[thirdparty/man-pages.git] / man4 / null.4

.\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
.\"     Fri Apr  2 11:32:09 MET DST 1993
.\"
.\" SPDX-License-Identifier: GPL-2.0-or-later
.\"
.\" 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
.I /dev/null
and
.I /dev/zero
special files is discarded.
.PP
Reads from
.I /dev/null
always return end of file (i.e.,
.BR read (2)
returns 0), whereas reads from
.I /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
.I /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)
Commit	Line	Data
3d54a910 MK	1	.\" Copyright (c) 1993 Michael Haardt (michael@moria.de),
3d54a910 MK	2	.\" Fri Apr 2 11:32:09 MET DST 1993
fea681da	3	.\"
e4a74ca8	4	.\" SPDX-License-Identifier: GPL-2.0-or-later
c13182ef	5	.\"
fea681da	6	.\" Modified Sat Jul 24 17:00:12 1993 by Rik Faith (faith@cs.unc.edu)
5722c835	7	.TH NULL 4 2015-07-23 "Linux" "Linux Programmer's Manual"
fea681da MK	8	.SH NAME
	9	null, zero \- data sink
	10	.SH DESCRIPTION
de347a67	11	Data written to the
1ae6b2c7	12	.I /dev/null
de347a67	13	and
1ae6b2c7	14	.I /dev/zero
de347a67	15	special files is discarded.
fea681da	16	.PP
de347a67	17	Reads from
1ae6b2c7	18	.I /dev/null
de347a67	19	always return end of file (i.e.,
3508b1f1	20	.BR read (2)
de347a67	21	returns 0), whereas reads from
1ae6b2c7	22	.I /dev/zero
6c22e323	23	always return bytes containing zero (\(aq\e0\(aq characters).
dd3568a1	24	.PP
de347a67	25	These devices are typically created by:
bdd915e2 MK	26	.PP
	27	.in +4n
	28	.EX
4d9b6984	29	mknod \-m 666 /dev/null c 1 3
4d9b6984	30	mknod \-m 666 /dev/zero c 1 5
c6f59edf	31	chown root:root /dev/null /dev/zero
bdd915e2 MK	32	.EE
bdd915e2 MK	33	.in
fea681da MK	34	.SH FILES
	35	.I /dev/null
	36	.br
	37	.I /dev/zero
2b2581ee MK	38	.SH NOTES
	39	If these devices are not writable and readable for all users, many
	40	programs will act strangely.
2dad4c59	41	.PP
dcc9ee34 MK	42	Since Linux 2.6.31,
	43	.\" commit 2b83868723d090078ac0e2120e06a1cc94dbaef0
	44	reads from
1ae6b2c7	45	.I /dev/zero
dcc9ee34 MK	46	are interruptible by signals.
	47	(This change was made to help with bad latencies for large reads from
	48	.IR /dev/zero .)
47297adb	49	.SH SEE ALSO
fea681da	50	.BR chown (1),
c0ae5dbd MK	51	.BR mknod (1),
c0ae5dbd MK	52	.BR full (4)