1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
.\" Copyright (c) 1995 James R. Van Zandt <jrv@vanzandt.mv.com>
.\" Sat Feb 18 09:11:07 EST 1995
.\"
.\" %%%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
.\" License along with this manual; if not, see
.\" <http://www.gnu.org/licenses/>.
.\" %%%LICENSE_END
.\"
.\" Modified, Sun Feb 26 15:08:05 1995, faith@cs.unc.edu
.\" 2007-12-17, Samuel Thibault <samuel.thibault@ens-lyon.org>:
.\" document the VT_GETHIFONTMASK ioctl
.\" "
.TH VCS 4 2020-11-01 "Linux" "Linux Programmer's Manual"
.SH NAME
vcs, vcsa \- virtual console memory
.SH DESCRIPTION
.I /dev/vcs0
is a character device with major number 7 and minor number
0, usually with mode 0644 and ownership root:tty.
It refers to the memory of the currently
displayed virtual console terminal.
.PP
.I /dev/vcs[1\-63]
are character devices for virtual console
terminals, they have major number 7 and minor number 1 to 63, usually
mode 0644 and ownership root:tty.
.IR /dev/vcsa[0\-63]
are the same, but
using
.IR "unsigned short" s
(in host byte order) that include attributes,
and prefixed with four bytes giving the screen
dimensions and cursor position:
.IR lines ,
.IR columns ,
.IR x ,
.IR y .
.RI ( x
=
.I y
= 0 at the top left corner of the screen.)
.PP
When a 512-character font is loaded,
the 9th bit position can be fetched by applying the
.BR ioctl (2)
.B VT_GETHIFONTMASK
operation
(available in Linux kernels 2.6.18 and above)
on
.IR /dev/tty[1\-63] ;
the value is returned in the
.I "unsigned short"
pointed to by the third
.BR ioctl (2)
argument.
.PP
These devices replace the screendump
.BR ioctl (2)
operations of
.BR ioctl_console (2),
so the system
administrator can control access using filesystem permissions.
.PP
The devices for the first eight virtual consoles may be created by:
.PP
.in +4n
.EX
for x in 0 1 2 3 4 5 6 7 8; do
mknod \-m 644 /dev/vcs$x c 7 $x;
mknod \-m 644 /dev/vcsa$x c 7 $[$x+128];
done
chown root:tty /dev/vcs*
.EE
.in
.PP
No
.BR ioctl (2)
requests are supported.
.SH FILES
.I /dev/vcs[0\-63]
.br
.I /dev/vcsa[0\-63]
.\" .SH AUTHOR
.\" Andries Brouwer <aeb@cwi.nl>
.SH VERSIONS
Introduced with version 1.1.92 of the Linux kernel.
.SH EXAMPLES
You may do a screendump on vt3 by switching to vt1 and typing
.PP
.in +4n
.EX
cat /dev/vcs3 >foo
.EE
.in
.PP
Note that the output does not contain
newline characters, so some processing may be required, like
in
.PP
.in +4n
.EX
fold \-w 81 /dev/vcs3 | lpr
.EE
.in
.PP
or (horrors)
.PP
.in +4n
.EX
setterm \-dump 3 \-file /proc/self/fd/1
.EE
.in
.PP
The
.I /dev/vcsa0
device is used for Braille support.
.PP
This program displays the character and screen attributes under the
cursor of the second virtual console, then changes the background color
there:
.PP
.EX
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/vt.h>
int
main(void)
{
int fd;
char *device = "/dev/vcsa2";
char *console = "/dev/tty2";
struct {unsigned char lines, cols, x, y;} scrn;
unsigned short s;
unsigned short mask;
unsigned char attrib;
int ch;
fd = open(console, O_RDWR);
if (fd < 0) {
perror(console);
exit(EXIT_FAILURE);
}
if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
perror("VT_GETHIFONTMASK");
exit(EXIT_FAILURE);
}
(void) close(fd);
fd = open(device, O_RDWR);
if (fd < 0) {
perror(device);
exit(EXIT_FAILURE);
}
(void) read(fd, &scrn, 4);
(void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), SEEK_SET);
(void) read(fd, &s, 2);
ch = s & 0xff;
if (s & mask)
ch |= 0x100;
attrib = ((s & \(timask) >> 8);
printf("ch=%#03x attrib=%#02x\en", ch, attrib);
s \(ha= 0x1000;
(void) lseek(fd, \-2, SEEK_CUR);
(void) write(fd, &s, 2);
exit(EXIT_SUCCESS);
}
.EE
.SH SEE ALSO
.BR ioctl_console (2),
.BR tty (4),
.BR ttyS (4),
.BR gpm (8)
.SH COLOPHON
This page is part of release 5.10 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
|
