Hi all,
I've always enjoyed doing stuff in CLI rather than GUI when possible. That lead to the fact that currently I do almost everything in CLI. I've wanted to use multiple monitors on CLI for a very long time but never found out how to do it. Until now that is. I'm so happy I finally got it working that I'd like to share how I did it.
So what do you need?
- Basic Linux command line skills
- 2 monitors
- 2 (identical?) video cards,
- a mother board that supports at least two video cards
- an editor like vi(m), emac, nano, ...
- a compiler
- electricity.
So let's get rolling.
I assume you've got your hardware all set up properly and you just booted with the 2 videocards with on each video card a screen attached. There's a big chance one of your monitors is working and the other one isn't or is a mirror of the first monitor.
Either way, let's check if they were detected properly.
Code:
username@host:~$ lspci | grep -i vga
01:00.0 VGA compatible controller: NVIDIA Corporation NV44 [GeForce 6200 TurboCache(TM)] (rev a1)
02:00.0 VGA compatible controller: NVIDIA Corporation NV44 [GeForce 6200 TurboCache(TM)] (rev a1)
username@host:~$ ls /dev/fb*
/dev/fb0 /dev/fb1
username@host:~$
If you see 2 separate video cards and if you see 2 framebuffer devices (/dev/fb0 and /dev/fb1 then the hardest part is over :-).
The next step is creating a file with the following C code in it an compile it. If you don't have a compiler installed or if you are not sure you can always install it yourself:
On Debian
Code:
apt-get upgrade
apt-get install build-essential
On CentOS, it should be something like this:
Code:
yum groupinstall "Development Tools" "Development Libraries"
Then create a text file with
this content. And in case this website ever goes down, I included the code here:
Code:
/* this is userspace utility which allows you to redirect console to another fb device
* You can specify devices & consoles by both numbers and devices. Framebuffers numbers
* are zero based (/dev/fb0 ... ), consoles begins with 1 (/dev/tty1 ... )
*/
#include <linux/fb.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char* argv[]) {
struct fb_con2fbmap c2m;
char* fbPath;
u_int32_t con, fb;
char* e;
char* progname = strrchr(argv[0], '/');
int f;
if (progname)
progname++;
else
progname = argv[0];
if (argc < 3) {
fprintf(stderr, "usage: %s fbdev console\n", progname);
return 1;
}
fb = strtoul(argv[1], &e, 10);
if (*e) {
struct stat sbf;
if (stat(argv[1], &sbf)) {
fprintf(stderr, "%s: are you sure that %s can be used to describe fbdev?\n", progname, argv[1]);
return 1;
}
if (!S_ISCHR(sbf.st_mode)) {
fprintf(stderr, "%s: %s must be character device\n", progname, argv[1]);
return 1;
}
fb = sbf.st_rdev & 0xFF;
if (fb >= 32)
fb >>= 5;
fbPath = argv[1];
} else
fbPath = "/dev/fb0";
con = strtoul(argv[2], &e, 10);
if (*e) {
struct stat sbf;
if (stat(argv[2], &sbf)) {
fprintf(stderr, "%s: are you sure that %s can be used to describe vt?\n", progname, argv[2]);
return 1;
}
if (!S_ISCHR(sbf.st_mode)) {
fprintf(stderr, "%s: %s must be character device\n", progname, argv[2]);
return 1;
}
con = sbf.st_rdev & 0xFF;
}
c2m.console = con;
c2m.framebuffer = fb;
f = open(fbPath, O_RDWR);
if (f < 0) {
fprintf(stderr, "%s: Cannot open %s\n", progname, fbPath);
return 1;
}
if (ioctl(f, FBIOPUT_CON2FBMAP, &c2m)) {
fprintf(stderr, "%s: Cannot set console mapping\n", progname);
close(f);
return 1;
}
close(f);
return 0;
}
Save the file and compile it with gcc. Once it has compiled try to run it.
Code:
username@host:~$ gcc -o con2fb con2fb.c
username@host:~$ ./conf2fb /dev/fb0 /dev/tty1
username@host:/$ ./conf2fb /dev/fb1 /dev/tty2
The second line connected the first framebuffer device (/dev/fb0) to your first terminal device (/dev/tty1). If you press Ctrl-Alt-F1 now, your cursor on one monitor should start blinking and everything you type should go to that monitor. If you type Ctrl-Alt-F2, the cursor should go to the other screen and the keyboard is "attached" to the other screen.
Congratulations! You've got yourself a helluva working multi-monitor setup :-)
Feel free to comment. This is a very short howto.
- Make the configuration persistent across reboots
- Why exactly does the monitor that does not have the focus stop updating? Is there a fix or workaround for that?
- Check if it works with two different video cards. I have tested this before with a AMD and NVIDIA combination but that did not work (only /dev/fb0 and no /dev/fb1 created, also one video card not detected while both work well separately)
- Can this also work with one video card with 2 outputs? (I've tested it but I only get /dev/fb0 and no /dev/fb1. Do we really need 2 separate video cards?)
- Check if it works with more than 2 monitors
- Include more troubleshooting
