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
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_ioctl(4), 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.
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)
xetterm −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); }
This page is part of release 4.07 of the Linux man-pages
project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
Copyright (c) 1995 James R. Van Zandt <jrvvanzandt.mv.com> Sat Feb 18 09:11:07 EST 1995 %%%LICENSE_START(GPLv2+_DOC_FULL) 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, see <http://www.gnu.org/licenses/>. %%%LICENSE_END Modified, Sun Feb 26 15:08:05 1995, faithcs.unc.edu 2007-12-17, Samuel Thibault <samuel.thibaultens-lyon.org>: document the VT_GETHIFONTMASK ioctl " |