The Logitech Unifying Receiver is a USB plug that can listen to several computer peripherals. A single plug can be paired with one mouse, and one keyboard. It should be noted that newer Logitech products support Bluetooth. This is useful if you for example forget or drop the Unifying Receiver USB plug. However, Unifying Receivers can be purchased separately. Note that the following devices are vulnerable to MouseJacking attack when they are connected to the Unifying Receiver: K360, K400r, K750, K830 (source)

Solaar (instead of Logitech's proprietary Unifying Software) "is a Linux manager for many Logitech keyboards, mice, and trackpads that connect wirelessly to a USB Unifying, Bolt, Lightspeed, or Nano receiver; connect directly via a USB cable; or connect via Bluetooth." solaar is packaged for many distros! A typical use case is that you can set the DPI to higher values than your desktop environment allows.

The Logitech Unifying Receiver is paired with the hardware that it ships with. However, USB plugs can be paired and unpaired with some Logitech branded mice and keyboard with the recommended software.

lsusb

Bus 003 Device 078: ID 046d:c52b Logitech, Inc. Unifying Receiver

lsusb -v

Bus 003 Device 078: ID 046d:c52b Logitech, Inc. Unifying Receiver
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        32
  idVendor           0x046d Logitech, Inc.
  idProduct          0xc52b Unifying Receiver
  bcdDevice           24.00
  iManufacturer           1 Logitech
  iProduct                2 USB Receiver
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           84
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          4 RQR24.00_B0018
    bmAttributes         0xa0
      (Bus Powered)
      Remote Wakeup
    MaxPower               98mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      1 Boot Interface Subclass
      bInterfaceProtocol      1 Keyboard
      iInterface              0 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.11
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      59
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval               8
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      1 Boot Interface Subclass
      bInterfaceProtocol      2 Mouse
      iInterface              0 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.11
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength     148
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval               2
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      0 No Subclass
      bInterfaceProtocol      0 None
      iInterface              0 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.11
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      98
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0020  1x 32 bytes
        bInterval               2
Device Status:     0x0000
  (Bus Powered)

dmesg

[144778.649419] usb 3-2: new full-speed USB device number 78 using xhci_hcd
[144778.816720] usb 3-2: New USB device found, idVendor=046d, idProduct=c52b
[144778.816725] usb 3-2: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[144778.816727] usb 3-2: Product: USB Receiver
[144778.816729] usb 3-2: Manufacturer: Logitech
[144778.826690] logitech-djreceiver 0003:046D:C52B.000A: hiddev0,hidraw0: USB HID v1.11 Device [Logitech USB Receiver] on usb-0000:00:14.0-2/input2
[144778.878759] input: Logitech Unifying Device. Wireless PID:4017 as /devices/pci0000:00/0000:00:14.0/usb3/3-2/3-2:1.2/0003:046D:C52B.000A/0003:046D:C52B.000B/input/input43
[144778.879129] logitech-djdevice 0003:046D:C52B.000B: input,hidraw1: USB HID v1.11 Mouse [Logitech Unifying Device. Wireless PID:4017] on usb-0000:00:14.0-2:1

Works perfectly out of the box on Trisquel 7.0 (Linux 3.13.0-39-lowlatency):

Mute and volume buttons work perfectly.

Yellow mouse button (located above ESC) works perfectly (i.e., as an additional left mouse button).

Year of commercialization: 2020
Still produced: Yes
Compatible wireless receiver: Unifying USB Receiver (included) with unencrypted connection, Bluetooth with encrypted connection. Encryption status from solaar
Tested on: Trisquel 11
Does it work with free software?: Yes
Note: Worked with both the Unifying USB Receiver, and Bluetooth

Year of commercialization: 2010
Still produced: No
Compatible wireless receiver: Unifying USB Receiver (included) with unencrypted connection. Encryption status from solaar
Tested on: Trisquel 11
Does it work with free software?: Yes

If this receiver-wireless keyboard solution is used as the primary method of data entry in a setup in which the root mount point is inside an encrypted partition, the receiver doesn't work between its use in the Grub Menu and the loading of the modules by the Operating System, preventing the decryption password from being entered, stopping loading of the Operating System. In order to fix that, append these lines to /etc/initramfs-tools/modules

:

hid_logitech
hid_logitech_dj
#One of the above may not be alway be required and my produce a warning

And per instructions on the file itself, one must run update-initramfs for the change to take effect. If the changes didn't seem to take effect, verify that the kernel configuration file in /boot/ have the following values equal to "m" as in "module". CONFIG_HID_LOGITECH=m CONFIG_HID_LOGITECH_DJ=m [/p]