+\1f
+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'
+ 1.23 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'
+
+\1f
+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
+