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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 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  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

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