- 1/ Snap Applications are launched as
user; Snap Services/Deamons are always launched asroot - 2/ Canonical allows snaps to read/write folders only from the one who launched the snap ; thus Applications are allowed to read/write in
user-owned folders only ; Servics/Daemons are allowed to read/write inroot-owned folders only. - 3/ Thus, for Services/Daemons Canonical doesn't allow snaps to read base
/homefolder (except special authorizations), but you can read subfolders owned byrootwith following trick:
removable-media interface allows direct access to /media and /mnt folders ; do not forget to connect it:
sudo snap connect <snap_name>:removable-media
Easiest way to access your /home subfolder is by mounting a bind in the /media folder:
sudo mkdir /home/$USER/myfolder
sudo mkdir -p /media/home
sudo mount --bind /home/$USER/myfolder /media/home
You can now access /home/$USER/myfolder in the app through /media/home.
To make it permanent, this mount bind must be stored in /etc/fstab
sudo nano /etc/fstab
Add this line to the end of the file with your appropriate folders' modifications :
# Content of /etc/fstab
/home/<your_username>/myfolder/ /media/home none bind 0 0
To apply changes without restarting the OS :
sudo mount -a
sudo systemctl daemon-reload
Go in base directory and build:
snapcraft -v
To resolve problems, you may check snapcraft documentation.
Easy resolution is often to perform a clean:
snapcraft clean
Warning
Core20 ONLY ! This won't work with Core22 or Core24 :-)
Cross compilation requires target architectures repositories to be able to find the snap's required packages.
Add target architecture sources (armhf, arm64):
sudo dpkg --add-architecture armhf
sudo dpkg --add-architecture arm64
Add package repository sources at end of sources.list.d:
sudo nano /etc/apt/sources.list.d/ubuntu.sources
Notice Architectures: amd64 added to the 2 original parts to avoid non-resolved ports
(armhf and arm64 does not exist in http://archive.ubuntu.com/ubuntu ).
Noble (Core24) and Focal (Core20) repositories are then added
(armhf, arm64 and other different ports are in http://ports.ubuntu.com/ubuntu-ports ).
# This is the content of /etc/apt/sources.list.d/ubuntu.sources
# System repository (amd64 system here)
Types: deb
URIs: http://archive.ubuntu.com/ubuntu
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Architectures: amd64
Types: deb
URIs: http://security.ubuntu.com/ubuntu
Suites: noble-security
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Architectures: amd64
# X-Compilation noble (armhf, arm64)
Types: deb
URIs: http://ports.ubuntu.com/ubuntu-ports
Suites: noble noble-updates noble-backports
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Architectures: armhf arm64
Types: deb
URIs: http://ports.ubuntu.com/ubuntu-ports
Suites: noble-security
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Architectures: armhf arm64
# X-Compilation focal (armhf, arm64)
Types: deb
URIs: http://ports.ubuntu.com/ubuntu-ports
Suites: focal focal-updates focal-backports focal-security
Components: main universe restricted multiverse
Signed-By: /usr/share/keyrings/ubuntu-archive-keyring.gpg
Architectures: armhf arm64
- TODO: Add library dependencies checking info
Build with:
snapcraft --enable-experimental-target-arch --target-arch=armhf --destructive-mode
snapcraft --enable-experimental-target-arch --target-arch=arm64 --destructive-mode
LXD/LXC supports only virtual machine of same architecture, thus the idea of cross-building snaps has been dropped. Yet still possible:
Extract from https://snapcraft.io/docs/remote-build :
There are two methods for building snaps on Canonical-hosted servers, and both are available to every snap publisher:
- Build from GitHub
This is a build service integrated into every publisher’s Developer Account on snapcraft.io. It works by linking a snap’s GitHub repository with our Launchpad build service. See Build from GitHub for further details. - Snapcraft remote-build
The snapcraft remote-build command offloads the snap build process to the Launchpad build farm, pushing the potentially multi-architecture snap back to your machine. See below for further details.
Warning
But beware of the version of Snapcraft on the servers ; the farm may fail on some ports while it will work locally (w/ or w/o cross-compilation).
- For building, it's possible, but good luck and you must be trustful in a system which can even not output the console properly :-)\
- For betatesting, it does quite the job.
- TODO: Add QEMU img section
Given you have enough resources (especially RAM), what a very nice option to compile directly on the arch !
Some boards:
-
For ARMHF and ARM64: Rasberry PI 5 or 4 will do the job
-
For RISC-V64: BeagleV®-Ahead
More or less supported/open/working boards on https://wiki.ubuntu.com/RISC-V/
Warning
Current version of Snapcraft (8.4.1) fails to pack snaps
Current versionning of my snaps follows the exact same one from the source.
If a re-build is needed, new build version appends source version with a '-v2' ; following builds increment this one '-v3', '-v4',... etc
Even if not ideal, to simplify the management with snapcraft, re-build increment is based on current stable published version for now (i.e. there can be several different -v2 rc/beta/edge releases published ; but each stable release has a different version)
- TODO: Modifiy if there is a way with snapcraft to have build versionning and update with final version