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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'
     1.26 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'.

Compression

Using Less Space through Compression

Attributes

Handling File Attributes

Portability

Making `tar' Archives More Portable

cpio

Comparison of `tar' and `cpio'