What's new? | Linux Software | Linux RPM Database | Linux Howtos | Add Software |

Free eBook: The 7 Things that IT Security Professionals MUST KNOW!

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 admin-
       istrator 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  charac-
       ters,  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 <aebcwi.nl>

HISTORY
       Introduced with version 1.1.92 of the Linux kernel.

SEEALSO
       console(4), tty(4), ttys(4), selection(1)



Linux                             1995-02-19                            VCS(4)