projects / thirdparty / man-pages.git / blame
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1 | .\" Copyright (c) 1993 Michael Haardt (michael@moria.de), |
| 2 | .\" Fri Apr 2 11:32:09 MET DST 1993 | |
| fea681da | 3 | .\" |
| 1dd72f9c | 4 | .\" %%%LICENSE_START(GPLv2+_DOC_FULL) |
| fea681da MK |
5 | .\" This is free documentation; you can redistribute it and/or |
| 6 | .\" modify it under the terms of the GNU General Public License as | |
| 7 | .\" published by the Free Software Foundation; either version 2 of | |
| 8 | .\" the License, or (at your option) any later version. | |
| 9 | .\" | |
| 10 | .\" The GNU General Public License's references to "object code" | |
| 11 | .\" and "executables" are to be interpreted as the output of any | |
| 12 | .\" document formatting or typesetting system, including | |
| 13 | .\" intermediate and printed output. | |
| 14 | .\" | |
| 15 | .\" This manual is distributed in the hope that it will be useful, | |
| 16 | .\" but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 17 | .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
| 18 | .\" GNU General Public License for more details. | |
| 19 | .\" | |
| 20 | .\" You should have received a copy of the GNU General Public | |
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21 | .\" License along with this manual; if not, see |
| 22 | .\" <http://www.gnu.org/licenses/>. | |
| 6a8d8745 | 23 | .\" %%%LICENSE_END |
| c13182ef | 24 | .\" |
| fea681da | 25 | .\" Modified Sat Jul 24 17:00:12 1993 by Rik Faith (faith@cs.unc.edu) |
| 5722c835 | 26 | .TH NULL 4 2015-07-23 "Linux" "Linux Programmer's Manual" |
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27 | .SH NAME |
| 28 | null, zero \- data sink | |
| 29 | .SH DESCRIPTION | |
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30 | Data written to the |
| 31 | .IR /dev/null | |
| 32 | and | |
| 33 | .IR /dev/zero | |
| 34 | special files is discarded. | |
| fea681da | 35 | .PP |
| de347a67 MK |
36 | Reads from |
| 37 | .IR /dev/null | |
| 38 | always return end of file (i.e., | |
| 3508b1f1 | 39 | .BR read (2) |
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40 | returns 0), whereas reads from |
| 41 | .IR /dev/zero | |
| 6c22e323 | 42 | always return bytes containing zero (\(aq\e0\(aq characters). |
| dd3568a1 | 43 | .PP |
| de347a67 | 44 | These devices are typically created by: |
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45 | .PP |
| 46 | .in +4n | |
| 47 | .EX | |
| 4d9b6984 | 48 | mknod \-m 666 /dev/null c 1 3 |
| 4d9b6984 | 49 | mknod \-m 666 /dev/zero c 1 5 |
| c6f59edf | 50 | chown root:root /dev/null /dev/zero |
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51 | .EE |
| 52 | .in | |
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53 | .SH FILES |
| 54 | .I /dev/null | |
| 55 | .br | |
| 56 | .I /dev/zero | |
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57 | .SH NOTES |
| 58 | If these devices are not writable and readable for all users, many | |
| 59 | programs will act strangely. | |
| 2dad4c59 | 60 | .PP |
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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 .) | |
| 47297adb | 68 | .SH SEE ALSO |
| fea681da | 69 | .BR chown (1), |
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70 | .BR mknod (1), |
| 71 | .BR full (4) |