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Signed-off-by: Daniel Baumann <daniel@debian.org>
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doc/tarlz.info
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@ -1,6 +1,6 @@
This is tarlz.info, produced by makeinfo version 4.13+ from tarlz.texi.
INFO-DIR-SECTION Data Compression
INFO-DIR-SECTION Archiving
START-INFO-DIR-ENTRY
* Tarlz: (tarlz). Archiver with multimember lzip compression
END-INFO-DIR-ENTRY
@ -11,7 +11,7 @@ File: tarlz.info, Node: Top, Next: Introduction, Up: (dir)
Tarlz Manual
************
This manual is for Tarlz (version 0.22, 5 January 2022).
This manual is for Tarlz (version 0.23, 23 September 2022).
* Menu:
@ -69,9 +69,9 @@ archive, but it has the following advantages:
* The resulting multimember tar.lz archive can be decompressed in
parallel, multiplying the decompression speed.
* New members can be appended to the archive (by removing the EOF
member), and unwanted members can be deleted from the archive. Just
like an uncompressed tar archive.
* New members can be appended to the archive (by removing the
end-of-archive member), and unwanted members can be deleted from the
archive. Just like an uncompressed tar archive.
* It is a safe POSIX-style backup format. In case of corruption, tarlz
can extract all the undamaged members from the tar.lz archive,
@ -99,19 +99,24 @@ File: tarlz.info, Node: Invoking tarlz, Next: Portable character set, Prev: I
The format for running tarlz is:
tarlz [OPTIONS] [FILES]
tarlz OPERATION [OPTIONS] [FILES]
All operations except '--concatenate' and '--compress' operate on whole
trees if any FILE is a directory. All operations except '--compress'
overwrite output files without warning.
overwrite output files without warning. If no archive is specified, tarlz
tries to read it from standard input or write it to standard output. Tarlz
refuses to read archive data from a terminal or write archive data to a
terminal. Tarlz detects when the archive being created or enlarged is among
the files to be archived, appended, or concatenated, and skips it.
On archive creation or appending tarlz archives the files specified, but
removes from member names any leading and trailing slashes and any file name
prefixes containing a '..' component. On extraction, leading and trailing
slashes are also removed from member names, and archive members containing
a '..' component in the file name are skipped. Tarlz detects when the
archive being created or enlarged is among the files to be dumped, appended
or concatenated, and skips it.
Tarlz does not use absolute file names nor file names above the current
working directory (perhaps changed by option '-C'). On archive creation or
appending tarlz archives the files specified, but removes from member names
any leading and trailing slashes and any file name prefixes containing a
'..' component. On extraction, leading and trailing slashes are also
removed from member names, and archive members containing a '..' component
in the file name are skipped. Tarlz does not follow symbolic links during
extraction; not even symbolic links replacing intermediate directories.
On extraction and listing, tarlz removes leading './' strings from
member names in the archive or given in the command line, so that
@ -122,8 +127,7 @@ member names in the archive or given in the command line, so that
setting is used. For example '-9 --solid --uncompressed -1' is equivalent
to '-1 --solid'.
tarlz supports the following options: *Note Argument syntax:
(arg_parser)Argument syntax.
tarlz supports the following operations:
'--help'
Print an informative help message describing the options and exit.
@ -140,39 +144,22 @@ to '-1 --solid'.
standard output. All the archives involved must be regular (seekable)
files, and must be either all compressed or all uncompressed.
Compressed and uncompressed archives can't be mixed. Compressed
archives must be multimember lzip files with the two end-of-file
archives must be multimember lzip files with the two end-of-archive
blocks plus any zero padding contained in the last lzip member of each
archive. The intermediate end-of-file blocks are removed as each new
archive is concatenated. If the archive is uncompressed, tarlz parses
and skips tar headers until it finds the end-of-file blocks. Exit with
archive. The intermediate end-of-archive blocks are removed as each
new archive is concatenated. If the archive is uncompressed, tarlz
parses tar headers until it finds the end-of-archive blocks. Exit with
status 0 without modifying the archive if no FILES have been specified.
'-B BYTES'
'--data-size=BYTES'
Set target size of input data blocks for the option '--bsolid'. *Note
--bsolid::. Valid values range from 8 KiB to 1 GiB. Default value is
two times the dictionary size, except for option '-0' where it
defaults to 1 MiB. *Note Minimum archive sizes::.
Concatenating archives containing files in common results in two or
more tar members with the same name in the resulting archive, which
may produce nondeterministic behavior during multi-threaded extraction.
*Note mt-extraction::.
'-c'
'--create'
Create a new archive from FILES.
'-C DIR'
'--directory=DIR'
Change to directory DIR. When creating or appending, the position of
each '-C' option in the command line is significant; it will change the
current working directory for the following FILES until a new '-C'
option appears in the command line. When extracting or comparing, all
the '-C' options are executed in sequence before reading the archive.
Listing ignores any '-C' options specified. DIR is relative to the
then current working directory, perhaps changed by a previous '-C'
option.
Note that a process can only have one current working directory (CWD).
Therefore multi-threading can't be used to create an archive if a '-C'
option appears after a relative file name in the command line.
'-d'
'--diff'
Compare and report differences between archive and file system. For
@ -188,10 +175,6 @@ to '-1 --solid'.
on archive creation: 'tarlz -C / -d'. Alternatively, tarlz may be run
from the root directory to perform the comparison.
'--ignore-ids'
Make '--diff' ignore differences in owner and group IDs. This option is
useful when comparing an '--anonymous' archive.
'--delete'
Delete files and directories from an archive in place. It currently can
delete only from uncompressed archives and from archives with files
@ -210,12 +193,102 @@ to '-1 --solid'.
be dangerous. A corrupt archive, a power cut, or an I/O error may cause
data loss.
'--exclude=PATTERN'
Exclude files matching a shell pattern like '*.o'. A file is considered
to match if any component of the file name matches. For example, '*.o'
matches 'foo.o', 'foo.o/bar' and 'foo/bar.o'. If PATTERN contains a
'/', it matches a corresponding '/' in the file name. For example,
'foo/*.o' matches 'foo/bar.o'.
'-r'
'--append'
Append files to the end of an archive. The archive must be a regular
(seekable) file either compressed or uncompressed. Compressed members
can't be appended to an uncompressed archive, nor vice versa. If the
archive is compressed, it must be a multimember lzip file with the two
end-of-archive blocks plus any zero padding contained in the last lzip
member of the archive. It is possible to append files to an archive
with a different compression granularity. Appending works as follows;
first the end-of-archive blocks are removed, then the new members are
appended, and finally two new end-of-archive blocks are appended to
the archive. If the archive is uncompressed, tarlz parses and skips
tar headers until it finds the end-of-archive blocks. Exit with status
0 without modifying the archive if no FILES have been specified.
Appending files already present in the archive results in two or more
tar members with the same name, which may produce nondeterministic
behavior during multi-threaded extraction. *Note mt-extraction::.
'-t'
'--list'
List the contents of an archive. If FILES are given, list only the
FILES given.
'-x'
'--extract'
Extract files from an archive. If FILES are given, extract only the
FILES given. Else extract all the files in the archive. To extract a
directory without extracting the files under it, use
'tarlz -xf foo --exclude='dir/*' dir'. Tarlz removes files and empty
directories unconditionally before extracting over them. Other than
that, it will not make any special effort to extract a file over an
incompatible type of file. For example, extracting a file over a
non-empty directory will usually fail.
'-z'
'--compress'
Compress existing POSIX tar archives aligning the lzip members to the
tar members with choice of granularity (--bsolid by default, --dsolid
works like --asolid). The input archives are kept unchanged. Existing
compressed archives are not overwritten. A hyphen '-' used as the name
of an input archive reads from standard input and writes to standard
output (unless the option '--output' is used). Tarlz can be used as
compressor for GNU tar using a command like
'tar -c -Hustar foo | tarlz -z -o foo.tar.lz'. Note that tarlz only
works reliably on archives without global headers, or with global
headers whose content can be ignored.
The compression is reversible, including any garbage present after the
end-of-archive blocks. Tarlz stops parsing after the first
end-of-archive block is found, and then compresses the rest of the
archive. Unless solid compression is requested, the end-of-archive
blocks are compressed in a lzip member separated from the preceding
members and from any non-zero garbage following the end-of-archive
blocks. '--compress' implies plzip argument style, not tar style. Each
input archive is compressed to a file with the extension '.lz' added
unless the option '--output' is used. When '--output' is used, only
one input archive can be specified. '-f' can't be used with
'--compress'.
'--check-lib'
Compare the version of lzlib used to compile tarlz with the version
actually being used at run time and exit. Report any differences
found. Exit with error status 1 if differences are found. A mismatch
may indicate that lzlib is not correctly installed or that a different
version of lzlib has been installed after compiling tarlz. Exit with
error status 2 if LZ_API_VERSION and LZ_version_string don't match.
'tarlz -v --check-lib' shows the version of lzlib being used and the
value of LZ_API_VERSION (if defined). *Note Library version:
(lzlib)Library version.
tarlz supports the following options: *Note Argument syntax:
(arg_parser)Argument syntax.
'-B BYTES'
'--data-size=BYTES'
Set target size of input data blocks for the option '--bsolid'. *Note
--bsolid::. Valid values range from 8 KiB to 1 GiB. Default value is
two times the dictionary size, except for option '-0' where it
defaults to 1 MiB. *Note Minimum archive sizes::.
'-C DIR'
'--directory=DIR'
Change to directory DIR. When creating or appending, the position of
each '-C' option in the command line is significant; it will change the
current working directory for the following FILES until a new '-C'
option appears in the command line. When extracting or comparing, all
the '-C' options are executed in sequence before reading the archive.
Listing ignores any '-C' options specified. DIR is relative to the
then current working directory, perhaps changed by a previous '-C'
option.
Note that a process can only have one current working directory (CWD).
Therefore multi-threading can't be used to create an archive if a '-C'
option appears after a relative file name in the command line.
'-f ARCHIVE'
'--file=ARCHIVE'
@ -228,14 +301,6 @@ to '-1 --solid'.
Archive or compare the files they point to instead of the links
themselves.
'--mtime=DATE'
When creating or appending, use DATE as the modification time for
files added to the archive instead of their actual modification times.
The value of DATE may be either '@' followed by the number of seconds
since the epoch, or a date in format 'YYYY-MM-DD HH:MM:SS', or the
name of an existing file starting with '.' or '/'. In the latter case,
the modification time of that file is used.
'-n N'
'--threads=N'
Set the number of (de)compression threads, overriding the system's
@ -268,65 +333,11 @@ to '-1 --solid'.
'--quiet'
Quiet operation. Suppress all messages.
'-r'
'--append'
Append files to the end of an archive. The archive must be a regular
(seekable) file either compressed or uncompressed. Compressed members
can't be appended to an uncompressed archive, nor vice versa. If the
archive is compressed, it must be a multimember lzip file with the two
end-of-file blocks plus any zero padding contained in the last lzip
member of the archive. It is possible to append files to an archive
with a different compression granularity. Appending works as follows;
first the end-of-file blocks are removed, then the new members are
appended, and finally two new end-of-file blocks are appended to the
archive. If the archive is uncompressed, tarlz parses and skips tar
headers until it finds the end-of-file blocks. Exit with status 0
without modifying the archive if no FILES have been specified.
'-t'
'--list'
List the contents of an archive. If FILES are given, list only the
FILES given.
'-v'
'--verbose'
Verbosely list files processed. Further -v's (up to 4) increase the
verbosity level.
'-x'
'--extract'
Extract files from an archive. If FILES are given, extract only the
FILES given. Else extract all the files in the archive. To extract a
directory without extracting the files under it, use
'tarlz -xf foo --exclude='dir/*' dir'. Tarlz will not make any special
effort to extract a file over an incompatible type of file. For
example, extracting a link over a directory will usually fail.
(Principle of least surprise).
'-z'
'--compress'
Compress existing POSIX tar archives aligning the lzip members to the
tar members with choice of granularity (--bsolid by default, --dsolid
works like --asolid). The input archives are kept unchanged. Existing
compressed archives are not overwritten. A hyphen '-' used as the name
of an input archive reads from standard input and writes to standard
output (unless the option '--output' is used). Tarlz can be used as
compressor for GNU tar using a command like
'tar -c -Hustar foo | tarlz -z -o foo.tar.lz'. Note that tarlz only
works reliably on archives without global headers, or with global
headers whose content can be ignored.
The compression is reversible, including any garbage present after the
EOF blocks. Tarlz stops parsing after the first EOF block is found,
and then compresses the rest of the archive. Unless solid compression
is requested, the EOF blocks are compressed in a lzip member separated
from the preceding members and from any non-zero garbage following the
EOF blocks. '--compress' implies plzip argument style, not tar style.
Each input archive is compressed to a file with the extension '.lz'
added unless the option '--output' is used. When '--output' is used,
only one input archive can be specified. '-f' can't be used with
'--compress'.
'-0 .. -9'
Set the compression level for '--create', '--append', and
'--compress'. The default compression level is '-6'. Like lzip, tarlz
@ -354,8 +365,8 @@ to '-1 --solid'.
'--asolid'
When creating or appending to a compressed archive, use appendable
solid compression. All the files being added to the archive are
compressed into a single lzip member, but the end-of-file blocks are
compressed into a separate lzip member. This creates a solidly
compressed into a single lzip member, but the end-of-archive blocks
are compressed into a separate lzip member. This creates a solidly
compressed appendable archive. Solid archives can't be created nor
decoded in parallel.
@ -375,20 +386,20 @@ to '-1 --solid'.
When creating or appending to a compressed archive, compress each file
specified in the command line separately in its own lzip member, and
use solid compression for each directory specified in the command
line. The end-of-file blocks are compressed into a separate lzip
line. The end-of-archive blocks are compressed into a separate lzip
member. This creates a compressed appendable archive with a separate
lzip member for each file or top-level directory specified.
'--no-solid'
When creating or appending to a compressed archive, compress each file
separately in its own lzip member. The end-of-file blocks are
separately in its own lzip member. The end-of-archive blocks are
compressed into a separate lzip member. This creates a compressed
appendable archive with a lzip member for each file.
'--solid'
When creating or appending to a compressed archive, use solid
compression. The files being added to the archive, along with the
end-of-file blocks, are compressed into a single lzip member. The
end-of-archive blocks, are compressed into a single lzip member. The
resulting archive is not appendable. No more files can be later
appended to the archive. Solid archives can't be created nor decoded
in parallel.
@ -406,22 +417,50 @@ to '-1 --solid'.
If GROUP is not a valid group name, it is decoded as a decimal numeric
group ID.
'--exclude=PATTERN'
Exclude files matching a shell pattern like '*.o'. A file is considered
to match if any component of the file name matches. For example, '*.o'
matches 'foo.o', 'foo.o/bar' and 'foo/bar.o'. If PATTERN contains a
'/', it matches a corresponding '/' in the file name. For example,
'foo/*.o' matches 'foo/bar.o'. Multiple '--exclude' options can be
specified.
'--ignore-ids'
Make '--diff' ignore differences in owner and group IDs. This option is
useful when comparing an '--anonymous' archive.
'--ignore-overflow'
Make '--diff' ignore differences in mtime caused by overflow on 32-bit
systems with a 32-bit time_t.
'--keep-damaged'
Don't delete partially extracted files. If a decompression error
happens while extracting a file, keep the partial data extracted. Use
this option to recover as much data as possible from each damaged
member. It is recommended to run tarlz in single-threaded mode
(-threads=0) when using this option.
(--threads=0) when using this option.
'--missing-crc'
Exit with error status 2 if the CRC of the extended records is missing.
When this option is used, tarlz detects any corruption in the extended
records (only limited by CRC collisions). But note that a corrupt
'GNU.crc32' keyword, for example 'GNU.crc33', is reported as a missing
CRC instead of as a corrupt record. This misleading 'Missing CRC'
message is the consequence of a flaw in the POSIX pax format; i.e.,
the lack of a mandatory check sequence in the extended records. *Note
crc32::.
Exit with error status 2 if the CRC of the extended records is
missing. When this option is used, tarlz detects any corruption in the
extended records (only limited by CRC collisions). But note that a
corrupt 'GNU.crc32' keyword, for example 'GNU.crc33', is reported as a
missing CRC instead of as a corrupt record. This misleading
'Missing CRC' message is the consequence of a flaw in the POSIX pax
format; i.e., the lack of a mandatory check sequence of the extended
records. *Note crc32::.
'--mtime=DATE'
When creating or appending, use DATE as the modification time for
files added to the archive instead of their actual modification times.
The value of DATE may be either '@' followed by the number of seconds
since (or before) the epoch, or a date in format
'[-]YYYY-MM-DD HH:MM:SS' or '[-]YYYY-MM-DDTHH:MM:SS', or the name of
an existing reference file starting with '.' or '/' whose modification
time is used. The time of day 'HH:MM:SS' in the date format is
optional and defaults to '00:00:00'. The epoch is
'1970-01-01 00:00:00 UTC'. Negative seconds or years define a
modification time before the epoch.
'--out-slots=N'
Number of 1 MiB output packets buffered per worker thread during
@ -431,17 +470,6 @@ to '-1 --solid'.
more memory. Valid values range from 1 to 1024. The default value is
64.
'--check-lib'
Compare the version of lzlib used to compile tarlz with the version
actually being used at run time and exit. Report any differences
found. Exit with error status 1 if differences are found. A mismatch
may indicate that lzlib is not correctly installed or that a different
version of lzlib has been installed after compiling tarlz. Exit with
error status 2 if LZ_API_VERSION and LZ_version_string don't match.
'tarlz -v --check-lib' shows the version of lzlib being used and the
value of LZ_API_VERSION (if defined). *Note Library version:
(lzlib)Library version.
'--warn-newer'
During archive creation, warn if any file being archived has a
modification time newer than the archive creation time. This option
@ -453,9 +481,9 @@ to '-1 --solid'.
Exit status: 0 for a normal exit, 1 for environmental problems (file not
found, files differ, invalid flags, I/O errors, etc), 2 to indicate a
corrupt or invalid input file, 3 for an internal consistency error (e.g.
bug) which caused tarlz to panic.
found, files differ, invalid command line options, I/O errors, etc), 2 to
indicate a corrupt or invalid input file, 3 for an internal consistency
error (e.g., bug) which caused tarlz to panic.

File: tarlz.info, Node: Portable character set, Next: File format, Prev: Invoking tarlz, Up: Top
@ -473,9 +501,7 @@ The set of characters from which portable file names are constructed.
characters, respectively.
File names are identifiers. Therefore, archiving works better when file
names use only the portable character set without spaces added. Unicode is
for human consumption. It should be avoided in computing environments,
specially in file names. *Note why not Unicode: (moe)why not Unicode.
names use only the portable character set without spaces added.

File: tarlz.info, Node: File format, Next: Amendments to pax format, Prev: Portable character set, Up: Top
@ -512,10 +538,11 @@ limitations of the ustar format.
Each tar member contains one file archived, and is represented by the
following sequence:
* An optional extended header block with extended header records. This
header block is of the form described in pax header block, with a
typeflag value of 'x'. The extended header records are included as the
data for this header block.
* An optional extended header block followed by one or more blocks that
contain the extended header records as if they were the contents of a
file; i.e., the extended header records are included as the data for
this header block. This header block is of the form described in pax
header block, with a typeflag value of 'x'.
* A header block in ustar format that describes the file. Any fields
defined in the preceding optional extended header records override the
@ -529,9 +556,11 @@ split over two or more lzip members, the archive must be decoded
sequentially. *Note Multi-threaded decoding::.
At the end of the archive file there are two 512-byte blocks filled with
binary zeros, interpreted as an end-of-archive indicator. These EOF blocks
are either compressed in a separate lzip member or compressed along with
the tar members contained in the last lzip member.
binary zeros, interpreted as an end-of-archive indicator. These EOA blocks
are either compressed in a separate lzip member or compressed along with the
tar members contained in the last lzip member. For a compressed archive to
be recognized by tarlz as appendable, the last lzip member must contain
between 512 and 32256 zeros alone.
The diagram below shows the correspondence between each tar member
(formed by one or two headers plus optional data) in the tar archive and
@ -540,7 +569,7 @@ compression is used: *Note File format: (lzip)File format.
tar
+========+======+=================+===============+========+======+========+
| header | data | extended header | extended data | header | data | EOF |
| header | data | extended header | extended data | header | data | EOA |
+========+======+=================+===============+========+======+========+
tar.lz
@ -572,25 +601,57 @@ space, equal-sign, and newline.
These are the <keyword> values currently supported by tarlz:
'atime'
The signed decimal representation of the access time of the following
file in seconds since (or before) the epoch, obtained from the function
'stat'. The atime record is created only for files with a modification
time outside of the ustar range. *Note ustar-mtime::.
'gid'
The unsigned decimal representation of the group ID of the group that
owns the following file. The gid record is created only for files with
a group ID greater than 2_097_151 (octal 7777777). *Note
ustar-uid-gid::.
'linkpath'
The pathname of a link being created to another file, of any type,
The file name of a link being created to another file, of any type,
previously archived. This record overrides the field 'linkname' in the
following ustar header block. The following ustar header block
determines the type of link created. If typeflag of the following
header block is 1, it will be a hard link. If typeflag is 2, it will
be a symbolic link and the linkpath value will be used as the contents
of the symbolic link.
of the symbolic link. The linkpath record is created only for links
with a link name that does not fit in the space provided by the ustar
header.
'mtime'
The signed decimal representation of the modification time of the
following file in seconds since (or before) the epoch, obtained from
the function 'stat'. This record overrides the field 'mtime' in the
following ustar header block. The mtime record is created only for
files with a modification time outside of the ustar range. *Note
ustar-mtime::.
'path'
The pathname of the following file. This record overrides the fields
'name' and 'prefix' in the following ustar header block.
The file name of the following file. This record overrides the fields
'name' and 'prefix' in the following ustar header block. The path
record is created for files with a name that does not fit in the space
provided by the ustar header, but is also created for files that
require any other extended record so that the fields 'name' and
'prefix' in the following ustar header block can be zeroed.
'size'
The size of the file in bytes, expressed as a decimal number using
digits from the ISO/IEC 646:1991 (ASCII) standard. This record
overrides the size field in the following ustar header block. The size
record is used only for files with a size value greater than
8_589_934_591 (octal 77777777777). This is 2^33 bytes or larger.
overrides the field 'size' in the following ustar header block. The
size record is created only for files with a size value greater than
8_589_934_591 (octal 77777777777); that is, 8 GiB (2^33 bytes) or
larger.
'uid'
The unsigned decimal representation of the user ID of the file owner
of the following file. The uid record is created only for files with a
user ID greater than 2_097_151 (octal 7777777). *Note ustar-uid-gid::.
'GNU.crc32'
CRC32-C (Castagnoli) of the extended header data excluding the 8 bytes
@ -643,18 +704,18 @@ and groups, tarlz will use the byte values in these names unmodified.
character strings except when all characters in the array contain non-null
characters including the last character.
The fields 'prefix' and 'name' produce the pathname of the file. A new
pathname is formed, if prefix is not an empty string (its first character
is not null), by concatenating prefix (up to the first null character), a
slash character, and name; otherwise, name is used alone. In either case,
name is terminated at the first null character. If prefix begins with a
null character, it is ignored. In this manner, pathnames of at most 256
characters can be supported. If a pathname does not fit in the space
provided, an extended record is used to store the pathname.
The fields 'name' and 'prefix' produce the file name. A new file name is
formed, if prefix is not an empty string (its first character is not null),
by concatenating prefix (up to the first null character), a slash
character, and name; otherwise, name is used alone. In either case, name is
terminated at the first null character. If prefix begins with a null
character, it is ignored. In this manner, file names of at most 256
characters can be supported. If a file name does not fit in the space
provided, an extended record is used to store the file name.
The field 'linkname' does not use the prefix to produce a pathname. If
the linkname does not fit in the 100 characters provided, an extended record
is used to store the linkname.
The field 'linkname' does not use the prefix to produce a file name. If
the link name does not fit in the 100 characters provided, an extended
record is used to store the link name.
The field 'mode' provides 12 access permission bits. The following table
shows the symbolic name of each bit and its octal value:
@ -667,7 +728,9 @@ S_IRGRP 00040 S_IWGRP 00020 S_IXGRP 00010
S_IROTH 00004 S_IWOTH 00002 S_IXOTH 00001
The fields 'uid' and 'gid' are the user and group IDs of the owner and
group of the file, respectively.
group of the file, respectively. If the file uid or gid are greater than
2_097_151 (octal 7777777), an extended record is used to store the uid or
gid.
The field 'size' contains the octal representation of the size of the
file in bytes. If the field 'typeflag' specifies a file of type '0'
@ -680,7 +743,10 @@ header. If the file size is larger than 8_589_934_591 bytes
The field 'mtime' contains the octal representation of the modification
time of the file at the time it was archived, obtained from the function
'stat'.
'stat'. If the modification time is negative or larger than 8_589_934_591
(octal 77777777777) seconds since the epoch, an extended record is used to
store the modification time. The ustar range of mtime goes from
'1970-01-01 00:00:00 UTC' to '2242-03-16 12:56:31 UTC'.
The field 'chksum' contains the octal representation of the value of the
simple sum of all bytes in the header logical record. Each byte in the
@ -694,7 +760,8 @@ file archived:
Regular file.
''1''
Hard link to another file, of any type, previously archived.
Hard link to another file, of any type, previously archived. Hard
links must not contain file data.
''2''
Symbolic link.
@ -712,8 +779,8 @@ file archived:
''7''
Reserved to represent a file to which an implementation has associated
some high-performance attribute. Tarlz treats this type of file as a
regular file (type 0).
some high-performance attribute (contiguous file). Tarlz treats this
type of file as a regular file (type 0).
The field 'magic' contains the ASCII null-terminated string "ustar". The
@ -735,9 +802,9 @@ Tarlz creates safe archives that allow the reliable detection of invalid or
corrupt metadata during decoding even when the integrity checking of lzip
can't be used because the lzip members are only decompressed partially, as
it happens in parallel '--diff', '--list', and '--extract'. In order to
achieve this goal, tarlz makes some changes to the variant of the pax
format that it uses. This chapter describes these changes and the concrete
reasons to implement them.
achieve this goal and avoid some other flaws in the pax format, tarlz makes
some changes to the variant of the pax format that it uses. This chapter
describes these changes and the concrete reasons to implement them.
5.1 Add a CRC of the extended records
@ -775,45 +842,73 @@ In order to allow the extraction of pax archives by a tar utility conforming
to the POSIX-2:1993 standard, POSIX.1-2008 recommends selecting extended
header field values that allow such tar to create a regular file containing
the extended header records as data. This approach is broken because if the
extended header is needed because of a long file name, the fields 'prefix'
and 'name' will be unable to contain the full pathname of the file.
Therefore the files corresponding to both the extended header and the
overridden ustar header will be extracted using truncated file names,
perhaps overwriting existing files or directories. It may be a security risk
to extract a file with a truncated file name.
extended header is needed because of a long file name, the fields 'name'
and 'prefix' will be unable to contain the full file name. (Some tar
implementations store the truncated name in the field 'name' alone,
truncating the name to only 100 bytes instead of 256). Therefore the files
corresponding to both the extended header and the overridden ustar header
will be extracted using truncated file names, perhaps overwriting existing
files or directories. It may be a security risk to extract a file with a
truncated file name.
To avoid this problem, tarlz writes extended headers with all fields
zeroed except size, chksum, typeflag, magic and version. This prevents old
tar programs from extracting the extended records as a file in the wrong
place. Tarlz also sets to zero those fields of the ustar header overridden
by extended records. Finally, tarlz skips members without name when decoding
except when listing. This is needed to detect certain format violations
during parallel extraction.
zeroed except 'size' (which contains the size of the extended records),
'chksum', 'typeflag', 'magic', and 'version'. In particular, tarlz sets the
fields 'name' and 'prefix' to zero. This prevents old tar programs from
extracting the extended records as a file in the wrong place. Tarlz also
sets to zero those fields of the ustar header overridden by extended
records. Finally, tarlz skips members with zeroed 'name' and 'prefix' when
decoding, except when listing. This is needed to detect certain format
violations during parallel extraction.
If an extended header is required for any reason (for example a file size
larger than 8 GiB or a link name longer than 100 bytes), tarlz moves the
file name also to the extended header to prevent an ustar tool from trying
to extract the file or link. This also makes easier during parallel decoding
the detection of a tar member split between two lzip members at the boundary
between the extended header and the ustar header.
If an extended header is required for any reason (for example a file
size of 8 GiB or larger, or a link name longer than 100 bytes), tarlz also
moves the file name to the extended records to prevent an ustar tool from
trying to extract the file or link. This also makes easier during parallel
decoding the detection of a tar member split between two lzip members at
the boundary between the extended header and the ustar header.
5.3 As simple as possible (but not simpler)
===========================================
The tarlz format is mainly ustar. Extended pax headers are used only when
needed because the length of a file name or link name, or the size of a file
exceed the limits of the ustar format. Adding 1 KiB of extended headers to
each member just to record subsecond timestamps seems wasteful for a backup
format. Moreover, minimizing the overhead may help recovering the archive
with lziprecover in case of corruption.
needed because the length of a file name or link name, or the size or other
attribute of a file exceed the limits of the ustar format. Adding 1 KiB of
extended header and records to each member just to save subsecond
timestamps seems wasteful for a backup format. Moreover, minimizing the
overhead may help recovering the archive with lziprecover in case of
corruption.
Global pax headers are tolerated, but not supported; they are parsed and
ignored. Some operations may not behave as expected if the archive contains
global headers.
5.4 Avoid misconversions to/from UTF-8
5.4 Improve reproducibility
===========================
Pax includes by default the process ID of the pax process in the ustar name
of the extended headers, making the archive not reproducible. Tarlz stores
the true name of the file just once, either in the ustar header or in the
extended records, making it easier to produce reproducible archives.
Pax allows an extended record to have length x-1 or x if x is a power of
ten; '99<97_bytes>' or '100<97_bytes>'. Tarlz minimizes the length of the
record and always produces a length of x-1 in these cases.
5.5 No data in hard links
=========================
Tarlz does not allow data in hard link members. The data (if any) must be in
the member determining the type of the file (which can't be a link). If all
the names of a file are stored as hard links, the type of the file is lost.
Not allowing data in hard links also prevents invalid actions like
extracting file data for a hard link to a symbolic link or to a directory.
5.6 Avoid misconversions to/from UTF-8
======================================
There is no portable way to tell what charset a text string is coded into.
@ -968,12 +1063,12 @@ headers must provide their own integrity checking.
Multi-threaded extraction may produce different output than single-threaded
extraction in some cases:
During multi-threaded extraction, several independent processes are
During multi-threaded extraction, several independent threads are
simultaneously reading the archive and creating files in the file system.
The archive is not read sequentially. As a consequence, any error or
weirdness in the archive (like a corrupt member or an EOF block in the
middle of the archive) won't be usually detected until part of the archive
beyond that point has been processed.
weirdness in the archive (like a corrupt member or an end-of-archive block
in the middle of the archive) won't be usually detected until part of the
archive beyond that point has been processed.
If the archive contains two or more tar members with the same name,
single-threaded extraction extracts the members in the order they appear in
@ -986,6 +1081,9 @@ unspecified which of the tar members is extracted.
names resolve to the same file in the file system), the result is undefined.
(Probably the resulting file will be mangled).
Extraction of a hard link may fail if it is extracted before the file it
links to.

File: tarlz.info, Node: Minimum archive sizes, Next: Examples, Prev: Multi-threaded decoding, Up: Top
@ -1054,7 +1152,7 @@ Example 4: Create a compressed appendable archive containing directories
'dir1', 'dir2' and 'dir3' with a separate lzip member per directory. Then
append files 'a', 'b', 'c', 'd' and 'e' to the archive, all of them
contained in a single lzip member. The resulting archive 'archive.tar.lz'
contains 5 lzip members (including the EOF member).
contains 5 lzip members (including the end-of-archive member).
tarlz --dsolid -cf archive.tar.lz dir1 dir2 dir3
tarlz --asolid -rf archive.tar.lz a b c d e
@ -1081,7 +1179,7 @@ Example 7: Extract files 'a' and 'c', and the whole tree under directory
Example 8: Copy the contents of directory 'sourcedir' to the directory
'destdir'.
tarlz -C sourcedir -c . | tarlz -C destdir -x
tarlz -C sourcedir --uncompressed -cf - . | tarlz -C destdir -xf -
Example 9: Compress the existing POSIX archive 'archive.tar' and write the
@ -1091,6 +1189,18 @@ other members can still be extracted).
tarlz -z --no-solid archive.tar
Example 10: Compress the archive 'archive.tar' and write the output to
'foo.tar.lz'.
tarlz -z -o foo.tar.lz archive.tar
Example 11: Concatenate and compress two archives 'archive1.tar' and
'archive2.tar', and write the output to 'foo.tar.lz'.
tarlz -A archive1.tar archive2.tar | tarlz -z -o foo.tar.lz

File: tarlz.info, Node: Problems, Next: Concept index, Prev: Examples, Up: Top
@ -1133,23 +1243,26 @@ Concept index

Tag Table:
Node: Top223
Node: Introduction1214
Node: Invoking tarlz4022
Ref: --data-size6436
Ref: --bsolid16388
Node: Portable character set21224
Node: File format22019
Ref: key_crc3226944
Node: Amendments to pax format32572
Ref: crc3233236
Ref: flawed-compat34547
Node: Program design37348
Node: Multi-threaded decoding41273
Node: Minimum archive sizes45764
Node: Examples47902
Node: Problems49918
Node: Concept index50473
Node: Top216
Node: Introduction1210
Node: Invoking tarlz4029
Ref: --data-size12880
Ref: --bsolid17192
Node: Portable character set22788
Node: File format23431
Ref: key_crc3230188
Ref: ustar-uid-gid33452
Ref: ustar-mtime34254
Node: Amendments to pax format36254
Ref: crc3236963
Ref: flawed-compat38274
Node: Program design42364
Node: Multi-threaded decoding46289
Ref: mt-extraction49570
Node: Minimum archive sizes50876
Node: Examples53014
Node: Problems55381
Node: Concept index55936

End Tag Table