1VCS(4)                     Linux Programmer's Manual                    VCS(4)
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NAME

6       vcs, vcsa - virtual console memory
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DESCRIPTION

9       /dev/vcs0 is a character device with major number 7 and minor number 0,
10       usually of mode 0644 and owner root.tty.  It refers to  the  memory  of
11       the currently displayed virtual console terminal.
12
13       /dev/vcs[1-63]  are  character  devices  for virtual console terminals,
14       they have major number 7 and minor number 1 to 63,  usually  mode  0644
15       and  owner  root.tty.  /dev/vcsa[0-63] are the same, but using unsigned
16       shorts (in host byte order) that include attributes, and prefixed  with
17       four  bytes  giving  the  screen dimensions and cursor position: lines,
18       columns, x, y.  (x = y = 0 at the top left corner of the screen.)
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20       When a 512-character font is  loaded,  the  9th  bit  position  can  be
21       fetched  by applying the ioctl(2) VT_GETHIFONTMASK operation (available
22       in Linux kernels 2.6.18 and above)  on  /dev/tty[1-63];  the  value  is
23       returned  in  the unsigned short pointed to by the third ioctl(2) argu‐
24       ment.
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26       These devices replace the screendump ioctl(2) operations of  ioctl_con‐
27       sole(2),  so the system administrator can control access using filesys‐
28       tem permissions.
29
30       The devices for the first eight virtual consoles may be created by:
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32           for x in 0 1 2 3 4 5 6 7 8; do
33               mknod -m 644 /dev/vcs$x c 7 $x;
34               mknod -m 644 /dev/vcsa$x c 7 $[$x+128];
35           done
36           chown root:tty /dev/vcs*
37
38       No ioctl(2) requests are supported.
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FILES

41       /dev/vcs[0-63]
42       /dev/vcsa[0-63]
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VERSIONS

45       Introduced with version 1.1.92 of the Linux kernel.
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EXAMPLE

48       You may do a screendump on vt3 by switching to vt1 and typing
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50           cat /dev/vcs3 >foo
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52       Note that the output does not contain newline characters, so some  pro‐
53       cessing may be required, like in
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55           fold -w 81 /dev/vcs3 | lpr
56
57       or (horrors)
58
59           xetterm -dump 3 -file /proc/self/fd/1
60
61       The /dev/vcsa0 device is used for Braille support.
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63       This  program  displays  the  character and screen attributes under the
64       cursor of the second virtual console, then changes the background color
65       there:
66
67       #include <unistd.h>
68       #include <stdlib.h>
69       #include <stdio.h>
70       #include <fcntl.h>
71       #include <sys/ioctl.h>
72       #include <linux/vt.h>
73
74       int
75       main(void)
76       {
77           int fd;
78           char *device = "/dev/vcsa2";
79           char *console = "/dev/tty2";
80           struct {unsigned char lines, cols, x, y;} scrn;
81           unsigned short s;
82           unsigned short mask;
83           unsigned char ch, attrib;
84
85           fd = open(console, O_RDWR);
86           if (fd < 0) {
87               perror(console);
88               exit(EXIT_FAILURE);
89           }
90           if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
91               perror("VT_GETHIFONTMASK");
92               exit(EXIT_FAILURE);
93           }
94           (void) close(fd);
95           fd = open(device, O_RDWR);
96           if (fd < 0) {
97               perror(device);
98               exit(EXIT_FAILURE);
99           }
100           (void) read(fd, &scrn, 4);
101           (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
102           (void) read(fd, &s, 2);
103           ch = s & 0xff;
104           if (attrib & mask)
105               ch |= 0x100;
106           attrib = ((s & ~mask) >> 8);
107           printf("ch='%c' attrib=0x%02x\n", ch, attrib);
108           attrib ^= 0x10;
109           (void) lseek(fd, -1, 1);
110           (void) write(fd, &attrib, 1);
111           exit(EXIT_SUCCESS);
112       }
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SEE ALSO

115       ioctl_console(2), tty(4), ttyS(4), gpm(8)
116

COLOPHON

118       This  page  is  part of release 4.16 of the Linux man-pages project.  A
119       description of the project, information about reporting bugs,  and  the
120       latest     version     of     this    page,    can    be    found    at
121       https://www.kernel.org/doc/man-pages/.
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125Linux                             2017-05-03                            VCS(4)