Rock Ridge

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The Rock Ridge Interchange Protocol (RRIP, IEEE P1282) is an extension to the ISO 9660 volume format, commonly used on CDROM and DVD media, which adds POSIX file system semantics. The availability of these extension properties allows for better integration with Unix and Unix-like operating systems.

RRIP was developed by Andrew Young of Young Minds, Inc. in the early 1990s. The standard takes its name from the fictional town Rock Ridge in Mel Brooks' film Blazing Saddles.

The RRIP extensions are, briefly:


Method of extension

The RRIP extensions are built upon a related standard System Use Sharing Protocol (SUSP, IEEE P1281). SUSP provides a generic way of including additional properties for any directory entry reachable from the primary volume descriptor (PVD).

In an ISO 9660 volume, every directory entry has an optional system use area whose contents are undefined and left to be interpreted by the system. SUSP defines a method to subdivide that area into multiple system use fields, each identified by a two-character signature tag. The idea behind SUSP was that it would enable any number of independent extensions to ISO 9660 (not just RRIP) to be created and included on a volume without conflicting. It also allows for the inclusion of property data that would otherwise be too large to fit within the limits of the system use area.

SUSP defines several common tags and system use fields:

  • CE - Continuation area
  • PD - Padding field
  • SP - System use sharing protocol indicator
  • ST - System use sharing protocol terminator
  • ER - Extensions reference
  • ES - Extension selector

RRIP defines additional SUSP tags for support of POSIX semantics, along with the format and meaning of the corresponding system use fields:

  • RR - Rock Ridge extensions in-use indicator (note: dropped from standard after version 1.09)
  • PX - POSIX file attributes
  • PN - POSIX device numbers
  • SL - symbolic link
  • NM - alternate name
  • CL - child link
  • PL - parent link
  • RE - relocated directory
  • TF - time stamp
  • SF - sparse file data

Other known SUSP fields include:

  • AA - Apple extension, preferred
  • AB - Apple extension, old
  • AS - Amiga file properties (see below)

Note that the Apple ISO 9660 Extensions do not technically follow the SUSP standard; however the basic structure of the AA and AB fields defined by Apple are forward compatible with SUSP; so that, with care, a volume can use both Apple extensions as well as RRIP extensions.

Amiga Rock Ridge

Amiga Rock Ridge is similar to RRIP, except it provides additional properties used by the Amiga operating system. It too is built on the SUSP standard by defining an "AS"-tagged system use field. Thus both Amiga Rock Ridge and the POSIX RRIP may be used simultaneously on the same volume.

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