VCS(4) Linux Programmer's Manual VCS(4)NAME
vcs, vcsa - virtual console memory
DESCRIPTION
/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 admin‐
istrator 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.
EXAMPLE
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 charac‐
ters, 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;
}
FILES
/dev/vcs[0-63]
/dev/vcsa[0-63]
AUTHOR
Andries Brouwer <aeb@cwi.nl>
HISTORY
Introduced with version 1.1.92 of the Linux kernel.
SEE ALSOgpm(8), console(4), tty(4), ttyS(4)Linux 1995-02-19 VCS(4)