# vcs

## 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 short_ s (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 since Linux 2.6.18) 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 Linux 1.1.92.
    


## 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);
           }
    


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