Using the Input Subsystem, Part II

No matter how many buttons an input device has or how many kinds of events it can generate, you can now work with it from user space.
Force Feedback

Three additional ioctl functions may be used for controlling force-feedback devices: EVIOCSFF, EVIOCRMFF and EVIOCGEFFECT. These functions currently send a force-feedback effect, remove a force-feedback effect and determine how many simultaneous effects can be used, respectively. Because the force-feedback support is still emerging and substantial work remains to be done, it is a little premature to fully document the API. The web sites listed in the Resources section of this article may have updated information by the time you read this.



Brad Hards is the technical director for Sigma Bravo, a small professional services company in Canberra, Australia. In addition to Linux, his technical focus includes aircraft system integration and certification, GPS and electronic warfare. Comments on this article may be sent to



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Full example source.

waeva I dont care's picture

I am making a full source code basic tutorial for copy pasting should be done in a few days I'll post the link. It will also include handling a joystick.
A forward note in the 2.6 version of kernel you need root permissions to open event# files. So you need to run under sudo or make a dev rule.

Best Way to Detect Hotplug from App

E Franz's picture

To Solusrex: I have the same issue. I see at
that the kernel should call /sbin/hotplug which calls device-specific scripts to handle the add or remove event. I'm going to try to instrument the associated script to somehow send a message to my app to notify it. You might try the same.
E Franz

Seriously, how hard is it to give useful code examples?

Bryan Ischo's picture

WHY would you not include the entire code fragment in each example? WHY are you obfuscating some parameter types? Example: you describe getting the unique identifier of a device using the EVIOCGUNIQ ioctl. But you reference a magical variable called 'uniq' the type of which you do not define anywhere. Exactly how is hiding this information supposed to be useful? Who edited this? Why are you trying to make my life more difficult? WTF?!?!

What is the best way to

Solusrex's picture

What is the best way to detect from an app that a USB input device was plugged/unplugged beside polling it using open() function?

Hello, you can write a small

Uwe's picture


you can write a small app that is called from a udev rule.
(You have to add a small rule for this)

Inside of the app you can broadcast a small message on a local socket.

Every app that listens on this socket, receive this notification.


Retrieve Scan Infor

sfog's picture

Hi all...

I need to retrieve all data (position x,y) from the driver when i try to draw something on the pad tablet....

can anyone tell me how to get the ABS when i got event scan ??

bad code

Anonymous's picture

The author clearly does not understand the beauty of copy and paste. Each listing of code just will never compile because the variables are not defined. People have to pull their hair to figure it out.

HELP: Retrieving Input from a Device

Fatih Isler's picture

Hi All,

In one of my project, I need to retrieve events from keyboard in Linux environment. For doing that in my code firstly I opened /dev/input/event0 file and it was successfully opened. However, when I was trying to read something from that file. The read() function stuck and my program can't execute any further steps. Does anybody know why this kind of problem that I encounter and how can I solve this problem. Here is my code:

P.S: In order to execute program you need to be super user and then need to execute code. Otherwise, program will can give "File can not open" error.

#define FILE_PATH "/dev/input/event0"

int main()
	printf("Starting KeyEvent Module\n");

	//int file, version;
	size_t file;
	const char *str = FILE_PATH;

	printf("File Path: %s\n", str);

	if((file = open(str, O_RDWR)) < 0)
		printf("ERROR:File can not open\n");

	struct input_event event[64];

        size_t reader;
        reader = read(file, &event, sizeof(struct input_event) * 64);

        printf("DO NOT COME HERE...\n");

	return 0;

change this : reader =

Anonymous's picture

change this :
reader = read(file, &event, sizeof(struct input_event) * 64);
reader = read(file, event, sizeof(struct input_event) * 64);

You need one more flag

FireHL's picture

change this:

if((file = open(str, O_RDWR)) < 0)


if((file = open(str, O_RDWR|O_NDELAY)) < 0)

and check manual by 'man 2 open'

nice to see, but how many users have figured how to get a joysti

jago25_98's picture

I for one can figure out how /etc/devfsd.conf needs to be edited to setup /dev/joysticks, or /dev/js* with nothing under /dev/input being created either.

linux/Doc*/devices says digital joysticks are char-15,128 while the help doc under makeconfig states char 13:0+ - /dev/input/jsX

neither of this help me much.

If there was documentation somewhere in the world about how to setup joysticks we could hopefully have more people using this code :)