UCI (Unified Configuration Interface) – Technical Reference

This is the Technical Reference. Please see UCI (Unified Configuration Interface) – Usage

Source code is available here http://git.openwrt.org/project/uci.git

UCI is a small utility written in C (a shell script-wrapper is available as well) and is intended to centralize the whole configuration of a device running OpenWrt. UCI is the successor of the NVRAM based configuration found in the historical OpenWrt branch White Russian and a wrapper for the standard configuration files programs bring with them, like e.g. /etc/network/interfaces, /etc/exports, /etc/dnsmasq.conf, /etc/samba/samba.conf etc.

UCI configuration files are located in the directory /etc/config/
Their documentation can be accessed online in the OpenWrt-Wiki under UCI configuration files.

They can be altered with any text editor or with the command line utility program uci or through various programming APIs (like Shell, Lua and C). The WUI luci e.g. uses Lua to manipulate them.

  • libuci a small library for UCI written in C
    • libuci-lua is a libuci-plugin for Lua which is utilized by e.g. luci

Both are maintained in the same git as UCI.

The functionality is provided by the two packages uci and libuci. The package libuci-lua is also available.

Name Size in Bytes Description
uci 7196 Utility for the Unified Configuration Interface (UCI)
libuci 18765 C library for the Unified Configuration Interface (UCI)
libuci-lua ~6000 libuci-plugin for Lua, e.g. luci makes use of it


path/file file type Description
/sbin/uci binary uci executable
/lib/config/uci.sh shell script Shell script compatibility wrappers for /sbin/uci


path/file file type Description
/lib/libuci.so symlink symlink to libuci.so.xxx
/lib/libuci.so.2011-01-19 binary Library


path/file file type Description
/usr/lib/lua/uci.so binary Library

All uci set, uci add, uci rename and uci delete commands are staged in /tmp/.uci and written to flash at once with uci commit. Note that subsequent calls to uci get before uci commit will return the staged value.

The reload_config script will reload the necessary configurations based on the last uci commit.

This obviously does not apply to people using text editors, but to scripts, guis and other programs working with uci files.

If you want to access or modify uci configuration via ubus, rpcd implements this. It has its own set of commands which are not exactly the same as those in the CLI.

Significantly, it has its own apply/confirm/reload_config mechanism designed to support the LuCI frontend, and it does not do exactly the same thing as the reload_config script. Also, if provided with a ubus_rpc_session as the LuCI does, rather than storing staged changes in /tmp/.uci it stores them in /tmp/run/rpcd/uci-<ubus_rpc_session> (you can get the CLI to use or view these changes with -t/-p/-P).

The LuCI frontend most commonly interacts with UCI via uci.js. This pretends that it has ordinary get/set methods, but these get/set methods do not make calls of the backend, as it maintains its own staged changes (i.e. separate from the staged changes on the backend). The basic flow is:

  • uci.load('someconfig') # loads all of someconfig into memory via ubus
  • uci.set('someconfig', 'somesection', 'someoption', 'somevalue') # adds to the list of changes to someconfig (similar to how staged changes work in the backend)
  • uci.save() # stage the changes in the backend via ubus
  • uci.apply() # apply the changes in the backend, but with a 10 sec automatic rollback if not confirmed, implemented via ubus

However, the standard frontend handleSave/handleSaveApply methods do _not_ call uci.apply(), but instead call ui.changes.apply. This in turn calls a separate HTTP endpoint (not via uhttp-mod-ubus) implemented in lua (⇐OpenWrt 22) or ucode (>=OpenWrt 23), which itself calls ubus.

Warning: as well as the backend uci maintaining staged changes, and the frontend uci.js maintaining staged changes, the form elements (AbstractValues) have their own view of the config (cfgvalue) which is used to determine if they should save changes (i.e. saves only occur if the cfgvalue is different from the formvalue).

For those who like lua, UCI can be accessed in your code via the package libuci-lua. Just install the package then, in your lua code do


The api is quite simple

top level entry point

uci.cursor() instantiates a uci context instance, e.g:

x = uci.cursor()

if you want to involve state vars:

x = uci.cursor(nil, "/var/state")

if you need to work on UCI config files that are located in a non standard directory:

x = uci.cursor("/etc/mypackage/config", "/tmp/mypackage/.uci")

Get value (returns string or nil if not found):

x:get("config", "sectionname", "option")
-- real world example:
x:get("network", "lan", "proto")

Set simple string value:

x:set("config", "sectionname", "option", "value")
-- real world example:
x:set("network", "lan", "proto", "dhcp")

Set list value:

x:set("config", "sectionname", "option", { "foo", "bar" })
-- real world example:
x:set("system", "ntp", "server", {

Delete option:

x:delete("config", "section", "option")
-- real world example:
x:delete("network", "lan", "force_link")

Delete section:

x:delete("config", "section")
-- real world example:
x:delete("network", "wan6")

Add new anonymous section “type” and return its name:

x:add("config", "type")
> -- real world example from interpreter:
> name = x:add("network", "switch")
> print(name)

Add new section “name” with type “type”:

x:set("config", "name", "type")
-- real world example:
x:set("network", "wan6", "interface")

Iterate over all section of type “type” and invoke a callback function:

x:foreach("config", "type", function(s) ... end)

In the preceding example, s is a table containing all options and two special properties:

  • s['.type'] → section type
  • s['.name'] → section name

If the callback function returns false [NB: not nil!], foreach() will terminate at that point without iterating over any remaining sections. foreach() returns true if at least one section exists and the callback function didn't raise an error for it; false otherwise.

Here's another example:

> -- real world example from interpreter:
> x:foreach("system", "led", function(s)
>>     print('------------------')
>>     for key, value in pairs(s) do
>>         print(key .. ': ' .. tostring(value))
>>     end
>> end)
dev: 1-1.1
.anonymous: false
trigger: usbdev
.index: 2
name: USB1
interval: 50
.name: led_usb1
.type: led
sysfs: tp-link:green:usb1
dev: 1-1.2
.anonymous: false
trigger: usbdev
.index: 3
name: USB2
interval: 50
.name: led_usb2
.type: led
sysfs: tp-link:green:usb2
.name: led_wlan2g
.type: led
name: WLAN2G
trigger: phy0tpt
sysfs: tp-link:blue:wlan2g
.anonymous: false
.index: 4

Move a section to another position. Position starts at 0. This is for example handy to change the wireless config order (changing priority).

x:reorder("config", "sectionname", position)

Discard any changes made to the configuration, that have not yet been committed:


commits (saves) the changed configuration to the corresponding file in /etc/config


That's basically all you need.

About uci structure

It took me some time to understand the difference between “section” and “type”. Let's start with an example:

#uci show system
system.@rdate[0].server=ac-ntp0.net.cmu.edu ptbtime1.ptb.de ac-ntp1.net.cmu.edu ntp.xs4all.nl ptbtime2.ptb.de cudns.cit.cornell.edu ptbtime3.ptb.de

Here, x:get(“system”,“@rdate[0]”,“server”) won't work. rdate is a type, not a section.

Here is the return of x:get_all(“system”):

  cfg02f02f = {
    [".name"] = "cfg02f02f",
    [".type"] = "system",
    hostname = "OpenWrt",
    [".index"] = 0,
    [".anonymous"] = true,
    timezone = "UTC"
  cfg04e10c = {
    [".name"] = "cfg04e10c",
    [".type"] = "rdate",
    [".index"] = 1,
    [".anonymous"] = true,
    server = {

[“.type”] gives the type of the section;

[“.name”] gives the real name of the section (note that these names are auto-generated);

[“.index”] is the index of the list (starting from 1);

From what I know, there seem to be no way to access “@rdate[0]” directly. You have to iterate with x:foreach to list all the elements of a given type.

I use the following function:

function getConfType(conf,type)
   local curs=uci.cursor()
   local ifce={}
   curs:foreach(conf,type,function(s) ifce[s[".index"]]=s end)
   return ifce

getConfType(“system”,“rdate”) returns:

    [".name"] = "cfg04e10c",
    [".type"] = "rdate",
    [".index"] = 1,
    [".anonymous"] = true,
    server = {

So if you want to modify system.@rdate[0].server you need to iterate the type, retrieve the section name [“.name”] and then call:


Hope this helps.


(Luci has however a Cursor:get_first function that is similar to get except it takes a type instead as section as second argument.)

If you want to use the libuci apart from OpenWrt (for e.g. you are developing an application in C on your host computer) then prepare as follows: Note that libuci depends on [libubox]

Grab the source.

git clone https://git.openwrt.org/project/uci.git

Go to the source directory (where the CMakeLists.txt lives) and optionally configure the build without Lua bindings:

cd uci/; cmake [-D BUILD_LUA:BOOL=OFF] .

Build and install uci as root (this will install uci into /usr/local/, see this thread on how to install and use uci without root permissions in your home directory: https://forum.openwrt.org/viewtopic.php?id=40547):

make install

Setup library search paths using ld.so.conf

Setting your system library search path can be done in many ways, and is largely out of scope of the OpenWrt wiki.

Open /etc/ld.so.conf and add the place where you installed the uci library:

vi /etc/ld.so.conf

Add this line somewhere to /etc/ld.so.conf


Execute ldconfig as root to apply the changes to /etc/ld.so.conf


Setup library search paths using Using LD_LIBRARY_PATH

Alternatively, just

export LD_LIBRARY_PATH=<where/you/installed/the/.so>

Building your own application

To compile your application you have to link it against the uci library. Append -luci in your Makefile:

$(CC) test.o -o test -luci

And examples on how to use UCI in C can be found in this thread: https://forum.openwrt.org/viewtopic.php?pid=183335#p183335 To get more examples look into the source directory of uci which you got by git clone and open cli.c or ucimap-example.c

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  • Last modified: 2023/11/23 06:01
  • by wryun