Jigdo (a portmanteau of "Jigsaw" and "download") is a utility typically used for downloading to piece together a large file, most commonly an optical disk image such as a CD, DVD or Blu-ray Disc (BD) image, from many smaller individual constituent files. The constituent files may be local and/or retrieved from one or more mirror sites. Jigdo's features are similar to BitTorrent, but unlike BitTorrent, Jigdo uses a client-server model, not peer-to-peer.
A quite common use would be to construct a Linux CD or DVD image for installation or distribution, where a slightly older version or release of same, or a cache or local partial mirror, already contains some or many of the needed constituent files. That would typically proceed as follows: Jigdo would typically be invoked using the jigdo-lite command, with a command line argument of the URL of a ".jigdo" file. Jigdo would then download that file, and after examining its contents, would generally also download a ".template" file. After inspecting the ".template" file, Jigdo would generally prompt for location of files to scan. The user would then generally enter (or select from list) location of files to scan, and Jigdo would scan that location for any files that may match any of the needed constituent files, and Jigdo would then use any such needed files found in constructing the target image. Jigdo likewise prompts again, and if the user gives a location, the process repeats - giving Jigdo opportunity to scan multiple locations for needed files. If the user enters no location, Jigdo then proceeds to download any still needed constituent files, and to then assemble the target image file.
The jigdo-file utility is generally used to create the ".jigdo" and ".template" files needed to create target images using Jigdo.
Other projects and sites may also do so or may be doing so - nothing inherently prevents such use.
Jigdo was designed to solve several issues. By leveraging redundant available data, Jigdo works to ease loads on mirror systems - both by providing means for such mirror systems to assemble the needed large images while avoiding much redundant downloading, and also by encouraging those downloading from the mirrors to likewise use Jigdo and avoid downloading unneeded redundant data. Additionally, Jigdo can download from multiple mirrors, easing and typically speeding downloads and making them somewhat more resistant to various interruptions in downloading.
Jigdo was initially designed to aid in the distribution and downloading of large Debian image files for installation. Development of Jigdo appears to go back to at least 1996‑01.
Debian has been available via Jigdo since at least 2002-01-09
Ubuntu has been available via Jigdo since at least 2004-11-12
By, or sometime after 2006-05 (release of Jigdo version 0.7.3), Jigdo is no longer undergoing active development, but is in "maintenance mode" - development has stopped. release. Fedora 8 discs as well as many other variants. were also made available via Jigdo. Fedora 15, released 2011-05-24, thus far appears to be the last Fedora release to have been made available via Jigdo by The Fedora Project.
Jigdo is no longer undergoing active development, but is in "maintenance mode" - development has stopped.
It may be difficult to know accurately how widely distributed and used Jigdo is, however some data are available.
as of 2015 September 7:
1.14% (2,082) of approximately 182,025 reporting Debian systems have Jigdo installed
as of 2015 April 19:
0.276% (7,494) of approximately 2,730,482 reporting Ubuntu systems have Jigdo installed