Tar file format

In computing, the tar file format is a type of archive file format: the Tape ARchive format. These files are produced by the Unix command tar and were standardized by POSIX.1-1998 and later POSIX.1-2001. It is used widely to archive and unarchive files, which means to accumulate a large collection of files into a single archive file (packer), while preserving file system information such as user and group permissions, dates, and directory structures. In the Unix tradition of "one job, one program", it does not support compression directly.

tar was originally developed for use with sequential access devices such as tape drives, specifically for backup purposes. Somewhere along the line the -f argument was added and tar is now more frequently used as a general archive utility. tar's linear roots can still be seen in its slow partial extraction performance, when it has to read through the whole archive to extract only the final file. Commonly a tar file is referred to as a tarball.

tar is most commonly used in tandem with an external compression utility such as gzip, bzip2 or, formerly, compress, since it has no built in data compression facilities. These compression utilities generally only compress a single file, hence the pairing with tar, which can produce a single file from many files. One might think this requires more steps, but it is possible to use the Unix pipe capability to combine the two steps manually. Also, the GNU version of tar supports the command line options -z (gzip), -j (bzip2), and -Z (compress), which will compress the archive file it creates.

Usage

• To pack files, use the following commands:
  • Simple tar file: tar -cf packed_files.tar file_to_pack1 file_to_pack2 ...
  • To pack and compess one step at a time:
    • tar -cf packed_files.tar file_to_pack1 file_to_pack2 ...
gzip packed_files.tar
  • To pack and compress all at once:
    • tar -cf - file_to_pack1 file_to_pack2 ... | gzip -c > packed_files.tar.gz
• To unpack tar files, use the following commands:
  • Simple tar file: tar -xf file_to_unpack.tar
  • One step at a time
    • gunzip packed_files.tar.gz
tar -xf packed_files.tar
  • All at once:
    • <code>gunzip -c packed_files.tar.gz | tar -xf -

To use bzip2 instead of gzip, simply replace the commands above with bzip2 where gzip is used and bunzip2 where gunzip is used.

Using GNU tar's compression flag feature:

• To pack and compress:
  • Using gzip: tar -czf packed_files.tgz file_to_pack1 file_to_pack2 ...
  • Using bzip2: tar -cjf packed_files.tbz2 file_to_pack1 file_to_pack2 ...
  • Using compress: tar -cZf packed_files.tar.Z file_to_pack1 file_to_pack2 ...
  • Using some other arbitrary compression utility that works as a filter: tar --use-compress-program=name_of_program -cf packed_files.tar.XXX file_to_pack1 file_to_pack2 ...
• To uncompress and unpack:
  • gzip compressed tar file: tar -xzf file_to_unpack.tar.gz
  • bzip2 compressed tar file: tar -xjf file_to_unpack.tar.bz2
  • compress compressed tar file: tar -xZf file_to_unpack.tar.Z
  • Arbitrary compression utility compressed tar file: tar --use-compress-program=name_of_program -xf file_to_unpack.tar.XXX

Filename extension

• .tar
• .tar.gz or .tgz (only when compressed by gzip)
• .tar.bz2 or .tbz2 (only when compressed by bzip2)
• .tar.Z (only when compressed by compress)

MIME-Type

• application/x-tar

See also

• ar (Unix)
• shar