VCS (4)
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
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.
EXAMPLES
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.
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 <stdio.h>
#include <fcntl.h>
void main()
{ int fd;
struct {char lines, cols, x, y;} scrn;
char ch, attrib;
fd = open("/dev/vcsa2", O_RDWR);
(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);
}
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 ALSO
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