Im Xorg.log steht auch nichts erhellendes drin:
[ 35251.484] (II) XINPUT: Adding extended input device "Power Button" (type: KEYBOARD, id 8)
[ 35251.484] (**) Option "xkb_rules" "evdev"
[ 35251.484] (**) Option "xkb_model" "pc105"
[ 35251.484] (**) Option "xkb_layout" "de"
[ 35251.484] (II) config/udev: Adding drm device (/dev/dri/card0) card0 /sys/devices/pci0000:00/0000:00:02.0/drm/card0
[ 35251.484] (II) config/udev: Ignoring already known drm device (/dev/dri/card0)
[ 35251.484] (II) config/udev: Adding input device HDA Intel HDMI HDMI/DP,pcm=3 (/dev/input/event9)
[ 35251.484] (II) No input driver specified, ignoring this device.
[ 35251.484] (II) This device may have been added with another device file.
[ 35251.485] (II) config/udev: Adding input device HDA Intel HDMI HDMI/DP,pcm=7 (/dev/input/event8)
[ 35251.485] (II) No input driver specified, ignoring this device.
[ 35251.485] (II) This device may have been added with another device file.
[ 35251.485] (II) config/udev: Adding input device HDA Intel HDMI HDMI/DP,pcm=8 (/dev/input/event7)
[ 35251.485] (II) No input driver specified, ignoring this device.
[ 35251.485] (II) This device may have been added with another device file.
[ 35251.485] (II) config/udev: Adding input device Logitech Unifying Device. Wireless PID:1024 (/dev/input/event2)
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: Applying InputClass "evdev pointer catchall"
[ 35251.485] (II) Using input driver 'evdev' for 'Logitech Unifying Device. Wireless PID:1024'
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: always reports core events
[ 35251.485] (**) evdev: Logitech Unifying Device. Wireless PID:1024: Device: "/dev/input/event2"
[ 35251.485] (--) evdev: Logitech Unifying Device. Wireless PID:1024: Vendor 0x46d Product 0xc52b
[ 35251.485] (--) evdev: Logitech Unifying Device. Wireless PID:1024: Found 20 mouse buttons
[ 35251.485] (--) evdev: Logitech Unifying Device. Wireless PID:1024: Found scroll wheel(s)
[ 35251.485] (--) evdev: Logitech Unifying Device. Wireless PID:1024: Found relative axes
[ 35251.485] (--) evdev: Logitech Unifying Device. Wireless PID:1024: Found x and y relative axes
[ 35251.485] (II) evdev: Logitech Unifying Device. Wireless PID:1024: Configuring as mouse
[ 35251.485] (II) evdev: Logitech Unifying Device. Wireless PID:1024: Adding scrollwheel support
[ 35251.485] (**) evdev: Logitech Unifying Device. Wireless PID:1024: YAxisMapping: buttons 4 and 5
[ 35251.485] (**) evdev: Logitech Unifying Device. Wireless PID:1024: EmulateWheelButton: 4, EmulateWheelInertia: 10, EmulateWheelTimeout: 200
[ 35251.485] (**) Option "config_info" "udev:/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1/3-1.1/3-1.1.2/3-1.1.2:1.2/0003:046D:C52B.0003/input/input5/event2"
[ 35251.485] (II) XINPUT: Adding extended input device "Logitech Unifying Device. Wireless PID:1024" (type: MOUSE, id 9)
[ 35251.485] (II) evdev: Logitech Unifying Device. Wireless PID:1024: initialized for relative axes.
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: (accel) keeping acceleration scheme 1
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: (accel) acceleration profile 0
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: (accel) acceleration factor: 2.000
[ 35251.485] (**) Logitech Unifying Device. Wireless PID:1024: (accel) acceleration threshold: 4
[ 35251.486] (II) config/udev: Adding input device Logitech Unifying Device. Wireless PID:1024 (/dev/input/mouse0)
[ 35251.486] (II) No input driver specified, ignoring this device.
[ 35251.486] (II) This device may have been added with another device file.
[ 35251.486] (II) config/udev: Adding input device Logitech Unifying Device. Wireless PID:2011 (/dev/input/event3)
[ 35251.486] (**) Logitech Unifying Device. Wireless PID:2011: Applying InputClass "evdev keyboard catchall"
[ 35251.486] (II) Using input driver 'evdev' for 'Logitech Unifying Device. Wireless PID:2011'
[ 35251.486] (**) Logitech Unifying Device. Wireless PID:2011: always reports core events
[ 35251.486] (**) evdev: Logitech Unifying Device. Wireless PID:2011: Device: "/dev/input/event3"
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Vendor 0x46d Product 0xc52b
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Found 1 mouse buttons
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Found scroll wheel(s)
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Found relative axes
[ 35251.486] (II) evdev: Logitech Unifying Device. Wireless PID:2011: Forcing relative x/y axes to exist.
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Found absolute axes
[ 35251.486] (II) evdev: Logitech Unifying Device. Wireless PID:2011: Forcing absolute x/y axes to exist.
[ 35251.486] (--) evdev: Logitech Unifying Device. Wireless PID:2011: Found keys
[ 35251.486] (II) evdev: Logitech Unifying Device. Wireless PID:2011: Configuring as mouse
[ 35251.486] (II) evdev: Logitech Unifying Device. Wireless PID:2011: Configuring as keyboard
[ 35251.486] (II) evdev: Logitech Unifying Device. Wireless PID:2011: Adding scrollwheel support
[ 35251.486] (**) evdev: Logitech Unifying Device. Wireless PID:2011: YAxisMapping: buttons 4 and 5
[ 35251.486] (**) evdev: Logitech Unifying Device. Wireless PID:2011: EmulateWheelButton: 4, EmulateWheelInertia: 10, EmulateWheelTimeout: 200
[ 35251.486] (**) Option "config_info" "udev:/sys/devices/pci0000:00/0000:00:14.0/usb3/3-1/3-1.1/3-1.1.2/3-1.1.2:1.2/0003:046D:C52B.0003/input/input6/event3"
Der Logitech-Receiver war seit über zwei Jahren am gleichen USB-Port (2.x) angeschlossen. Er funktionierte auch an USB 3. Jetzt fkt. es ja noch außerhalb von Unity und überall mit der Maus.
Ich habe den Rechner jetzt mal mit einer Kabelmaus, ohne Tastatur gestartet. Dann ist es genauso. Ich kann das Passwort noch mit der Bildschirmtastatur eingeben. Danach ist Schluss.