UCI: how OpenWrt keeps every setting in /etc/config

Every service reads /etc/config. LuCI edits the same files.

In one sentence

UCI (Unified Configuration Interface) keeps the configuration for OpenWrt’s services in plain-text files under /etc/config/. LuCI and the uci command edit those same files.

How it works

There is one file per subsystem, such as network, wireless, dhcp, firewall and system.
uci set, uci add, uci rename and uci delete are staged first. uci commit writes them to flash in one go.
A committed change takes effect only after the service reloads or restarts through its init script. The official example changes the uhttpd port, commits, then runs /etc/init.d/uhttpd restart.
LuCI is a front end: its pages read and write the same UCI files through APIs.

See it on your router

These commands only read:

uci show network.lan
uci get network.lan.ipaddr
uci export dhcp

Watch out

A change you commit but never reload is not live yet. It takes effect at the next service restart or reboot, which can be long after you have forgotten about it.
Copy /etc/config somewhere safe before you edit by hand. Backup and restore covers a full backup.

Sources

Router.Homes

Independent OpenWrt notes. Every page states the firmware, device, package manager and way back.

Icons: Solar by 480 Design, CC BY 4.0