1VCS(4) Linux Programmer's Manual VCS(4)
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6 vcs, vcsa - virtual console memory
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9 /dev/vcs0 is a character device with major number 7 and minor number 0,
10 usually of mode 0644 and owner root.tty. It refers to the memory of
11 the currently displayed virtual console terminal.
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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 owner root.tty. /dev/vcsa[0-63] are the same, but including
16 attributes, and prefixed with four bytes giving the screen dimensions
17 and cursor position: lines, columns, x, y. (x = y = 0 at the top left
18 corner of the screen.)
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20 These replace the screendump ioctls of console(4), so the system admin‐
21 istrator can control access using file system permissions.
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23 The devices for the first eight virtual consoles may be created by:
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25 for x in 0 1 2 3 4 5 6 7 8; do
26 mknod -m 644 /dev/vcs$x c 7 $x;
27 mknod -m 644 /dev/vcsa$x c 7 $[$x+128];
28 done
29 chown root:tty /dev/vcs*
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31 No ioctl() requests are supported.
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34 You may do a screendump on vt3 by switching to vt1 and typing cat
35 /dev/vcs3 >foo. Note that the output does not contain newline charac‐
36 ters, so some processing may be required, like in fold -w 81 /dev/vcs3
37 | lpr or (horrors) setterm -dump 3 -file /proc/self/fd/1.
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39 The /dev/vcsa0 device is used for Braille support.
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41 This program displays the character and screen attributes under the
42 cursor of the second virtual console, then changes the background color
43 there:
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45 #include <unistd.h>
46 #include <stdlib.h>
47 #include <stdio.h>
48 #include <fcntl.h>
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50 int main() {
51 int fd;
52 char *device = "/dev/vcsa2";
53 struct {unsigned char lines, cols, x, y;} scrn;
54 char ch, attrib;
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56 fd = open(device, O_RDWR);
57 if (fd < 0) {
58 perror(device);
59 exit(1);
60 }
61 (void) read(fd, &scrn, 4);
62 (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
63 (void) read(fd, &ch, 1);
64 (void) read(fd, &attrib, 1);
65 printf("ch='%c' attrib=0x%02x\n", ch, attrib);
66 attrib ^= 0x10;
67 (void) lseek(fd, -1, 1);
68 (void) write(fd, &attrib, 1);
69 return 0;
70 }
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74 /dev/vcs[0-63]
75 /dev/vcsa[0-63]
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78 Andries Brouwer <aeb@cwi.nl>
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81 Introduced with version 1.1.92 of the Linux kernel.
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84 gpm(8), console(4), tty(4), ttyS(4)
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88Linux 1995-02-19 VCS(4)