vcs, vcsa — virtual console memory
/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 ioctl
s 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.
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> int main(void) { 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); exit(EXIT_SUCCESS); }
gpm(8), console(4), tty(4), ttyS(4)
|