This manual is for Lziprecover (version 1.14-rc3, 23 April 2013).
Copyright © 2009, 2010, 2011, 2012, 2013 Antonio Diaz Diaz.
This manual is free documentation: you have unlimited permission to copy, distribute and modify it.
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.
Lziprecover is able to efficiently extract a range of bytes from a multi-member file, because it only decompresses the members containing the desired data.
Lziprecover can print correct total file sizes and ratios even for multi-member files.
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 rec01file.lz > rec01file
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. See 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.
The format for running lziprecover is:
lziprecover [options] [files]
Lziprecover supports the following options:
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
The names of the files produced are in the form
`rec01file.lz', `rec02file.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. The number of digits used in
the names varies depending on the number of members in `file'.
Numbers given as arguments to options may be followed by a multiplier and an optional `B' for "byte".
Table of SI and binary prefixes (unit multipliers):
|k||kilobyte (10^3 = 1000)|||||Ki||kibibyte (2^10 = 1024)
|M||megabyte (10^6)|||||Mi||mebibyte (2^20)
|G||gigabyte (10^9)|||||Gi||gibibyte (2^30)
|T||terabyte (10^12)|||||Ti||tebibyte (2^40)
|P||petabyte (10^15)|||||Pi||pebibyte (2^50)
|E||exabyte (10^18)|||||Ei||exbibyte (2^60)
|Z||zettabyte (10^21)|||||Zi||zebibyte (2^70)
|Y||yottabyte (10^24)|||||Yi||yobibyte (2^80)
Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away.
— Antoine de Saint-Exupery
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.
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 -D 10KiB file.lz
Example 4: Decompress `file.lz' partially from decompressed byte 10000 to decompressed byte 15000 (5000 bytes are produced).
lziprecover -D 10000-15000 file.lz
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 with error-checked merging of copies (See the 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_dbfrom two copies, `big_db1_00001.lz' and `big_db2_00001.lz', with member 07 damaged in the first copy, member 18 damaged in the second copy, and member 12 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 rec07big_db1_00001.lz: crc mismatch rec12big_db1_00001.lz: crc mismatch lziprecover -t rec*big_db2_00001.lz rec12big_db2_00001.lz: crc mismatch rec18big_db2_00001.lz: crc mismatch lziprecover -m -v rec12big_db1_00001.lz rec12big_db2_00001.lz Input files merged successfully cp rec07big_db2_00001.lz rec07big_db1_00001.lz cp rec12big_db1_00001_fixed.lz rec12big_db1_00001.lz cp rec12big_db1_00001_fixed.lz rec12big_db2_00001.lz cp rec18big_db1_00001.lz rec18big_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
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 email@example.com. Include the version number, which you can find by running `lziprecover --version'.