VCS(4)			   Linux Programmers 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) argu
       ment.

       These devices replace the screendump ioctl(2) operations of console(4),
       so  the	system administrator can control access using file system per
       missions.

       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 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 
       #include 
       #include 
       #include 
       #include 
       #include 

       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\n", 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 3.05 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)