Linux / UNIX: Device files

by on July 31, 2007 · 13 comments· LAST UPDATED August 6, 2007

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Q. Can you explain me what is device files and how do I access or see device files? Why UNIX / Linux has device files?

A. Under Linux and UNIX each and every hardware device treated as a file. A device file allows to accesses hardware devices so that end users do not need to get technical details about hardware.

In short, a device file (also called as a special file) is an interface for a device driver that appears in a file system as if it were an ordinary file. This allows software to interact with the device driver using standard input/output system calls, which simplifies many tasks.

Device file two types

There are two types of device files based upon how data written to them and read from them is processed by the operating system and hardware:

  • Character special files or Character devices
  • Block special files or Block devices

Understanding Character special files or Character devices

  • Talks to devices in a character by character (1 byte at a time)
  • Examples: Virtual terminals, terminals and serial modems etc

Understanding Block special files or Block devices

  • Talks to devices 1 block at a time ( 1 block = 512 bytes to 32KB)
  • Examples: Hard disk, DVD/CD ROM, and memory regions etc

Why use device files?

Device file allows transparent communication between user space applications and computer hardware.

Device file location

All device files are stored in /dev directory. Use cd and ls command to browse the directory:
cd /dev/
ls -l

How do I find out the device file type?

Simply use ls -l command:
ls -l /dev
Look for file's type in the first column output.

A character device is marked with a c as the first letter of the permissions strings.
$ ls -l /dev/console
A block device is marked with a b as the first letter of the permissions strings:
$ ls -l /dev/sdb1

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{ 13 comments… read them below or add one }

1 Rajesh January 15, 2009 at 6:21 pm

Simple explaination, yet effective. thanks,

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2 izee March 8, 2009 at 5:35 am

v gud explanation thnx dude……………

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3 max March 24, 2009 at 10:09 am

cat /proc/devices shows list of character & block files.

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4 Rits August 15, 2009 at 10:23 am

Yes , very clear explanation indeed… Thanks it answered my query !

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5 Anonymous June 14, 2010 at 5:55 am

great ..cleared all my doubts

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6 Anold Eliapenda Mathayo July 5, 2010 at 5:35 am

Thanks to linux for answering my questions. I am a Tanzanian boy studying an Information Technology degree. I am aged 22 years.

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7 sree March 15, 2012 at 6:35 am

Can u plz tell how to view the contents of those file. When i tried to open a tty file(/dev) it gave for me a message “permission denied”. Can i see the code written inside that file? If so plz let me know how can i view it?

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8 ravindranath April 3, 2012 at 5:20 am

thanks a lot………

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9 hds January 6, 2013 at 5:43 pm

Thanks for such a good explanation

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10 Ajay patwal August 24, 2013 at 6:40 am

nice one …………………

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11 Tanqulity September 29, 2013 at 8:39 am

which type of devices are marked with “d” as the first letter?
drwxr-xr-x root root 200 sep 29 18:43 snd
it is a directory right?

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12 shweta February 1, 2014 at 9:00 am

thank u so much…vry nyc ans

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13 aaaa February 18, 2014 at 5:11 am

cant get simpler than this!!Thanks you..

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