A snap is a bundle of an app and its dependencies that works without modification across many different Linux distributions. Snaps are discoverable and installable from the Snap Store, an app store with an audience of millions.
The following sections provide a basic overview of using snaps, from their installation to their management and manipulation.
The snapd daemon manages the snap environment on the local system. Its installation will include the snap tool for interacting with snaps. You can check both are installed by attempting to run
snap version on the command line:
$ snap version snap 2.36.1 snapd 2.36.1 series 16 ubuntu 18.04 kernel 4.15.0-39-generic
If all is well, version numbers for the main system components will be output, as shown above, albeit with potentially different versions and Linux distribution identifier.
If the snap command is not found, or if the command takes a while to respond before reporting that snapd is unavailable, make sure snapd is properly installed before continuing.
With snapd installed, snaps can be discovered, searched for, and installed from the Snap Store, from the Snap Store desktop app, and directly from the command line. For example, the following command returns a list of media players:
$ snap find "media player" Name Version Developer Notes Summary (...) vlc 3.0.4 videolan✓ - The ultimate media player. mpv 0.26.0 casept - a free, open source, and cross-platform media player. (...)
✓ alongside videolan in the above output indicates that the snap publisher has been verified.
The snap info command makes it easy to find more details about a specific snap. These details include what a snap does, who publishes it, the command(s) it provides and which channel versions are available for installation:
$ snap info vlc name: vlc summary: The ultimate media player publisher: VideoLAN✓ contact: https://www.videolan.org/support/ description: | VLC is the VideoLAN project's media player. (...) snap-id: RT9mcUhVsRYrDLG8qnvGiy26NKvv6Qkd commands: - vlc channels: stable: 3.0.0 (158) 197MB - candidate: 3.0.0 (158) 197MB - beta: 3.0.0-5-g407d4ba (160) 197MB - edge: 4.0.0-dev-1218-g201542f (159) 197MB
Installing a snap is straightforward:
$ sudo snap install vlc
Channels are an important snap concept. They define which release of a snap is installed and tracked for updates. The stable channel is used by default, but opting to install from a different channel is easily accomplished:
$ sudo snap install --channel=edge vlc
After installation, the channel being tracked can be changed with:
$ sudo snap switch --channel=stable vlc
A snap’s installed applications can be found under
/snap/bin, and subsequently, often added to $PATH. This makes commands directly accessible from the command line.
For example, the command installed via the VLC snap is simply vlc:
$ which vlc /snap/bin/vlc
If executing a command directly doesn’t work, try prefixing it with the /snap/bin path:
snap list to show a list of snaps installed on your system:
$ snap list Name Version Rev Tracking Publisher Notes core 16-2.35.1 5419 beta canonical✓ core spotify 184.108.40.2063 19 stable spotify✓ - vlc 3.0.4 555 stable videolan✓ -
Some snaps, such as core listed above, are installed by automatically by snapd to satisfy the requirements of other snaps.
Snaps are updated automatically. However, to manually check for updates, use the following command:
$ sudo snap refresh vlc
The above will check the channel being tracked by the snap. If a newer version of the snap is available, it will be downloaded and installed.
Changing the channel being tracked and refreshing the snap can be accomplished with a single command:
$ sudo snap refresh --channel=beta vlc
Updates are automatically installed within 6 hours of a revision being made to a tracked channel, keeping most systems up-to-date. This schedule can be tuned via configuration options.
Versions and revisions convey different details about one specific release of a snap:
The version is a string that was assigned to a project by its developers, according to their development practices. It tells the user what content to expect from a snap. The revision is an automatic number assigned by the Snap store, giving the snap it a unique identity within the channel.
Neither the version nor the revision enforce an order of release. The local system will simply attempt to install whatever snap is recommended by the publisher in the channel being tracked.
A snap may be reverted to a previously used revision with the
snap revert command:
$ sudo snap revert vlc vlc reverted to 3.0.5-1
This operation will revert both the snap revision and the data associated with the software. If the previously used revision of the snap is from a different channel, that snap will be installed but the channel being tracked won’t change.
A snap won’t automatically update to a version previously reverted from, and the output from
snap refresh will continue to state All snaps up to date. A reverted snap will be automatically updated when a new and different revision is made available by the publisher.
However, explicitly adding the snap name to
snap refresh will update the snap, regardless of whether the latest revision was previously reverted from or not:
$ snap list --all vlc Name Version Rev Tracking Publisher Notes vlc 3.0.5-1 768 stable videolan✓ - vlc 3.0.6 770 stable videolan✓ disabled $ sudo snap refresh All snaps up to date. $ sudo snap refresh vlc vlc 3.0.6 from VideoLAN✓ refreshed
On an Ubuntu Core system, such as Ubuntu Core 18 and Ubuntu Core 16, reverting twice will work too. This is because snapd attempts to keep three revisions of a snap: the most recently installed plus the two previous installations. On classic systems like Ubuntu 18.04 LTS or Ubuntu 16.04 LTS, two revisions are retained by default. This behaviour can be modified with the refresh.retain system option.
The following command lists all revisions available for every installed snap, and also highlights which particular revisions are disabled at the moment:
$ snap list --all vlc Name Version Rev Tracking Publisher Notes vlc 4.0.0-dev-4620 560 edge videolan✓ disabled vlc 3.0.4 555 edge videolan✓ -
A previously used snap that was reverted from will display disabled in the Notes column of the output.
Manually keeping track of which snap revisions available is generally unnecessary. A single revision will only ever be in use at a time, and snapd will remove old revisions automatically.
If a snaps is temporarily undesired, it can be disabled and later enabled again. This avoids having to remove and reinstall them in the system:
$ sudo snap disable vlc vlc disabled $ sudo snap enable vlc vlc enabled
To remove a snap from your system, along with its internal user, system and configuration data, use the remove command:
$ sudo snap remove vlc vlc removed
By default, all of a snap’s revisions are also removed. To remove a specific revision, add the
--revision=<revision-number> argument to the remove command.
Prior to removal (except on Ubuntu Core systems), a snap’s internal user, system, and configuration data is saved as a snapshot (snapd 2.39+), and retained for 31 days. A snapshot can be used to restore the state of your snap upon reinstallation. See Snapshots for further details.
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