man4/null.4

   1 .\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
   2 .\"     Fri Apr  2 11:32:09 MET DST 1993
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  25 .\" Modified Sat Jul 24 17:00:12 1993 by Rik Faith (faith@cs.unc.edu)
  26 .TH NULL 4 2015-07-23 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 null, zero \- data sink
  29 .SH DESCRIPTION
  30 Data written to the
  31 .IR /dev/null
  32 and
  33 .IR /dev/zero
  34 special files is discarded.
  35 .PP
  36 Reads from
  37 .IR /dev/null
  38 always return end of file (i.e.,
  39 .BR read (2)
  40 returns 0), whereas reads from
  41 .IR /dev/zero
  42 always return bytes containing zero (\(aq\e0\(aq characters).
  43 .PP
  44 These devices are typically created by:
  45 .PP
  46 .in +4n
  47 .EX
  48 mknod \-m 666 /dev/null c 1 3
  49 mknod \-m 666 /dev/zero c 1 5
  50 chown root:root /dev/null /dev/zero
  51 .EE
  52 .in
  53 .SH FILES
  54 .I /dev/null
  55 .br
  56 .I /dev/zero
  57 .SH NOTES
  58 If these devices are not writable and readable for all users, many
  59 programs will act strangely.
  60 .PP
  61 Since Linux 2.6.31,
  62 .\" commit 2b83868723d090078ac0e2120e06a1cc94dbaef0
  63 reads from
  64 .IR /dev/zero
  65 are interruptible by signals.
  66 (This change was made to help with bad latencies for large reads from
  67 .IR /dev/zero .)
  68 .SH SEE ALSO
  69 .BR chown (1),
  70 .BR mknod (1),
  71 .BR full (4)