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(EXIT_FAILURE); } (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)
Copyright (c) 1995 James R. Van Zandt <jrv@vanzandt.mv.com> Sat Feb 18 09:11:07 EST 1995 This is free documentation; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. The GNU General Public License's references to "object code" and "executables" are to be interpreted as the output of any document formatting or typesetting system, including intermediate and printed output. This manual is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this manual; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. Modified, Sun Feb 26 15:08:05 1995, faith@cs.unc.edu " |