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¶
This page is part of release 3.44 of the Linux
man-pages project. A
description of the project, and information about reporting bugs, can be found
at
http://www.kernel.org/doc/man-pages/.