MiniOS is a subset of thanOS, also known as the Network Based Recovery Project (go/cros-nbr). MiniOS consumer facing feature used to help recover devices using only a network or ethernet connection. Once connected to the network, MiniOS will automatically repartition the disk, wipe the stateful partition and all user data, and update to the latest stable version. The UI theme and elements are an extension of the Groot recovery flow.
The main MiniOS components include D-bus, update_engine, and network manager.
MiniOS graphics are done with frecon-lite and can show images and draw shapes. The layout of MiniOS elements is based on the frecon canvas size and scaling factor which are from frecon.conf. The images are created with Pango during build time with no run time size or color changes supported.
KeyReader is how MiniOS processes input. There are two types of input KeyReader handles.
The first type is basic navigation using the up, down, and enter keys. This is used to navigate between screens and make basic selections. This type of input uses an Epoll file descriptor which sends all input to ScreenController so each screen can decide what action to take based on user input.
The other kind of functionality KeyReader supports is taking in alphanumeric input, which is used for things like the network password; this does not use the watcher. For this type of input, KeyReader must be given a keyboard layout to correctly map key codes to characters. Currently, there is no foolproof way to do this, but the region information is read from VPD and then mapped to a list of supported chrome keyboard layouts using cros-regions.json. Due to the size and complexity constraints of MiniOS, only standard ASCII characters are processed. Other special characters such as “ê” are ignored even if they are a part of the keyboard layout.