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

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

46       Introduced with version 1.1.92 of the Linux kernel.
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EXAMPLES

49       You may do a screendump on vt3 by switching to vt1 and typing
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51           cat /dev/vcs3 >foo
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53       Note  that the output does not contain newline characters, so some pro‐
54       cessing may be required, like in
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56           fold -w 81 /dev/vcs3 | lpr
57
58       or (horrors)
59
60           setterm -dump 3 -file /proc/self/fd/1
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62       The /dev/vcsa0 device is used for Braille support.
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64       This program displays the character and  screen  attributes  under  the
65       cursor of the second virtual console, then changes the background color
66       there:
67
68       #include <unistd.h>
69       #include <stdlib.h>
70       #include <stdio.h>
71       #include <fcntl.h>
72       #include <sys/ioctl.h>
73       #include <linux/vt.h>
74
75       int
76       main(void)
77       {
78           int fd;
79           char *device = "/dev/vcsa2";
80           char *console = "/dev/tty2";
81           struct {unsigned char lines, cols, x, y;} scrn;
82           unsigned short s;
83           unsigned short mask;
84           unsigned char attrib;
85           int ch;
86
87           fd = open(console, O_RDWR);
88           if (fd < 0) {
89               perror(console);
90               exit(EXIT_FAILURE);
91           }
92           if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
93               perror("VT_GETHIFONTMASK");
94               exit(EXIT_FAILURE);
95           }
96           (void) close(fd);
97           fd = open(device, O_RDWR);
98           if (fd < 0) {
99               perror(device);
100               exit(EXIT_FAILURE);
101           }
102           (void) read(fd, &scrn, 4);
103           (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), SEEK_SET);
104           (void) read(fd, &s, 2);
105           ch = s & 0xff;
106           if (s & mask)
107               ch |= 0x100;
108           attrib = ((s & ~mask) >> 8);
109           printf("ch=0x%03x attrib=0x%02x\n", ch, attrib);
110           s ^= 0x1000;
111           (void) lseek(fd, -2, SEEK_CUR);
112           (void) write(fd, &s, 2);
113           exit(EXIT_SUCCESS);
114       }
115

SEE ALSO

117       ioctl_console(2), tty(4), ttyS(4), gpm(8)
118

COLOPHON

120       This page is part of release 5.07 of the Linux  man-pages  project.   A
121       description  of  the project, information about reporting bugs, and the
122       latest    version    of    this    page,    can     be     found     at
123       https://www.kernel.org/doc/man-pages/.
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127Linux                             2020-06-09                            VCS(4)