vcsa(4) -- Linux man page

NAME

DESCRIPTION

/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

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

AUTHOR

HISTORY

SEE ALSO