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 opera-
       tion (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
       This  page  is  part of release 3.25 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)