/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.
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 <stdio.h> #include <fcntl.h> void main() { int fd; struct {char lines, cols, x, y;} scrn; char ch, attrib; fd = open("/dev/vcsa2", O_RDWR); (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); }