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-File: tar.info, Node: Formats, Next: Media, Prev: Date input formats, Up: Top
-
-8 Controlling the Archive Format
-********************************
-
-Due to historical reasons, there are several formats of tar archives.
-All of them are based on the same principles, but have some subtle
-differences that often make them incompatible with each other.
-
- GNU tar is able to create and handle archives in a variety of
-formats. The most frequently used formats are (in alphabetical order):
-
-gnu
- Format used by GNU `tar' versions up to 1.13.25. This format
- derived from an early POSIX standard, adding some improvements
- such as sparse file handling and incremental archives.
- Unfortunately these features were implemented in a way
- incompatible with other archive formats.
-
- Archives in `gnu' format are able to hold file names of unlimited
- length.
-
-oldgnu
- Format used by GNU `tar' of versions prior to 1.12.
-
-v7
- Archive format, compatible with the V7 implementation of tar. This
- format imposes a number of limitations. The most important of them
- are:
-
- 1. The maximum length of a file name is limited to 99 characters.
-
- 2. The maximum length of a symbolic link is limited to 99
- characters.
-
- 3. It is impossible to store special files (block and character
- devices, fifos etc.)
-
- 4. Maximum value of user or group ID is limited to 2097151
- (7777777 octal)
-
- 5. V7 archives do not contain symbolic ownership information
- (user and group name of the file owner).
-
- This format has traditionally been used by Automake when producing
- Makefiles. This practice will change in the future, in the
- meantime, however this means that projects containing file names
- more than 99 characters long will not be able to use GNU `tar'
- 1.21 and Automake prior to 1.9.
-
-ustar
- Archive format defined by POSIX.1-1988 specification. It stores
- symbolic ownership information. It is also able to store special
- files. However, it imposes several restrictions as well:
-
- 1. The maximum length of a file name is limited to 256
- characters, provided that the file name can be split at a
- directory separator in two parts, first of them being at most
- 155 bytes long. So, in most cases the maximum file name
- length will be shorter than 256 characters.
-
- 2. The maximum length of a symbolic link name is limited to 100
- characters.
-
- 3. Maximum size of a file the archive is able to accommodate is
- 8GB
-
- 4. Maximum value of UID/GID is 2097151.
-
- 5. Maximum number of bits in device major and minor numbers is
- 21.
-
-star
- Format used by Jo"rg Schilling `star' implementation. GNU `tar'
- is able to read `star' archives but currently does not produce
- them.
-
-posix
- Archive format defined by POSIX.1-2001 specification. This is the
- most flexible and feature-rich format. It does not impose any
- restrictions on file sizes or file name lengths. This format is
- quite recent, so not all tar implementations are able to handle it
- properly. However, this format is designed in such a way that any
- tar implementation able to read `ustar' archives will be able to
- read most `posix' archives as well, with the only exception that
- any additional information (such as long file names etc.) will in
- such case be extracted as plain text files along with the files it
- refers to.
-
- This archive format will be the default format for future versions
- of GNU `tar'.
-
-
- The following table summarizes the limitations of each of these
-formats:
-
-Format UID File Size File Name Devn
---------------------------------------------------------------------
-gnu 1.8e19 Unlimited Unlimited 63
-oldgnu 1.8e19 Unlimited Unlimited 63
-v7 2097151 8GB 99 n/a
-ustar 2097151 8GB 256 21
-posix Unlimited Unlimited Unlimited Unlimited
-
- The default format for GNU `tar' is defined at compilation time.
-You may check it by running `tar --help', and examining the last lines
-of its output. Usually, GNU `tar' is configured to create archives in
-`gnu' format, however, future version will switch to `posix'.
-
-* Menu:
-
-* Compression:: Using Less Space through Compression
-* Attributes:: Handling File Attributes
-* Portability:: Making `tar' Archives More Portable
-* cpio:: Comparison of `tar' and `cpio'
-
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-File: tar.info, Node: Compression, Next: Attributes, Up: Formats
-
-8.1 Using Less Space through Compression
-========================================
-
-* Menu:
-
-* gzip:: Creating and Reading Compressed Archives
-* sparse:: Archiving Sparse Files
-