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diff --git a/doc/lziprecover.texi b/doc/lziprecover.texi index a15e710..731515b 100644 --- a/doc/lziprecover.texi +++ b/doc/lziprecover.texi @@ -6,8 +6,8 @@ @finalout @c %**end of header -@set UPDATED 12 February 2018 -@set VERSION 1.20 +@set UPDATED 4 January 2019 +@set VERSION 1.21 @dircategory Data Compression @direntry @@ -40,6 +40,7 @@ This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}). * Data safety:: Protecting data from accidental loss * Repairing files:: Fixing bit flips and similar errors * Merging files:: Fixing several damaged copies +* Tarlz:: Options supporting the tar.lz format * File names:: Names of the files produced by lziprecover * File format:: Detailed format of the compressed file * Trailing data:: Extra data appended to the file @@ -50,7 +51,7 @@ This manual is for Lziprecover (version @value{VERSION}, @value{UPDATED}). @end menu @sp 1 -Copyright @copyright{} 2009-2018 Antonio Diaz Diaz. +Copyright @copyright{} 2009-2019 Antonio Diaz Diaz. This manual is free documentation: you have unlimited permission to copy, distribute and modify it. @@ -60,15 +61,22 @@ to copy, distribute and modify it. @chapter Introduction @cindex introduction -Lziprecover is a data recovery tool and decompressor for files in the -lzip compressed data format (.lz). Lziprecover is able to repair -slightly damaged files, produce a correct file by merging the good parts -of two or more damaged copies, extract data from damaged files, -decompress files and test integrity of files. +@uref{http://www.nongnu.org/lzip/lziprecover.html,,Lziprecover} is a +data recovery tool and decompressor for files in the lzip compressed +data format (.lz). Lziprecover is able to repair slightly damaged files, +produce a correct file by merging the good parts of two or more damaged +copies, extract data from damaged files, decompress files and test +integrity of files. + +Lziprecover can remove the damaged members from multimember files, for +example multimember tar.lz archives. Lziprecover provides random access to the data in multimember files; it only decompresses the members containing the desired data. +Lziprecover facilitates the management of metadata stored as trailing +data in lzip files. + Lziprecover is not a replacement for regular backups, but a last line of defense for the case where the backups are also damaged. @@ -126,7 +134,7 @@ lziprecover -D0 -i -o file -q file.lz 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. +damaged files themselves are kept unchanged. When decompressing or testing file integrity, lziprecover behaves like lzip or lunzip. @@ -164,6 +172,7 @@ Print an informative help message describing the options and exit. @item -V @itemx --version Print the version number of lziprecover on the standard output and exit. +This version number should be included in all bug reports. @anchor{--trailing-error} @item -a @@ -227,12 +236,15 @@ Force overwrite of output files. @item -i @itemx --ignore-errors -Make @samp{--range-decompress} ignore data errors and continue -decompressing the remaining members in the file. For example, +Make @samp{--range-decompress} ignore errors and continue decompressing +the remaining members in the file. For example, @w{@samp{lziprecover -D0 -i file.lz > file}} decompresses all the recoverable data in all members of @samp{file.lz} without having to split it first. +Make @samp{--list}, @samp{--dump}, @samp{--remove} and @samp{--strip} +ignore format errors. + @item -k @itemx --keep Keep (don't delete) input files during decompression. @@ -246,18 +258,22 @@ final line containing the cumulative sizes is printed. With @samp{-v}, the dictionary size, the number of members in the file, and the amount of trailing data (if any) are also printed. With @samp{-vv}, the positions and sizes of each member in multimember files are also -printed. @samp{-lq} can be used to verify quickly (without -decompressing) the structural integrity of the specified files. (Use -@samp{--test} to verify the data integrity). @samp{-alq} additionally -verifies that none of the specified files contain trailing data. +printed. With @samp{-i}, format errors are ignored, and with +@samp{-ivv}, gaps between members are shown. The member numbers shown +coincide with the file numbers produced by @samp{--split}. + +@samp{-lq} can be used to verify quickly (without decompressing) the +structural integrity of the specified files. (Use @samp{--test} to +verify the data integrity). @samp{-alq} additionally verifies that none +of the specified files contain trailing data. @item -m @itemx --merge Try to produce a correct file by merging the good parts of two or more damaged copies. If successful, a repaired copy is written to the file @samp{@var{file}_fixed.lz}. The exit status is 0 if a correct file could -be produced, 2 otherwise. See the chapter @samp{Merging files} -(@pxref{Merging files}) for a complete description of the merge mode. +be produced, 2 otherwise. @xref{Merging files}, for a complete +description of the merge mode. @item -o @var{file} @itemx --output=@var{file} @@ -280,16 +296,21 @@ Quiet operation. Suppress all messages. Try to repair a file with small errors (up to one single-byte error per member). If successful, a repaired copy is written to the file @samp{@var{file}_fixed.lz}. @samp{@var{file}} is not modified at all. -The exit status is 0 if the file could be repaired, 2 otherwise. See the -chapter @samp{Repairing files} (@pxref{Repairing files}) for a complete -description of the repair mode. +The exit status is 0 if the file could be repaired, 2 otherwise. +@xref{Repairing files}, for a complete description of the repair mode. @item -s @itemx --split Search for members in @samp{@var{file}} and write each member in its own -@samp{.lz} file. You can then use @samp{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. +file. Gaps between members are detected and each gap is saved in its own +file. Trailing data (if any) are saved alone in the last file. You can +then use @samp{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. Gaps may contain garbage +or may be members with corrupt headers or trailers. If other lziprecover +functions fail to work on a multimember @var{file} because of damage in +headers or trailers, try to split @var{file} and then work on each +member individually. The names of the files produced are in the form @samp{rec01@var{file}}, @samp{rec02@var{file}}, etc, and are designed so that the use of @@ -326,33 +347,75 @@ bytes are so similar to the magic bytes of a lzip header that they can be confused with a corrupt header. Use this option if a file triggers a "corrupt header" error and the cause is not indeed a corrupt header. -@item --dump-tdata -Dump the trailing data (if any) of one or more regular files to standard +@item --dump=[@var{member_list}][:damaged][:tdata] +Dump the members listed, the damaged members (if any), or the trailing +data (if any) of one or more regular multimember files to standard output, or to a file if the @samp{--output} option is used. If more than -one file is given, the trailing data of all files are concatenated. If a -file does not exist, can't be opened, or is not regular, lziprecover -continues processing the rest of the files. If the dump fails in one -file, lziprecover exits immediately without processing the rest of the -files. - -@item --remove-tdata -Remove the trailing data from regular files in place. The date of each -file is preserved if possible. If the removal fails in one file, -lziprecover continues processing the rest of the files. This option may -be dangerous if the file is corrupt or if the trailing data contain a -forbidden combination of characters. @xref{Trailing data}. Verify that -@w{@samp{lzip -cd file.lz | wc -c}} and the uncompressed size shown by -@w{@samp{lzip -l file.lz}} match before attempting the removal. - -@item --strip-tdata -Copy one or more regular files to standard output (or to a file if the -@samp{--output} option is used), stripping the trailing data (if any) -from each file. If more than one file is given, the files are -concatenated. If a file does not exist, can't be opened, or is not -regular, lziprecover continues processing the rest of the files. If a -file fails to copy, lziprecover exits immediately without processing the +one file is given, the elements dumped from all files are concatenated. +If a file does not exist, can't be opened, or is not regular, +lziprecover continues processing the rest of the files. If the dump +fails in one file, lziprecover exits immediately without processing the rest of the files. +The argument to @samp{--dump} is a colon-separated list of the following +element specifiers; a member list (1,3-6), a reverse member list +(r1,3-6), and the strings "damaged" and "tdata" (which may be shortened +to 'd' and 't' respectively). A member list selects the members (or +gaps) listed, whose numbers coincide with those shown by @samp{--list}. +A reverse member list selects the members listed counting from the last +member in the file (r1). Negated versions of both kinds of lists exist +(^1,3-6:r^1,3-6) which selects all the members except those in the list. +The strings "damaged" and "tdata" select the damaged members and the +trailing data respectively. If the same member is selected more than +once, for example by @code{1:r1} in a single-member file, it is dumped +just once. See the following examples: + +@multitable {@code{3,12:damaged:tdata}} {members 3, 12, damaged members, trailing data} +@headitem @code{--dump} argument @tab Elements dumped +@item @code{1,3-6} @tab members 1, 3, 4, 5 and 6 +@item @code{r1-3} @tab last 3 members in file +@item @code{^13,15} @tab all but 13th and 15th members in file +@item @code{r^1} @tab all but last member in file +@item @code{damaged} @tab all damaged members in file +@item @code{tdata} @tab trailing data +@item @code{1-5:r1:tdata} @tab members 1 to 5, last member, trailing data +@item @code{damaged:tdata} @tab damaged members, trailing data +@item @code{3,12:damaged:tdata} @tab members 3, 12, damaged members, trailing data +@end multitable + +@item --remove=[@var{member_list}][:damaged][:tdata] +Remove the members listed, the damaged members (if any), or the trailing +data (if any) from regular multimember files in place. The date of each +file is preserved if possible. If all members in a file are selected to +be removed, the file is left unchanged and the exit status is set to 2. +If a file does not exist, can't be opened, is not regular, or is left +unchanged, lziprecover continues processing the rest of the files. In +case of I/O error, lziprecover exits immediately without processing the +rest of the files. See @samp{--dump} above for a description of the +argument. + +This option may be dangerous even if only the trailing data is being +removed because the file may be corrupt or the trailing data may contain +a forbidden combination of characters. @xref{Trailing data}. It is +advisable to make a backup before attempting the removal. At least +verify that @w{@samp{lzip -cd file.lz | wc -c}} and the uncompressed +size shown by @w{@samp{lzip -l file.lz}} match before attempting the +removal of trailing data. + +@item --strip=[@var{member_list}][:damaged][:tdata] +Copy one or more regular multimember files to standard output (or to a +file if the @samp{--output} option is used), stripping the members +listed, the damaged members (if any), or the trailing data (if any) from +each file. If all members in a file are selected to be stripped, the +trailing data (if any) are also stripped even if @samp{tdata} is not +specified. If more than one file is given, the files are concatenated. +In this case the trailing data are also stripped from all but the last +file even if @samp{tdata} is not specified. If a file does not exist, +can't be opened, or is not regular, lziprecover continues processing the +rest of the files. If a file fails to copy, lziprecover exits +immediately without processing the rest of the files. See @samp{--dump} +above for a description of the argument. + @end table Numbers given as arguments to options may be followed by a multiplier @@ -521,6 +584,80 @@ than the number of corrupt bytes (3104) because contiguous corrupt bytes are counted as a single multibyte error. +@node Tarlz +@chapter Options supporting the tar.lz format +@cindex tarlz + +@uref{http://www.nongnu.org/lzip/manual/tarlz_manual.html,,Tarlz} is an +implementation of the tar archiver which by default creates archives +compressed with lzip on a per file basis. Tarlz can append files to the +end of such compressed archives because each tar member is compressed in +its own lzip member, as well as the end-of-file blocks. Thus tarlz +archives are multimember lzip files, which has some safety advantages +over solidly compressed tar.lz archives. For example, in case of +corruption, tarlz can extract all the undamaged members from the tar.lz +archive, skipping over the damaged members, just like the standard +(uncompressed) tar. In this chapter we'll explain the ways in which +lziprecover can recover and process multimember tar.lz archives. +@ifnothtml +@xref{Top,tarlz manual,,tarlz}. +@end ifnothtml + +@sp 1 +@section Recovering damaged multimember tar.lz archives + +If you have several copies of the damaged archive, try merging +them first because merging has a high probability of success. If the +command below prints something like +@w{@code{Input files merged successfully.}} you are done and +@code{archive.tar.lz} now contains the recovered archive: + +@example +lziprecover -m -v -o archive.tar.lz a/archive.tar.lz b/archive.tar.lz +@end example + +If you only have one copy of the damaged archive, you may try to repair +the archive, but this has a lower probability of success. If the command +below prints something like +@w{@code{Copy of input file repaired successfully.}} you are done and +@code{archive_fixed.tar.lz} now contains the recovered archive: + +@example +lziprecover -v -R archive.tar.lz +@end example + +If all the above fails, you may save the damaged members for later and +then copy the good members to another archive. If the two commands below +succeed, @code{bad_members.tar.lz} will contain all the damaged members +and @code{archive_cleaned.tar.lz} will contain a good archive with the +damaged members removed: + +@example +lziprecover -v --dump=damaged -o bad_members.tar.lz archive.tar.lz +lziprecover -v --strip=damaged -o archive_cleaned.tar.lz archive.tar.lz +@end example + +You can then use @code{tarlz --keep-damaged} to recover as much data as +possible from each damaged member in @samp{bad_members.tar.lz}: + +@example +mkdir tmp +cd tmp +tarlz --keep-damaged -xvf ../bad_members.tar.lz +@end example + +@sp 1 +@section Processing multimember tar.lz archives + +Lziprecover is able to copy a list of members from a file to another. +For example the command +@w{@code{lziprecover --dump=1-10:r1:tdata archive.tar.lz > subarch.tar.lz}} +creates a subset archive containing the first ten members, the +end-of-file blocks, and the trailing data (if any) of +@code{archive.tar.lz}. The @code{r1} part selects the last member, which +in an appendable tar.lz archive contains the end-of-file blocks. + + @node File names @chapter Names of the files produced by lziprecover @cindex file names @@ -581,10 +718,10 @@ Just in case something needs to be modified in the future. 1 for now. @item DS (coded dictionary size, 1 byte) The dictionary size is calculated by taking a power of 2 (the base size) -and substracting from it a fraction between 0/16 and 7/16 of the base +and subtracting from it a fraction between 0/16 and 7/16 of the base size.@* Bits 4-0 contain the base 2 logarithm of the base size (12 to 29).@* -Bits 7-5 contain the numerator of the fraction (0 to 7) to substract +Bits 7-5 contain the numerator of the fraction (0 to 7) to subtract from the base size to obtain the dictionary size.@* 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. @@ -675,11 +812,11 @@ Example 1: Add a comment or description to a compressed file. # First append the comment as trailing data to a lzip file echo 'This file contains this and that' >> file.lz # This command prints the comment to standard output -lziprecover --dump-tdata file.lz +lziprecover --dump=tdata file.lz # This command outputs file.lz without the comment -lziprecover --strip-tdata file.lz +lziprecover --strip=tdata file.lz # This command removes the comment from file.lz -lziprecover --remove-tdata file.lz +lziprecover --remove=tdata file.lz @end example @sp 1 @@ -690,8 +827,8 @@ to guarantee that both file and hash have not been maliciously replaced). @example sha256sum < file.lz >> file.lz -lziprecover --strip-tdata file.lz | sha256sum -c \ - <(lziprecover --dump-tdata file.lz) +lziprecover --strip=tdata file.lz | sha256sum -c \ + <(lziprecover --dump=tdata file.lz) @end example @@ -727,6 +864,10 @@ Don't do this cat file1.lz file2.lz file3.lz | lziprecover -d Do this instead lziprecover -cd file1.lz file2.lz file3.lz +You may also concatenate the compressed files like this + lziprecover --strip=tdata file1.lz file2.lz file3.lz > file123.lz +Or keeping the trailing data of the last file like this + lziprecover --strip=damaged file1.lz file2.lz file3.lz > file123.lz @end example @sp 1 @@ -777,13 +918,13 @@ lziprecover -tv rec*file.lz Example 8: Recover a compressed backup from two copies on CD-ROM with error-checked merging of copies. @ifnothtml -(@xref{Top,GNU ddrescue manual,,ddrescue}, +@xref{Top,GNU ddrescue manual,,ddrescue}, @end ifnothtml @ifhtml -(See the +See the @uref{http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html,,ddrescue manual} @end ifhtml -for details about ddrescue). +for details about ddrescue. @example ddrescue -d -r1 -b2048 /dev/cdrom cdimage1 mapfile1 @@ -862,15 +1003,15 @@ after the last byte of a member, producing a shorter but valid compressed file. Except in this latter case, please, report any false negative as a bug. -In order to compare the outputs, unzcrash needs a @samp{zcmp} program -able to understand the format being tested. For example the one provided +In order to compare the outputs, unzcrash needs a @samp{zcmp} program able +to understand the format being tested. For example the @samp{zcmp} provided by @samp{zutils}. @ifnothtml -@xref{Zcmp,,,zutils}, +@xref{Zcmp,,,zutils}. @end ifnothtml @ifhtml See -@uref{http://www.nongnu.org/zutils/manual/zutils_manual.html#Zcmp,,zcmp} +@uref{http://www.nongnu.org/zutils/manual/zutils_manual.html#Zcmp,,zcmp}. @end ifhtml The format for running unzcrash is: @@ -879,6 +1020,10 @@ The format for running unzcrash is: unzcrash [@var{options}] 'lzip -t' @var{file}.lz @end example +@noindent +@var{file}.lz must not contain errors and must be correctly decompressed +by the decompressor being tested for the comparisons to work. + unzcrash supports the following options: @table @code @@ -889,6 +1034,7 @@ Print an informative help message describing the options and exit. @item -V @itemx --version Print the version number of unzcrash on the standard output and exit. +This version number should be included in all bug reports. @item -b @var{range} @itemx --bits=@var{range} @@ -966,7 +1112,10 @@ Verbose mode. @item -z @itemx --zcmp=<command> Set zcmp command name and options. Defaults to @code{zcmp}. Use -@code{--zcmp=false} to disable comparisons. +@code{--zcmp=false} to disable comparisons. If testing a decompressor +different from the one used by default by zcmp, it is needed to force +unzcrash and zcmp to use the same decompressor with a command like +@w{@code{unzcrash --zcmp='zcmp --lz=plzip' 'plzip -t' @var{file}.lz}} @end table |