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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):
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
Archives in ‘gnu’ format are able to hold file names of unlimited length.
Format used by GNU
tar of versions prior to 1.12.
Archive format, compatible with the V7 implementation of tar. This format imposes a number of limitations. The most important of them are:
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 1.34 and
Automake prior to 1.9.
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:
Format used by Jörg Schilling
tar is able to read ‘star’ archives but
currently does not produce them.
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
The following table summarizes the limitations of each of these formats:
|Format||UID||File Size||File Name||Devn|
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’.
|8.1 Using Less Space through Compression|
|8.2 Handling File Attributes|
|8.3 Making |
|8.4 Comparison of |
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