Делаю по спецификации: http://www.galago-project.org/specs/notification/0.9/x408.html#command-notify
Если слать

dbus-send --print-reply --type=method_call --dest=org.freedesktop.Notifications /org/freedesktop/Notifications org.freedesktop.Notifications.Notify string: uint32:0 string: string:summary string:body array:string: dict:string:byte:urgency,1 int32:1000

Выдаёт

Error org.freedesktop.DBus.Error.InvalidArgs: Type of message, `(susssasa{sy}i)', does not match expected type `(susssasa{sv}i)'

Если слать

dbus-send --print-reply --type=method_call --dest=org.freedesktop.Notifications /org/freedesktop/Notifications org.freedesktop.Notifications.Notify string: uint32:0 string: string:summary string:body array:string: dict:string:variant:urgency,byte:1 int32:1000

Выдаёт

dbus-send: Unknown type «variant»

Баг в dbus-send?