https://github.com/chris2511/meta-s6-rc

Yocto layer adding support for the s6 init system and s6rc
https://github.com/chris2511/meta-s6-rc

init s6 s6-rc yocto-layer

Last synced: about 1 month ago
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Yocto layer adding support for the s6 init system and s6rc

Host: GitHub
URL: https://github.com/chris2511/meta-s6-rc
Owner: chris2511
License: mit
Created: 2021-07-21T21:45:04.000Z (almost 4 years ago)
Default Branch: mickledore
Last Pushed: 2024-06-11T18:49:20.000Z (11 months ago)
Last Synced: 2025-02-01T12:31:15.049Z (3 months ago)
Topics: init, s6, s6-rc, yocto-layer
Language: BitBake
Homepage:
Size: 113 KB
Stars: 5
Watchers: 1
Forks: 1
Open Issues: 0
Metadata Files:
- Readme: README.md
- License: COPYING.MIT

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README

# S6-RC: An alternative to SysV and Systemd

This layer introduces [s6-rc](https://skarnet.org/software/s6-rc) as init system.

## Quickstart

```sh
git clone git://git.yoctoproject.org/poky
(cd poky && git checkout -b kirkstone origin/kirkstone)
git clone https://github.com/chris2511/meta-s6-rc.git
. poky/oe-init-build-env
bitbake-layers add-layer ../meta-s6-rc
TCLIBC = "musl" INIT_MANAGER = "s6" bitbake core-image-minimal
runqemu serialstdio nographic kvm
```

Or as usual put them into your conf/local.conf:
```
TCLIBC = "musl"
INIT_MANAGER = "s6"
```

## Documentation

The S6 system itself is thoroughly documented by its author.

This layer adds the `s6rc.bbclass`, which allows to easily
create new services with dependencies. It populates the
`/etc/s6-rc/tree` directory with services declared by the following
variables:
- S6RC\_BUNDLES, S6RC\_BUNDLE\_% and S6RC\_BUNDLE\_%[ ]
- S6RC\_ONESHOTS and S6RC\_ONESHOT\_%[ ]
- S6RC\_LONGRUNS and S6RC\_LONGRUN\_%[ ] S6RC\_LONGRUN\_%\_log[ ]
- S6RC\_INITD\_SYMLINKS

`s6-init.bb` shows how to use them in practice.
Please read/know about the concepts documented in
[s6-rc-compile](https://skarnet.org/software/s6-rc/s6-rc-compile.html)

The S6RC\_DEBUG\_BOOT variable set to anything != "" allows to debug
the boot sequence by setting the option `-1` when calling
`s6-linux-init-maker`

### Bundles

`S6RC_BUNDLES` contains a space separated list of bundle-names.
Each `S6RC_BUNDLE_%` with % replaced by a bundle name contains a space separated
list of services and bundles that will be written to the
`contents` file of the bundle.

Example:
```
S6RC_BUNDLES = "bundleA bundleB"
S6RC_BUNDLE_bundleA = "service1 service2"
S6RC_BUNDLE_bundleB = "svcx svcy bundleA"
```
will result in
```
/etc/s6-rc/tree/bundleA/type (which contains 'bundle')
/etc/s6-rc/tree/bundleA/contents (which contains 'service1\nservice2')
/etc/s6-rc/tree/bundleB/type (which contains 'bundle')
/etc/s6-rc/tree/bundleB/contents (which contains 'svx\nsvy\nbundleA')
```

Adding bundles, oneshots and longruns to bundles defined in other recipes,
for example the `default` bundle, can be achieved by the
`S6RC_[LONGRUN|ONESHOT|BUNDLE]_[bundles]` variable.
Adding the longrun `dropbear` to the `default` and `network` bundle
is done by
```
S6RC_LONGRUN_dropbear[bundles] = "default networking"
```
Non-existing bundles will be created on-the-fly.

### Atomic services

All regular files recognized by s6-rc-compile can either be directly
added as `S6RC_ONESHOT_runner-a[dependencies] = "runner-b bundle-x"`
or provided as `.` file.
In this example a `runner-a.dependencies` will be used as runner-a/dependencies file verbatim.
This is especially useful for `up` and `run` files, which may become lengthy
and cumbersome to write in one line.

All atomic services may additionally contain the special file `influences`
which is the inverse of `dependencies`:
All atomics listed in `influences` of an other atomic
will depend on the other atomic.

### Oneshots

`S6RC_ONESHOTS` contains a space separated list of oneshot-names.
`S6RC_ONESHOT_%[ ]` declares properties with % replaced by a oneshot-name

Properties for oneshots are those documented in the [s6-rc-compile](https://skarnet.org/software/s6-rc/s6-rc-compile.html):

Example:
```
S6RC_ONESHOTS = "start mount-procsysdev networking"
S6RC_ONESHOT_start[up] = 'echo "init-stage2 starting."'
S6RC_ONESHOT_mount-procsysdev[dependencies] = "start"
```
will result in
```
/etc/s6-rc/tree/start/type (which contains 'oneshot')
/etc/s6-rc/tree/start/up (which contains 'echo "init-stage2 starting."')
/etc/s6-rc/tree/mount-procsysdev/type (which contains 'oneshot')
/etc/s6-rc/tree/mount-procsysdev/dependencies (which contains 'start')
```
An existing file `${S}/mount-procsysdev.up` will be copied verbatim to
`/etc/s6-rc/tree/mount-procsysdev/up`

### Longruns

`S6RC_LONGRUNS` contains a space separated list of longrun-names.
`S6RC_LONGRUN_%[ ]` declares properties with % replaced by a longrun-name

The functionality and behavior is analog to the oneshots, just with the
longrun properties.
The `producer-for` and `consumer-for` entries don't have to appear pairwise.
The s6rc class will resolve missing entries as it does with the `influences`
entry as the reverse of `depends`.
This allows to declare dependencies unidirectional if depending services are
declared in different layers.

#### Filedescriptor storage

Longruns may have an additional verb `filedescriptors`, which is an execline
script, creating filedescriptors via `piperw` or `s6-tcpserver-socketbinder`
and storing them in the new fd-holder service called `fdstore`. It canm be
done as usual as inline declaration or by a `.filedescriptors`
file with `s6-fdholder-store /service/fdstore/s [socket|write|read]:`.

The all-in-one logger of templates also uses this mechanism.

The oneshot `fdstore-fill` executes all `filedescriptors` scripts.
Longruns using this mechanisms must depend on the `fdstorage` bundle
to be sure the descriptors are ready. This is automatically done by the
`s6rc.bbclass`

#### Logging

A log service will always be setup, unless `S6RC_LONGRUN_%[no-log]`
exists. `S6RC_LONGRUN_%_log[]` properties are evaluated
with the following property files:
- name: `-log`
- notification-fd: 3
- consumer-for: ``
- dependencies: mount-temp
- run: `umask {umask} s6-setuidgid {user} s6-log -d3 {script} {dir}`
with {...} replaced by overrideable defaults:
- umask: 0037
- user: logger
- script: `T s100000 n10`
- dir: `/var/log/`

All properties can be overwritten (and not extended) by an explicit
value. For example: `S6RC_LONGRUN_%_log[dependencies] = "mount-temp other"`

Example:
```
S6RC_LONGRUNS = "getty syslogd"
S6RC_LONGRUN_getty[run] = "fdmove -c 2 1 /sbin/getty -L 0 console 2>&1"
S6RC_LONGRUN_getty[dependencies] = "mount-procsysdev hostname"
S6RC_LONGRUN_getty[down-signal] = "9"
S6RC_LONGRUN_syslogd[dependencies] = "mount-procsysdev"
S6RC_LONGRUN_syslogd[notification-fd] = "3"
S6RC_LONGRUN_syslogd_log[user] = "logger"
```
The `syslogd/run` file is expected to be found in "${S}/syslogd.run"

### Templates

`S6RC_TEMPLATES` contains a space separated list of templates that
can be instantiated by the [*rc-dynamic*](#rc-dynamic) command.
`S6RC_TEMPLATE_%[ ]` declares service properties with % replaced by a template-name.
A *run* script is mandatory

A log service will be setup if `S6RC_TEMPLATE_%_log[mode]` exists and contains a valid value. For template services, there are two log modes available "all-in-one" and "per-instance".

With `all-in-one` a single log file service will be setup that can be used to collect the log entries of all service instances. For this to work, the log service stores a file descriptor in the s6-fdholder service `fdstore` that must be retrieved by each service instance.

The file descriptor can be retrieved with `s6-fdholder-retrieve /service/fdstore/s write:${TEMPLATE}-log`. See also [*Filedescriptor storage*](#filedescriptor-storage).
When instantiating templates inside a [*Oneshot*](#oneshots)

The mode `per-instance` creates a minimal log service for each service instance. Stdout will be automatically forwarded to this log service.

## Additional commands

### rc-recompile

After manually modifying the `/etc/s6-rc/tree` the rc-recompile script
will do the `s6-rc-compile, s6-rc-update, symlink` magic
as proposed in [Managing compiled databases](https://skarnet.org/software/s6-rc/faq.html#compiledmanagement)
just that `rc-recompile` toggles between "compiledA" and "compiledB"

### rc-config

usage: `rc-config [enable|disable] `

Adds or removes the given services, oneshots and bundles
to the `default` bundle, which is the default bundle when booting.

It first modifies the source tree in `/etc/s6-rc/tree/default/contents`,
then adds or removes it to the compiled database by
`s6-rc-bundle -f add default ...`
and finally updates the live state by `s6-rc -up -v2 change default`.

### rc-dynamic

usage `rc-dynamic [setup|teardown]

Create an instance from an [S6RC\_TEMPLATE](#templates). The name of the dynamic service is **instance@template**
The template from the directory */etc/s6-rc/templates/* is copied with the whole service name
to */run/service*. An envfile called *env/instance* is created inside the service with 2 variables:
- INSTANCE="\"
- TEMPLATE="\"

The run and finish scripts may source it or the execlie way: *envfile env/instance* it and
use the INSTANCE variable name for starting this specific instance.
An optional executable file in the template: *data/check-instance* may be used to validate
the instance name. It will be called with the instance-name as argument and must exit 0
if the instance is valid. If it exits non-zero, the instance creation fails.

### s6-startstop

The script `/etc/init.d/s6-startstop` is never called directly, but called
via a symlink, which determines the service to act on.
It provides the following subcommands:
- *enable:* permanently enable and start the service
- *disable:* permanently stop and disable the service
- *start:* temporarily start the service and all its dependencies until
reboot. After a reboot it returns to the enabled/disabled state
- *stop:* temporarily stop the service and all its dependencies until reboot.
After a reboot it returns to the enabled/disabled state
- *restart:* same as start, but terminates the service
if it is already running.
- *status:* prints the `s6-svstat` output
- *pid:* prints the pid of the service
- *crashes:* prints the death tally of the service
- *logs:* prints the complete log
- *logf:* does a tail -f of the last logs

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