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 using unsigned shorts (in host byte order) that include 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.)

       When a 512-character font is loaded, the 9th bit position can be fetched by applying the ioctl(2) VT_GETHIFONTMASK operation (available	in
       Linux kernels 2.6.18 and above) on /dev/tty[1-63]; the value is returned in the unsigned short pointed to by the third ioctl(2) argument.

       These  devices  replace	the screendump ioctl(2) operations 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.

FILES

       /dev/vcs[0-63]
       /dev/vcsa[0-63]

VERSIONS

       Introduced with version 1.1.92 of the Linux kernel.

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 characters, so some processing may be required, like in

	   old -w 81 /dev/vcs3 | lpr

       or (horrors)

	   xetterm -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>
       #include <sys/ioctl.h>
       #include <linux/vt.h>

       int
       main(void)
       {
	   int fd;
	   char *device = "/dev/vcsa2";
	   char *console = "/dev/tty2";
	   struct {unsigned char lines, cols, x, y;} scrn;
	   unsigned short s;
	   unsigned short mask;
	   unsigned char ch, attrib;

	   fd = open(console, O_RDWR);
	   if (fd < 0) {
	       perror(console);
	       exit(EXIT_FAILURE);
	   }
	   if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
	       perror("VT_GETHIFONTMASK");
	       exit(EXIT_FAILURE);
	   }
	   (void) close(fd);
	   fd = open(device, O_RDWR);
	   if (fd < 0) {
	       perror(device);
	       exit(EXIT_FAILURE);
	   }
	   (void) read(fd, &scrn, 4);
	   (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
	   (void) read(fd, &s, 2);
	   ch = s & 0xff;
	   if (attrib & mask)
	       ch |= 0x100;
	   attrib = ((s & ~mask) >> 8);
	   printf("ch='%c' attrib=0x%02x
", ch, attrib);
	   attrib ^= 0x10;
	   (void) lseek(fd, -1, 1);
	   (void) write(fd, &attrib, 1);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       console(4), tty(4), ttyS(4), gpm(8)

COLOPHON

       This  page is part of release 3.53 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2007-12-17								    VCS(4)