Device files provide access to drivers through files.

They are listed under /dev. There are two kinds of device drivers (as shown with ls -l) c: character device b: block device

• Character devices provide a stream of bytes (e. g. serial ports, USB, system consoles …)
• Block devices allow random access of blocks of information (e. g. HD, SSD …).

The device files have a major and a minor number. The same major number means that the same device driver is responsible for the file/device. The minor number is used to distinguish different devices of the same type that use the same device driver.

Functions

A file descriptor for a device file can be aquired by the common open() function. Afer use it can be closed with close(). Reading and writing to the file is donne with read() and write().

Contol of device drivers is acomplished with the ioctl() function.

Man page: man ioctl and man ioctl_list (only Linux).

Special Device Files

• /dev/null: used to redirect unused streams to ‘nowhere’
• /dev/zero: ‘infinite’ sized file filled with 0 (s.a. mmap())
• /dev/pts/: virtual consoles (s.a. stackexchange)
• /dev/random and /dev/urandom: provide random numbers (/dev/random might block (high entropy), /dev/urandom doesn’t block)
• /dev/full: can be used to simulate writing to a file when the disk is full (sets errno to ENOSPC)