Cannot capture keystrokes in C [Ubuntu 16.04LTS]

Question

I've been trying to make a keylogger on Ubuntu 16.04LTS for a while now, and this is what I have so far:

#include <stdio.h>
#include <fcntl.h>
#include <linux/input.h>
#include <stdbool.h>

int main()
{
        char devname[] = "/dev/input/event0";
        int device = open(devname, O_RDONLY);
        struct input_event ev; 
        bool logging = true;

        while(logging)
        {
                if (read(device,&ev, sizeof(ev)) >= 0){ 
                        printf("Key: %i State: %i Type: %i\n",ev.code,ev.value,ev.type);
                }
        }

}

However when I compile and run it (gcc), it does not output anything! I've tried every device listed in /dev/input/by-id andthensome,but nothing seems to work.

When I compile the code using GCC, I get the warning:

keylogger.c: In function ‘main’:
keylogger.c:15:7: warning: implicit declaration of function ‘read’ [-Wimplicit-function-declaration]
   if (read(device,&ev, sizeof(ev)) >= 0){       
       ^

Which I have no idea if this has to do with the functionality of the program.

Any help is appreciated! Thanks!

`read` has its prototype in `unistd.h` .. whenever you get this type implicit function declaration warning do `man **function_name**`.. `man` has multiple pages..and `read` is in page 2 ...so you do `man 2 read` — Parnab Sanyal, Sep 18 '16 at 16:11
@ParnabSanyal Thanks, but unfortunately it is still not working. To check, the default keyboard in Ubuntu is /dev/input/event0, correct? — Logan Darby, Sep 18 '16 at 16:34
I know...I have not given you the solution.I don't have it yet .I have told you the way to fix implicit function warnings. — Parnab Sanyal, Sep 18 '16 at 16:42
It's Okay. Do a thing. After the read function call.. do `printf("%s\n",strerror(errno));`. And see what it says. Do two imports `errno.h` and `string.h` — Parnab Sanyal, Sep 18 '16 at 16:46
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/123643/discussion-between-parnab-sanyal-and-logan-darby). — Parnab Sanyal, Sep 18 '16 at 16:54

Logan Darby · Answer 1 · 2016-09-18T17:54:02.827

1

I figured it out, it was a simple matter of not having superuser permissions. I excecuted the file using sudo and now everything is fine.

edited Sep 18 '16 at 17:54

answered Sep 18 '16 at 17:37

Logan Darby

145
16

have you tried to run the executable as `sudo`. Instead of changing the file permission. – Parnab Sanyal Sep 18 '16 at 17:47
That's sad :-( . anyway glad that you have figured it out. – Parnab Sanyal Sep 18 '16 at 17:53
Whoops, nevermind! I compiled it using sudo but didnt excecute it with sudo, my bad. – Logan Darby Sep 18 '16 at 17:53
well, try and see what happens. – Parnab Sanyal Sep 18 '16 at 17:53

Cannot capture keystrokes in C [Ubuntu 16.04LTS]

1 Answers1