the number of literal position bits. The minimum is
.B 0
and the maximum is
.BR 4 ;
the default is
.BR 0 .
.TP
.BI pb= pb
Specify the number of position bits. The minimum is
.B 0
and the maximum is
.BR 4 ;
the default is
.BR 2 .
.TP
.BI mode= mode
Compression
.I mode
specifies the function used to analyze the data produced by the match finder.
Supported
.I modes
are
.B fast
and
.BR normal .
The default is
.B fast
for
.I presets
.BR 0 \- 2
and
.B normal
for
.I presets
.BR 3 \- 9 .
.TP
.BI mf= mf
Match finder has a major effect on encoder speed, memory usage, and
compression ratio. Usually Hash Chain match finders are faster than
Binary Tree match finders. Hash Chains are usually used together with
.B mode=fast
and Binary Trees with
.BR mode=normal .
The memory usage formulas are only rough estimates,
which are closest to reality when
.I dict
is a power of two.
.RS
.TP
.B hc3
Hash Chain with 2- and 3-byte hashing
.br
Minimum value for
.IR nice :
3
.br
Memory usage:
.I dict
* 7.5 (if
.I dict
<= 16 MiB);
.br
.I dict
* 5.5 + 64 MiB (if
.I dict
> 16 MiB)
.TP
.B hc4
Hash Chain with 2-, 3-, and 4-byte hashing
.br
Minimum value for
.IR nice :
4
.br
Memory usage:
.I dict
* 7.5
.TP
.B bt2
Binary Tree with 2-byte hashing
.br
Minimum value for
.IR nice :
2
.br
Memory usage:
.I dict
* 9.5
.TP
.B bt3
Binary Tree with 2- and 3-byte hashing
.br
Minimum value for
.IR nice :
3
.br
Memory usage:
.I dict
* 11.5 (if
.I dict
<= 16 MiB);
.br
.I dict
* 9.5 + 64 MiB (if
.I dict
> 16 MiB)
.TP
.B bt4
Binary Tree with 2-, 3-, and 4-byte hashing
.br
Minimum value for
.IR nice :
4
.br
Memory usage:
.I dict
* 11.5
.RE
.TP
.BI nice= nice
Specify what is considered to be a nice length for a match. Once a match
of at least
.I nice
bytes is found, the algorithm stops looking for possibly better matches.
.IP
.I nice
can be 2\-273 bytes. Higher values tend to give better compression ratio
at expense of speed. The default depends on the
.I preset
level.
.TP
.BI depth= depth
Specify the maximum search depth in the match finder. The default is the
special value
.BR 0 ,
which makes the compressor determine a reasonable
.I depth
from
.I mf
and
.IR nice .
.IP
Using very high values for
.I depth
can make the encoder extremely slow with carefully crafted files.
Avoid setting the
.I depth
over 1000 unless you are prepared to interrupt the compression in case it
is taking too long.
.RE
.IP
When decoding raw streams
.RB ( \-\-format=raw ),
LZMA2 needs only the value of
.BR dict .
LZMA1 needs also
.BR lc ,
.BR lp ,
and
.BR pb.
.TP
\fB\-\-x86\fR[\fB=\fIoptions\fR]
.TP
\fB\-\-powerpc\fR[\fB=\fIoptions\fR]
.TP
\fB\-\-ia64\fR[\fB=\fIoptions\fR]
.TP
\fB\-\-arm\fR[\fB=\fIoptions\fR]
.TP
\fB\-\-armthumb\fR[\fB=\fIoptions\fR]
.TP
\fB\-\-sparc\fR[\fB=\fIoptions\fR]
Add a branch/call/jump (BCJ) filter to the filter chain. These filters
can be used only as non-last filter in the filter chain.
.IP
A BCJ filter converts relative addresses in the machine code to their
absolute counterparts. This doesn't change the size of the data, but
it increases redundancy, which allows e.g. LZMA2 to get better
compression ratio.
.IP
The BCJ filters are always reversible, so using a BCJ filter for wrong
type of data doesn't cause any data loss. However, applying a BCJ filter
for wrong type of data is a bad idea, because it tends to make the
compression ratio worse.
.IP
Different instruction sets have have different alignment:
.RS
.RS
.TS
tab(;);
l n l
l n l.
Filter;Alignment;Notes
x86;1;32-bit and 64-bit x86
PowerPC;4;Big endian only
ARM;4;Little endian only
ARM-Thumb;2;Little endian only
IA-64;16;Big or little endian
SPARC;4;Big or little endian
.TE
.RE
.RE
.IP
Since the BCJ-filtered data is usually compressed with LZMA2, the compression
ratio may be improved slightly if the LZMA2 options are set to match the
alignment of the selected BCJ filter. For example, with the IA-64 filter,
it's good to set
.B pb=4
with LZMA2 (2^4=16). The x86 filter is an exception; it's usually good to
stick to LZMA2's default four-byte alignment when compressing x86 executables.
.IP
All BCJ filters support the same
.IR options :
.RS
.TP
.BI start= offset
Specify the start
.I offset
that is used when converting between relative and absolute addresses.
The
.I offset
must be a multiple of the alignment of the filter (see the table above).
The default is zero. In practice, the default is good; specifying
a custom
.I offset
is almost never useful.
.IP
Specifying a non-zero start
.I offset
is probably useful only if the executable has multiple sections, and there
are many cross-section jumps or calls. Applying a BCJ filter separately for
each section with proper start offset and then compressing the result as
a single chunk may give some improvement in compression ratio compared
to applying the BCJ filter with the default
.I offset
for the whole executable.
.RE
.TP
\fB\-\-delta\fR[\fB=\fIoptions\fR]
Add Delta filter to the filter chain. The Delta filter
can be used only as non-last filter in the filter chain.
.IP
Currently only simple byte-wise delta calculation is supported. It can
be useful when compressing e.g. uncompressed bitmap images or uncompressed
PCM audio. However, special purpose algorithms may give significantly better
results than Delta + LZMA2. This is true especially with audio, which
compresses faster and better e.g. with FLAC.
.IP
Supported
.IR options :
.RS
.TP
.BI dist= distance
Specify the
.I distance
of the delta calculation as bytes.
.I distance
must be 1\-256. The default is 1.
.IP
For example, with
.B dist=2
and eight-byte input A1 B1 A2 B3 A3 B5 A4 B7, the output will be
A1 B1 01 02 01 02 01 02.
.RE
.SS "Other options"
.TP
.BR \-q ", " \-\-quiet
Suppress warnings and notices. Specify this twice to suppress errors too.
This option has no effect on the exit status. That is, even if a warning
was suppressed, the exit status to indicate a warning is still used.
.TP
.BR \-v ", " \-\-verbose
Be verbose. If standard error is connected to a terminal,
.B xz
will display a progress indicator.
Specifying
.B \-\-verbose
twice will give even more verbose output (useful mostly for debugging).
.TP
.BR \-Q ", " \-\-no\-warn
Don't set the exit status to
.B 2
even if a condition worth a warning was detected. This option doesn't affect
the verbosity level, thus both
.B \-\-quiet
and
.B \-\-no\-warn
have to be used to not display warnings and to not alter the exit status.
.TP
.BR \-h ", " \-\-help
Display a help message describing the most commonly used options,
and exit successfully.
.TP
.BR \-H ", " \-\-long\-help
Display a help message describing all features of
.BR xz ,
and exit successfully
.TP
.BR \-V ", " \-\-version
Display the version number of
.B xz
and liblzma.
.SH "EXIT STATUS"
.TP
.B 0
All is good.
.TP
.B 1
An error occurred.
.TP
.B 2
Something worth a warning occurred, but no actual errors occurred.
.PP
Notices (not warnings or errors) printed on standard error don't affect
the exit status.
.SH ENVIRONMENT
.TP
.B XZ_OPT
A space-separated list of options is parsed from
.B XZ_OPT
before parsing the options given on the command line. Note that only
options are parsed from
.BR XZ_OPT ;
all non-options are silently ignored. Parsing is done with
.BR getopt_long (3)
which is used also for the command line arguments.
.SH "LZMA UTILS COMPATIBILITY"
The command line syntax of
.B xz
is practically a superset of
.BR lzma ,
.BR unlzma ,
and
.BR lzcat
as found from LZMA Utils 4.32.x. In most cases, it is possible to replace
LZMA Utils with XZ Utils without breaking existing scripts. There are some
incompatibilities though, which may sometimes cause problems.
.SS "Compression preset levels"
The numbering of the compression level presets is not identical in
.B xz
and LZMA Utils.
The most important difference is how dictionary sizes are mapped to different
presets. Dictionary size is roughly equal to the decompressor memory usage.
.RS
.TS
tab(;);
c c c
c n n.
Level;xz;LZMA Utils
\-1;64 KiB;64 KiB
\-2;512 KiB;1 MiB
\-3;1 MiB;512 KiB
\-4;2 MiB;1 MiB
\-5;4 MiB;2 MiB
\-6;8 MiB;4 MiB
\-7;16 MiB;8 MiB
\-8;32 MiB;16 MiB
\-9;64 MiB;32 MiB
.TE
.RE
.PP
The dictionary size differences affect the compressor memory usage too,
but there are some other differences between LZMA Utils and XZ Utils, which
make the difference even bigger:
.RS
.TS
tab(;);
c c c
c n n.
Level;xz;LZMA Utils 4.32.x
\-1;2 MiB;2 MiB
\-2;5 MiB;12 MiB
\-3;13 MiB;12 MiB
\-4;25 MiB;16 MiB
\-5;48 MiB;26 MiB
\-6;94 MiB;45 MiB
\-7;186 MiB;83 MiB
\-8;370 MiB;159 MiB
\-9;674 MiB;311 MiB
.TE
.RE
.PP
The default preset level in LZMA Utils is
.B \-7
while in XZ Utils it is
.BR \-6 ,
so both use 8 MiB dictionary by default.
.SS "Streamed vs. non-streamed .lzma files"
Uncompressed size of the file can be stored in the
.B .lzma
header. LZMA Utils does that when compressing regular files.
The alternative is to mark that uncompressed size is unknown and
use end of payload marker to indicate where the decompressor should stop.
LZMA Utils uses this method when uncompressed size isn't known, which is
the case for example in pipes.
.PP
.B xz
supports decompressing
.B .lzma
files with or without end of payload marker, but all
.B .lzma
files created by
.B xz
will use end of payload marker and have uncompressed size marked as unknown
in the
.B .lzma
header. This may be a problem in some (uncommon) situations. For example, a
.B .lzma
decompressor in an embedded device might work only with files that have known
uncompressed size. If you hit this problem, you need to use LZMA Utils or
LZMA SDK to create
.B .lzma
files with known uncompressed size.
.SS "Unsupported .lzma files"
The
.B .lzma
format allows
.I lc
values up to 8, and
.I lp
values up to 4. LZMA Utils can decompress files with any
.I lc
and
.IR lp ,
but always creates files with
.B lc=3
and
.BR lp=0 .
Creating files with other
.I lc
and
.I lp
is possible with
.B xz
and with LZMA SDK.
.PP
The implementation of the LZMA1 filter in liblzma requires
that the sum of
.I lc
and
.I lp
must not exceed 4. Thus,
.B .lzma
files which exceed this limitation, cannot be decompressed with
.BR xz .
.PP
LZMA Utils creates only
.B .lzma
files which have dictionary size of
.RI "2^" n
(a power of 2), but accepts files with any dictionary size.
liblzma accepts only
.B .lzma
files which have dictionary size of
.RI "2^" n
or
.RI "2^" n " + 2^(" n "\-1)."
This is to decrease false positives when autodetecting
.B .lzma
files.
.PP
These limitations shouldn't be a problem in practice, since practically all
.B .lzma
files have been compressed with settings that liblzma will accept.
.SS "Trailing garbage"
When decompressing, LZMA Utils silently ignore everything after the first
.B .lzma
stream. In most situations, this is a bug. This also means that LZMA Utils
don't support decompressing concatenated
.B .lzma
files.
.PP
If there is data left after the first
.B .lzma
stream,
.B xz
considers the file to be corrupt. This may break obscure scripts which have
assumed that trailing garbage is ignored.
.SH NOTES
.SS Compressed output may vary
The exact compressed output produced from the same uncompressed input file
may vary between XZ Utils versions even if compression options are identical.
This is because the encoder can be improved (faster or better compression)
without affecting the file format. The output can vary even between different
builds of the same XZ Utils version, if different build options are used or
if the endianness of the hardware is different for different builds.
.PP
The above means that implementing
.B \-\-rsyncable
to create rsyncable
.B .xz
files is not going to happen without freezing a part of the encoder
implementation, which can then be used with
.BR \-\-rsyncable .
.SS Embedded .xz decompressors
Embedded
.B .xz
decompressor implementations like XZ Embedded don't necessarily support files
created with
.I check
types other than
.B none
and
.BR crc32 .
Since the default is \fB\-\-check=\fIcrc64\fR, you must use
.B \-\-check=none
or
.B \-\-check=crc32
when creating files for embedded systems.
.PP
Outside embedded systems, all
.B .xz
format decompressors support all the
.I check
types, or at least are able to decompress the file without verifying the
integrity check if the particular
.I check
is not supported.
.PP
XZ Embedded supports BCJ filters, but only with the default start offset.
.SH "SEE ALSO"
.BR xzdec (1),
.BR gzip (1),
.BR bzip2 (1)
.PP
XZ Utils: <http://tukaani.org/xz/>
.br
XZ Embedded: <http://tukaani.org/xz/embedded.html>
.br
LZMA SDK: <http://7-zip.org/sdk.html>