TAR Archives

tar is a file archive format that allows multiple files to be stored in a single file, called an “archive”. It’s commonly used for distributing and storing collections of files on Unix-like operating systems.

Here’s a brief overview of the tar file format:

History: The tar command was first introduced in 1979 as part of the Seventh Edition Unix. The name “tar” comes from “tape archive”, as it was originally designed to create archives for backup purposes on magnetic tapes.

Format Structure: A tar archive consists of a series of blocks, each containing a file’s metadata (e.g., filename, permissions, ownership) followed by the file’s contents. Each block is 512 bytes long, and the archive is typically written in a sequential manner.

Here’s a high-level breakdown of the tar format:

  1. File Header (512 bytes): Contains metadata about the file, including:
    • Filename (up to 100 characters)
    • File mode (permissions)
    • User ID
    • Group ID
    • File size
    • Timestamps (last modification and last access times)
  2. File Contents: The actual contents of the file, padded with zeros to a multiple of 512 bytes.
  3. Block Padding (optional): If the file size is not a multiple of 512 bytes, padding is added to fill the block.

Types of tar Archives: There are several variations of the tar format:

  • V7 Tar (original): This is the oldest and most basic format.
  • Ustar Tar (POSIX.1-1988): An extension of V7 tar, with additional features like file sizes greater than 2 GB.
  • GNU Tar (GNU extensions): Adds features like sparse files, incremental backups, and multi-volume support.

tar archives can be compressed using various algorithms, such as gzip (tar.gz) or bzip2 (tar.bz2), to reduce storage size.

Overall, the tar format has become a de facto standard for archiving files on Unix-like systems, and its versatility and simplicity have made it a popular choice for distributing software packages, backing up data, and more.