man:vcs
VCS(4) Linux Programmer's Manual VCS(4)
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) argu- ment.
These devices replace the screendump ioctl(2) operations of ioctl_con- sole(2), so the system administrator can control access using filesys- tem 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 pro- cessing 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); }
SEE ALSO
ioctl_console(2), tty(4), ttyS(4), gpm(8)
COLOPHON
This page is part of release 4.16 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/.
Linux 2017-05-03 VCS(4)
/data/webs/external/dokuwiki/data/pages/man/vcs.txt · Last modified: 2019/05/17 09:47 by 127.0.0.1