libinput: FAQs - Frequently Asked Questions

FAQs - Frequently Asked Questions

Frequently asked questions about libinput.

# Why doesn't libinput support ...?

First, read What is libinput? If you have a feature that you think libinput needs to support, please file a bug report. See Reporting bugs for more details.

# My mouse moves too fast, even at the slowest setting

This is a symptom of high-dpi mice (greater than 1000dpi). These devices need a udev hwdb entry to normalize their motion. See Normalization of relative motion for a detailed explanation.

# My trackpoint moves too slow or too fast

This is a symptom of an invalid trackpoint range. These devices need a udev hwdb entry to specify the range available so libinput can adjust the pointer acceleration accordingly. See Motion range on trackpoints for a detailed explanation.

# Why isn't touchpad tap-to-click enabled by default

See Tap-to-click default setting

# Why does my touchpad lose track of touches

The most common cause for this is an incorrect pressure threshold range. See Touchpad pressure-based touch detection for more info.

# Kinetic scrolling does not work

The X.Org synaptics driver implemented kinetic scrolling in the driver. It measures the scroll speed and once the finger leaves the touchpad the driver keeps sending scroll events for a predetermined time. This effectively provides for kinetic scrolling without client support but triggers an unfixable bug: the client cannot know that the events are from a kinetic scroll source. Scroll events in X are always sent to the current cursor position, a movement of the cursor after lifting the finger will send the kinetic scroll events to the new client, something the user does not usually expect. A key event during the kinetic scroll procedure causes side-effects such as triggering zoom.

libinput does not implement kinetic scrolling for touchpads. Instead it provides the libinput_event_pointer_get_axis_source() function that enables callers to implement kinetic scrolling on a per-widget basis, see Scroll sources.

# Is libinput GPL-licensed?

No, libinput is MIT licensed. The Linux kernel header file linux/input.h in libinput's tree is provided to ensure the same behavior regardless of which kernel version libinput is built on. It does not make libinput GPL-licensed.

# Where is the configuration stored?

libinput does not store configuration options, it is up to the caller to manage these and decide which configuration option to apply to each device. This must be done at startup, after a resume and whenever a new device is detected.

One commonly used way to configure libinput is to have the Wayland compositor expose a compositor-specific configuration option. For example, in a GNOME stack, the gnome-control-center modifies dconf entries. These changes are read by mutter and applied to libinput. Changing these entries via the gsettings commandline tool has the same effect.

Another commonly used way to configure libinput is to have xorg.conf.d snippets. When libinput is used with the xf86-input-libinput driver in an X.Org stack, these options are read on startup and apply to each device. Changing properties at runtime with the xinput commandline tool has the same effect.

In both cases, the selection of available options and how they are exposed depends on the libinput caller (e.g. mutter or xf86-input-libinput).

This has an effect on the availability of configuration options: if an option is not exposed by the intermediary, it cannot be configured by the client. Also some configuration options that are provided by the intermediary may not be libinput-specific configuration options.

# How do I configure my device on Wayland?

See Where is the configuration stored? Use the configuration tool provided by your desktop environment (e.g. gnome-control-center) or direct access to your desktop environment's configuration storage (e.g. gsettings).

# How do I configure my device on X?

See Where is the configuration stored? If your desktop environment does not provide a graphical configuration tool you can use an xorg.conf.d snippet. Usually, such a snippet looks like this:

    $> cat /etc/X11/xorg.conf.d/99-libinput-custom-config.conf
    Section "InputClass"
      Identifier "something to identify this snippet"
      MatchDriver "libinput"
      MatchProduct "substring of the device name"
      Option "some option name" "the option value"
    EndSection

The identifier is merely a human-readable string that shows up in the log file. The MatchProduct line should contain the device name or a substring of the device name that the snippet should apply to. For a full list of option names and permitted values, see the libinput man page. xorg.conf.d snippets like the above apply to hotplugged devices but can be overwritten at runtime by desktop tools. Multiple snippets may be placed into the same file.

For run-time configuration and testing, the xinput debugging tool can modify a devices' properties. See the libinput man page for supported property names and values. Usually, an invocation looks like this:

    $> xinput set-prop "the device name" "the property name" value [value2] [value3]

Note
  Changes performed by xinput do not persist across device hotplugs. xinput is considered a debugging and testing tool only and should not be used for permanent configurations.

# Can you add a configuration option for $FEATURE?

No. At least that's going to be the initial answer. Read Why libinput doesn't have a lot of configuration options first. Configuration options for most features are a signal that we are incapable of handling it correctly. To get to that point, we want to be sure we're truly incapable of doing so. libinput has several features that are handled automatically (and correctly) that users wanted to have configuration options for initially.

So the answer to this question will almost always be 'no'. A configuration option is, in most cases, a cop-out.

# Why don't synclient and syndaemon work with libinput?

Synclient and syndaemon rely on X input device properties that are specific to the xf86-input-synaptics X.Org input driver. Both were written when the synaptics driver was the only commmon touchpad driver in existence. They assume that if the properties aren't available, no touchpad is available either. The xf86-input-libinput X.Org input driver does not export these driver-specific properties, synclient/syndaemon will thus not detect the touchpad and refuse to work. Other tools that rely on synclient/syndaemon or those same properties also do not work with xf86-input-libinput.

Most of syndaemon's functionality is built into libinput, see Disable-while-typing. synclient is merely a configuration tool, see How do I configure my device on X? for similar functionality.

See also the blog posts The definitive guide to synclient and The future of xinput, xmodmap, setxkbmap, xsetwacom and other tools under Wayland

# Does libinput support non-Wacom tablets?

Yes, though unfortunately many non-Wacom tablets suffer from bad firmware and don't send the required events. But they should all work nonetheless. If you have a tablet that does not work with libinput, please file a bug.

# My tablet doesn't work

If you see the message

    libinput bug: device does not meet tablet criteria. Ignoring this device.

or the message

    missing tablet capabilities [...] Ignoring this device.

your tablet device does not have the required capabilities to be treated as a tablet. This is usually a problem with the device and the kernel driver. See Required tablet capabilities for more details.

# How to apply hwdb changes

Sometimes users are asked to test updates to the udev hwdb or patches that include a change to the hwdb. See Configuring the hwdb for details on the hwdb and how to modify it locally.

# What causes the "timer offset negative" warning?

libinput relies on the caller to call libinput_dispatch() whenever data is available on the epoll-fd. Doing so will process the state of all devices and can trigger some timers to be set (e.g. palm detection, tap-to-click, disable-while-typing, etc.). Internally, libinput's time offsets are always based on the event time of the triggering event.

For example, a touch event with time T may trigger a timer for the time T + 180ms. When setting a timer, libinput checks the wall clock time to ensure that this time T + offset is still in the future. If not, the warning is logged.

When this warning appears, it simply means that too much time has passed between the event occurring (and the epoll-fd triggering) and the current time. In almost all cases this is an indication of the caller being overloaded and not handling events as speedily as required.

The warning has no immediate effect on libinput's behavior but some of the functionality that relies on the timer may be impeded (e.g. palms are not detected as they should be).