This is lziprecover.info, produced by makeinfo version 4.13 from lziprecover.texinfo. INFO-DIR-SECTION Data Compression START-INFO-DIR-ENTRY * Lziprecover: (lziprecover). Data recovery tool for lzipped files END-INFO-DIR-ENTRY  File: lziprecover.info, Node: Top, Next: Introduction, Up: (dir) Lziprecover Manual ****************** This manual is for Lziprecover (version 1.13-rc1, 12 November 2011). * Menu: * Introduction:: Purpose and features of lziprecover * Invoking Lziprecover:: Command line interface * File Format:: Detailed format of the compressed file * Examples:: A small tutorial with examples * Problems:: Reporting bugs * Concept Index:: Index of concepts Copyright (C) 2009, 2010, 2011 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it.  File: lziprecover.info, Node: Introduction, Next: Invoking Lziprecover, Prev: Top, Up: Top 1 Introduction ************** Lziprecover is a data recovery tool and decompressor for files in the lzip compressed data format (.lz) able to repair slightly damaged files, recover badly damaged files from two or more copies, extract undamaged members from multi-member files, decompress files and test integrity of files. Lziprecover is able to recover or decompress files produced by any of the compressors in the lzip family; lzip, plzip, minilzip/lzlib, clzip and pdlzip. This recovery capability contributes to make the lzip format one of the best options for long-term data archiving. When recovering data, lziprecover takes as arguments the names of the damaged files and writes zero or more recovered files depending on the operation selected and whether the recovery succeeded or not. The damaged files themselves are never modified. When decompressing or testing file integrity, lziprecover behaves like lzip or lunzip. If the files are too damaged for lziprecover to repair them, data from damaged members can be partially recovered writing it to stdout as shown in the following example (the resulting file may contain some garbage data at the end): lziprecover -cd rec00001file.lz > rec00001file If the cause of file corruption is damaged media, the combination GNU ddrescue + lziprecover is the best option for recovering data from multiple damaged copies. *Note ddrescue-example::, for an example. Return values: 0 for a normal exit, 1 for environmental problems (file not found, invalid flags, I/O errors, etc), 2 to indicate a corrupt or invalid input file, 3 for an internal consistency error (eg, bug) which caused lziprecover to panic.  File: lziprecover.info, Node: Invoking Lziprecover, Next: File Format, Prev: Introduction, Up: Top 2 Invoking Lziprecover ********************** The format for running lziprecover is: lziprecover [OPTIONS] [FILES] Lziprecover supports the following options: `-h' `--help' Print an informative help message describing the options and exit. `-V' `--version' Print the version number of lziprecover on the standard output and exit. `-c' `--stdout' 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. `-d' `--decompress' Decompress. `-f' `--force' Force overwrite of output files. `-k' `--keep' Keep (don't delete) input files during decompression. `-m' `--merge' Try to produce a correct file merging the good parts of two or more damaged copies. The copies must be single-member files. The merge will fail if the copies have too many damaged areas or if the same byte is damaged in all copies. If successful, a repaired copy is written to the file `FILE_fixed.lz'. The exit status is 0 if the file could be repaired, 2 otherwise. To give you an idea of its possibilities, when merging two copies each of them with one damaged area affecting 1 percent of the copy, the probability of obtaining a correct file is about 98 percent. With three such copies the probability rises to 99.97 percent. For large files with small errors, the probability approaches 100 percent even with only two copies. `-o FILE' `--output=FILE' Place the output into `FILE' instead of into `FILE_fixed.lz'. If splitting, the names of the files produced are in the form `rec00001FILE', `rec00002FILE', etc. If decompressing from standard input and `--stdout' has not been specified, use `FILE' as the name of the decompressed file. `-q' `--quiet' Quiet operation. Suppress all messages. `-R' `--repair' Try to repair a small error, affecting only one byte, in a single-member FILE. If successful, a repaired copy is written to the file `FILE_fixed.lz'. `FILE' is not modified at all. The exit status is 0 if the file could be repaired, 2 otherwise. `-s' `--split' Search for members in `FILE' and write each member in its own `.lz' file. You can then use `lziprecover -t' to test the integrity of the resulting files, decompress those which are undamaged, and try to repair or partially decompress those which are damaged. The names of the files produced are in the form `rec00001FILE.lz', `rec00002FILE.lz', etc, and are designed so that the use of wildcards in subsequent processing, for example, `lziprecover -cd rec*FILE.lz > recovered_data', processes the files in the correct order. `-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. `-v' `--verbose' Verbose mode. When decompressing or testing, further -v's (up to 4) increase the verbosity level, showing status, dictionary size, compression ratio, trailer contents (CRC, data size, member size), and up to 6 bytes of trailing garbage (if any).  File: lziprecover.info, Node: File Format, Next: Examples, Prev: Invoking Lziprecover, Up: Top 3 File Format ************* In the diagram below, a box like this: +---+ | | <-- the vertical bars might be missing +---+ represents one byte; a box like this: +==============+ | | +==============+ represents a variable number of bytes. A lzip file consists of a series of "members" (compressed data sets). The members simply appear one after another in the file, with no additional information before, between, or after them. Each member has the following structure: +--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID string | VN | DS | Lzma stream | CRC32 | Data size | Member size | +--+--+--+--+----+----+=============+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ All multibyte values are stored in little endian order. `ID string' A four byte string, identifying the lzip format, with the value "LZIP". `VN (version number, 1 byte)' Just in case something needs to be modified in the future. Valid values are 0 and 1. Version 0 files are deprecated. They can contain only one member and lack the `Member size' field. `DS (coded dictionary size, 1 byte)' Bits 4-0 contain the base 2 logarithm of the base dictionary size. Bits 7-5 contain the number of "wedges" to substract from the base dictionary size to obtain the dictionary size. The size of a wedge is (base dictionary size / 16). Valid values for dictionary size range from 4KiB to 512MiB. `Lzma stream' The lzma stream, finished by an end of stream marker. Uses default values for encoder properties. `CRC32 (4 bytes)' CRC of the uncompressed original data. `Data size (8 bytes)' Size of the uncompressed original data. `Member size (8 bytes)' Total size of the member, including header and trailer. This facilitates safe recovery of undamaged members from multimember files.  File: lziprecover.info, Node: Examples, Next: Problems, Prev: File Format, Up: Top 4 A small tutorial with examples ******************************** Example 1: Restore a regular file from its compressed version `file.lz'. If the operation is successful, `file.lz' is removed. lziprecover -d file.lz Example 2: Verify the integrity of the compressed file `file.lz' and show status. lziprecover -tv file.lz Example 3: Decompress `file.lz' partially until 10KiB of decompressed data are produced. lziprecover -cd file.lz | dd bs=1024 count=10 Example 4: Decompress `file.lz' partially from decompressed byte 10000 to decompressed byte 15000 (5000 bytes are produced). lziprecover -cd file.lz | dd bs=1000 skip=10 count=5 Example 5: Repair a one-byte corruption in the single-member file `file.lz'. (Indented lines are abridged error messages from lziprecover). lziprecover -v -R file.lz Copy of input file repaired successfully. mv file_fixed.lz file.lz Example 6: Split the multi-member file `file.lz' and write each member in its own `recXXXXXfile.lz' file. Then use `lziprecover -t' to test the integrity of the resulting files. lziprecover -s file.lz lziprecover -tv rec*file.lz Example 7: Recover a compressed backup from two copies on CD-ROM (see the GNU ddrescue manual for details about ddrescue) ddrescue -b2048 /dev/cdrom cdimage1 logfile1 mount -t iso9660 -o loop,ro cdimage1 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued1.tar.lz umount /mnt/cdimage (insert second copy in the CD drive) ddrescue -b2048 /dev/cdrom cdimage2 logfile2 mount -t iso9660 -o loop,ro cdimage2 /mnt/cdimage cp /mnt/cdimage/backup.tar.lz rescued2.tar.lz umount /mnt/cdimage lziprecover -m -v -o rescued.tar.lz rescued1.tar.lz rescued2.tar.lz Example 8: Recover the first volume of those created with the command `lzip -b 32MiB -S 650MB big_db' from two copies, `big_db1_00001.lz' and `big_db2_00001.lz', with member 00007 damaged in the first copy, member 00018 damaged in the second copy, and member 00012 damaged in both copies. Two correct copies are produced and compared. lziprecover -s big_db1_00001.lz lziprecover -s big_db2_00001.lz lziprecover -t rec*big_db1_00001.lz rec00007big_db1_00001.lz: crc mismatch rec00012big_db1_00001.lz: crc mismatch lziprecover -t rec*big_db2_00001.lz rec00012big_db2_00001.lz: crc mismatch rec00018big_db2_00001.lz: crc mismatch lziprecover -m -v rec00012big_db1_00001.lz rec00012big_db2_00001.lz Input files merged successfully cp rec00007big_db2_00001.lz rec00007big_db1_00001.lz cp rec00012big_db1_00001_fixed.lz rec00012big_db1_00001.lz cp rec00012big_db1_00001_fixed.lz rec00012big_db2_00001.lz cp rec00018big_db1_00001.lz rec00018big_db2_00001.lz cat rec*big_db1_00001.lz > big_db3_00001.lz cat rec*big_db2_00001.lz > big_db4_00001.lz zcmp big_db3_00001.lz big_db4_00001.lz  File: lziprecover.info, Node: Problems, Next: Concept Index, Prev: Examples, Up: Top 5 Reporting Bugs **************** There are probably bugs in lziprecover. There are certainly errors and omissions in this manual. If you report them, they will get fixed. If you don't, no one will ever know about them and they will remain unfixed for all eternity, if not longer. If you find a bug in lziprecover, please send electronic mail to . Include the version number, which you can find by running `lziprecover --version'.  File: lziprecover.info, Node: Concept Index, Prev: Problems, Up: Top Concept Index ************* [index] * Menu: * bugs: Problems. (line 6) * examples: Examples. (line 6) * file format: File Format. (line 6) * getting help: Problems. (line 6) * introduction: Introduction. (line 6) * invoking lziprecover: Invoking Lziprecover. (line 6)  Tag Table: Node: Top231 Node: Introduction898 Node: Invoking Lziprecover2684 Node: File Format6150 Node: Examples8156 Ref: ddrescue-example9409 Node: Problems11188 Node: Concept Index11738  End Tag Table