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uBus IPC/RPC System
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== uBus - IPC/RPC

uBus is the interconnect system used by most services running on a _LEDE_ setup.
Services can connect to the bus and provide methods that can be called by other services or clients.

There is a CLI that can be used to communicate with services on the bus.

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root@lede:/# ubus
Usage: ubus [<options>] <command> [arguments...]
Options:
-s <socket>:		Set the unix domain socket to connect to
-t <timeout>:		Set the timeout (in seconds) for a command to complete
-S:			Use simplified output (for scripts)
-v:			More verbose output

Commands:
- list [<path>]			List objects
- call <path> <method> [<message>]	Call an object method
- listen [<path>...]			Listen for events
- send <type> [<message>]		Send an event
- wait_for <object> [<object>...]	Wait for multiple objects to appear on ubus
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To find out which services are currently running on the bus simply use the list command. This will show a complete list.

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root@lede:/# ubus list
dhcp
log
network
network.device
network.interface
network.interface.loopback
network.interface.wan
network.interface.wan6
network.wireless
service
system
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To find out which methods a specific service provides also use the list command but add a few more parameters to see a complete list

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root@OpenWrt:/# ubus -v list system
'system' @6b093875
	"board":{}
	"info":{}
	"upgrade":{}
	"watchdog":{"frequency":"Integer","timeout":"Integer","stop":"Boolean"}
	"signal":{"pid":"Integer","signum":"Integer"}
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You can now call a remote method and receive a reply. A reply may be a simple integer return code or a more complete reply. Internally the bus uses a blob format, the CLI conveniently converts this to JSON.

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root@lede:/# ubus call system board
{
	"kernel": "4.4.6",
	"hostname": "lede",
	"system": "MIPS Malta",
	"release": {
		"distribution": "LEDE",
		"version": "HEAD",
		"revision": "3",
		"codename": "designated_driver",
		"target": "malta\/le",
		"description": "LEDE Designated Driver 3"
	}
}
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You can call a method and pass it some parameters by simply appending a JSON structure to the CLI command.
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root@lede:/# ubus call system signal '{ "pid": 123, "signum": 9 }'
root@lede:/# echo $?
0
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