A snap’s confinement level is the degree of isolation it has from your system. There are three levels of snap confinement:
Used by the majority of snaps. Strictly confined snaps run in complete isolation, up to a minimal access level that’s deemed always safe. Consequently, strictly confined snaps can not access your files, network, processes or any other system resource without requesting specific access via an interface (see below).
Allows access to your system’s resources in much the same way traditional packages do. To safeguard against abuse, publishing a classic snap requires manual approval, and installation requires the
--classiccommand line argument.
A special mode for snap creators and developers. A devmode snap runs as a strictly confined snap with full access to system resources, and produces debug output to identify unspecified interfaces. Installation requires the
--devmodecommand line argument. Devmode snaps cannot be released to the stable channel, do not appear in search results, and do not automatically refresh.
Strict confinement uses security features of the Linux kernel, including AppArmor, seccomp and namespaces, to prevent applications and services accessing the wider system.
You can discover the confinement mode for any snap using the
snap info --verbose command:
$ snap info --verbose vlc [...] confinement: strict devmode: false [...]
To see which installed snaps are using classic confinement, look for classic under the Notes column in the output of
$ snap list Name Version Rev Tracking Publisher Notes vlc 3.0.6 770 stable videolan✓ - code 0dd516dd 5 stable vscode✓ classic wormhole 0.11.2 112 stable snapcrafters -
Interfaces and confinement
Each snap’s interface is carefully selected by a snap’s creator to provide specific access to a resource, according to a snap’s requirements. Common interfaces provide network access, desktop access and sound for example.
An interface needs to be connected to be active, and connections are made either automatically (at install time) or manually, depending on their function. The desktop interface is connected automatically, for instance, whereas the camera interface is not. See the Auto-connect column in Supported interfaces table for details on whether an interface automatically connects or not.
As with classic confinement, a snap’s publisher can request an assertion to automatically connect an otherwise non-auto-connecting interface. For example, the guvcview snap requested the camera interface be automatically-connected when the snap is installed.
If a snap is upgraded and includes a new assertion, the user will still need to connect the interface manually. Similarly, if an installed classic snap is upgraded to use strict confinement, its interfaces won’t be automatically configured.
You can see which interfaces are connected and disconnected with the
snap connections command (
vlc:camera is disconnected in the following example):
$ snap connections vlc Interface Plug Slot Notes camera vlc:camera - - desktop vlc:desktop :desktop - desktop-legacy vlc:desktop-legacy :desktop-legacy - home vlc:home :home - mount-observe vlc:mount-observe - - [...]
See Interface management for further interface details, including how to disconnect interfaces and make manual connections, and Security policy and sandboxing for more information on how confinement is implemented.
Last updated 2 years ago.