usb_modeswitch_dispatcher

usb_modeswitch_dispatcher is not typically executed directly by users with command-line arguments. Instead, it is usually invoked automatically by udev rules.

The invocation context typically involves udev passing device information via environment variables:
/usr/sbin/usb_modeswitch_dispatcher [udev_environment_variables]

While it doesn't take standard command-line options in the conventional sense, it relies heavily on environment variables populated by udev to identify and process the specific USB device.

usb_modeswitch_dispatcher is a crucial helper script for the usb-modeswitch utility on Linux systems. Its primary function is to automate the process of switching multi-mode USB devices, such as 3G/4G modems, from their initial default mode (often appearing as a CD-ROM drive or flash storage) to their intended functional mode (e.g., a serial modem or network interface).

This dispatcher is typically invoked automatically by udev rules whenever a new USB device is detected. It parses device attributes provided by udev (like Vendor ID, Product ID, and device path) to determine if the connected device is one that requires mode-switching. Upon identification, it then calls the main usb_modeswitch binary with the appropriate configuration details, ensuring the device becomes usable without manual intervention. It acts as the bridge between the system's hotplug events and the actual mode-switching logic, making the use of such devices largely plug-and-play. Its intelligent design handles a wide array of devices by leveraging a comprehensive database of device-specific configurations.

• Dependency on udev: This dispatcher relies entirely on udev for its invocation and device information. If udev rules are not correctly configured or the daemon is not running, the automatic switching will fail.
• Configuration Files: Its functionality depends on the presence and correctness of usb_modeswitch configuration files, typically located in /etc/usb_modeswitch.conf and /etc/usb_modeswitch.d/. Missing or incorrect configurations for a specific device will prevent successful mode-switching.
• Kernel Modules: For the switched device to function, the appropriate kernel modules (e.g., option, cdc_ether) must be loaded and available.
• Timing Issues: In some rare cases, especially on slower systems or with particular USB controllers, timing issues during device detection and switching can occur, leading to the device not being properly initialized.

usb_modeswitch_dispatcher is not a standalone command intended for direct user execution. It is a critical part of the usb-modeswitch package's automatic mode-switching capabilities. Its execution is managed by udev rules, which are typically defined in files like /lib/udev/rules.d/40-usb_modeswitch.rules. These rules monitor USB device hotplug events and invoke the dispatcher script when a known multi-mode device is detected.

While usb_modeswitch performs the actual device command sending, the dispatcher's role is to act as an intelligent intermediary. It reads the device's Vendor ID and Product ID (provided by udev), looks up the correct switching command in the usb_modeswitch configuration database, and then executes usb_modeswitch with the specific parameters for that device. This abstraction simplifies the udev rules and centralizes the logic for device identification and parameter selection.

usb_modeswitch_dispatcher emerged as a necessary component to automate the functionality of usb_modeswitch, which was initially designed for manual invocation. As the number of multi-mode USB devices (especially 3G/4G modems) proliferated, manually running usb_modeswitch for each connection became impractical. The dispatcher script was developed to integrate seamlessly with the Linux udev system, allowing for automatic detection and switching of devices upon connection. This evolution significantly improved the user experience, transforming what was once a manual troubleshooting step into a plug-and-play operation for a wide range of mobile broadband devices, solidifying usb-modeswitch's role in network connectivity management on Linux.

usb_modeswitch(1), udev(7), udevadm(8)