| .\" Copyright (c) 1993 Michael Haardt (michael@moria.de), |
| .\" Fri Apr 2 11:32:09 MET DST 1993 |
| .\" |
| .\" %%%LICENSE_START(GPLv2+_DOC_FULL) |
| .\" This is free documentation; you can redistribute it and/or |
| .\" modify it under the terms of the GNU General Public License as |
| .\" published by the Free Software Foundation; either version 2 of |
| .\" the License, or (at your option) any later version. |
| .\" |
| .\" The GNU General Public License's references to "object code" |
| .\" and "executables" are to be interpreted as the output of any |
| .\" document formatting or typesetting system, including |
| .\" intermediate and printed output. |
| .\" |
| .\" This manual is distributed in the hope that it will be useful, |
| .\" but WITHOUT ANY WARRANTY; without even the implied warranty of |
| .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| .\" GNU General Public License for more details. |
| .\" |
| .\" You should have received a copy of the GNU General Public |
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| .\" <http://www.gnu.org/licenses/>. |
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| .\" |
| .\" Modified Sat Jul 24 17:00:12 1993 by Rik Faith (faith@cs.unc.edu) |
| .TH NULL 4 2015-07-23 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| null, zero \- data sink |
| .SH DESCRIPTION |
| Data written to the |
| .IR /dev/null |
| and |
| .IR /dev/zero |
| special files is discarded. |
| .PP |
| Reads from |
| .IR /dev/null |
| always return end of file (i.e., |
| .BR read (2) |
| returns 0), whereas reads from |
| .IR /dev/zero |
| always return bytes containing zero (\(aq\e0\(aq characters). |
| .PP |
| These devices are typically created by: |
| .PP |
| .in +4n |
| .EX |
| mknod \-m 666 /dev/null c 1 3 |
| mknod \-m 666 /dev/zero c 1 5 |
| chown root:root /dev/null /dev/zero |
| .EE |
| .in |
| .SH FILES |
| .I /dev/null |
| .br |
| .I /dev/zero |
| .SH NOTES |
| If these devices are not writable and readable for all users, many |
| programs will act strangely. |
| .PP |
| Since Linux 2.6.31, |
| .\" commit 2b83868723d090078ac0e2120e06a1cc94dbaef0 |
| reads from |
| .IR /dev/zero |
| are interruptible by signals. |
| (This change was made to help with bad latencies for large reads from |
| .IR /dev/zero .) |
| .SH SEE ALSO |
| .BR chown (1), |
| .BR mknod (1), |
| .BR full (4) |