3.2.6. /proc/devices

3.2.6. /proc/devices

This file displays the various character and block devices currently configured (not including devices whose modules are not loaded). Below is a sample output from this file:

Character devices:  
  1 mem   
  4 /dev/vc/0   
  4 tty   
  4 ttyS   
  5 /dev/tty   
  5 /dev/console   
  5 /dev/ptmx   
  7 vcs  
  10 misc  
  13 input  
  29 fb  
  36 netlink 
  128 ptm 
  136 pts 
  180 usb   
  
Block devices:   
  1 ramdisk   
  3 ide0   
  9 md  
  22 ide1 
  253 device-mapper 
  254 mdp

The output from /proc/devices includes the major number and name of the device, and is broken into two major sections: Character devices and Block devices.

Character devices are similar to block devices, except for two basic differences:

  1. Character devices do not require buffering. Block devices have a buffer available, allowing them to order requests before addressing them. This is important for devices designed to store information — such as hard drives — because the ability to order the information before writing it to the device allows it to be placed in a more efficient order.

  2. Character devices send data with no preconfigured size. Block devices can send and receive information in blocks of a size configured per device.

For more information about devices refer to the following installed documentation:

/usr/share/doc/kernel-doc-<version>/Documentation/devices.txt

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