NAME

       vcs, vcsa - virtual console memory

DESCRIPTION

       /dev/vcs0  is a character device with major number 7 and minor number 0, usually with mode
       0644 and ownership 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 ownership 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  ioctl_console(2),  so  the
       system administrator can control access using filesystem 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.

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>
       #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 attrib;
           int ch;

           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), SEEK_SET);
           (void) read(fd, &s, 2);
           ch = s & 0xff;
           if (s & mask)
               ch |= 0x100;
           attrib = ((s & ~mask) >> 8);
           printf("ch=%#03x attrib=%#02x\n", ch, attrib);
           s ^= 0x1000;
           (void) lseek(fd, -2, SEEK_CUR);
           (void) write(fd, &s, 2);
           exit(EXIT_SUCCESS);
       }

SEE ALSO

       ioctl_console(2), tty(4), ttyS(4), gpm(8)

COLOPHON

       This  page  is  part of release 5.13 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at https://www.kernel.org/doc/man-pages/.