Logitech K780 switch media and function keys on linux

k780.md

Media/function keys on K780

K780 doesn't have a hard switch to lock the function keys. Logitech provides a utility to do this on Windows and iOS but not on Linux. You need to manually remap the keys.

Below works for Arch Linux, other systemd based distros should be about the same.

There's a problem with the F1-F3 keys as they're hardware specific and don't emit an event if pressed on their own and therefore can't be remapped. I might be wrong as I haven't spend any time on researching that.

Edit: about htat, see @tangruize comments below https://gist.github.com/andrejcremoznik/e56234138305226abd41fe4d1d2561a3#gistcomment-3390489

Create file /etc/udev/hwdb.d/95-k780.hwdb

# Logitech K780 map:
# Fn + F4/F5/F6 ==> F4/F5/F6
evdev:input:b0003v046Dp405B*
  KEYBOARD_KEY_c0223=f4
  KEYBOARD_KEY_70065=f5
  KEYBOARD_KEY_c0224=f6

Rebuild hwdb.bin and apply new keys

sudo systemd-hwdb update
sudo udevadm trigger

Make permanent

Make sure the ConditionNeedsUpdate=/etc is commented out in /usr/lib/systemd/system/systemd-hwdb-update.service. If it isn't create an override:

sudo systemctl edit --full systemd-hwdb-update.service

Comment out:
#ConditionNeedsUpdate=/etc

This creates a replacement systemd unit file in /etc/systemd/system/systemd-hwdb-update.service. If some update breaks anything related to this, remove it and recreate with systemctl edit like before.

Read more

• https://wiki.archlinux.org/index.php/Keyboard_input#Identifying_keycodes
• https://wiki.archlinux.org/index.php/Map_scancodes_to_keycodes

I spent some time to research this problem. F1 and F3 are frequently used but key map doesn't support to invert it. And I think @HoinzeyBear's method won't work. @adriankontny's method is useful if you use a Logitech unifying receiver. However, Solaar doesn't support Bluetooth. I learned how to analyze the communication to the HID device. And here is my workaround:

SCRIPT_FILE=/usr/local/bin/logi-fn-swap.pl
vim $SCRIPT_FILE

#!/usr/bin/perl

# Add K780. Related resources:
## https://askubuntu.com/questions/326959/how-can-i-make-the-function-keys-the-default-on-a-logitech-k760-bluetooh-keyboar
## http://www.trial-n-error.de/posts/2012/12/31/logitech-k810-keyboard-configurator
## https://www.spinics.net/lists/linux-input/msg24280.html
## https://gist.github.com/andrejcremoznik/e56234138305226abd41fe4d1d2561a3

use strict;
use warnings;

use constant HIDIOCGRAWINFO         => 2148026371;
#use constant BUS_BLUETOOTH          =>          5;
use constant HID_VENDOR_ID_LOGITECH =>       1133;
use constant HID_DEVICE_ID_K760     =>     -19690;
use constant HID_DEVICE_ID_K760_ALT =>     -19688;
use constant HID_DEVICE_ID_K810     =>     -19687;
use constant HID_DEVICE_ID_K780     =>     -19653;
use constant HID_DEVICE_ID_K780_USB =>      16475;

my %message = (
    HID_DEVICE_ID_K760() => {
        on   => (pack "C*", 0x10, 0xff, 0x05, 0x14, 0x00, 0x00, 0x00),
        off  => (pack "C*", 0x10, 0xff, 0x05, 0x14, 0x01, 0x00, 0x00),
    },
    HID_DEVICE_ID_K760_ALT() => {
        on   => (pack "C*", 0x10, 0xff, 0x05, 0x14, 0x00, 0x00, 0x00),
        off  => (pack "C*", 0x10, 0xff, 0x05, 0x14, 0x01, 0x00, 0x00),
    },
    HID_DEVICE_ID_K780() => {
        on   => (pack "C*", 0x11, 0xff, 0x0c, 0x1d, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
        off  => (pack "C*", 0x11, 0xff, 0x0c, 0x1d, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
    },
    HID_DEVICE_ID_K780_USB() => {
        on   => (pack "C*", 0x11, 0xff, 0x0c, 0x1d, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
        off  => (pack "C*", 0x11, 0xff, 0x0c, 0x1d, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00),
    },
    HID_DEVICE_ID_K810() => {
        on   => (pack "C*", 0x10, 0xff, 0x06, 0x15, 0x00, 0x00, 0x00),
        off  => (pack "C*", 0x10, 0xff, 0x06, 0x15, 0x01, 0x00, 0x00),
    },
);

#die
#   "usage: $0 [on|off]\n",
#   "\ton  makes the media keys the default\n",
#   "\toff makes the function keys the default\n"
#unless @ARGV == 1 and my ($choice) = $ARGV[0] =~ /^(on|off)$/;
my ($choice) = @ARGV ? $ARGV[0] =~ /^(on|off)$/ : "off";

my $device;

# find the first device we can set the option on
# TODO: add a parameter to directly specify a device
# TODO: add a parameter to make it set all devices
FILE_SEARCH:
for my $file (</sys/class/hidraw/hidraw*/device/uevent>) {
    open my $fh, "<", $file or do {
        warn "could not open $file: $!\n";
        next;
    };

    while (<$fh>) {
        if (/HID_NAME=(Logitech|Keyboard) K(76|78|81)0/) {
            my ($hid_raw_name) = $file =~ m{(hidraw[^/]+)};
            $device = "/dev/$hid_raw_name";
            last FILE_SEARCH;
        }
    }
}

die "sorry, could not find a suported device on your machine\n" unless $device;

# re-exec with sudo if we can't open the device
unless (-r $device and -w $device) {
    # unless we are already root
    exec "sudo", $^X, $0, @ARGV unless $> == 0;
}

open my $dev, "+<", $device or die "could not open device $device: $!\n";

my $success = ioctl $dev, HIDIOCGRAWINFO, my $struct = "";

die "could not determine if $device is supported\n" unless $success;

my ($bus_type, $vendor, $product) = unpack "Lss", $struct;

#die "detected device $device is not a Bluetooth device\n"
#    unless $bus_type == BUS_BLUETOOTH;

die "detected device $device is not a Logitech product\n"
    unless $vendor == HID_VENDOR_ID_LOGITECH;

die "detected device $device is not a supported product\n"
    unless exists $message{$product};

syswrite $dev, $message{$product}{$choice};

close $dev;

chmod +x $SCRIPT_FILE

Now, connect your K780 (via Bluetooth or Logitech unifying USB receiver) and check if this script works:

$SCRIPT_FILE on

It should work if you use a K780/K760/K810 keyboard (but only K780 supports unifying USB). If it works, you can add an action to udev:

vim /etc/udev/rules.d/00-k780.rules

SUBSYSTEM=="hidraw", ACTION=="add", RUN+="$SCRIPT_FILE on"

You should replace $SCRIPT_FILE with your path. Now restart udev:

sudo service udev restart

It should work automatically when you disconnect and reconnect. Enjoy!

The $SCRIPT_FILE can be simplified:

#!/bin/bash

set -euo pipefail

if grep -q K780 /sys/class/hidraw/$1/device/uevent; then
    echo -en '\x11\xff\x0c\x1d' | cat - /dev/zero | dd of=/dev/$1 count=20 iflag=count_bytes oflag=nonblock
fi

And modify /etc/udev/rules.d/00-k780.rules:

SUBSYSTEM=="hidraw", ACTION=="add", RUN+="$SCRIPT_FILE $name"

$SCRIPT_FILE can substitute for your script location, like /usr/local/bin/k780-fn-on.sh. $name should remain unchanged.

bit late to the party, but what worked for me was using the receiver and changing the settings via a windows device with Logitech options. So stupid there isn't a hard key to change.

I just wanted to thank all of you for this excellent and informative thread. I am currently using the simplified script by @tangruize and so far it is working perfectly with my new K780.

If you are using a unifying USB receiver and do not want to install solaar, here is a simplified udev rule that can swap FN keys for K780:

/etc/udev/rules.d/00-k780.rules:

ACTION=="change", SUBSYSTEM=="power_supply", ATTR{model_name}=="K780 Multi-Device Wireless Keyboard", ATTR{online}=="1", RUN+="/bin/bash -c 'printf \"\x11\xff\x0c\x1d\" | cat - /dev/zero | dd of=/dev/$$(ls $$0/device/hidraw) count=20 iflag=count_bytes oflag=nonblock' %S%p"

After editing the above udev file, run sudo udevadm trigger to enable to rule.

Reference: https://github.com/sta-c0000/logitech-keyboard-udev-rules

@tangruize Thanks for this concise solution and all the work that lead to it. Working perfectly for me!

I created an Arch PKGBUILD for it: Roman2K/arch-k780-fnkey

The $SCRIPT_FILE can be simplified:
...

SUBSYSTEM=="hidraw", ACTION=="add", RUN+="$SCRIPT_FILE $name"

I found that it doesn't work sometimes (for bluetooth), and I improved it:

Delete the above rule and script file, and append below contents to /etc/udev/rules.d/00-k780.rules:

ACTION=="bind", KERNEL=="0005:046D:B33B*", SUBSYSTEM=="hid", RUN+="/bin/bash -c 'printf \"\x11\xff\x0c\x1d\" | cat - /dev/zero | dd of=/dev/$$(ls $$0/hidraw) count=20 iflag=count_bytes oflag=nonblock' %S%p"

For what it is worth, my K780 & logitech devices report with slightly different USB addresses:

[ 3247.931263] logitech-djreceiver 0003:046D:C52B.0016: hiddev0,hidraw0: USB HID v1.11 Device [Logitech USB Receiver] on usb-0000:00:14.0-10/input2
[ 3248.043856] input: Logitech K780 as /devices/pci0000:00/0000:00:14.0/usb1/1-10/1-10:1.2/0003:046D:C52B.0016/0003:046D:405B.0017/input/input45
[ 3248.144901] logitech-hidpp-device 0003:046D:405B.0017: input,hidraw1: USB HID v1.11 Keyboard [Logitech K780] on usb-0000:00:14.0-10/input2:1
[ 3248.151857] input: Logitech M585/M590 as /devices/pci0000:00/0000:00:14.0/usb1/1-10/1-10:1.2/0003:046D:C52B.0016/0003:046D:406B.0018/input/input46
[ 3248.238210] logitech-hidpp-device 0003:046D:406B.0018: input,hidraw2: USB HID v1.11 Keyboard [Logitech M585/M590] on usb-0000:00:14.0-10/input2:2

So I modified the udev line from https://gist.github.com/andrejcremoznik/e56234138305226abd41fe4d1d2561a3?permalink_comment_id=4237309#gistcomment-4237309 accordingly:

ACTION=="bind", KERNEL=="0003:046D:405B*", SUBSYSTEM=="hid", RUN+="/bin/bash -c 'printf \"\x11\xff\x0c\x1d\" | cat - /dev/zero | dd of=/dev/$$(ls $$0/hidraw) count=20 iflag=count_bytes oflag=nonblock' %S%p"

But I still have to hit Fn-F2 to get F2 working.

@satmandu Sorry I haven't used K780 in a while. You can try this script: https://gist.github.com/andrejcremoznik/e56234138305226abd41fe4d1d2561a3?permalink_comment_id=3390489#gistcomment-3390489. Since you're using USB receiver, I think Solaar might also help solve your problem if the script doesn't work.