USB tethering working?

[Moem]

@slowcyclist Have you set your USB setting to USB Tethering?

[slowcyclist]

@Moem of course, that's what triggers the messages in the journal. In French it's called "partage de connexion USB" and
I've tried both from the system settings and UT tweaks.

[Moem]

@slowcyclist Okay, just checking
It's always good to check the easy stuff first. Not everyone thinks of the things that you thought of.

[gpatel-fr]

@slowcyclist

while my experience with USB tethering is non existent on UT, I'd guess that RNDIS support is not compiled in the FP5 kernel.

phablet@ubuntu-phablet:~$ zgrep RNDIS /proc/config.gz
# CONFIG_USB_NET_RNDIS_HOST is not set
# CONFIG_USB_NET_RNDIS_WLAN is not set
# CONFIG_USB_CONFIGFS_RNDIS is not set

a quick test shows that the FP5 is seen as mass storage by the (Linux) computer.

févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: /sys/kernel/config/usb_gadget/g1//functions/rndis.usb0: mkdir failed: No such file or directory
févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: function rndis.usb0 is not registered
févr. 14 23:19:56 ubuntu-phablet usb_moded[2309]: /sys/kernel/config/usb_gadget/g1//UDC: write failure: Invalid argument

A quick internet search comes up with a thingy called NCM that the FP5 kernel is supposed to have

phablet@ubuntu-phablet:~$ zgrep NCM /proc/config.gz
CONFIG_USB_NET_CDC_NCM=y
# CONFIG_USB_NET_HUAWEI_CDC_NCM is not set
CONFIG_USB_F_NCM=y
CONFIG_USB_CONFIGFS_NCM=y

however trying to access it generates an error:

phablet@ubuntu-phablet:~$ cat /sys/kernel/config/usb_gadget/g1/functions/ncm.usb0/ifname
cat: /sys/kernel/config/usb_gadget/g1/functions/ncm.usb0/ifname: No such device

there is no rndis.usb0 under /sys/kernel/config/usb_gadget/g1/functions

Note that as far as I can tell, the kernel version has changed with 24.04-1 RC (289 -> 302). Also many things have changed between August 2025 and now.

[slowcyclist]

@gpatel-fr thanks for digging into this. So, right, it's supposed to use ncm and not rndis, but usb-moded should handle tethering with that .
The file you tried to cat is restricted to root access, but even with sudo, it's not accessible, and that probably explains why the configuration script fails, falling back to charging only.
Maybe the fp5 is missing the corresponding kernel module now, while it had it back in August?
I created a ticket.

[FlavioMala]

Here's what happened to me (FP5):

USB tethering WORKED until February 22nd (2026), when I installed the candidate release (version 10).

Today I noticed it no longer worked.

I tried switching to the "daily" release channel: I installed "1007" and it still doesn't work.

Then I switched to the stable version ("3") and it still doesn't work.

In the settings, when I log out and log back in, it switches from "tethering" to "charging only"... but sometimes it stays on tethering (but nothing changes).

Even using the UT Tweak Tool, things don't change.

---

It seems that, installing the new RC, something got corrupted and now it no longer works with any release (but it worked until February 22nd, at least with the previous RC channel, which I was on since the switch to "24 noble").

NB: Connecting a PC, decoder, etc. to the GSM (handy) network via (handy) Wi-Fi/Wlan -> works out of the box... only via USB cable no longer works...

[gpatel-fr]

@FlavioMala

I'm pretty sure that it is linked to the relatively large Linux kernel upgrade that happened then. It was linked to the Bluetooth stack upgrade, but maybe it involved other changes. I had not the time to track these changes.

I just verified it but the installer don't allow to install the previous stable channel there is a 'More..' button under the channel selection but it don't seem to do anything. Definitely things that could be improved in the installer and in the general system, there is no easy way to uninstall a system upgrade and revert to the previous one.

[FlavioMala]

Juste une précision:
Je suis passé de "RC" à "Daily", etc. sans utiliser le programme/ordinateur...
c’est-à-dire, directement depuis mon téléphone.

Precisazione:
da "RC" a "Daily", ecc. senza installer/PC, ma direttamente da FP5/telefonino.

Note:
from "RC" to "Daily" to "Stable" directly from FP5 (no installer/PC).

[gpatel-fr]

@FlavioMala

I don't think that the way the update is installed does any difference.

As UT is a read-only filesystem, all system upgrades involve a replacement of the whole rootfs including the kernel. If the kernel has been upgraded at some point in the daily channel for 24.04-1.x, the change will be transferred (of course) in the 24.04.1.2RC and later stable. The FP5 linux kernel is not the same for 24.04-1.1 and 24.04-1.2 stable versions.

The installer then can no longer install back 24.04.1.1 on a phone, that was the point of my post: you can't revert to the previous version whatever method you use, even with the installer. That you can't do it from the phone is a misfeature, even more so from the installer. I did not file an issue with the installer since there are already more than 2000 of them

[slowcyclist]

@gpatel-fr @FlavioMala, indeed the newer Bluetooth stack had the side effect of breaking usb_tethering.
I could fix it by applying a small patch and recompiling the kernel. The patch is attached to the issue.