sysfs is a

pseudo file system In computer science, a synthetic file system or a pseudo file system is a hierarchical interface to non-file objects that appear as if they were regular files in the tree of a disk-based or long-term-storage file system. These non-file objects m ...

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 A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

through

virtual file In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

s. 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 sysctl is a software utility of some Unix-like operating systems that reads and modifies the attributes of the system kernel such as its version number, maximum limits, and security settings. It is available both as a system call for compiled ...

mechanism found in BSD

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also i ...

s, 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 The proc filesystem (procfs) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized meth ...

, 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: * No unified method of representing driver-device relationships existed. * There was no generic

hotplug Hot swapping is the replacement or addition of components to a computer system without stopping, shutting down, or rebooting the system; hot plugging describes the addition of components only. Components which have such functionality are said ...

mechanism. *

was cluttered with non-process information. Sysfs was designed to export the information present in the

device tree In computing, a devicetree (also written device tree) is a data structure describing the hardware components of a particular computer so that the operating system's kernel can use and manage those components, including the CPU or CPUs, the memor ...

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 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 mount point. If it is not mounted during initialization, you can always mount it using the command: "mount -t sysfs sysfs /sys"

Supported buses

; ACPI : Exports information about

ACPI Advanced Configuration and Power Interface (ACPI) is an open standard that operating systems can use to discover and configure computer hardware components, to perform power management (e.g. putting unused hardware components to sleep), auto c ...

devices. ; PCI : Exports information about PCI and PCI Express devices. ; PCI Express : Exports information about PCI Express devices. ; USB : Exports information about

USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...

devices. ; SCSI : Exports information about

mass storage In computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. In general, the term is used as large in relation to contemporaneous hard disk drives, but it has been used large in relati ...

devices, including

SATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...

and

NVMe NVM Express (NVMe) or Non-Volatile Memory Host Controller Interface Specification (NVMHCIS) is an open, logical-device interface specification for accessing a computer's non-volatile storage media usually attached via PCI Express (PCIe) bus. The ...

interfaces. ; S/390 buses : As the S/390 architecture contains devices not found elsewhere, special buses have been created: :* ''css'': Contains subchannels (currently the only driver provided is for I/O subchannels). :* ''ccw'': Contains channel attached devices (driven by CCWs). :* ''ccwgroup'': Artificial devices, created by the user and consisting of ccw devices. Replaces some of the 2.4 chandev functionality. :* ''iucv'': Artificial devices like netiucv devices which use VM's IUCV interface.

Sysfs and userspace

Sysfs is used by several utilities to access information about hardware and its driver ( kernel modules) such as

udev udev (userspace ) is a device manager for the Linux kernel. As the successor of devfsd and hotplug, udev primarily manages device nodes in the directory. At the same time, udev also handles all user space events raised when hardware devices ...

or HAL. Scripts have been written to access information previously obtained via

, and some scripts configure device drivers and devices via their attributes.

References

External links

Driver model overview from the LWN porting to 2.6 serieskobjects and sysfs from the LWN porting to 2.6 seriesRamfsThe sysfs Filesystem, OLS'05Documentation/filesystems/sysfs.txt
Linux kernel documentation for sysfs {{File systems Free special-purpose file systems Interfaces of the Linux kernel Linux kernel features Pseudo file systems supported by the Linux kernel

History

Supported buses

Sysfs and userspace

See also

References

External links