Kernels

Kernels

In one sentence: the kernel is the engine underneath Linux; you can choose Unisoc's own 5.4 (oldest, longest tested), mainline 6.18 (long-term support) or mainline 7.2 (newest), and change your mind later with one command.

The simple version: all three engines drive the same car: hotspot, mobile data, SMS, Bluetooth, VPN, GPU. 5.4 is the one the factory built and the most proven; 6.18 and 7.2 are the regular Linux everyone uses, with newer parts.

The choice, as the installer puts it

choice	kernel
1	5.4	Unisoc's vendor kernel (Android 12 base): the longest tested, everything this project supports
2	6.18	mainline Linux, the current long-term (LTS) release: newer drivers and security fixes, the same functions (hotspot, mobile data, SMS, Bluetooth, VPN, GPU); no USB-C video output yet
3	7.2	the newest stable mainline release (7.2 for now): the newest drivers, the same functions as 6.18; tested less than 6.18

Which one should I take?

flowchart TD
    A{Ubuntu 26.04?} -->|yes| M[6.18 or 7.2]
    A -->|no| B{U30 Air and you want USB host mode<br/>flash drives, keyboards, USB modems?}
    B -->|yes| M
    B -->|no| C{WireGuard VPN profiles?}
    C -->|yes| M
    C -->|no| D[5.4 is fine: the longest tested]

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• Ubuntu 26.04 needs 6.18 or 7.2. Its programs use system calls 5.4 does not have.
• USB host mode on the U30 Air (mu300-usb host) needs a mainline kernel.
• WireGuard: the VPN module notes that the 5.4 vendor kernel has no WireGuard; mainline does.
• KVM (/dev/kvm) is on all three.
• The mainline bundles carry about 360 modules: WireGuard, SQM, tunnels, USB adapters and modems, NTFS/exFAT/btrfs/NFS/CIFS, dm-crypt, containers.
• U30 Air battery: readings work on every kernel. Charging on the mainline kernels is driven by the bq256xx driver from v2026.10.12 on; the mainline kernels of v2026.10.11 and older leave charging off, so use 5.4 there. From v2026.10.20 the mainline kernels also read the current a Type-C port offers (1.5 or 3 A), so charging on such a port runs at up to 2 A instead of 500 mA; the charge limit (0-100 %) works on every kernel.
• dae (the VPN module's eBPF engine) needs 6.18 or 7.2 of v2026.10.20 or newer: those kernels (6.18.56 and 7.2.10) carry BTF and the BPF JIT. 5.4 cannot run it. kprobes are left out on purpose: with them 7.2 failed 2 boots in 36, so dae trace is not available.

The versions in v2026.10.23

kernel	version	notes
5.4	5.4.254	Unisoc's vendor kernel with the project's patches; rebuilt in v2026.10.23 with NFT_QUEUE (nftables' queue verdict, for userspace packet tools); since v2026.10.21 it no longer panics when a network namespace goes away (#103), and the Wi-Fi driver's routine lines are no longer errors (#140)
6.18	6.18.56	longterm; BTF, BPF JIT, FunctionFS (for adb); v2026.10.23 adds the mu300_thermal module (the board's temperature as a thermal zone); since v2026.10.22 the F50's SD slot has real card detect (the EIC controller's six banks mapped), so an empty slot is no longer polled and no mmc1 register dumps fill the log (#181); since v2026.10.21 the Wi-Fi driver can be unloaded (#146) and is quieter (#140)
7.2	7.2.10	stable; the same additions, the same card-detect fix, the same modules

The point releases bring, among others, a DWC3 USB fix for an IRQ storm that could panic the board, netfilter flowtable and fq_codel fixes, Bluetooth and USB-serial use-after-free fixes. The BTF data costs about 4 MB of the boot image and 4 MiB of RAM.

Known issue: a rare hang on 6.18

About once in 20 boots on one board, 6.18 stopped in its first seconds; the device then falls back to Android (it can take around 20 minutes, because each hang uses up several tries). Another F50 showed 0 hangs in 100 boots, as did 7.2. Start Linux again with su -c mu300-linux in Android or the Magisk module's Action button. Details: FINDINGS 31m.

Changing the kernel later

On the device:

sudo mu300-update kernel            # shows the current one
sudo mu300-update kernel 6.18       # or 5.4, 7.2
sudo reboot

The previous kernel and boot image are kept: sudo mu300-update rollback-boot goes back. A new kernel that does not start sends the device back to Android after the usual number of failed boots, even when Linux is locked (see Going Back to Android).

Where the kernels come from

• 5.4 is built from ZTE's published GPL source for the U30 Air (mirrored at dikeckaan/zte-ums9620-kernel-5.4.254), with Wi-Fi, Bluetooth and GPU drivers from realme's C51/C53 kernel release.
• 6.18 and 7.2 are Linux from kernel.org with this project's patches and the vendor drivers ported to them (upstream/). A CI job builds the port every week against the newest longterm and stable kernels.

The F50 and the U30 Air run the same kernel; the U30 Air's boot image loads a handful of different drivers for its charger and LEDs.