OpenWrt Router Operating System Explained

OpenWrt is an open-source router operating system that's been around since 2004. It was initially based on the Linux kernel version 2.4.

The main goal of OpenWrt is to provide a highly customizable and flexible operating system for routers, allowing users to easily install and manage their own software packages.

One of the key benefits of OpenWrt is its ability to run on a wide range of router hardware, thanks to its modular design and support for various architectures.

For another approach, see: Openwrt Build System Setup

OpenWrt can be installed on a wide range of devices, including routers, access points, and even some smartphones.

To start the installation process, you'll need to download the OpenWrt image for your specific device from the official OpenWrt website. This image is a compressed file that contains the entire OpenWrt system.

You'll need a tool like TFTP or a specialized firmware upgrade tool to upload the OpenWrt image to your device. This process typically involves booting your device into a special mode, such as recovery mode, and then uploading the image via the tool.

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To download OpenWrt firmware, you can use the Firmware Selector. This tool helps you find a factory image that's compatible with your device.

The Firmware Selector is a great place to start, as it allows you to quickly find a usable image to migrate from vendor stock firmware to OpenWrt.

If your device is supported, you can follow the Info link to see install instructions or consult the support resources listed below.

For more complex tasks, such as downloading additional packages or tools, you can try the wiki download page.

Here are the resources you can use to download OpenWrt firmware:

To get started with the installation process, you'll want to run the following commands in sequence.

First, update all the latest package definitions by running `./scripts/feeds update -a`. This will fetch the latest package definitions from the feeds.conf and feeds.conf.default files.

Next, install symlinks for all obtained packages into package/feeds/ by running `./scripts/feeds install -a`. This step is crucial for setting up the necessary links for the build process.

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Once you have the package definitions and symlinks in place, you can configure your toolchain, target system, and firmware packages using `make menuconfig`. This will give you a chance to select your preferred configuration options.

Finally, run `make` to build your firmware. This command will download all the necessary sources, build the cross-compile toolchain, and then cross-compile the GNU/Linux kernel and all chosen applications for your target system.

For another approach, see: Openwrt Firmware

OpenWrt features a writeable root file system, enabling users to modify any file and easily install additional software.

This is a game-changer for users who want to customize their devices without rebuilding and flashing a complete firmware image. With OpenWrt, you can install any of the approximately 8000 packages available in the package repository.

The package manager, opkg, makes it easy to find and install the software you need. And with regular bug fixes and security updates, you can rest assured that your device will stay safe and secure.

OpenWrt also provides a unified configuration interface called UCI, which simplifies configuration through the command-line interface. And if you prefer a web interface, LuCI is available, along with other options like Gargoyle.

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The OpenWrt project has a rich history, and understanding its milestones can help you appreciate its capabilities. In 2003, Linksys released the WRT54G router with support for IEEE 802.11g, which sparked interest in the open source community.

This community pressure led Linksys to release the firmware source code in July 2003, marking the beginning of custom router firmware. The OpenWrt project was born the same year, with its first version released using the Linksys open source firmware.

The LuCI project was started to provide a user-friendly web interface for embedded devices, using the Lua programming language. OpenWrt adopted LuCI in the Kamikaze 8.09 release, making it an integral part of the project.

In 2015, the OpenWrt Summit was organized in Dublin, Ireland, to discuss OpenWrt technology and support the movement. Chaos Calmer 15.05.1 was released later that year, a maintenance update to the Chaos Calmer 15.05 branch.

Linux Embedded Development Environment (LEDE) was born as a fork of OpenWrt in 2016, due to dissatisfaction with OpenWrt's processes and lack of transparency. LEDE promised a more open and transparent development process, which eventually led to a merger with OpenWrt.

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OpenWrt offers a writeable root file system, allowing users to modify any file and easily install additional software. This is a game-changer for those who want to customize their device without rebuilding and flashing a complete firmware image.

The package repository contains approximately 8000 packages, giving users a vast array of options for adding new features and functionality.

OpenWrt can be configured through a command-line interface or a web interface called LuCI, making it easy to manage and customize your device.

Additional web interfaces, such as Gargoyle, are also available for those who prefer a more user-friendly interface.

Regular bug fixes and security updates are provided for devices that are no longer supported by their manufacturers, ensuring that users can stay safe and secure.

Here are some of the key features that OpenWrt offers:

To build your own OpenWrt firmware, you'll need a GNU/Linux, BSD, or macOS system with a case sensitive filesystem. Cygwin is not supported due to its lack of a case sensitive file system.

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The development environment and build system, known as OpenWrt Buildroot, is based on a heavily modified Buildroot system. It automates the process of building a complete Linux-based OpenWrt system for an embedded device, by building and using an appropriate cross-compilation toolchain.

OpenWrt Buildroot provides a number of features that make it easy to port software across architectures, including an integrated cross-compiler toolchain, abstraction for autotools, and handling of the standard OpenWrt image build workflow.

Additional reading: Building Openwrt

To build your own firmware, you'll need a GNU/Linux, BSD, or macOS system with a case-sensitive filesystem. Cygwin is unsupported due to the lack of a case-sensitive file system.

You can't just build OpenWrt on any system, it needs a specific operating system to work properly.

OpenWrt is licensed under GPL-2.0, so you'll need to keep that in mind when working with the code.

The Build System Setup documentation has a complete list of distribution-specific packages you'll need to compile OpenWrt.

OpenWrt Buildroot is a set of Makefiles and patches that automates the process of building a complete Linux-based OpenWrt system for an embedded device.

OpenWrt runs on many different routers, and you can find a table of compatible hardware on its website.

The most recommended wireless chipsets are from Qualcomm's Atheros and Ralink (now MediaTek), as well as any vendor with open source drivers and specifications.

It's also a good idea to choose a device with a minimum of 16 MB of flash and 128 MB of RAM, but preferably higher amounts.

Broadcom chipsets are generally avoided due to having limited features, mainly because they lack open drivers.

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OpenWrt's Buildroot build system has been adopted as the structure for other projects.

The AltiWi project, for example, is a "one-time-fee-only" replacement for Cloudtrax, leveraging OpenWrt's capabilities.

Bufferbloat.net, also known as Cerowrt, is another project that has adopted OpenWrt's technology.

Freifunk and other mesh network communities have also adopted OpenWrt for their network infrastructure.

The IETF IPv6 integration projects HIPnet and HomeNet are built on top of OpenWrt's framework.

prplOS, a carrier-grade framework, is designed to power ISPs' routers and gateways, and it's based on OpenWrt.

The SIMET Box, developed by NIC.br, is another example of a project that uses OpenWrt as its foundation.

Here are some examples of projects that have adopted OpenWrt:

OpenWrt's package management system is incredibly powerful. It's called opkg, the Open Package Manager.

You can install packages for a wide range of applications, including VPNs like wireguard and openvpn. This means you can secure your network and access remote servers with ease.

Ad-blocking packages like adblock and banIP are also available, allowing you to customize your browsing experience. You can say goodbye to annoying ads and hello to a cleaner online experience.

Monitoring packages like collectd and luci-app-statistics make it easy to keep an eye on your device's performance. Whether you're a developer or a user, this feature is a game-changer.

Some examples of other packages you can install include web servers, proxy servers, and NAS functions. You can even set up mesh routing with packages like B.A.T.M.A.N. and 802.11s.

Here are some examples of packages you can install with opkg:

OpenWrt's networking capabilities are a major strength, and it's all thanks to its flexibility. The operating system manages key components of the networking stack with ease.

One of the key components is the firewall, which uses nftables (or iptables in older versions) for packet filtering, NAT, and port forwarding. This allows for easy rule management and helps keep your network secure.

Firewall zones, such as LAN and WAN, are defined for easy rule management, making it simple to set up and configure your network's security settings.

OpenWrt's real power lies in its networking flexibility. Its networking stack is designed to be highly customizable.

OpenWrt uses nftables (or iptables in older versions) for packet filtering, NAT, and port forwarding. This allows for advanced firewall management.

Firewall zones, such as LAN and WAN, are defined for easy rule management. This makes it simple to set up and manage network rules.

OpenWrt's networking flexibility makes it a great choice for advanced network configurations. Whether you're a seasoned IT professional or a curious hobbyist, OpenWrt's networking stack has something to offer.

Dhcp/Dns (Dnsmasq) is a lightweight DNS and DHCP server that serves local IP addresses and hostname resolution. It's an essential component in many networks.

A key feature of dnsmasq is its ability to serve local IP addresses. This allows devices on the network to communicate with each other without needing to access the internet.

Dnsmasq can also handle hostname resolution, which means it can translate domain names into IP addresses. This is useful for accessing websites and online services.

By using dnsmasq, network administrators can simplify their DNS and DHCP configurations, making it easier to manage their network.

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The Wireless Stack (hostapd/wpad) is a crucial component of your network's wireless configuration. It manages the SSID, which is the name of your network that devices connect to.

You can configure your wireless radios using either hostapd or wpad. Both tools are used for managing encryption, which is essential for keeping your network secure.

WPA2 and WPA3 are two types of encryption that hostapd and wpad support. WPA2 is a widely used encryption protocol, while WPA3 is a more secure and modern alternative.

Multiple interfaces can also be managed using hostapd and wpad, allowing you to configure different wireless settings for various devices or networks.

Interface Management (netifd) is responsible for creating logical interfaces such as LAN, WAN, VLANs, bridges, and tunnels.

The configuration for these interfaces is defined in /etc/config/network and is handled by netifd.

This means that any changes to your network settings will be managed by netifd, making it a crucial component of your system's networking capabilities.

The interfaces handled by netifd are created based on the configuration files in /etc/config/network.

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Remote Access & Automation is a crucial aspect of modern networking and security. With the ability to access and manage your system remotely, you can save time and increase productivity.

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SSH access out of the box allows you to securely connect to your system from anywhere. This means you can perform tasks and troubleshoot issues without having to physically be there.

Public key authentication provides an additional layer of security, ensuring that only authorized users can access your system. This is especially important in a world where security breaches are becoming increasingly common.

Cron jobs for automation enable you to schedule tasks and scripts to run at specific intervals, freeing up your time for more important things.

Remote syslog allows you to collect and monitor system logs from a central location, making it easier to detect and respond to potential security threats.

SNMP and Prometheus exporters provide valuable insights into your system's performance and health, helping you identify potential issues before they become major problems.

MQTT for IoT applications enables seamless communication between devices, making it easier to integrate and manage your IoT ecosystem.

You can remotely manage your system using APIs, CLI, or custom scripts, giving you the flexibility to work the way that's most comfortable for you.

Routing is handled by the Linux kernel's routing table. This table can be extended with various options to ensure efficient network traffic management.

Static routes can be added to the routing table to manually configure network paths. This is particularly useful for networks with complex or dynamic topologies.

Dynamic routing protocols like OSPF via quagga or bird can be used to automatically adjust network paths based on network conditions. These protocols help ensure that network traffic is always routed through the most efficient paths.

VPN routes, such as those provided by WireGuard or OpenVPN, can be added to the routing table to securely extend network connectivity over the internet.

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OpenWrt's configuration system is built around its Unified Configuration Interface (UCI), which stores all configs in specific files. You can edit these files directly or use UCI commands.

These files are located in the /etc/config directory, and each one corresponds to a specific system setting. For example, network settings are stored in /etc/config/network, while wireless settings are stored in /etc/config/wireless.

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Here are the specific files where you can find different types of settings:

OpenWrt also comes with a lightweight web interface called LuCI, which provides a user-friendly way to manage system settings. LuCI runs on an embedded web server and exposes all config options in a dynamic, JavaScript-enabled form.

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OpenWrt uses its own Unified Configuration Interface (UCI) for managing system settings. This makes it easy to configure and manage the router.

All configs are stored in specific files within the /etc/config directory. This is a standard location for configuration files in Linux-based systems.

You can find the network configuration in the /etc/config/network file, which handles interfaces, VLANs, and bridges. This file is a crucial part of setting up your network.

The wireless configuration is stored in the /etc/config/wireless file, which deals with radios and SSIDs. This file is essential for setting up your wireless network.

The firewall configuration is found in the /etc/config/firewall file, which handles zone policies and rules. This file is important for securing your network.

The system configuration is stored in the /etc/config/system file, which covers hostname and timezone settings. This file is useful for customizing your router's settings.

Here are some specific files where you can find different types of configurations:

OpenWrt's web interface, LuCI, is a lightweight and modular solution that makes configuration and administration a breeze. It's built on top of an embedded web server, such as uhttpd or lighttpd.

LuCI uses dynamic rendering via Lua and JavaScript to provide a user-friendly interface for accessing all config options. This means you can easily find and adjust settings without delving into complex command-line interfaces.

One of the standout features of LuCI is its extensibility through modules, such as luci-app-sqm and luci-app-ddns. These modules can add new functionality to the interface, making it an even more powerful tool for managing your OpenWrt device.

You can install LuCI separately or opt for a CLI-only setup if you're an advanced user who prefers working directly with the command line.

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OpenWrt's system performance is impressive, especially considering it can run on devices with as little as 8MB flash and 64MB RAM.

This means it's optimized for minimal memory usage, which is a huge advantage for devices with limited resources.

Background service trimming is another feature that helps keep things running smoothly, by automatically disabling unnecessary services to free up memory and CPU resources.

This approach ensures that OpenWrt can continue to function even when resources are low, making it a reliable choice for devices with limited capacity.

Here are some key benefits of OpenWrt's system performance:

As you can see, OpenWrt is designed to handle devices with limited resources, but it can also scale well to more powerful hardware, supporting features like multi-core load balancing and gigabit routing.

The boot process of OpenWrt is a straightforward affair. It uses the standard embedded Linux boot sequence, which consists of a bootloader, Linux kernel, and init system (procd).

The bootloader is responsible for loading the Linux kernel, which in turn initializes the system. This process is crucial for getting your device up and running.

OpenWrt's filesystem is built around SquashFS + OverlayFS, a combination that provides a compressed, read-only root filesystem and a writable layer on top of it. This design allows for fast boot times, system resets, and minimal storage use.

Here are the key components of OpenWrt's filesystem:

OpenWrt's filesystem is built around SquashFS + OverlayFS, which allows for a compressed, read-only root filesystem containing the core OS. This design enables fast boot times.

SquashFS is a compressed, read-only root filesystem containing the core OS. It's a great way to store the core operating system, making it efficient and space-saving.

The filesystem is composed of two main parts: SquashFS and OverlayFS. SquashFS contains the core OS, while OverlayFS provides a writable layer on top of it. This allows for persistent configuration and package installation without altering the base image.

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This design also allows for system resets, which can be done by simply wiping the overlay. This is a convenient feature for when you need to restore your device to its factory settings.

Here are the benefits of OpenWrt's filesystem design:

The boot process is a crucial step in getting your OpenWrt device up and running. It's a standard embedded Linux boot sequence that consists of three main stages.

The bootloader is the first stage, responsible for loading the Linux kernel into memory. This can be U-Boot or CFE, depending on your device.

The Linux kernel is the second stage, which takes over from the bootloader and starts the boot process. It initializes the hardware and sets up the system environment.

The init system, procd, is the final stage, which configures the system and starts the user space processes. It's the last piece of the puzzle that gets your device fully operational.

Here's a brief overview of the boot process stages: