Sysfs


sysfs is a pseudo file system provided by the Linux kernel that exports information about various kernel subsystems, hardware devices, and associated device drivers from the kernel's device model to user space through virtual files. In addition to providing information about various devices and kernel subsystems, exported virtual files are also used for their configuration.
sysfs provides functionality similar to the sysctl mechanism found in BSD operating systems, with the difference that sysfs is implemented as a virtual file system instead of being a purpose-built kernel mechanism, and that, in Linux, sysctl configuration parameters are made available at /proc/sys/ as part of procfs, not sysfs which is mounted at /sys/.

History

During the 2.5 development cycle, the Linux driver model was introduced to fix the following shortcomings of version 2.4:
Sysfs was designed to export the information present in the device tree which would then no longer clutter up procfs. It was written by Patrick Mochel. Maneesh Soni later wrote the sysfs backing store patch to reduce memory usage on large systems.
During the next year of 2.5 development the infrastructural capabilities of the driver model and driverfs, formerly called ddfs, began to prove useful to other subsystems. kobjects were developed to provide a central object management mechanism and driverfs was renamed to sysfs to represent its subsystem agnosticism.
Sysfs is mounted under the /sys mount point. If it is not mounted during initialization, you can always mount it using the command: "mount -t sysfs sysfs /sys"

Supported buses

; PCI
; USB
; S/390 buses

Sysfs and userspace

Sysfs is used by several utilities to access information about hardware and its driver such as udev or HAL. Scripts have been written to access information previously obtained via procfs, and some scripts configure device drivers and devices via their attributes.