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

6       vcs, vcsa - virtual console memory
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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 un‐
16       signed 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 re‐
24       turned in the unsigned short pointed to by the third ioctl(2) argument.
25
26       These devices replace the screendump ioctl(2) operations of  ioctl_con‐
27       sole(2),  so the system administrator can control access using filesys‐
28       tem permissions.
29
30       The devices for the first eight virtual consoles may be created by:
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32           for x in 0 1 2 3 4 5 6 7 8; do
33               mknod -m 644 /dev/vcs$x c 7 $x;
34               mknod -m 644 /dev/vcsa$x c 7 $[$x+128];
35           done
36           chown root:tty /dev/vcs*
37
38       No ioctl(2) requests are supported.
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FILES

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

45       Introduced with version 1.1.92 of the Linux kernel.
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EXAMPLES

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

SEE ALSO

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

COLOPHON

119       This  page  is  part of release 5.12 of the Linux man-pages project.  A
120       description of the project, information about reporting bugs,  and  the
121       latest     version     of     this    page,    can    be    found    at
122       https://www.kernel.org/doc/man-pages/.
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126Linux                             2020-11-01                            VCS(4)