DeviceDateien

DeviceDateien, or device files, are special files found in Unix-like operating systems that provide interfaces to hardware devices or kernel subsystems. They do not store user data themselves; instead, they serve as access points through which software can perform input, output, or control operations with the corresponding hardware or driver.

There are two main types: character devices and block devices. Character devices handle data as a stream, with data read or written sequentially (for example, /dev/null or /dev/tty). Block devices expose data in fixed-size blocks and generally support buffering and random access (for example, /dev/sda or /dev/hd0). Device files are represented in the filesystem with a type indicator and are linked to drivers via major and minor numbers, which the kernel uses to dispatch I/O requests to the appropriate device driver.

Creation and management of device files has evolved. Traditionally, they could be created with the mknod command by specifying the major and minor numbers. Modern Linux systems typically populate /dev dynamically at boot or when devices are detected, using devtmpfs and udev or other hotplug daemons. Some device files may be created statically in initramfs. Permissions and ownership on device files control which processes can access the corresponding devices.

Interaction with device files occurs through standard system calls such as open, read, write, and ioctl (for device-specific control operations). Device drivers in the kernel translate these requests into actual hardware actions. Access to device files is subject to security measures like file permissions, appropriate groups, and capabilities, reflecting the privileged nature of many hardware interfaces.