Index · Directives systemd 254


libudev — API for enumerating and introspecting local devices


#include <libudev.h>

pkg-config --cflags --libs libudev


libudev.h provides an API to introspect and enumerate devices on the local system. This library is supported, but should not be used in new projects. Please see sd-device(3) for an equivalent replacement with a more modern API.

All functions require a libudev context to operate. This context can be created via udev_new(3). It is used to track library state and link objects together. No global state is used by libudev, everything is always linked to a udev context.

All functions listed here are thread-agnostic and only a single specific thread may operate on a given object during its entire lifetime. It's safe to allocate multiple independent objects and use each from a specific thread in parallel. However, it's not safe to allocate such an object in one thread, and operate or free it from any other, even if locking is used to ensure these threads don't operate on it at the very same time.

The code described here uses getenv(3), which is declared to be not multi-thread-safe. This means that the code calling the functions described here must not call setenv(3) from a parallel thread. It is recommended to only do calls to setenv() from an early phase of the program when no other threads have been started.

To introspect a local device on a system, a udev device object can be created via udev_device_new_from_syspath(3) and friends. The device object allows one to query current state, read and write attributes and lookup properties of the device in question.

To enumerate local devices on the system, an enumeration object can be created via udev_enumerate_new(3).

To monitor the local system for hotplugged or unplugged devices, a monitor can be created via udev_monitor_new_from_netlink(3).

Whenever libudev returns a list of objects, the udev_list_entry(3) API should be used to iterate, access and modify those lists.

Furthermore, libudev also exports legacy APIs that should not be used by new software (and as such are not documented as part of this manual). This includes the hardware database known as udev_hwdb (please use the new sd-hwdb(3) API instead) and the udev_queue object to query the udev daemon (which should not be used by new software at all).

See Also

udev_new(3), udev_device_new_from_syspath(3), udev_enumerate_new(3), udev_monitor_new_from_netlink(3), udev_list_entry(3), systemd(1), sd-device(3), sd-hwdb(3), pkg-config(1)