Getting started with ffx

This doc will guide you through some of the features of ffx. For an overview of the design and components of ffx, see the ffx overview.

Contacting the ffx team

If you discover possible bugs or have questions or suggestions, file a bug.


To follow the examples in this doc, you'll need a Fuchsia device running. If you don't have a physical device connected, you can use an emulator.

To start an emulator with networking enabled but without graphical user interface support, run ffx emu start --headless.

For more information on configuring the emulator see, Start the Fuchsia emulator.

Your device must be running a core product configuration or a product configuration that extends core (such as workstation_eng).

Optionally, you can run ffx log, which will provide some additional information about the interactions between ffx and your Fuchsia target device.


After following all the prerequisites, run the following in a terminal:

fx ffx help

This will list all of the available ffx subcommands. You'll see something like:

Usage: ffx [-c <config>] [-e <env>] [-t <target>] [<command>] [<args>]

Fuchsia's developer tool

  -c, --config      override default configuration
  -e, --env         override default environment settings
  -t, --target      apply operations across single or multiple targets
  -o, --log-output  specify destination of log output
  --help            display usage information

  component         Discover and manage components
  config            View and switch default and user configurations
  daemon            Interact with/control the ffx daemon
  diagnostic        Run diagnostic tests on Fuchsia targets
  docs              View suite of docs for ffx and for Fuchsia
  doctor            Run common checks for the ffx tool and host environment
  emulator          Start and manage Fuchsia emulators
  overnet           Interact with the Overnet mesh
  package           Create and publish Fuchsia packages
  sdk               Modify or query the installed SDKs
  target            Interact with a target device or emulator
  vendor            Run partner plugins
  version           Print out ffx tool and daemon versions

You can use fx ffx help <subcommand> or fx ffx <subcommand> --help to see more about any subcommand.

Interacting with target devices

In a terminal, run the following:

fx ffx target list

You'll see a list of devices that ffx has discovered. For example, with a single emulator running, output looks like:

NAME                    SERIAL       TYPE       STATE      ADDRS/IP                       RCS
fuchsia-emulator  <unknown>    Unknown    Product    [fe80::5054:ff:fe63:5e7a%4]    N

RCS: Indicates whether there is a reachable instance of the Remote Control Service (RCS) running on the device.

In order to get ffx to automatically connect to a device, you must either have set the target's nodename to be the default target, or attempt to interact with the device.

To set the target to be the default, run:

fx ffx target default set $NODENAME

If the default target has been set prior to starting the daemon, waiting a few seconds should yield a change to the RCS status to show Y.

If the default target has been set after starting the daemon, attempting to interact with the target should be sufficient to kick off a connection, like the following

fx ffx component list

Then the next time you list targets you should see that an RCS connection is active.

$ fx ffx target list
NAME                    SERIAL       TYPE       STATE      ADDRS/IP                       RCS
fuchsia-emulator  <unknown>    Unknown    Product    [fe80::5054:ff:fe63:5e7a%4]    Y

If a target has been set as default there will be a * next to it.

If you had ffx log running, you should also see something like the following in the logs:

[00009.776170][28540][28542][remote-control, remote_control_bin] INFO: published remote control service to overnet

NOTE: if the RCS column remains N for an extended amount of time and you have already set this target's nodename to target.default before initially starting ffx, reach out to the ffx team.

On Default Targets

Above we covered setting the default target using the command

fx ffx target default set

It is also possible to set the default target on a per-command basis using the --target flag like so.

fx ffx --target $NODENAME component list

Interacting with multiple devices

TODO: fill this out.

Controlling the state of target devices

You can use the target off and target reboot subcommands to power-off or reboot a device, respectively.

ffx logs


Logs normally go to a cache directory (on Linux, usually $HOME/.local/share/Fuchsia/ffx/cache/logs). The location can be found by running

fx ffx config get log.dir

However, the location can be overridden with -o/--log-output <destination>, where <destination> can be a filename, or stdout (by specifying stdout or -), or stderr (by specifying stderr).

Log Level

The debugging level can be specified with -l/--log-level <level>, where <level> is one of off, error, warn, info, debug, or trace. The default is info.

It can also be permanently set by configuring log.level, e.g.:

fx ffx config set log.level debug

Interactive Use

A common use of the above options is to see debugging for a specific command:

fx ffx -l debug -o - target echo

The above command will produce debugging logs on the command line as part of the invocation.

Target Levels

Specific log "targets" can have a different level, by specifying configuration entries under log.target_levels. For instance, to see debug logs only for analytics:

fx ffx config set debug

Log "targets" are simply prefixes to a log line.


See documentation for the config command.

Interacting with Components


Many ffx commands that use components take monikers as a parameter. You can read more about monikers and their syntax in component moniker documentation.

Finding components

The component list command will output monikers of all components that currently exist in the component topology.

$ fx ffx component list

You can use the component select capability command to search for components that use/expose a capability with a given name.

The following command will display all components that use/expose the diagnostics capability:

$ fx ffx component capability diagnostics

Inspecting a component

You can use the component show command to get detailed information about a specific component.

component show allows partial matching on URL, moniker and component instance ID.

The following command will display information about the /core/network/dhcpd component:

$ fx ffx component show dhcpd
               Moniker:  /core/network/dhcpd
                   URL:  #meta/
           Instance ID:  20b2c7aba6793929c252d4e933b8a1537f7bfe8e208ad228c50a896a18b2c4b5
                  Type:  CML Component
       Component State:  Resolved
 Incoming Capabilities:  /svc/
  Exposed Capabilities:
           Merkle root:  521109a2059e15acc93bf77cd20546d106dfb625f2d1a1105bb71a5e5ea6b3ca
       Execution State:  Running
          Start reason:  '/core/network/netcfg' requested capability ''
         Running since:  2022-09-15 16:07:48.469094140 UTC
                Job ID:  28641
            Process ID:  28690
 Outgoing Capabilities:

Verifying capability routes

You can use the component doctor command to verify that all capabilities exposed and used by a component are successfully routed.

For example:

$ fx ffx component doctor /bootstrap/archivist
Querying component manager for /bootstrap/archivist
URL: fuchsia-boot:///#meta/
Instance ID: None

      Used Capability                      Error
 [✓]  fuchsia.boot.ReadOnlyLog             N/A
 [✓]  fuchsia.boot.WriteOnlyLog            N/A
 [✓]  fuchsia.component.DetectBinder       N/A
 [✓]  fuchsia.component.KcounterBinder     N/A
 [✓]  fuchsia.component.PersistenceBinder  N/A
 [✓]  fuchsia.component.SamplerBinder      N/A
 [✓]  fuchsia.sys.internal.ComponentEvent  N/A
 [✓]  fuchsia.sys.internal.LogConnector    N/A
 [✓]  config-data                          N/A

      Exposed Capability                   Error
 [✓]  fuchsia.diagnostics.FeedbackArchive  N/A
 [✓]  fuchsia.diagnostics.LegacyMetricsAr  N/A
 [✓]  fuchsia.diagnostics.LoWPANArchiveAc  N/A
 [✓]  diagnostics                          N/A
 [✓]  fuchsia.diagnostics.ArchiveAccessor  N/A
 [✓]  fuchsia.diagnostics.LogSettings      N/A
 [✓]  fuchsia.logger.Log                   N/A
 [✓]  fuchsia.logger.LogSink               N/A
$ fx ffx component doctor /core/feedback
Querying component manager for /core/feedback
URL: fuchsia-pkg://
Instance ID: eb345fb7dcaa4260ee0c65bb73ef0ec5341b15a4f603f358d6631c4be6bf7080

      Used Capability                      Error
 [✓]  fuchsia.boot.ReadOnlyLog             N/A
 [✓]  fuchsia.boot.WriteOnlyLog            N/A
 [✓]  fuchsia.diagnostics.FeedbackArchive  N/A
 [✓]  fuchsia.hardware.power.statecontrol  N/A
 [✓]  fuchsia.hwinfo.Board                 N/A
 [✓]  fuchsia.hwinfo.Product               N/A
 [✓]  fuchsia.metrics.MetricEventLoggerFa  N/A
 [✓]              N/A
 [✓]  fuchsia.process.Launcher             N/A
 [✓]  fuchsia.sysinfo.SysInfo              N/A
 [✓]  fuchsia.ui.activity.Provider         N/A
 [✗]    `/core/feedback` tried to use `` from its parent,
                                           but the parent does not offer that capability. Note, use clauses in CML default to
                                           using from parent.

Running a component

The component run command can create and launch components in a given isolated collection.

Here's an example of running the Rust hello-world component in the /core/ffx-laboratory collection. First, you'll need the hello-world package in your universe:

$ fx set <product>.<board> --with //examples/hello_world/rust:hello-world-rust && fx build

Then use the component run command to create and launch a component instance from the URL fuchsia-pkg:// with the moniker /core/ffx-laboratory:hello-world-rust:

$ fx ffx component run /core/ffx-laboratory:hello-world-rust fuchsia-pkg://
URL: fuchsia-pkg://
Moniker: /core/ffx-laboratory:hello-world-rust
Creating component instance...
$ fx ffx component show hello-world-rust
               Moniker: /core/ffx-laboratory:hello-world-rust
                   URL: fuchsia-pkg://
                  Type: v2 dynamic component
       Execution State: Running
                Job ID: 50775
            Process ID: 50819

Resolving connectivity issues

If you're experiencing problems communicating with a target device using ffx, you can use the doctor command to diagnose and attempt to resolve them. If you file a bug that involves a target device, we'll typically ask for the output from ffx doctor to provide information about where the problem is.

doctor will attempt to communicate with the ffx daemon, killing and restarting it if needed. If this is successful, it will attempt to SSH into a target device and start the Remote Control Service.

If you try running ffx doctor under normal circumstances, you should see:

$ fx ffx doctor
Checking for a running daemon...none running.
Attempting to kill any zombie daemons...killed at least one daemon.
Starting a new daemon instance...success
Attempting to connect to the daemon. This may take a couple seconds...success
Attempting to communicate with the daemon...success
Attempting to list targets...success
Attempting to get an RCS connection...success
Attempting to communicate with RCS...success

SUCCESS. You should be able to run ffx commands now.

If doctor fails, it will try to suggest a resolution to the problem. You can file a bug for the ffx team if you persistently have problems. For example, if doctor is unable to start the RCS, you would see the following:

$ fx ffx doctor
Checking for a running daemon...found
Attempting to connect to the daemon. This may take a couple seconds...success
Attempting to communicate with the daemon...success
Attempting to list targets...success
Attempting to get an RCS connection...success
Attempting to communicate with RCS...FAILED. Timed out.

Attempt 2 of 3
Attempting to list targets...success
Attempting to get an RCS connection...success
Attempting to communicate with RCS...FAILED. Timed out.

Attempt 3 of 3
Attempting to list targets...success
Attempting to get an RCS connection...success
Attempting to communicate with RCS...FAILED. Timed out.

Connecting to RCS failed after maximum attempts. To resolve this issue, try
rebooting your device. If this persists, please file a bug at the link below
and include 1) all output
above and 2) device syslog if available.Bug link: ...

Testing with ffx

The ffx command is useful when writing integration tests which need to interact with the Fuchsia environment. However, since ffx is primarily designed for developers, it inspects the current environment for configuration and also starts a daemon in the background to coordinate communication with Fuchsia devices. This makes it more complex to write automated tests that use ffx since the configuration and daemon should be isolated in order to avoid side effects, or interference from the global environment.

To achieve this isolation, test authors need to use isolate directories when running tests which use ffx.

Next steps