LinuxQuestions.org - Multi monitor CLI adventures

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