mirror of https://github.com/mkerrisk/man-pages
115 lines
3.5 KiB
Groff
115 lines
3.5 KiB
Groff
.\" Copyright (c) 1995 James R. Van Zandt <jrv@vanzandt.mv.com>
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.\" Sat Feb 18 09:11:07 EST 1995
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.\"
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, write to the Free
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.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
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.\" USA.
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.\"
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.\" Modified, Sun Feb 26 15:08:05 1995, faith@cs.unc.edu
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.\" "
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.TH VCS 4 1995-02-19 "Linux" "Linux Programmer's Manual"
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.SH NAME
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vcs, vcsa \- virtual console memory
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.SH DESCRIPTION
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\fI/dev/vcs0\fP is a character device with major number 7 and minor number
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0, usually of mode 0644 and owner root.tty. It refers to the memory
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of the currently
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displayed virtual console terminal.
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.LP
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\fI/dev/vcs[1\-63]\fP are character devices for virtual console
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terminals, they have major number 7 and minor number 1 to 63, usually
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mode 0644 and owner root.tty. \fI/dev/vcsa[0\-63]\fP are the same, but
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including attributes, and prefixed with four bytes giving the screen
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dimensions and cursor position: \fIlines\fP, \fIcolumns\fP, \fIx\fP, \fIy\fP.
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(\fIx\fP = \fIy\fP = 0 at the top left corner of the screen.)
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.PP
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These replace the screendump
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.IR ioctl s
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of \fBconsole\fP(4), so the system
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administrator can control access using file system permissions.
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.PP
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The devices for the first eight virtual consoles may be created by:
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.nf
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for x in 0 1 2 3 4 5 6 7 8; do
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mknod \-m 644 /dev/vcs$x c 7 $x;
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mknod \-m 644 /dev/vcsa$x c 7 $[$x+128];
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done
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chown root:tty /dev/vcs*
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.fi
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No
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.BR ioctl ()
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requests are supported.
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.SH EXAMPLES
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You may do a screendump on vt3 by switching to vt1 and typing
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\fIcat /dev/vcs3 >foo\fP. Note that the output does not contain
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newline characters, so some processing may be required, like
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in \fIfold \-w 81 /dev/vcs3 | lpr\fP or (horrors)
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\fIsetterm \-dump 3 \-file /proc/self/fd/1\fP.
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.LP
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The \fI/dev/vcsa0\fP device is used for Braille support.
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This program displays the character and screen attributes under the
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cursor of the second virtual console, then changes the background color
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there:
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.nf
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdio.h>
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#include <fcntl.h>
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int main() {
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int fd;
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char *device = "/dev/vcsa2";
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struct {unsigned char lines, cols, x, y;} scrn;
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char ch, attrib;
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fd = open(device, O_RDWR);
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if (fd < 0) {
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perror(device);
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exit(1);
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}
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(void)read(fd, &scrn, 4);
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(void)lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
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(void)read(fd, &ch, 1);
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(void)read(fd, &attrib, 1);
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printf("ch='%c' attrib=0x%02x\\n", ch, attrib);
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attrib ^= 0x10;
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(void)lseek(fd, \-1, 1);
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(void)write(fd, &attrib, 1);
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return 0;
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}
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.fi
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.SH FILES
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/dev/vcs[0\-63]
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.br
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/dev/vcsa[0\-63]
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.SH AUTHOR
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Andries Brouwer <aeb@cwi.nl>
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.SH HISTORY
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Introduced with version 1.1.92 of the Linux kernel.
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.SH "SEE ALSO"
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.BR gpm (8),
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.BR console (4),
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.BR tty (4),
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.BR ttyS (4)
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