Originální popis anglicky:
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() 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() {
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);
return 0;
}
/dev/vcs[0-63]
/dev/vcsa[0-63]
Andries Brouwer <aeb@cwi.nl>
Introduced with version 1.1.92 of the Linux kernel.
selection(1),
console(4),
tty(4),
ttys(4)
