Glossary

Glossary

Every word in plain language first, then what it means for this device. Grouped by topic.

The device and its insides

SoC (system on a chip): The one chip that holds the processor, graphics, modem and more, like the brain and heart in one. Here: the Unisoc T760.

Unisoc T760 / UMS9620: Two names for the same chip, made by Unisoc. Here: both the F50 and the U30 Air use it on the board ums9620_2h10_feimao. The U30 Pro uses a different chip (UMS9632) and is not supported.

Modem: The part that talks to the mobile network, like a phone without a screen. Here: it needs a few Android programs (modem_control and friends) that Linux runs in a sandbox.

eMMC: The built-in storage chip, like a soldered-in memory card. Here: about 58 GiB on the 64 GB device; Linux uses the part no partition owns.

Partition: A fenced-off area of the storage with a name, like rooms in a house. Here: Android has many (boot, system, userdata, …); Linux does not get one, it lives in the unfenced space behind them.

Partition table (GPT): The map that says where each partition starts and ends. Here: the installer never changes it, except when you choose to shrink userdata on the 32 GB variant.

userdata: Android's partition for apps, settings and files. Here: it is encrypted as a whole, so Linux cannot keep its files inside it; on the 32 GB variant it fills the disk.

misc: A tiny partition where the bootloader keeps notes, such as which slot to start and how many tries are left. Here: the installer writes 32 bytes of it to tell the bootloader to try Linux.

OpenCL / GPU: The GPU is the graphics processor; OpenCL lets programs use it for number crunching. Here: the Mali-G57 runs OpenCL 3.0 without a screen.

KVM: A Linux feature for running virtual machines fast. Here: /dev/kvm exists on all three kernels.

zram: Compressed swap kept in RAM, so more fits in memory. Here: mu300-zram adds lz4 zram of half the RAM.

OTG / USB host: Normally the device is the "guest" on your computer's USB; in host mode it is the "boss" and you can plug things into it. Here: the U30 Air can be a USB host on the mainline kernels (sudo mu300-usb host); the F50's port is its power supply, so no.

Starting up

Bootloader (LK): The first small program that runs at power-on and decides what to start. Here: Unisoc's LK picks the slot from the notes in misc.

Slot (A/B): The device has two copies of the boot partitions, A and B, so an update can be tried on one while the other stays safe. Here: Android uses one slot; Linux's boot image goes into the other.

Boot image: A package holding the kernel and a small starter program (initramfs) that the bootloader loads. Here: the Linux boot image is built from your device's own Android boot image plus this project's kernel.

Kernel: The core of an operating system, which talks to the hardware. Here: you choose 5.4, 6.18 or 7.2 (Kernels).

Vendor kernel vs. mainline kernel: A vendor kernel is the chip maker's own modified Linux; mainline is the official Linux from kernel.org. Here: 5.4 is the vendor kernel, 6.18 and 7.2 are mainline with this project's patches.

LTS (long-term support): A version that gets fixes for years. Here: Ubuntu 24.04/26.04 LTS and Linux 6.18 LTS.

initramfs: A tiny temporary system inside the boot image that prepares everything before the real system starts. Here: it loads the drivers, finds the Linux filesystem (SD card or free eMMC space) and counts failed boots.

Trial boot: Starting something on probation: if it does not report back as healthy, it does not count as good. Here: each Linux boot must be confirmed by mu300-boot-ok about 30 s after the USB network and SSH are up.

Fallback: Going back to the safe option automatically. Here: after N unconfirmed Linux boots in a row (1-6, default 5) the device starts Android.

Rollback: Undoing an update. Here: mu300-update rollback (system) and rollback-boot (kernel and boot image).

Android side

Root: Full administrator rights on Android. Here: required before installing; getting it is not part of this project.

Unlock: Allowing the bootloader to start software it was not shipped with. Here: the device must already boot a modified Android boot image.

Magisk: A popular tool that gives Android root and can install "modules". Here: the installer adds a module whose Action button (or su -c mu300-linux) starts Linux; releases also ship Magisk zips that install Linux from the device.

adb: Android Debug Bridge, a computer program that talks to an Android device over USB. Here: the installer uses it; Linux offers it too, on by default and for every computer, with a root shell and no password (sudo mu300-usb adb auth keys lets in only computers whose key you authorised, sudo mu300-usb adb off turns it off).

USB debugging: The Android setting that lets adb connect. Here: must be on.

Linux and systems

Distribution: A complete Linux system: kernel plus programs plus a way to install more. Here: Ubuntu and OpenWrt are offered.

Ubuntu: A widely used general-purpose Linux distribution, with apt for software. Here: 24.04 LTS (default) or 26.04 LTS (needs a mainline kernel).

OpenWrt: A Linux distribution made for routers: small and network-focused. Here: 25.12, plain or with the MU300 control panel.

LuCI: OpenWrt's web interface. Here: at http://192.168.77.1 (U30 Air: .78.1).

UCI: OpenWrt's settings system (uci set …; uci commit). Here: updates keep your UCI configuration.

rootfs / filesystem: The tree of folders and files a system lives in. Here: each system is a folder on the Linux disk (/ubuntu, /openwrt, /openwrt-luci).

ext4: The standard Linux way of organising files on a disk. Here: the Linux disk is ext4, labelled mu300root (internal) or mu300sd (SD card).

SSH: A secure way to type commands on another computer over the network. Here: ssh ubuntu@192.168.77.1.

Serial console: A plain text connection that works even when the network does not. Here: over the same USB cable, screen /dev/cu.usbmodem* 115200 on macOS.

Networking

Hotspot / access point: A Wi-Fi network the device creates for others to join. Here: 5 GHz or 2.4 GHz, one at a time.

Wi-Fi client / station: The device joining someone else's Wi-Fi, like a phone does. Here: wifi-client; the radio is either hotspot or client, decided at boot.

WPA2 / WPA3 / SAE: Wi-Fi password security standards; SAE is the handshake WPA3 uses. Here: the driver has no SAE, so WPA3-only networks cannot be joined; WPA2 and mixed mode work.

NCM / ECM / RNDIS: Ways for a USB device to appear as a network card to a computer. Here: NCM is the default, ECM the fallback, RNDIS selectable.

LTE: 4G mobile data.

5G NSA / EN-DC: "Non-standalone" 5G, which uses a 4G connection as an anchor and adds 5G on top; EN-DC is the name of that combination. Here: mobile data runs on 5G NSA or LTE; the panel can lock EN-DC.

Band lock: Telling the modem to use only certain frequency bands or cells. Here: in the panel's Network locks; stored in the modem, so it also applies in Android until reset.

APN: The name of the "door" into your carrier's data network. Here: leave it empty to use what the SIM defines.

PDP context: The data session the modem opens with the carrier, using the APN. Here: MU300_PDP_TYPE sets its type on Ubuntu.

AT commands: Short text commands for talking to a modem (they start with AT). Here: the panel has a guarded AT terminal; all tools share one channel through mu300-atd.

SMS / PDU: Text messages; PDU is the raw encoded form a modem uses. Here: sms uses PDU mode because text mode garbles some senders.

USSD: The short codes like *101# that ask the carrier for your balance. Here: sudo mu300-ussd '*101#'.

DHCP: How devices get an address automatically when they join a network. Here: the device hands out addresses to its clients.

DNS: The internet's phone book, turning names into addresses.

IPv6: The newer kind of internet address.

RA (router advertisement): An IPv6 message in which a router tells devices "here is the network and how to reach the internet". Here: the control-panel OpenWrt relays the carrier's RAs to the LAN.

NAT / NAT66: Sharing one public address among many devices; NAT66 is the IPv6 version. Here: how clients share the mobile connection.

TTL: A counter in every packet that drops by one at each router. Here: mu300-ttl set 64 fixes it for mobile data. Check your operator's terms first.

VPN

VPN: A protected tunnel to another server that your traffic goes through. Here: the optional mu300-vpn module.

Kill switch: A rule that blocks all traffic when the VPN is down, so nothing leaks. Here: on by default in mu300-vpn.

WireGuard: A modern, fast VPN built into the Linux kernel. Here: available on the mainline kernels.

OpenVPN: An older, widely used VPN program. Here: install the system's OpenVPN package to use .ovpn profiles.

Xray / sing-box / mihomo / dae: Proxy engines for protocols such as VLESS, VMess, Trojan and Shadowsocks, for Clash-style configs, and (dae) an eBPF proxy that runs inside the kernel. Here: the VPN module picks the engine that speaks your profile; from v2.0.0 each engine is an extra (vpn-xray, vpn-singbox, vpn-mihomo, vpn-dae), and dae needs kernel 6.18 or 7.2 of v2026.10.20 or newer.

BTF / eBPF: eBPF lets programs run safely inside the kernel; BTF is the type information such programs need to find their way around. Here: the mainline kernels carry BTF from v2026.10.20 so that dae can run.

DFS channel: A 5 GHz Wi-Fi channel (52-144) that radar also uses; an access point there must first listen for radar. Here: the Wi-Fi driver cannot, so the hotspot never uses one (a DFS channel you pick is replaced by 36 or 149).

Cockpit: Ubuntu's web console (terminal, logs, services, networking). Here: the optional panel extra on Ubuntu, with an MU300 page for the modem, SMS, VPN and power.

Subscription (VPN): A URL your VPN provider gives you that yields a list of profiles. Here: mu300-vpn subscription add, refreshed by hand or on a schedule; also in the panel's VPN menu.

Tailscale: A mesh VPN for reaching your own devices. Here: its traffic goes through the active tunnel by default.