uBus IPC/RPC System

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.

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

To find out which services are currently running on the bus simply use the list command. This will show a complete list.

root@lede:/# ubus list
dhcp
log
network
network.device
network.interface
network.interface.loopback
network.interface.wan
network.interface.wan6
network.wireless
service
system

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

root@OpenWrt:/# ubus -v list system
'system' @6b093875
        "board":{}
        "info":{}
        "upgrade":{}
        "watchdog":{"frequency":"Integer","timeout":"Integer","stop":"Boolean"}
        "signal":{"pid":"Integer","signum":"Integer"}

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.

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"
        }
}

You can call a method and pass it some parameters by simply appending a JSON structure to the CLI command.

root@lede:/# ubus call system signal '{ "pid": 123, "signum": 9 }'
root@lede:/# echo $?
0