What is an "AppImage"? How do I install it?
Basic Information
Regarding installation
I am quoting the appImage project page here:
AppImages can be downloaded and run without installation or the need for root rights.
Making it executable
You can make the appImage executable as follows:
chmod a+x exampleName.AppImage
Executing it
You can execute an appImage as follows:
./exampleName.AppImage
Additional Information
About appImage
You can find some general informations about appImage here.
I am quoting the appImage project page here:
The key idea of the AppImage format is one app = one file. Every AppImage contains an app and all the files the app needs to run. In other words, each AppImage has no dependencies other than what is included in the targeted base operating system(s).
Wikipedia adds
AppImage (and the predecessors klik and portablelinuxapps) do not install software in the traditional sense (i.e., it do not put files all over the place in the system).
It use one file per application. Each one is self-contained: it includes all libraries the application depends on and that are not part of the base system. In this regard, it is similar to "application virtualization". One can use a AppImage file even if they are not a superuser, or they are using a live CD. AppImage files are often simpler than compiling and installing an application, as no installation actually took place. The AppImage file is a compressed image which is temporarily mounted to allow access to the program, but not having to extract the program or modify the underlying system.
The README.md of the AppImageKit-project offers a lot additional informations like Use cases, the problem space and objectives.
Use Cases
As a user, I want to go to an upstream download page, download an application from the original author, and run it on my Linux desktop system just like I would do with a Windows or Mac application.
As a tester, I want to be able to get the latest bleeding-edge version of an application from a continuous build server and test it on my system, without needing to compile and without having to worry that I might mess up my system.
As an application author or ISV, I want to provide packages for Linux desktop systems just as I do for Windows and OS X, without the need to get it 'into' a distribution and without having to build for gazillions of different distributions.
Objectives
Be Simple.
AppImage is intended to be a very simple format that is easy to understand, create, and manage.
Maintain binary compatibility.
AppImage is a format for binary software distribution. Software packaged as AppImage is intended to be as binary-compatible as possible with as many systems as possible. The need for (re-)compilation of software should be greatly reduced.
Be distribution-agnostic.
An AppImage should run on all base operating systems (distributions) that it was created for (and later versions). For example, you could target Ubuntu 9.10, openSUSE 11.2, and Fedora 13 (and later versions) at the same time, without having to create and maintain separate packages for each target system.
Remove the need for installation.
AppImages contain the app in a format that allows it to run directly from the archive, without having to be installed first. This is comparable to a Live CD. Before Live CDs, operating systems had to be installed first before they could be used.
Keep apps compressed all the time.
Since the application remains packaged all the time, it is never uncompressed on the hard disk. The computer uncompresses the application on-the-fly while accessing it. Since decompression is faster than reading from hard disk on most systems, this has a speed advantage in addition to saving space. Also, the time needed for installation is entirely removed.
Allow to put apps anywhere.
AppImages are "relocatable", thus allowing the user to store and execute them from any location (including CD-ROMs, DVDs, removable disks, USB sticks).
Make applications read-only.
Since AppImages are read-only by design, the user can be reasonably sure that an app does not modify itself during operation.
Do not require recompilation.
AppImages must be possible to create from already-existing binaries, without the need for recompilation. This greatly speeds up the AppImage creation process, since no compiler has to be involved. This also allows third parties to package closed-source applications as AppImages. (Nevertheless, it can be beneficial for upstream application developers to build from source specifically for the purpose of generating an AppImage.)
Keep base operating system untouched.
Since AppImages are intended to run on plain systems that have not been specially prepared by an administrator, AppImages may not require any unusual preparation of the base operating system. Hence, they cannot rely on special kernel patches, kernel modules, or any applications that do not come with the targeted distributions by default.
Do not require root.
Since AppImages are intended to be run by end users, they should not reqiure an administrative account (root) to be installed or used. They may, however, be installed by an administrator (e.g., in multi-user scenarios) if so desired.
Before you can run an AppImage, you need to make it executable. This is a Linux security feature. There are two main ways to make an AppImage executable:
Using the GUI
or
Using command line
chmod a+x Some.Appimage
Now double-click your file to run it OR Right-click > Run
The basic idea might look similar between the two systems, but there are some design differences between snaps and Appimages.
Some "big" ones that come to my mind are:
Security, in terms of confinement: Snap packages run in a sandbox, and they are not allowed to escape from it and reach other parts of the system that they should not touch. This is a stronger security layer that runs parallel to the permission's system. Obviously it is a bit frustrating when dealing with it at the beginning (and also later on), but if you think about it in terms of system administration, this is the thing that an administrator wants for their users.
Security: Installing software taken from around the net, is as safe as going around licking poles in the streets. Sometimes nothing happens, sometimes you get some very big health issues. Snap packages have their proper repositories, that are controlled by Canonical, like the usual standard Ubuntu repositories. You can go on and install
.debfiles from around, but that will be your choice, and not a design issue.Installation: AppImages are meant to be the equivalent of the "portable Windows executables". All the libraries are self-contained and any user can just download and execute one of those. On the other hand,
snappackages are proper packages, and they need to be installed (asroot, or withsudo) via the apposite package manager (snap install tic-tac-toethrows an error: it needssudo!)Removal: To remove a snap package, you need to use the package manager
snap remove ...with the right permissions to do so. Appimages, on the other hand, they are just "there". So any user does not want that Appimage? He/she just removes the file and it is gone.
While I strongly suggest being cautious when using Appimages, I personally use some of them myself.
I find them particularly useful on my work system, where I do not have root access (only the admin has that) but I need the latest version of a particular software that, fortunately, the developer has provided in Appimage form.
I am a bit afraid that some malign code is indeed contained in them, so I checked as much as possible the identity of the publisher. I am not 100% sure that this software is benign, but I have done all I could.