Environment variables are widely used across Linux to provide convenient access to system and application properties.
Both Snapcraft and snapd consume, set, and pass-through specific environment variables to support building and running snaps.
See below for the various environment variables available to snap applications. For environment variables connected to Snapcraft, see Parts environment variables.
Snap specific environment variables
List environment variables
Each snap runs in a custom environment specifically made for it. To get an overview of the variables in it, you can open a shell as the snap and run the env command.
$ snap run --shell <snap>.<command>
$ env
XDG_VTNR=1
SSH_AGENT_PID=5543
XDG_SESSION_ID=2
SNAP_USER_COMMON=/home/<user>/snap/<snap>/common
SNAP_LIBRARY_PATH=/var/lib/snapd/lib/gl:
SNAP_COMMON=/var/snap/<snap>/common
[...]
Alongside the many system-specific variables, this environment will include the following:
SNAP
Directory where the snap is mounted. This is where all the files in your snap are visible in the filesystem. All of the data in the snap is read-only and cannot be changed.
Typical value: /snap/hello-world/27
SNAP_USER_DATA
Directory for user data.
This directory is backed up and restored across snap refresh and snap revert operations.
Typical value: /home/zyga/snap/hello-world/27
The final number there is $SNAP_REVISION.
SNAP_USER_COMMON
Directory for user data that is common across revisions of a snap.
Unlike SNAP_USER_DATA, data present in this directory is not backed up or restored across snap refresh and snap revert operations. The directory is suitable for large data that the application can access even if it was made or modified by a future version of a snap.
Typical value /home/zyga/snap/hello-world/common
SNAP_DATA
Directory for system data of a snap.
This directory is owned and writable by root and is meant to be used by background applications (daemons, services). Unlike SNAP_COMMON this directory is backed up and restored across snap refresh and snap revert operations.
Typical value /var/snap/hello-world/27
SNAP_COMMON
Directory for system data that is common across revisions of a snap.
This directory is owned and writable by root and is meant to be used by background applications (daemons, services). Unlike SNAP_DATA this directory is not backed up and restored across snap refresh and revert operations.
Typical value: /var/snap/hello-world/common
SNAP_SAVE_DATA
This variable is only exposed on Ubuntu Core systems.
It points to a snap-specific location on the ubuntu-save partition where the snap is allowed to store persistent files (like certificates or configuration files) that will survive a factory reset of the Ubuntu Core device.
See ubuntu-save in the Ubuntu Core documentation for more details on storage layout with this specific partition.
Requires snapd 2.57+.
SNAP_INSTANCE_NAME
The name of snap instance, including instance key if one is set.
For example snap hello-world with instance key foo has instance name equal to hello-world_foo.
Typical value: hello-world
Requires snapd 2.36+
SNAP_INSTANCE_KEY
Instance key if one was set during installation or empty.
For example instance hello-world_foo has an instance key foo.
Typical value: none
Requires snapd 2.36+
SNAP_NAME
The name of the snap as specified in the snapcraft.yaml file.
Typical value: hello-world
SNAP_REVISION
Revision of the snap, as allocated by the Snap Store on upload or as allocated by snapd for locally installed snaps.
The Snap Store assigns monotonic revisions to each upload of a given snap. Snapd uses Snap Store revisions if accompanying assertions are available or uses a locally generated number. Locally generated numbers are prefixed with x to distinguish them from Snap Store uploads.
Typical value: 27 or x1
SNAP_ARCH
CPU architecture of the running system.
Typical value amd64
Other values are: i386, armhf, arm64.
SNAP_UID
This variable contains the user ID (uid) of the user running this snap instance. See also SNAP_EUID.
For this variable to be exposed by a snap, the snap developer will need to include the following assumes value:
assumes: [snap-uid-envvars]
Requires snapd 2.59+.
SNAP_EUID
This variable contains the effective user ID (euid) of the user running the snap instance. See also SNAP_UID.
For this variable to be exposed by a snap, the snap developer will need to include the following assumes value:
assumes: [snap-uid-envvars]
Requires snapd 2.59+.
SNAP_LAUNCHER_ARCH_TRIPLET
Only available in snaps built with a desktop extension.
The host architecture triplet on which the snap is running. For amd64 it’s x86_64-linux-gnu. The runtime counterpart of CRAFT_ARCH_TRIPLET_BUILD_FOR.
SNAP_LIBRARY_PATH
Directory with additional system libraries. This variable is used internally by snapcraft.
The value is always /var/lib/snapd/lib/gl: Please note the colon at the end of that value, the variable is a colon-separated list.
The referenced directory is typically empty unless Nvidia proprietary drivers are in use.
SNAP_VERSION
The version string as specified in the snapcraft.yaml
Typical value 6.3
SNAP_REAL_HOME
The vanilla HOME environment variable before snapd-induced remapping, refer to Any way to acquire the originally set HOME environment variable? - snapcraft - snapcraft.io for more info.
Requires snapd 2.46+.
Generic variables
HOME
For non-classic snaps, this environment variable is re-written to SNAP_USER_DATA by snapd so that each snap appears to have a dedicated home directory that is a subdirectory of the real home directory.
For classic confinement snaps, the value remains unchanged.
Typical value: /home/_user_name_/snap/_snap_name_/_snap_revision_ (e.g. /home/zyga/snap/hello-world/27)
PATH
This environment variable is re-written by snapd so that it is consistent with the view of the filesystem presented to snap applications.
The value is always:
-
For non-classic confinement snaps:
$SNAP/usr/sbin:$SNAP/usr/bin:$SNAP/sbin:$SNAP/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games -
For classic confinement snaps:
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games
Last updated 6 months ago.