Tar (computing) - Problems and Limitations

Problems and Limitations

The original tar format was created in the early days of UNIX, and despite current widespread use, many of its design features are considered dated.

Many old tar implementations (such as GNU tar) do not record extended attributes (xattrs) or ACLs. In 2001, star introduced support for ACLs and extended attributes. Later, major Linux distributions created their own patched versions of GNU tar that fully support ACL.

In 1997, Sun proposed a method for adding extensions to the tar format. This method was later accepted for the POSIX.1-2001 standard. This format is known as extended tar-format or pax-format. The new tar format allows you to add any type of vendor-tagged vendor-specific enhancements. The following enhancement tags are defined by the POSIX standard:

• all three time stamps of a file in arbitrary resolution (most implementations use nanosecond granularity)
• path names of unlimited length and character set coding
• symlink target names of unlimited length and character set coding
• user and group names of unlimited length and character set coding
• files with unlimited size (the historic tar format is limited to 8 GB)
• userid and groupid without limitation (this historic tar format was is limited to a max. id of 2097151)
• a character set definition for path names and user/group names

In 2001, Star became the first tar to support the new format. In 2004, GNU tar supported the new format.

Other formats have been created to address the shortcomings of tar. These formats include DAR (Disk Archiver) and rdiff-backup (see Duplicity branch of the Savannah software site). However, these formats are not part of any official standard.