1VCS(4) Linux Programmer's Manual VCS(4)
2
6 vcs, vcsa - virtual console memory
7
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 /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.)
19 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.
25 These devices replace the screendump ioctl(2) operations of console(4),
27 so the system administrator can control access using file system per‐
28 missions.
29 The devices for the first eight virtual consoles may be created by:
31 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 No ioctl(2) requests are supported.
39
41 /dev/vcs[0-63]
42 /dev/vcsa[0-63]
43
45 Introduced with version 1.1.92 of the Linux kernel.
46
48 You may do a screendump on vt3 by switching to vt1 and typing cat
49 /dev/vcs3 >foo. Note that the output does not contain newline charac‐
50 ters, so some processing may be required, like in fold -w 81 /dev/vcs3
51 | lpr or (horrors) setterm -dump 3 -file /proc/self/fd/1.
52 The /dev/vcsa0 device is used for Braille support.
54 This program displays the character and screen attributes under the
56 cursor of the second virtual console, then changes the background color
57 there:
58 #include <unistd.h>
60 #include <stdlib.h>
61 #include <stdio.h>
62 #include <fcntl.h>
63 #include <sys/ioctl.h>
64 #include <linux/vt.h>
65 int
67 main(void)
68 {
69 int fd;
70 char *device = "/dev/vcsa2";
71 char *console = "/dev/tty2";
72 struct {unsigned char lines, cols, x, y;} scrn;
73 unsigned short s;
74 unsigned short mask;
75 unsigned char ch, attrib;
76 fd = open(console, O_RDWR);
78 if (fd < 0) {
79 perror(console);
80 exit(EXIT_FAILURE);
81 }
82 if (ioctl(fd, VT_GETHIFONTMASK, &mask) < 0) {
83 perror("VT_GETHIFONTMASK");
84 exit(EXIT_FAILURE);
85 }
86 (void) close(fd);
87 fd = open(device, O_RDWR);
88 if (fd < 0) {
89 perror(device);
90 exit(EXIT_FAILURE);
91 }
92 (void) read(fd, &scrn, 4);
93 (void) lseek(fd, 4 + 2*(scrn.y*scrn.cols + scrn.x), 0);
94 (void) read(fd, &s, 2);
95 ch = s & 0xff;
96 if (attrib & mask)
97 ch |= 0x100;
98 attrib = ((s & ~mask) >> 8);
99 printf("ch='%c' attrib=0x%02x\n", ch, attrib);
100 attrib ^= 0x10;
101 (void) lseek(fd, -1, 1);
102 (void) write(fd, &attrib, 1);
103 exit(EXIT_SUCCESS);
104 }
105
107 console(4), tty(4), ttyS(4), gpm(8)
108
110 This page is part of release 3.22 of the Linux man-pages project. A
111 description of the project, and information about reporting bugs, can
112 be found at http://www.kernel.org/doc/man-pages/.
113Linux 2007-12-17 VCS(4)