USB tethering has been broken for me for some time but I recently had an extended outage with my internet provider which has brought the problem back into focus.
I found the following thread from over a year ago without resolution:
Starting with dmesg I see the following where the last line doesn’t look promising:
[3012527.535542] usb 1-3: new high-speed USB device number 17 using xhci_hcd
[3012527.783976] usb 1-3: New USB device found, idVendor=05ac, idProduct=12a8, bcdDevice=14.05
[3012527.783983] usb 1-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[3012527.783986] usb 1-3: Product: iPhone
[3012527.783989] usb 1-3: Manufacturer: Apple Inc.
[3012527.783992] usb 1-3: SerialNumber: <redacted>
[3012527.924958] ipheth 1-3:4.2: ipheth_enable_ncm: usb_control_msg: 0
[3012527.925232] ipheth 1-3:4.2: Apple iPhone USB Ethernet device attached
[3012527.930578] ipheth 1-3:4.2 enp2s0f0u3c4i2: renamed from eth0
[3012583.162199] ipheth 1-3:4.2: ipheth_rcvbulk_callback: urb status: -32
After googling and installing libimobiledevice-utils packages that is not installed by default, I can see I have an old phone “paired” from when it used to work but have been unable to remove it:
$ idevicepair list
00008020-0019786C3C33002E
The help/man page are severely lacking on the proper method of removing this device.
I also learned the usbmuxd is started automatically and it does but there seem to be problems:
[2199941.187342] systemd[1]: Started usbmuxd.service - Socket daemon for the usbmux protocol used by Apple devices.
[2199941.189689] usbmuxd[1175926]: [07:26:21.941][3] usbmuxd v1.1.1^20230720git61b99ab starting up
[2199941.190588] usbmuxd[1175926]: [07:26:21.942][3] Successfully dropped privileges to 'usbmuxd'
...skipping...
[3014567.190714] usbmuxd[3501007]: [17:43:27.942][1] ERROR: Failed to read '/var/lib/lockdown/<redacted unique id>.plist': No such file or directory
The last line is repeated every few seconds and the phone is not prompting me to trust my computer. Nothing is writing the “plist” file to /var/lib/lockdown
This may be the crux of the problem?