vm_tools - Utilities for Virtual Machine (VM) orchestration

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.


vm_concierge is a system daemon that runs in Chrome OS userspace and is responsible for managing the lifetime of all VMs. It exposes a D-Bus API for starting and stopping VMs.

When 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.

When 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 vm_concierge.

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 vm_cicerone and 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 vm_cicerone.


The p9 directory holds a server implementation of the 9p file system protocol. It is used by crosvm and the 9s daemon to share files and directories between the host and the VM.


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 now, this is only capable of launching a shell on the VM itself, but this may later be extended to launch a shell in a specific container inside of the VM.


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 forwards them on to the host syslog service. This ensures that the VM logs are captured in any feedback reports that are uploaded to Google's servers.

Additionally, vm_syslog reads kernel logs from /dev/kmsg (inside the VM) and forwards those to the logging service running on the host.

See docs/logging.md for more details on log handling.


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.

VM <-> host communication

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).

See docs/vsock.md for more details about vsock.


Since each 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.

Wire format

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.