Pax file Formats

Pax interchange format archives are an extension of the older ustar format that adds a separate entry with additional attributes stored as key/value pairs. The presence of this additional entry is the only difference between pax interchange format and the older ustar format. The extended attributes are of unlimited length and are stored as UTF-8 Uni- code strings. Keywords defined in the standard are in all lower- case; vendors are allowed to define custom keys by preceding them with the vendor name in all uppercase.

A pax archive tape format shall contain a series of blocks. The physical layout of the archive shall be identical to the USTAR format described in USTAR Interchange Format. Each file archived shall be represented by the following sequence:

•   »   An optional header block with extended header records. This header block is of the form described in pax Header Block , with a typeflag value of x or g. The extended header records, described in pax Extended Header , shall be included as the data for this header block.
•   »   A header block that describes the file. Any fields in the preceding optional extended header shall override the associated fields in this header block for this file.
•   »   Zero or more blocks that contain the contents of the file.

At the end of the archive file there shall be two 512-byte blocks filled with binary zeros, interpreted as an end-of-archive indicator.

  WinTar can read and write POSIX-compliant pax interchange format archives. When writing pax archives, WinTar uses many of the SCHILY keys defined by Joerg Schilling's star archiver. WinTar can read most of the SCHILY keys. It silently ignores any keywords that it does not understand.

Restricted Pax

  WinTar can also write pax archives in which it attempts to suppress the extended attributes entry whenever possible. The result will be identical to a ustar archive unless the extended attributes entry is required to store a long file name, long linkname, extended ACL, file flags, or if any of the standard ustar data (user name, group name, UID, GID, etc) cannot be fully represented in the ustar header.

Related file formats

---

•  archive file formats

•  CAB archive format

•  Zip archive format

•  Tar archive format