1VCS(4)                     Linux Programmer's Manual                    VCS(4)
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NAME

6       vcs, vcsa - virtual console memory
7

DESCRIPTION

9       /dev/vcs0 is a character device with major number 7 and minor number 0,
10       usually with mode 0644 and ownership root:tty.  It refers to the memory
11       of the currently displayed virtual console terminal.
12
13       /dev/vcs[1-63]  are  character  devices  for virtual console terminals,
14       they have major number 7 and minor number 1 to 63,  usually  mode  0644
15       and  ownership  root:tty.   /dev/vcsa[0-63]  are  the  same,  but using
16       unsigned shorts (in host byte order) that include attributes, and  pre‐
17       fixed with four bytes giving the screen dimensions and cursor position:
18       lines, columns, x, y.  (x = y =  0  at  the  top  left  corner  of  the
19       screen.)
20
21       When  a  512-character  font  is  loaded,  the  9th bit position can be
22       fetched by applying the ioctl(2) VT_GETHIFONTMASK operation  (available
23       in  Linux  kernels  2.6.18  and  above) on /dev/tty[1-63]; the value is
24       returned in the unsigned short pointed to by the third  ioctl(2)  argu‐
25       ment.
26
27       These  devices replace the screendump ioctl(2) operations of ioctl_con‐
28       sole(2), so the system administrator can control access using  filesys‐
29       tem permissions.
30
31       The devices for the first eight virtual consoles may be created by:
32
33           for x in 0 1 2 3 4 5 6 7 8; do
34               mknod -m 644 /dev/vcs$x c 7 $x;
35               mknod -m 644 /dev/vcsa$x c 7 $[$x+128];
36           done
37           chown root:tty /dev/vcs*
38
39       No ioctl(2) requests are supported.
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FILES

42       /dev/vcs[0-63]
43       /dev/vcsa[0-63]
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VERSIONS

46       Introduced with version 1.1.92 of the Linux kernel.
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EXAMPLE

49       You may do a screendump on vt3 by switching to vt1 and typing
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51           cat /dev/vcs3 >foo
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53       Note  that the output does not contain newline characters, so some pro‐
54       cessing may be required, like in
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56           fold -w 81 /dev/vcs3 | lpr
57
58       or (horrors)
59
60           setterm -dump 3 -file /proc/self/fd/1
61
62       The /dev/vcsa0 device is used for Braille support.
63
64       This program displays the character and  screen  attributes  under  the
65       cursor of the second virtual console, then changes the background color
66       there:
67
68       #include <unistd.h>
69       #include <stdlib.h>
70       #include <stdio.h>
71       #include <fcntl.h>
72       #include <sys/ioctl.h>
73       #include <linux/vt.h>
74
75       int
76       main(void)
77       {
78           int fd;
79           char *device = "/dev/vcsa2";
80           char *console = "/dev/tty2";
81           struct {unsigned char lines, cols, x, y;} scrn;
82           unsigned short s;
83           unsigned short mask;
84           unsigned char attrib;
85           int ch;
86
87           fd = open(console, O_RDWR);
88           if (fd < 0) {
89               perror(console);
90               exit(EXIT_FAILURE);
91           }
92           if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
93               perror("VT_GETHIFONTMASK");
94               exit(EXIT_FAILURE);
95           }
96           (void) close(fd);
97           fd = open(device, O_RDWR);
98           if (fd < 0) {
99               perror(device);
100               exit(EXIT_FAILURE);
101           }
102           (void) read(fd, &scrn, 4);
103           (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), SEEK_SET);
104           (void) read(fd, &s, 2);
105           ch = s & 0xff;
106           if (s & mask)
107               ch |= 0x100;
108           attrib = ((s & ~mask) >> 8);
109           printf("ch=0x%03x attrib=0x%02x\n", ch, attrib);
110           s ^= 0x1000;
111           (void) lseek(fd, -2, SEEK_CUR);
112           (void) write(fd, &s, 2);
113           exit(EXIT_SUCCESS);
114       }
115

SEE ALSO

117       ioctl_console(2), tty(4), ttyS(4), gpm(8)
118

COLOPHON

120       This page is part of release 5.04 of the Linux  man-pages  project.   A
121       description  of  the project, information about reporting bugs, and the
122       latest    version    of    this    page,    can     be     found     at
123       https://www.kernel.org/doc/man-pages/.
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127Linux                             2019-03-06                            VCS(4)
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