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authorDaniel Baumann <mail@daniel-baumann.ch>2016-05-29 17:17:10 +0000
committerDaniel Baumann <mail@daniel-baumann.ch>2016-05-29 17:17:40 +0000
commit5fcb0d00fb1cdc480ceae6aff80d0ed3ddd602cf (patch)
tree986e0e9aa7aaa4c5402455481822c5edfba12566 /doc/clzip.info
parentReleasing debian version 1.7-2. (diff)
downloadclzip-5fcb0d00fb1cdc480ceae6aff80d0ed3ddd602cf.tar.xz
clzip-5fcb0d00fb1cdc480ceae6aff80d0ed3ddd602cf.zip
Merging upstream version 1.8.
Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>
Diffstat (limited to 'doc/clzip.info')
-rw-r--r--doc/clzip.info189
1 files changed, 127 insertions, 62 deletions
diff --git a/doc/clzip.info b/doc/clzip.info
index 786d8c1..c590473 100644
--- a/doc/clzip.info
+++ b/doc/clzip.info
@@ -11,7 +11,7 @@ File: clzip.info, Node: Top, Next: Introduction, Up: (dir)
Clzip Manual
************
-This manual is for Clzip (version 1.7, 7 July 2015).
+This manual is for Clzip (version 1.8, 13 May 2016).
* Menu:
@@ -19,12 +19,13 @@ This manual is for Clzip (version 1.7, 7 July 2015).
* Invoking clzip:: Command line interface
* File format:: Detailed format of the compressed file
* Algorithm:: How clzip compresses the data
+* Trailing data:: Extra data appended to the file
* Examples:: A small tutorial with examples
* Problems:: Reporting bugs
* Concept index:: Index of concepts
- Copyright (C) 2010-2015 Antonio Diaz Diaz.
+ Copyright (C) 2010-2016 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission to
copy, distribute and modify it.
@@ -53,7 +54,7 @@ availability:
recovery means. The lziprecover program can repair bit-flip errors
(one of the most common forms of data corruption) in lzip files,
and provides data recovery capabilities, including error-checked
- merging of damaged copies of a file. *note Data safety:
+ merging of damaged copies of a file. *Note Data safety:
(lziprecover)Data safety.
* The lzip format is as simple as possible (but not simpler). The
@@ -73,15 +74,14 @@ corrupt byte near the beginning is a thing of the past.
The member trailer stores the 32-bit CRC of the original data, the
size of the original data and the size of the member. These values,
-together with the value remaining in the range decoder and the
-end-of-stream marker, provide a 4 factor integrity checking which
-guarantees that the decompressed version of the data is identical to
-the original. This guards against corruption of the compressed data,
-and against undetected bugs in clzip (hopefully very unlikely). The
-chances of data corruption going undetected are microscopic. Be aware,
-though, that the check occurs upon decompression, so it can only tell
-you that something is wrong. It can't help you recover the original
-uncompressed data.
+together with the end-of-stream marker, provide a 3 factor integrity
+checking which guarantees that the decompressed version of the data is
+identical to the original. This guards against corruption of the
+compressed data, and against undetected bugs in clzip (hopefully very
+unlikely). The chances of data corruption going undetected are
+microscopic. Be aware, though, that the check occurs upon
+decompression, so it can only tell you that something is wrong. It
+can't help you recover the original uncompressed data.
Clzip uses the same well-defined exit status values used by lzip and
bzip2, which makes it safer than compressors returning ambiguous warning
@@ -128,14 +128,14 @@ two or more compressed files. The result is the concatenation of the
corresponding uncompressed files. Integrity testing of concatenated
compressed files is also supported.
- Clzip can produce multi-member files and safely recover, with
+ Clzip can produce multimember files and safely recover, with
lziprecover, the undamaged members in case of file damage. Clzip can
also split the compressed output in volumes of a given size, even when
reading from standard input. This allows the direct creation of
multivolume compressed tar archives.
Clzip is able to compress and decompress streams of unlimited size by
-automatically creating multi-member output. The members so created are
+automatically creating multimember output. The members so created are
large, about 2 PiB each.

@@ -148,6 +148,10 @@ The format for running clzip is:
clzip [OPTIONS] [FILES]
+'-' used as a FILE argument means standard input. It can be mixed with
+other FILES and is read just once, the first time it appears in the
+command line.
+
Clzip supports the following options:
'-h'
@@ -158,6 +162,13 @@ The format for running clzip is:
'--version'
Print the version number of clzip on the standard output and exit.
+'-a'
+'--trailing-error'
+ Exit with error status 2 if any remaining input is detected after
+ decompressing the last member. Such remaining input is usually
+ trailing garbage that can be safely ignored. *Note
+ concat-example::.
+
'-b BYTES'
'--member-size=BYTES'
Set the member size limit to BYTES. A small member size may
@@ -166,14 +177,19 @@ The format for running clzip is:
'-c'
'--stdout'
- Compress or decompress to standard output. Needed when reading
- from a named pipe (fifo) or from a device. Use it to recover as
- much of the uncompressed data as possible when decompressing a
- corrupt file.
+ Compress or decompress to standard output; keep input files
+ unchanged. If compressing several files, each file is compressed
+ independently. This option is needed when reading from a named
+ pipe (fifo) or from a device. Use it also to recover as much of
+ the uncompressed data as possible when decompressing a corrupt
+ file.
'-d'
'--decompress'
- Decompress.
+ Decompress the specified file(s). If a file does not exist or
+ can't be opened, clzip continues decompressing the rest of the
+ files. If a file fails to decompress, clzip exits immediately
+ without decompressing the rest of the files.
'-f'
'--force'
@@ -211,12 +227,13 @@ The format for running clzip is:
'-s BYTES'
'--dictionary-size=BYTES'
- Set the dictionary size limit in bytes. Valid values range from 4
- KiB to 512 MiB. Clzip will use the smallest possible dictionary
- size for each file without exceeding this limit. Note that
- dictionary sizes are quantized. If the specified size does not
- match one of the valid sizes, it will be rounded upwards by adding
- up to (BYTES / 16) to it.
+ Set the dictionary size limit in bytes. Clzip will use the smallest
+ possible dictionary size for each file without exceeding this
+ limit. Valid values range from 4 KiB to 512 MiB. Values 12 to 29
+ are interpreted as powers of two, meaning 2^12 to 2^29 bytes. Note
+ that dictionary sizes are quantized. If the specified size does
+ not match one of the valid sizes, it will be rounded upwards by
+ adding up to (BYTES / 8) to it.
For maximum compression you should use a dictionary size limit as
large as possible, but keep in mind that the decompression memory
@@ -228,16 +245,17 @@ The format for running clzip is:
Split the compressed output into several volume files with names
'original_name00001.lz', 'original_name00002.lz', etc, and set the
volume size limit to BYTES. Each volume is a complete, maybe
- multi-member, lzip file. A small volume size may degrade
- compression ratio, so use it only when needed. Valid values range
- from 100 kB to 4 EiB.
+ multimember, lzip file. A small volume size may degrade compression
+ ratio, so use it only when needed. Valid values range from 100 kB
+ to 4 EiB.
'-t'
'--test'
Check integrity of the specified file(s), but don't decompress
them. This really performs a trial decompression and throws away
the result. Use it together with '-v' to see information about
- the file.
+ the file(s). If a file fails the test, clzip continues checking
+ the rest of the files.
'-v'
'--verbose'
@@ -246,18 +264,19 @@ The format for running clzip is:
processed. A second '-v' shows the progress of compression.
When decompressing or testing, further -v's (up to 4) increase the
verbosity level, showing status, compression ratio, dictionary
- size, and trailer contents (CRC, data size, member size).
+ size, trailer contents (CRC, data size, member size), and up to 6
+ bytes of trailing data (if any).
'-0 .. -9'
Set the compression parameters (dictionary size and match length
- limit) as shown in the table below. Note that '-9' can be much
- slower than '-0'. These options have no effect when decompressing.
+ limit) as shown in the table below. The default compression level
+ is '-6'. Note that '-9' can be much slower than '-0'. These
+ options have no effect when decompressing.
The bidimensional parameter space of LZMA can't be mapped to a
linear scale optimal for all files. If your files are large, very
- repetitive, etc, you may need to use the '--match-length' and
- '--dictionary-size' options directly to achieve optimal
- performance.
+ repetitive, etc, you may need to use the '--dictionary-size' and
+ '--match-length' options directly to achieve optimal performance.
Level Dictionary size Match length limit
-0 64 KiB 16 bytes
@@ -327,12 +346,12 @@ additional information before, between, or after them.
Each member has the following structure:
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
-| ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size |
+| ID string | VN | DS | LZMA stream | CRC32 | Data size | Member size |
+--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
All multibyte values are stored in little endian order.
-'ID string'
+'ID string (the "magic" bytes)'
A four byte string, identifying the lzip format, with the value
"LZIP" (0x4C, 0x5A, 0x49, 0x50).
@@ -350,8 +369,8 @@ additional information before, between, or after them.
Example: 0xD3 = 2^19 - 6 * 2^15 = 512 KiB - 6 * 32 KiB = 320 KiB
Valid values for dictionary size range from 4 KiB to 512 MiB.
-'Lzma stream'
- The lzma stream, finished by an end of stream marker. Uses default
+'LZMA stream'
+ The LZMA stream, finished by an end of stream marker. Uses default
values for encoder properties. *Note Stream format: (lzip)Stream
format, for a complete description.
@@ -365,11 +384,11 @@ additional information before, between, or after them.
Total size of the member, including header and trailer. This field
acts as a distributed index, allows the verification of stream
integrity, and facilitates safe recovery of undamaged members from
- multi-member files.
+ multimember files.

-File: clzip.info, Node: Algorithm, Next: Examples, Prev: File format, Up: Top
+File: clzip.info, Node: Algorithm, Next: Trailing data, Prev: File format, Up: Top
4 Algorithm
***********
@@ -435,15 +454,48 @@ range encoding), Igor Pavlov (for putting all the above together in
LZMA), and Julian Seward (for bzip2's CLI).

-File: clzip.info, Node: Examples, Next: Problems, Prev: Algorithm, Up: Top
+File: clzip.info, Node: Trailing data, Next: Examples, Prev: Algorithm, Up: Top
+
+5 Extra data appended to the file
+*********************************
+
+Sometimes extra data is found appended to a lzip file after the last
+member. Such trailing data may be:
+
+ * Padding added to make the file size a multiple of some block size,
+ for example when writing to a tape.
+
+ * Garbage added by some not totally successful copy operation.
+
+ * Useful data added by the user; a cryptographically secure hash, a
+ description of file contents, etc.
+
+ * Malicious data added to the file in order to make its total size
+ and hash value (for a chosen hash) coincide with those of another
+ file.
-5 A small tutorial with examples
+ * In very rare cases, trailing data could be the corrupt header of
+ another member. In multimember or concatenated files the
+ probability of corruption happening in the magic bytes is 5 times
+ smaller than the probability of getting a false positive caused by
+ the corruption of the integrity information itself. Therefore it
+ can be considered to be below the noise level.
+
+ Trailing data can be safely ignored in most cases. In some cases,
+like that of user-added data, it is expected to be ignored. In those
+cases where a file containing trailing data must be rejected, the option
+'--trailing-error' can be used. *Note --trailing-error::.
+
+
+File: clzip.info, Node: Examples, Next: Problems, Prev: Trailing data, Up: Top
+
+6 A small tutorial with examples
********************************
WARNING! Even if clzip is bug-free, other causes may result in a corrupt
compressed file (bugs in the system libraries, memory errors, etc).
Therefore, if the data you are going to compress are important, give the
-'--keep' option to clzip and do not remove the original file until you
+'--keep' option to clzip and don't remove the original file until you
verify the compressed file with a command like
'clzip -cd file.lz | cmp file -'.
@@ -454,8 +506,8 @@ and show the compression ratio.
clzip -v file
-Example 2: Like example 1 but the created 'file.lz' is multi-member
-with a member size of 1 MiB. The compression ratio is not shown.
+Example 2: Like example 1 but the created 'file.lz' is multimember with
+a member size of 1 MiB. The compression ratio is not shown.
clzip -b 1MiB file
@@ -472,37 +524,46 @@ show status.
clzip -tv file.lz
-Example 5: Compress a whole floppy in /dev/fd0 and send the output to
+Example 5: Compress a whole device in /dev/sdc and send the output to
'file.lz'.
- clzip -c /dev/fd0 > file.lz
+ clzip -c /dev/sdc > file.lz
+
+
+Example 6: The right way of concatenating compressed files. *Note
+Trailing data::.
+
+ Don't do this
+ cat file1.lz file2.lz file3.lz | clzip -d
+ Do this instead
+ clzip -cd file1.lz file2.lz file3.lz
-Example 6: Decompress 'file.lz' partially until 10 KiB of decompressed
+Example 7: Decompress 'file.lz' partially until 10 KiB of decompressed
data are produced.
clzip -cd file.lz | dd bs=1024 count=10
-Example 7: Decompress 'file.lz' partially from decompressed byte 10000
+Example 8: Decompress 'file.lz' partially from decompressed byte 10000
to decompressed byte 15000 (5000 bytes are produced).
clzip -cd file.lz | dd bs=1000 skip=10 count=5
-Example 8: Create a multivolume compressed tar archive with a volume
+Example 9: Create a multivolume compressed tar archive with a volume
size of 1440 KiB.
tar -c some_directory | clzip -S 1440KiB -o volume_name
-Example 9: Extract a multivolume compressed tar archive.
+Example 10: Extract a multivolume compressed tar archive.
clzip -cd volume_name*.lz | tar -xf -
-Example 10: Create a multivolume compressed backup of a large database
-file with a volume size of 650 MB, where each volume is a multi-member
+Example 11: Create a multivolume compressed backup of a large database
+file with a volume size of 650 MB, where each volume is a multimember
file with a member size of 32 MiB.
clzip -b 32MiB -S 650MB big_db
@@ -510,7 +571,7 @@ file with a member size of 32 MiB.

File: clzip.info, Node: Problems, Next: Concept index, Prev: Examples, Up: Top
-6 Reporting bugs
+7 Reporting bugs
****************
There are probably bugs in clzip. There are certainly errors and
@@ -539,6 +600,7 @@ Concept index
* introduction: Introduction. (line 6)
* invoking: Invoking clzip. (line 6)
* options: Invoking clzip. (line 6)
+* trailing data: Trailing data. (line 6)
* usage: Invoking clzip. (line 6)
* version: Invoking clzip. (line 6)
@@ -546,13 +608,16 @@ Concept index

Tag Table:
Node: Top210
-Node: Introduction893
-Node: Invoking clzip6152
-Node: File format11705
-Node: Algorithm14108
-Node: Examples16933
-Node: Problems18900
-Node: Concept index19426
+Node: Introduction952
+Node: Invoking clzip6164
+Ref: --trailing-error6730
+Node: File format12728
+Node: Algorithm15150
+Node: Trailing data17980
+Node: Examples19355
+Ref: concat-example20537
+Node: Problems21544
+Node: Concept index22070

End Tag Table