AppImage
Filename extension
.AppImage
Magic number41 49 02 (3 bytes hexadecimal from offset 8)
Developed bySimon Peter
Initial release2004; 20 years ago (2004)
Latest release
13
December 31, 2020; 3 years ago (2020-12-31)
Container forSoftware installation
Open format?Yes
Free format?Yes
Websiteappimage.org

AppImage (formerly known as klik and PortableLinuxApps) is an open-source format for distributing portable software on Linux. It aims to allow the installation of binary software independently of specific Linux distributions, a concept often referred to as upstream packaging. As a result, one AppImage can be installed and run across Ubuntu, Arch Linux, and Red Hat Enterprise Linux without needing to use different files. It aims to be a format that is self-contained, rootless, and independent of the underlying Linux distribution.[1]

Released first in 2004 under the name klik, it was continuously developed, then renamed in 2011 to PortableLinuxApps and later in 2013 to AppImage. Version 2 was released in 2016.

History

AppImage's predecessor, klik, was designed in 2004 by Simon Peter.[2] The client-side software is licensed under the GNU GPL. klik integrated with web browsers on the user's computer. Users downloaded and installed software by typing a URL beginning with klik://. This downloaded a klik "recipe" file, which was used to generate a .cmg file. For the main ingredients, pre-built .deb packages from Debian Stable repositories were usually fed into the recipe's generation process. This way, one recipe could be used to supply packages to a wide variety of platforms. With klik, only eight programs could be run at once because of the limitation of mounting compressed images with the Linux kernel, unless FUSE was used. The file was remounted each time the program was run, meaning the user could remove the program entirely by simply deleting the file. The next version, klik2, was in development and would natively incorporate the FUSE kernel module, but it never reached past the beta stage.[3] Around 2011, the klik project went dormant, and the website went offline.[4]

Simon Peter started a successor project named PortableLinuxApps with similar goals around that time.[5] The technology was adopted, for instance, by the "portablelinuxgames.org" repository, which provided hundreds of mostly open-source video games.[6]

Around 2013, the software was renamed again from portableLinuxApps to AppImage; the license became the MIT license. AppImage is the format, and AppImageKit is a concrete open-source implementation. The development happens in a GitHub repository.[7]

In 2016, Version 2 of the AppImage specification was drafted. Version 2 is unrestricted in filesystem type (a draft implementation used SquashFS).[8][9] It removes the fixed offset for where the filesystem image begins in the file and enabled digital signatures to be embedded directly in the AppImage as opposed to as a separate file.

Design

klik installing an application

AppImage aims to be an application deployment system for Linux with the following objectives: simplicity, binary compatibility, portability, distro agnosticism, no installation, no root permission, and keeping the underlying operating system untouched.[10] Because of this, AppImage does not install software by placing executables in various locations. Instead, the file is a single filesystem image itself. When run, the file is mounted with FUSE. AppImage is designed to be simpler to use than traditional installer formats such as Deb and RPM, since it is not necessary to modify the operating system or user environment.

Each file is self-contained; it includes all libraries the application depends on that are not already part of the targeted system. A version 1.0 AppImage is an ISO 9660 Rock Ridge file (which can be optionally compressed via zisofs) containing a minimal AppDir and a runtime.[11]

AppImage allows the embedding of digital signatures, which need to be verified externally. The format does not require signatures to be validated, only that they may be included.[12] AppImage does not enforce sandboxing, but it may be done by some applications.[13]

Reception and usage

In 2007, Klik was the inspiration for Alexander Larsson's glick project, the precursor of Flatpak.[14]

In 2015, Linus Torvalds, creator of the Linux kernel, said that "[t]his is just very cool. I finally got around to play with the "AppImage" version of Subsurface, and it really does seem to "just work"."[15] Mark Shuttleworth stated that "AppImages are a pretty clean experience and I admire the work behind them."[16]

See also

References

  1. ^ Mobily, Tony (2006-04-07). "Free Software Magazine interview with Simon Peter". Free Software Magazine. Archived from the original on 2007-03-30. Retrieved 2007-05-05.
  2. ^ "Slashdot - Point-and-klik Linux Software Installation?". slashdot.com. 15 January 2005.
  3. ^ Screen capture video of Klik2 on video.google.com (archived)
  4. ^ "klik - Linux Software Download". Archived from the original on 2007-06-26.
  5. ^ Peter, Simon (2010). "AppImageKit Documentation 1.0" (PDF). PortableLinuxApps.org. pp. 2–3. Archived from the original (PDF) on 2010-11-29. Retrieved 2011-07-29.
  6. ^ "Portable Games for Linux".
  7. ^ "AppImageKit". github.com. 19 November 2021.
  8. ^ "AppImage/AppImageSpec". GitHub. 18 November 2021.
  9. ^ "The future of AppImage: Type 2 and new tools". AppImage. September 15, 2016.
  10. ^ AppImage: Linux apps that run anywhere on youtube.com by Simon Peter (June 2016)
  11. ^ Peter, Simon. "AppImageKit Documentation" (PDF). Archived from the original (PDF) on 2010-11-29. Retrieved 2011-08-03.
  12. ^ "Signing AppImages — AppImage documentation". docs.appimage.org. Archived from the original on 2019-10-29. Retrieved 2019-10-29.
  13. ^ Peter, Simon (2020-09-20). "AppImage Mythbusting" (PDF). GitHub. p. 17. Retrieved 2024-01-18.
  14. ^ "Experiments with runtime-less app-bundles – Alexander Larsson". 2007-08-07. Retrieved 2024-01-18.
  15. ^ Torvalds, Linus (2016-02-05). "This is just very cool. I finally got around to play with the "AppImage"…". Google Plus. Archived from the original on 2016-02-05. Retrieved 2024-01-18.
  16. ^ Shuttleworth, Mark (2017-04-09). "I would like to thank all of you for your spirit and intellect and energy in ..." Google Plus. Archived from the original on 2017-04-09. Retrieved 2024-01-18.