docs/development/workflows/fx.md

# fx workflows

`fx` is the front-door to a collection of scripts that make many tasks
related to Fuchsia development easier. It contains a large number of
subcommands, which can be discovered by running `fx help`. If you use `bash`
or `zsh` as a shell, you can get some auto-completion for `fx` by sourcing
`scripts/fx-env.sh` into your shell.

## Setting up fx

It is strongly recommended that you `source scripts/fx-env.sh` into your
shell. This is tested and regularly used with Bash and ZSH. It may work for
other compatible shells.

```shell
# In your fuchsia checkout:
$ cd fuchsia
# Add a configuration to your shell to include fx-env.sh
$ echo "source \"$PWD/scripts/fx-env.sh\"" >> "$HOME/.$(basename "$SHELL")rc"
# If you would like additional convenience tools from the Fuchsia scripts, also
# optionally run the following:
$ echo "fx-update-path" >> "$HOME/.$(basename "$SHELL")rc"
# Restart your shell
$ exec "$SHELL"
```

The above method provides the most well defined feature set, and should be
generally non-invasive. If it causes bugs in your shell environment, please
file project bugs.

If for some reason you need to work with multiple Fuchsia checkouts
(recommended workflows below should obviate such a need), then you may wish
to do something other than the above. In this case, there are a few well
supported methods:

* Always execute `$FUCHSIA_DIR/scripts/fx` explicitly
* Use something like a cdenter or dotenv feature to add
  `$FUCHSIA_DIR/.jiri_root/bin` to your `$PATH` while working in a particular
  Fuchsia directory.

It is NOT recommended (though presently works) to copy `fx` to other places,
such as `~/bin/fx` (as this could one day break), or to add
`$FUCHSIA_DIR/scripts` to your `$PATH` (as reviewers of code in `//scripts`)
do not block the addition of files in that directory which could lead to
unpredictable behaviors (for example, that directory contains binaries with
generic names like "bootstrap" which may unintentionally override the
behavior of other systems).

## Common Daily Tools

The first thing you will want to do after checking out a Fuchsia tree is to
build Fuchsia, and then get it onto a device. `fx` has some commands to help
with this:

* `fx set` [configure a build](#configure-a-build)
* `fx build` [execute a build](#execute-a-build)
* `fx flash ; fx mkzedboot` [flash a target; or prepare a zedboot USB key](#flash-a-board)
* `fx serve` [serve a build](#serve-a-build)
* `fx update` [update a target](#update-a-target-device)
* `fx run-test` [execute tests](#execute-tests)
* `fx shell` [connect to a target shell](#connect-to-a-target-shell)
* [and many other small tasks](#performing-other-common-tasks)

First let's configure the build. To do this we need to make a few choices:

* What [Product configuration](#key-product-configurations) do you want?
  (unsure: try `workstation`)
* What board are you building for? (unsure: try `x64`)
* What extra [Bundles](#key-bundles) do you want? (unsure: try `tools`, and if
  you're working on features, you probably want `tests`)

## Configure a build

*We are working on a new command for configuring a build. This section describes
the new command, which is currently being beta-tested.*

Armed with our above choices (if you didn't read above, do so now), you are
ready to configure your build:

```shell
$ fx set workstation.x64 --with //bundles:tools,//bundles:tests
```

This command stores the configuration in an `args.gn` file in the build
directory (which is `out/default` by default). You can edit this file using the
`fx args` command to create more elaborate configurations.

### What just happened?

* We selected the architecture `x64`
* We selected the product `workstation` (run `fx list-products` for a list of
  other product configurations)
* We selected the board `x64` (on arm64 boards, the board choice is very
  important! Run `fx list-boards` for a list of board configurations)
* We selected to "preinstall" various developer tools, this includes many basic
  tools like `cat` and `ls`, as well as more advanced tools, such as `trace`.
* We selected to build "tests", but not have them included in our
  [Paving](#what-is-paving) images.

So what are `base`, `cache` and `universe`? (new names)
So what are `monolith`, `preinstall` and `available`? (deprecated names)

Configurations ultimately specify dependencies (mostly packages) that
contribute to output artifacts of the build (mostly images and package
repositories). The build is parameterized to determine which dependencies
(mostly packages) are added to which output artifacts (images or package
repositories). The three axes are called "base", "cache", and "universe"
(previously called "monolith", "preinstall", and "available"):

* *Base* (*Monolith*): Packages that are added to the monolith are included in
  [Paving](#what-is-paving) images produced by the build. They are included
  in over-the-air updates, and are always updated as a single unit. Packages
  in the monolith can not be evicted from a device at runtime - they encode
  the minimum possible size of a configuration.
* *Cache* (*Preinstall*): Packages in preinstall are included in
  [Paving](#what-is-paving) images, but they are not included in over-the-air
  system updates, and are allowed to be evicted from the system in response
  to resource demands, such as disk-space pressure. Packages in preinstall
  can be updated at any time that updates are available, and each of
  these packages may be updated independently. This is software that is
  "optional", but is good to have available instantly "out of the box".
* *Universe* (*Available*): Packages in available are additional optional
  packages that can be fetched and run on-demand, but are not pre-baked into
  any [Paving](#what-is-paving) images.

The "board" and "product" configurations pick a predefined set of members for
each of these package sets. Most commonly the board configurations specify a
set of boot-critical drivers to add to the monolith package set, and could
for example include some optional but common peripheral drivers in the
preinstall set. The board configuration may also include some board-specific
development tools (more commonly host tools, rather than target packages) for
interacting with the board in "available". The product configurations make
choices to add more or less software to the monolith, preinstall or available
package sets based on the definition and feature set of the product they
represent. A speaker product, for example, adds many audio-media-related
packages to the monolith. A workstation product adds a wide range of GUI,
media and many other packages to the monolith.

### Key product configurations

There are many more than below, but the following three particularly
important configurations to be familiar with:

* `bringup` is a minimal feature set product that is focused on being very
  simple and very lean. It exists to provide fast builds and small images
  (primarily used in a [netboot](#what-is-netbooting) rather than
  [paved](#what-is-paving) fashion), and is great for working on very
  low-level facilities, such as the Zircon kernel or board-specific drivers
  and configurations. It lacks most network capabilities, and therefore is
  not able to add new software at runtime or upgrade itself.
* `core` is a minimal feature set that can install additional software (such as
  items added to the "available" build group). It is the starting point for
  all higher-level product configurations. It has common network capabilities
  and can update a system over-the-air.
* `workstation` is a basis for a general purpose development environment, good
  for working on UI, media and many other high-level features. This is also
  the best environment for enthusiasts to play with and explore.

### Key bundles

As with products, there are many more, but the following bundles are most
important to be familiar with:

* `tools` contains a broad array of the most common developer tools. This
  includes tools for spawning components from command-line shells, tools for
  reconfiguring and testing networks, making http requests, debugging programs,
  changing audio volume, and so on.
* `tests` causes all test programs to be built. Most test programs can be
  invoked using `run-test-component` on the device, or via `fx run-test`.
* `kitchen_sink` is a target that causes all other build targets to be
  included. It is useful when testing the impact of core changes, or when
  making large scale changes in the code base. It also may be a fun
  configuration for enthusiasts to play with, as it includes all software
  available in the source tree. Note that kitchen sink will produce more than
  20GB of build artifacts and requires at least 2GB of storage on the target
  device (size estimates from Q1/2019).

## Execute a build

For most use cases, only `fx build` is needed. The build is optimized
for fast incremental rebuilds, as such, repeating this command does the
minimal work required after code has been changed, and no work if the source
files are unchanged.

Additionally to `fx build`, a few other build related commands provide
more granular control:

* `fx build-zircon` builds only the Zircon portion of the build.
* `fx build` builds only the Fuchsia portion (all above Zircon, but not Zircon
  itself) of the build.
* `fx clean` clear out all build artifacts.
* `fx clean-build` perform a clean, then a build.
* `fx gen` repeat the `gn gen` process that `fx set` performed. Users making
  fine grained build argument changes (e.g. by editing `args.gn` directly) can
  run `fx gen` to reconfigure their build.

### Building a specific target

`fx build` can be given the name of a specific target or file to build. For
example, a target with the label `//foo/bar:blah` can be built with
`fx build foo/bar:blah`.

Note that this only works for targets declared in the default GN toolchain. For
targets in other toolchains, the path of an output file may be used instead. For
example, an executable target with the label
`//foo/bar:blah(//build/toolchain:host_x64)` can be built with
`fx build <output_dir>/host_x64/blah`.

## Flash a board / Prepare Zedboot

The exact preparation required to put Fuchsia onto a target device varies by
specific device, but there are two general groups in common use today, made
convenient behind `fx` commands:

* `fx flash` is used with most `arm64` devices to perform a raw write of
  Zedboot to the device, preparing it for [Paving](#what-is-paving).
* `fx mkzedboot` is used with most `x64` devices to prepare a bootable USB key
  that boots into Zedboot, preparing the device for [Paving](#what-is-paving).

### What is Zedboot?

Zedboot is a special configuration of Zircon that contains a simple network
stack, a simple device advertisement and discovery protocols, and a suite of
protocols to write Fuchsia to a target disk and/or to network boot a target
system. Zedboot is a term used for both the overall process, as well as a
special build configuration. Many people come to know it as "the blue screen
with ASCII art".

To enter Zedboot on an arm64 target, power on the device while triggering a
boot into fastboot flashing mode (often this involves holding a particular
button while rebooting or powering on that varies by particular hardware
target). Once in flashing mode, execute `fx flash` on the host system.

To enter Zedboot on an x64 target, first produce a Zedboot USB key using
`fx mkzedboot <path-to-usb-device>` (to list suitable USB devices on your
system, execute `fx list-usb-disks`). Remove the USB key after completion,
insert it to the target device, and reboot the target device, selecting "Boot
from USB" from the boot options, or in the device BIOS. There are additional
instructions for preparing a
[Pixelbook](../hardware/pixelbook.md).

### What is Paving?

Paving is in many ways similar to "flashing" from other worlds, however, it
has some differences. Specifically, paving refers to a group of processes and
protocols in Fuchsia to transfer a set of artifacts to a target system that
will be written into various partitions on a target system. By contrast, the
process of "flashing" is more of a raw process of writing a raw data stream
to a raw disk device, and not strictly partition-oriented.

Users can start a paving process by first flashing Zedboot using `fx flash`,
or by booting a Zedboot USB key made by `fx mkzedboot`, then executing `fx pave`
on the host system. In general most users actually will want to use `fx serve`
instead of `fx pave`. `fx serve` is covered in the [next section](#serve).

### What is Netbooting?

In Fuchsia, "netboot" refers to sending a set of artifacts to a Zedboot
instance that instead of making changes to the disk, will just be booted from
RAM. Users can perform a "netboot" by first booting a device into Zedboot by
using either `fx flash` (arm64) or `fx mkzedboot` (x64), and then executing
`fx netboot` on the host system.

Note: the `netboot` artifacts are not produced by all builds by default,
because for larger builds such as the "workstation" product configuration
such builds are extremely large, and producing them many times a day is both
slow as well as measurably wearing on host disk hardware. The `bringup`
configuration always prepares `netboot` artifacts. For all other build
configurations, a user can optionally build the netboot artifacts using
`fx build netboot`.

## Serve a build

A lot of build configurations for Fuchsia include software that is not
immediately included in the base images that a build produces, that are
written to devices during paving. Such software is instead made available to
target devices on-demand, which is often colloquially referred to as
"ephemeral software".

The command `fx serve` performs two functions internally:

* `fx pave` start a paving server, used for "fresh installs" of a Fuchsia
  device from a Zedboot state.
* `fx serve-updates` start a package repository server, used for dynamic
  installation of software at runtime, as well as whole-system updates.

Internally the `fx serve-updates` command also searches for a device to
configure, and upon discovery (which may be restricted/modulated with
`fx set-device` or `fx -d`) the target device is configured to use the
repository server as a source of dynamic packages and system updates.

## Update a target device

As described in prior sections, there are different groups of software on a
Fuchsia device:

* Software that is part of the core system "monolith", that is updated in a
  single transaction.
* Software that is part of Zedboot images other than the monolith (preinstall)
  that can be updated ephemerally.
* Software that is always ephemeral.

For new user development workflows, the most general command to assist with
updating a target device is `fx update`. The `fx update` command first
updates all "preinstall" software, and then performs an `fx ota` or, a core
system update. This command reboots the target device when it is complete.
The end result of this process should be indistinguishable in terms of
software versions from performing a fresh pave of a device.

As the `fx update` process causes a device reboot, it is sometimes not the
most efficient process for diagnosis, debugging or other non-testing based
workflows or needs. In these cases a user has some options for how to ensure
that software on a device is being regularly updated.

The `fx serve` process configures a Fuchsia software repository with
automatic update features. The repository informs the target device of newly
updated software every time the underlying repository is updated (which
happens at the end of every successful `fx build`). For many software
components, the easiest way to update them during development is to ensure
that they are not included in the monolith set, but instead included in
either "preinstall" or "available". In that case, simply restarting the
software on the target (e.g. by closing it completely, or by invoking
`killall`) will result in the software being immediately updated when it is
started again.

The commands `fx push-package` and `fx build-push` perform manual, forceful
updates of packages on a target device. These commands do not however know
how to re-start software on the device, as such they provide little benefit
over simply restarting software correctly which, along with `fx serve`, will
cause software to be updated as a natural course of restarting. These
commands are sometimes used to diagnose issues, or in cases where automatic
updates are disabled in special build configurations.

Note: some software may not appear to be updating because it is being run
inside of a "runner" process or some other surrounding environment that is
"holding on" to resources for the previous package version, only spawning
programs from the old package. As packages in Fuchsia are immutable and
content-addressed, when host environments retain resources in this manner,
there is nothing that the update system can do to forcefully trigger updates
in the rest of the system. Users who find themselves with this issue mostly
need to find efficient workflow methods to fully restart the relevant
software stack.

XXX: TODO: NEEDED: simple example command to restart all GUI / shell
components, e.g. if basemgr spawned things under a job or a component
topology, a method to restart that topology (e.g. `killall basemgr.cmx`,
however that's no good today).

## Execute tests

The Fuchsia codebase contains many tests. Most of these tests are themselves
Components, and can be launched on the target device in the same way as other
components. On the target device, some programs also assist with test
specific concerns for component launching, such as `runtests` and
`/bin/run-test-component`. The process can also conveniently be controlled
from the development host by way of `fx run-test`.

The command `fx run-test <package-name>` requires the user to specify a
particular package name to execute. A package may contain one or more tests.
Arguments after `fx run-test package-name` are passed to the program
`runtests`. One particularly common use case is to execute:
`fx run-test <package-of-many-tests> -t <name-of-one-test>` to execute only a
single test.

Some users find that an effective high focus workflow is to have the system
build, push and execute tests whenever they save their source code. This can
be achived with `fx` very easily, for example:

```shell
$ fx -i run-test rolldice-tests
```

The above command will execute the rolldice tests every time a change is made
to the source code in the tree. The `-i` flag to `fx` causes `fx` to repeat
the rest of it's command every time the source code in the tree is changed.
As the `fx run-test` command first performs a build, then executes a test on
a target, this combination provides a convenient auto-test loop, great for
high focus workflows like test driven development.

## Connect to a target shell

Most [product configurations](#key-product-configurations) include an SSH
server with a Fuchsia specific configuration. The command `fx shell` is a
convenient wrapper to connect to the target device over SSH and provides
access to a very simply POSIX-style shell. Users should note that while the
shell is a fork of a POSIX shell, it does not provide all features of a
common Unix shell. In particular users will find that CTRL+C has odd quirks,
and may often find quirks for sub-shell expressions and certain more advanced
IO redirections or environment variable propagations. These misfeatures are
side effects of Fuchsia not being a POSIX system.

Nonetheless the shell made available via `fx shell` is extremely useful for
imperatively executing programs on the Fuchsia target, as well as exploring
some of the diagnostic / debug interfaces made available in a filesystem
tree, such as `/hub` and `/dev`. It is also useful for invoking programs such
as `/bin/run` that provides facilities for launching Fuchsia components. If
the `tools` bundle is available in the build configuration, many tools common
to unix shell environments have been ported and are available, such as `ps`,
`ls`, `cat`, `curl`, `vim`, `fortune` and so on.

## Performing other common tasks

### Getting logs

`fx syslog` captures all logs from low-level and high-level programs,
including the kernel, drivers and other userspace programs. `fx syslog`
depends upon a working high level network stack and SSH. As such, `fx syslog`
does not work with Zedboot or "bringup" product configurations. If a device
is in a state where `fx syslog` ceases to function, it is often useful to
switch to `fx log` to capture more information about probable causes.

`fx log` captures only a low-level log stream called "klog". The klog stream
includes logs from the Zircon kernel itself, as well as a subset of userspace
software (most notably drivers and low-level core software). `fx log` depends
on a lightweight network stack called `netsvc` that has a tendency to remain
available even after problems in higher-level software. The netsvc suite is
also always available in "bringup" product configurations, as such, `fx log`
is most useful when working on low-level software, such as the Zircon kernel,
or drivers.

### Copying files

`fx cp` provides a basic wrapper around `scp`, similar to how `fx shell` is a
wrapper around `ssh`.

```shell
# copy ./book.txt from the host, to /tmp/book.txt on the target
$ fx cp book.txt /tmp/book.txt
# copy /tmp/poem.txt on the target to poem.txt on the host
$ fx cp --to-host /tmp/poem.txt poem.txt
```

### Start Fuchsia in QEMU

`fx run` starts a Fuchsia build under QEMU, a general purpose virtual
machine. Users on Linux host systems with KVM can execute `fx run -k` for
significantly improved performance.

The QEMU environment does not support any GUI programs. It also has limiting
network capabilities. Hardware devices are recommended for day-to-day Fuchsia
software development whenever possible.

### Using multiple Fuchsia devices with set-device

Some users will have more than one Fuchsia device on a network, and will want
to limit the effects of various commands to particular of those devices. The
`fx set-device` command exists to help with this use case.

The `fx set-device` command binds a particular device node name to a
particular build directory. This is particularly useful when a user wishes to
keep several different devices in several build configurations, and could be
setup as follows:

```shell
$ fx --dir out/workstation set workstation.x64
$ fx build
$ fx set-device <workstation-node-name>

$ fx --dir out/core set core.arm64
$ fx build
$ fx set-device <core-node-name>

# Start a server for the workstation:
$ fx --dir=out/workstation serve
# Set the default build-dir and target device to the arm64 core, and
# connect to a shell on that device:
$ fx use out/core
$ fx shell
```

Additionally, for users who wish to execute a command against a single
Fuchsia device from the current default build directory, as a one-off
command, the `fx` global flag `-d` allows overriding the target node name for
a single command invocation.

### Reboot a device

`fx reboot`

On some devices (most arm64 devices at present) there are also some useful flags:

* `fx reboot -r` reboot into "recovery" (Zedboot)
* `fx reboot -b` reboot into "bootloader" (Flash)

### Debugging and developing `fx` commands

* `fx -x` the `-x` flag turns on tracing for the `fx` scripts, printing out all
  expressions evaluated during the `fx` invocation.
* `fx exec` executes an abitrary program that follows inside of the current
  `fx` environment. As an example `fx exec env` prints all environment
  variables in that environment (`fx exec env | grep FUCHSIA` is likely of
  interest).

### Getting help with `fx`

`fx help <command>` provides the best introductory documentation for that
command. Some commands also support/provide `fx <command> -h` or
`fx <command> --help`, however this help is not available for all commands.
This is unusual, but is a function of implementation details. Internally many
`fx` commands just run other programs, most often those produced by the
build, and flags are in many cases passed on unaltered to those programs. In
those cases, passing the usual `-h` or `--help` flags may not provide
documentation for `fx <command>`, but instead for the program invoked
downstream of `fx`.

Users should always start with `fx help <command>`.

`fx help` with no other arguments provides a list of all available commands
in `fx`, as well as documentation for `fx` global flags.