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Linux 2.6 - man page for vcsa (linux section 4)

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  con-
       sole 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 filesystem 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\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 3.55 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)


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