move developer documentation from guide.md to service-script-guide.md
This commit is contained in:
William Hubbs
parent
918d955fd2
commit
14e3359a9e
125
guide.md
125
guide.md
|
|
@ -27,8 +27,8 @@ openrc scans the runlevels (default: `/etc/runlevels`) and builds a dependency
|
|||
graph, then starts the needed service scripts, either serialized (default) or in
|
||||
parallel.
|
||||
|
||||
When all the init scripts are started openrc terminates. There is no persistent
|
||||
daemon. (Integration with tools like monit, runit or s6 can be done)
|
||||
When all the service scripts are started openrc terminates. There is no
|
||||
persistent daemon. (Integration with tools like monit, runit or s6 can be done)
|
||||
|
||||
# Shutdown
|
||||
|
||||
|
|
@ -63,7 +63,7 @@ own if needed. This allows, for example, to have a default runlevel with
|
|||
disabled.
|
||||
|
||||
The `rc-status` helper will print all currently active runlevels and the state
|
||||
of init scripts in them:
|
||||
of services in them:
|
||||
|
||||
```
|
||||
# rc-status
|
||||
|
|
@ -74,7 +74,7 @@ Runlevel: default
|
|||
```
|
||||
|
||||
All runlevels are represented as folders in `/etc/runlevels/` with symlinks to
|
||||
the actual init scripts.
|
||||
the actual service scripts.
|
||||
|
||||
Calling openrc with an argument (`openrc default`) will switch to that
|
||||
runlevel; this will start and stop services as needed.
|
||||
|
|
@ -83,122 +83,13 @@ Managing runlevels is usually done through the `rc-update` helper, but could of
|
|||
course be done by hand if desired.
|
||||
e.g. `rc-update add nginx default` - add nginx to the default runlevel
|
||||
Note: This will not auto-start nginx! You'd still have to trigger `rc` or run
|
||||
the initscript by hand.
|
||||
the service script by hand.
|
||||
|
||||
FIXME: Document stacked runlevels
|
||||
|
||||
The default startup uses the runlevels `boot`, `sysinit` and `default`, in that
|
||||
order. Shutdown uses the `shutdown` runlevel.
|
||||
|
||||
|
||||
# Syntax of Service Scripts
|
||||
|
||||
Service scripts are shell scripts. OpenRC aims at using only the standardized
|
||||
POSIX sh subset for portability reasons. The default interpreter (build-time
|
||||
toggle) is `/bin/sh`, so using for example mksh is not a problem.
|
||||
|
||||
OpenRC has been tested with busybox sh, ash, dash, bash, mksh, zsh and possibly
|
||||
others. Using busybox sh has been difficult as it replaces commands with
|
||||
builtins that don't offer the expected features.
|
||||
|
||||
The interpreter for initscripts is `#!/sbin/openrc-run`.
|
||||
Not using this interpreter will break the use of dependencies and is not
|
||||
supported. (iow: if you insist on using `#!/bin/sh` you're on your own)
|
||||
|
||||
A `depend` function declares the dependencies of this service script.
|
||||
All scripts must have start/stop/status functions, but defaults are provided.
|
||||
Extra functions can be added easily:
|
||||
|
||||
```
|
||||
extra_commands="checkconfig"
|
||||
checkconfig() {
|
||||
doSomething
|
||||
}
|
||||
```
|
||||
|
||||
This exports the checkconfig function so that `/etc/init.d/someservice
|
||||
checkconfig` will be available, and it "just" runs this function.
|
||||
|
||||
While commands defined in `extra_commands` are always available, commands
|
||||
defined in `extra_started_commands` will only work when the service is started
|
||||
and those defined in `extra_stopped_commands` will only work when the service is
|
||||
stopped. This can be used for implementing graceful reload and similar
|
||||
behaviour.
|
||||
|
||||
Adding a restart function will not work, this is a design decision within
|
||||
OpenRC. Since there may be dependencies involved (e.g. network -> apache) a
|
||||
restart function is in general not going to work.
|
||||
restart is internally mapped to `stop()` + `start()` (plus handling dependencies).
|
||||
If a service needs to behave differently when it is being restarted vs
|
||||
started or stopped, it should test the `$RC_CMD` variable, for example:
|
||||
|
||||
```
|
||||
[ "$RC_CMD" = restart ] && do_something
|
||||
```
|
||||
|
||||
# The Depend Function
|
||||
|
||||
This function declares the dependencies for a service script. This
|
||||
determines the order the service scripts start.
|
||||
|
||||
```
|
||||
depend() {
|
||||
need net
|
||||
use dns logger netmount
|
||||
want coolservice
|
||||
}
|
||||
```
|
||||
|
||||
`need` declares a hard dependency - net always needs to be started before this
|
||||
service does
|
||||
|
||||
`use` is a soft dependency - if dns, logger or netmount is in this runlevel
|
||||
start it before, but we don't care if it's not in this runlevel.
|
||||
`want` is between need and use - try to start coolservice if it is
|
||||
installed on the system, regardless of whether it is in the
|
||||
runlevel, but we don't care if it starts.
|
||||
|
||||
`before` declares that we need to be started before another service
|
||||
|
||||
`after` declares that we need to be started after another service, without
|
||||
creating a dependency (so on calling stop the two are independent)
|
||||
|
||||
`provide` allows multiple implementations to provide one service type, e.g.:
|
||||
`provide cron` is set in all cron-daemons, so any one of them started
|
||||
satisfies a cron dependency
|
||||
|
||||
`keyword` allows platform-specific overrides, e.g. `keyword -lxc` makes this
|
||||
service script a noop in lxc containers. Useful for things like keymaps,
|
||||
module loading etc. that are either platform-specific or not available
|
||||
in containers/virtualization/...
|
||||
|
||||
FIXME: Anything missing in this list?
|
||||
|
||||
# The Default Functions
|
||||
|
||||
All service scripts are assumed to have the following functions:
|
||||
|
||||
```
|
||||
start()
|
||||
stop()
|
||||
status()
|
||||
```
|
||||
|
||||
There are default implementations in `lib/rc/sh/openrc-run.sh` - this allows very
|
||||
compact service scripts. These functions can be overridden per service script as
|
||||
needed.
|
||||
|
||||
The default functions assume the following variables to be set in the service
|
||||
script:
|
||||
|
||||
```
|
||||
command=
|
||||
command_args=
|
||||
pidfile=
|
||||
```
|
||||
|
||||
Thus the 'smallest' service scripts can be half a dozen lines long
|
||||
|
||||
# The Magic of `conf.d`
|
||||
|
||||
Most service scripts need default values. It would be fragile to
|
||||
|
|
@ -217,7 +108,7 @@ start() {
|
|||
}
|
||||
```
|
||||
|
||||
The big advantage of this split is that most of the time editing of the init
|
||||
The big advantage of this split is that most of the time editing of the service
|
||||
script can be avoided.
|
||||
|
||||
# Start-Stop-Daemon
|
||||
|
|
@ -271,7 +162,7 @@ happen automatically when the service is stopped.
|
|||
|
||||
# Caching
|
||||
|
||||
For performance reasons OpenRC keeps a cache of pre-parsed initscript metadata
|
||||
For performance reasons OpenRC keeps a cache of pre-parsed service metadata
|
||||
(e.g. `depend`). The default location for this is `/${RC_SVCDIR}/cache`.
|
||||
|
||||
The cache uses `mtime` to check for file staleness. Should any service script
|
||||
|
|
@ -281,5 +172,5 @@ change it'll re-source the relevant files and update the cache
|
|||
|
||||
OpenRC has wrappers for many common output tasks in libeinfo.
|
||||
This allows to print colour-coded status notices and other things.
|
||||
To make the output consistent the bundled initscripts all use ebegin/eend to
|
||||
To make the output consistent the bundled service scripts all use ebegin/eend to
|
||||
print nice messages.
|
||||
|
|
|
|||
|
|
@ -13,6 +13,115 @@ don't consider anything exotic, and assume that you will use
|
|||
start-stop-daemon to manage a fairly typical long-running UNIX
|
||||
process.
|
||||
|
||||
## Syntax of Service Scripts
|
||||
|
||||
Service scripts are shell scripts. OpenRC aims at using only the standardized
|
||||
POSIX sh subset for portability reasons. The default interpreter (build-time
|
||||
toggle) is `/bin/sh`, so using for example mksh is not a problem.
|
||||
|
||||
OpenRC has been tested with busybox sh, ash, dash, bash, mksh, zsh and possibly
|
||||
others. Using busybox sh has been difficult as it replaces commands with
|
||||
builtins that don't offer the expected features.
|
||||
|
||||
The interpreter for service scripts is `#!/sbin/openrc-run`.
|
||||
Not using this interpreter will break the use of dependencies and is not
|
||||
supported. (iow: if you insist on using `#!/bin/sh` you're on your own)
|
||||
|
||||
A `depend` function declares the dependencies of this service script.
|
||||
All scripts must have start/stop/status functions, but defaults are provided and should be used unless you have a very strong reason not to use them.
|
||||
|
||||
Extra functions can be added easily:
|
||||
|
||||
```
|
||||
extra_commands="checkconfig"
|
||||
checkconfig() {
|
||||
doSomething
|
||||
}
|
||||
```
|
||||
|
||||
This exports the checkconfig function so that `/etc/init.d/someservice
|
||||
checkconfig` will be available, and it "just" runs this function.
|
||||
|
||||
While commands defined in `extra_commands` are always available, commands
|
||||
defined in `extra_started_commands` will only work when the service is started
|
||||
and those defined in `extra_stopped_commands` will only work when the service is
|
||||
stopped. This can be used for implementing graceful reload and similar
|
||||
behaviour.
|
||||
|
||||
Adding a restart function will not work, this is a design decision within
|
||||
OpenRC. Since there may be dependencies involved (e.g. network -> apache) a
|
||||
restart function is in general not going to work.
|
||||
restart is internally mapped to `stop()` + `start()` (plus handling dependencies).
|
||||
If a service needs to behave differently when it is being restarted vs
|
||||
started or stopped, it should test the `$RC_CMD` variable, for example:
|
||||
|
||||
```
|
||||
[ "$RC_CMD" = restart ] && do_something
|
||||
```
|
||||
|
||||
## The Depend Function
|
||||
|
||||
This function declares the dependencies for a service script. This
|
||||
determines the order the service scripts start.
|
||||
|
||||
```
|
||||
depend() {
|
||||
need net
|
||||
use dns logger netmount
|
||||
want coolservice
|
||||
}
|
||||
```
|
||||
|
||||
`need` declares a hard dependency - net always needs to be started before this
|
||||
service does
|
||||
|
||||
`use` is a soft dependency - if dns, logger or netmount is in this runlevel
|
||||
start it before, but we don't care if it's not in this runlevel.
|
||||
`want` is between need and use - try to start coolservice if it is
|
||||
installed on the system, regardless of whether it is in the
|
||||
runlevel, but we don't care if it starts.
|
||||
|
||||
`before` declares that we need to be started before another service
|
||||
|
||||
`after` declares that we need to be started after another service, without
|
||||
creating a dependency (so on calling stop the two are independent)
|
||||
|
||||
`provide` allows multiple implementations to provide one service type, e.g.:
|
||||
`provide cron` is set in all cron-daemons, so any one of them started
|
||||
satisfies a cron dependency
|
||||
|
||||
`keyword` allows platform-specific overrides, e.g. `keyword -lxc` makes this
|
||||
service script a noop in lxc containers. Useful for things like keymaps,
|
||||
module loading etc. that are either platform-specific or not available
|
||||
in containers/virtualization/...
|
||||
|
||||
FIXME: Anything missing in this list?
|
||||
|
||||
## The Default Functions
|
||||
|
||||
All service scripts are assumed to have the following functions:
|
||||
|
||||
```
|
||||
start()
|
||||
stop()
|
||||
status()
|
||||
```
|
||||
|
||||
There are default implementations in `lib/rc/sh/openrc-run.sh` - this allows very
|
||||
compact service scripts. These functions can be overridden per service script as
|
||||
needed.
|
||||
|
||||
The default functions assume the following variables to be set in the service
|
||||
script:
|
||||
|
||||
```
|
||||
command=
|
||||
command_args=
|
||||
pidfile=
|
||||
```
|
||||
|
||||
Thus the 'smallest' service scripts can be half a dozen lines long
|
||||
|
||||
## Don't write your own start/stop functions
|
||||
|
||||
OpenRC is capable of stopping and starting most daemons based on the
|
||||
|
|
|
|||
Loading…
Reference in New Issue
Block a user