vcsa - phpMan

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  including 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.)

       These  replace the screendump ioctls 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() requests are supported.

EXAMPLES
       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>

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

                 fd = open(device, O_RDWR);
                 if (fd < 0) {
                      perror(device);
                      exit(1);
                 }
                 (void)read(fd, &scrn, 4);
                 (void)lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
                 (void)read(fd, &ch, 1);
                 (void)read(fd, &attrib, 1);
                 printf("ch=’%c’ attrib=0x%02x\n", ch, attrib);
                 attrib ^= 0x10;
                 (void)lseek(fd, -1, 1);
                 (void)write(fd, &attrib, 1);
                 return 0;
            }


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

AUTHOR
       Andries Brouwer <aeb AT cwi.nl>

HISTORY
       Introduced with version 1.1.92 of the Linux kernel.

SEE ALSO
       console(4), tty(4), ttys(4), selection(1)



Linux                             1995-02-19                            VCS(4)

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