This directory contains various tools for managing the lifetime of VM instances and for providing any services those VMs may need while they are running.
chunnel tunnels traffic for servers that listen on
localhost. This is a common developer use case since
localhost is allowed as a secure origin in Chrome.
chunneld binary runs on the Chrome OS host, and receives updates from
vm_cicerone notifying it of ports that should be listened to. When Chrome connects to
chunneld will accept the connection, open a vsock listener, and launch the
chunnel binary in the target container which will connect back to
vm_concierge receives a request to start a VM it allocates various resources for that VM (IPv4 address, vsock context id, etc) from a shared pool of resources. It then launches a new instance of crosvm to actually run the VM.
Once the VM has started up
vm_concierge communicates with the
maitred instance inside the VM to finish setting it up. This includes configuring the network and mounting disk images.
vm_cicerone is a system daemon that runs in Chrome OS userspace and is responsible for all communication directly with the container in a VM. It exposes a D-Bus API for doing things such as launching applications in containers, getting icons from containers and other container related functionality as it is extended. It also sends out signals for starting/stopping of containers.
vm_concierge communicates with
vm_cicerone to keep the list of running VMs in sync and also to retrieve status of containers and get security tokens.
vm_cicerone communicates with a container, it is interacting with the
garcon component running inside of that container and is doing so over gRPC.
maitred is the agent running inside the VM responsible for managing the VM instance. It acts as the init system, starting up system services, mounting file systems, and launching the container with the actual application that the user wants to run. It is responsible for shutting down the VM once the user's application exits or if requested to by
See docs/init.md for more details on the duties maitred carries out as pid 1.
garcon is a daemon that runs inside of a container within a VM. gRPC is used to communicate between
garcon. It is used to control/query things inside the contaienr such as application launching, accessibility, handling intents, opening files, etc. The communication is bi-directional. It uses TCP/IP for the transport and firewall rules ensure that only the container IPs are allowed to connect to the corresponding port for
garcon that is open in
upgrade_container is executed inside a container by Tremplin to upgrade the container e.g. a Debian Stretch container to Debian Buster.
seneschal is the steward of the user's /home directory. It manages processes that serve the 9p file system protocol. The 9p client lives in the guest kernel and communicates with the server over vsock.
Each server initially does not have access to any path but can be granted access to specific paths in the user‘s home directory by sending requests over dbus to
seneschal. These paths are bind-mounted into the server’s root directory and become visible to the 9p clients of that server.
This makes it possible to share different sets of paths with different VMs by giving each of them access to a different 9p server.
vsh is a vsock-based remote shell utility.
vshd runs on the guest/server, and
vsh runs on the host/client.
For more detailed docs, see
vm_syslog is the syslog daemon that runs inside the VM. It is automatically started by maitred and provides a socket at
/dev/log for applications to send it log records.
vm_syslog aggregates the log records and then forwards them outside the VM to the logging service running on the host. The logging service tags the records it receives with the unique identifier for the VM from which the logs originated and then either forwards them on to the host syslog service or writes them to a file in the user cryptohome. This ensures that the VM logs are captured in any feedback reports that are uploaded to Google's servers.
See docs/logging.md for more details on log handling.
vm_pstore_dump is the command to print the console output of the guest kernel. It runs in Chrome OS userspace and reads the file which is on the host file system and used as the backend of pstore of the guest kernel. It is intended to be used for collecting logs when the guest kernel fails to boot in its early stage and other tools (e.g. logcat) are not available.
crash_collector is responsible for collecting crash reports of applications running inside the VM and forwarding them out to the crash collector service running on the host system. When
maitred first starts up it configures
/proc/sys/kernel/core_pattern to start the
crash_collector program and send the core dump over a pipe to that program.
crash_collector then parses the core dump and converts it to a minidump before sending it out to the host. The host daemon passes the report on to
crash-reporter, which takes care of uploading it to Google servers.
metric_collector is an IO reporting daemon for the default Crostini container. It periodically polls the vmstats of the container (or really, the whole termina VM, since the stats are not namespaced) and reports those to UMA by invoking
All communication between
vm_concierge and the applications inside the VM happen over a vsock transport. The actual RPC communication uses the gRPC framework. Every
maitred instance listens on a known port in the vsock namespace (port 8888).
maitred instance listens on a known port number, it is possible for an application inside a VM to send a message to
maitred over a loopback interface. To prevent this we block all loopback connections over vsock.
It is not possible for processes in different VMs to send messages to each other over vsock. This is blocked by the host kernel driver that manages data transfer.
gRPC uses protocol buffers as the serialization format for messages sent over the vsock and IP transport. The proto directory holds the definitions for all the messages sent and services provided between the host and the VM/container.