If REF names an installed application, flatpak runs the
application in a sandboxed environment. Extra arguments are
passed on to the application.
If REF names a runtime, a shell is opened in the runtime. This is
useful for development and testing.
By default, flatpak will look for the application or runtime in
all per-user and system installations. This can be overridden
with the --user, --system and --installation options.
flatpak creates a sandboxed environment for the application to
run in by mounting the right runtime at /usr and a writable
directory at /var, whose content is preserved between application
runs. The application itself is mounted at /app.
The details of the sandboxed environment are controlled by the
application metadata and various options like --share and
--socket that are passed to the run command: Access is allowed if
it was requested either in the application metadata file or with
an option and the user hasn't overridden it.
The remaining arguments are passed to the command that gets run
in the sandboxed environment. See the --file-forwarding option
for handling of file arguments.
Environment variables are generally passed on to the sandboxed
application, with certain exceptions. The application metadata
can override environment variables, as well as the --env option.
Apart from that, Flatpak always unsets or overrides the following
variables, since their session values are likely to interfere
with the functioning of the sandbox:
PATH
LD_LIBRARY_PATH
XDG_CONFIG_DIRS
XDG_DATA_DIRS
SHELL
TMPDIR
PYTHONPATH
PERLLIB
PERL5LIB
XCURSOR_PATH
Flatpak also overrides the XDG environment variables to point
sandboxed applications at their writable filesystem locations
below ~/.var/app/$APPID/:
XDG_DATA_HOME
XDG_CONFIG_HOME
XDG_CACHE_HOME
The host values of these variables are made available inside the
sandbox via these HOST_-prefixed variables:
HOST_XDG_DATA_HOME
HOST_XDG_CONFIG_HOME
HOST_XDG_CACHE_HOME
Flatpak sets the environment variable FLATPAK_ID to the
application ID of the running app.
Flatpak also bind-mounts as read-only the host's /etc/os-release
(if available, or /usr/lib/os-release as a fallback) to
/run/host/os-release in accordance with the os-release
specification
If parental controls support is enabled, flatpak will check the
current user's parental controls settings, and will refuse to run
an app if it is blocklisted for the current user.
