vcs, vcsa — virtual console memory
/dev/vcs0 is a character
device with major number 7 and minor number 0, usually of
mode 0644 and owner root.tty. It refers to the memory of the
currently displayed virtual console terminal.
/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 owner root.tty. /dev/vcsa[0−63] are the same, but
including attributes, and prefixed with four bytes giving the
screen dimensions and cursor position: lines, columns, x, y. (x = y = 0 at the top left corner
of the screen.)
These replace the screendump ioctls of console(4),
so the system administrator can control access using file
system permissions.
The devices for the first eight virtual consoles may be created by:
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*
No ioctl(2) requests are supported.
You may do a screendump on vt3 by switching to vt1 and typing cat /dev/vcs3 >foo. Note that the output does not contain newline characters, so some processing may be required, like in fold −w 81 /dev/vcs3 | lpr or (horrors) setterm −dump 3 −file /proc/self/fd/1.
The /dev/vcsa0 device is
used for Braille support.
This program displays the character and screen attributes under the cursor of the second virtual console, then changes the background color there:
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
int
main(void)
{
int fd;
char *device = "/dev/vcsa2";
struct {unsigned char lines, cols, x, y;} scrn;
char ch, attrib;
fd = open(device, O_RDWR);
if (fd < 0) {
perror(device);
exit(1);
}
(void) read(fd, &scrn, 4);
(void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
(void) read(fd, &ch, 1);
(void) read(fd, &attrib, 1);
printf("ch='%c' attrib=0x%02x\n", ch, attrib);
attrib ^= 0x10;
(void) lseek(fd, −1, 1);
(void) write(fd, &attrib, 1);
exit(EXIT_SUCCESS);
}
gpm(8), console(4), tty(4), ttyS(4)
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