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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  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>
       #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

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       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.