uBus IPC/RPC System

uBus is the interconnect system used by most services running on a OpenWrt 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@OpenWrt:/# 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
 -m <type>:             (for monitor): include a specific message type
                        (can be used more than once)
 -M <r|t>               (for monitor): only capture received or transmitted traffic

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
 - monitor                              Monitor ubus traffic

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

root@OpenWrt:/# ubus list
dhcp
dnsmasq
file
iwinfo
log
luci
luci-rpc
network
network.device
network.interface
network.interface.lan
network.interface.loopback
network.rrdns
network.wireless
service
session
system
uci

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' @651f206c
        "board":{}
        "info":{}
        "reboot":{}
        "watchdog":{"frequency":"Integer","timeout":"Integer","magicclose":"Boolean","stop":"Boolean"}
        "signal":{"pid":"Integer","signum":"Integer"}
        "validate_firmware_image":{"path":"String"}
        "sysupgrade":{"path":"String","force":"Boolean","backup":"String","prefix":"String","command":"String","options":"Table"}

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@OpenWrt:/# ubus call system board
{
        "kernel": "4.9.198",
        "hostname": "OpenWrt",
        "system": "Qualcomm Atheros QCA956X ver 1 rev 0",
        "model": "TP-Link TL-WR1043N\/ND v4",
        "board_name": "tl-wr1043nd-v4",
        "release": {
                "distribution": "OpenWrt",
                "version": "18.06.5",
                "revision": "r7897-9d401013fc",
                "target": "ar71xx\/generic",
                "description": "OpenWrt 18.06.5 r7897-9d401013fc"
        }
}

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

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

Path only contains the first context. E.g. network for network.interface.wan