Glossary
Short, plain-English definitions of the terms used across this site.
- A/B update reliability
- An update scheme with two system slots. The update is written to the inactive slot and the device switches to it on reboot; if it fails to boot, it falls back to the previous slot.
- AArch64 (arm64) hardware
- The 64-bit execution state of the ARM architecture. Linux calls the corresponding port arm64, and many distributions publish images labelled aarch64 or arm64.
- ABI software
- Application Binary Interface: the low-level rules for how compiled code calls other compiled code. A binary built for a different ABI or CPU will not run.
- Access point (AP) networking
- A device that provides Wi-Fi to nearby clients and connects them to a wired network.
- ADC hardware
- An Analog-to-Digital Converter turns a voltage from a sensor into a number the CPU can read.
- AES security
- The Advanced Encryption Standard, the most widely used symmetric cipher. Many SoCs include hardware acceleration for it.
- AMQP protocols
- The Advanced Message Queuing Protocol, a more feature-rich messaging standard than MQTT, used for enterprise queues.
- Ansible tooling
- An agentless automation tool that configures machines over SSH using declarative playbooks.
- API software
- Application Programming Interface: the defined way one piece of software is used by another, at source level (a library) or over the network (a web API).
- apk software
- Alpine’s package manager, known for speed and small size.
- AppArmor security
- A Linux security module that confines programs using per-application profiles, generally simpler to configure than SELinux.
- Appliance concepts
- A device or image that does one job out of the box with little user configuration, as opposed to a general-purpose computer.
- ARM architecture hardware
- A family of processor architectures, licensed rather than manufactured by one company, that dominates phones, SBCs and embedded devices thanks to its low power use.
- ARMv7 (armhf) hardware
- A 32-bit ARM architecture version. ‘armhf’ names distribution builds for 32-bit ARM with hardware floating point, still common on older boards.
- ash software
- A small POSIX-style shell, and the default shell of BusyBox.
- ASIC (mining) mining
- An Application-Specific Integrated Circuit: a chip designed for one job. Bitcoin mining hardware uses ASICs built to compute the proof-of-work hash. The machine’s control board typically runs a small Linux system.
- ASLR security
- Address Space Layout Randomization places program memory at unpredictable addresses, making exploitation harder.
- Attack surface security
- The sum of ways an attacker can interact with a system: open ports, services, interfaces and installed software. Smaller is safer.
- Autotuning mining
- Firmware that adjusts each chip’s frequency and voltage to find the best trade-off between hashrate and power draw.
- Availability concepts
- The proportion of time a service is usable, often expressed as a percentage such as 99.9%.
- BACnet protocols
- A protocol for building automation, connecting heating, ventilation and lighting controllers.
- Bad blocks storage
- Flash blocks that are faulty from manufacture or worn out. Raw NAND filesystems must track and avoid them.
- Bare metal software
- Software that runs directly on hardware with no operating system, common on small microcontrollers.
- bash software
- The most common interactive Linux shell, feature-rich but larger than minimal shells.
- Bastion host tooling
- A hardened server that is the single entry point for administering machines behind it.
- Benchmark tooling
- A repeatable test measuring performance. Results only compare fairly when hardware, settings and method are the same.
- Bill of materials (BOM) concepts
- The list of every part that goes into a product, with quantities and costs.
- BIOS software
- The legacy PC firmware that initialises hardware and boots from the first sector of a disk. Largely superseded by UEFI.
- BIP mining
- A Bitcoin Improvement Proposal: a document describing a change or standard for Bitcoin.
- BitBake software
- The build engine used by Yocto that executes recipes and resolves their dependencies.
- Bitcoin mining
- A decentralised digital currency and network whose transactions are recorded on a public blockchain and secured by proof-of-work.
- Bitcoin Core mining
- The reference open-source implementation of a Bitcoin full node and wallet.
- Block mining
- A batch of transactions plus a header, added to the blockchain. Bitcoin targets roughly one block every ten minutes.
- Block device storage
- A device read and written in fixed-size blocks, such as a disk, SD card or partition.
- Block reward mining
- The new coins plus fees a miner may claim for finding a valid block.
- Blockchain mining
- A chain of blocks of transactions, each linked to the previous by a hash, so history cannot be altered without redoing the work.
- Bluetooth Low Energy (BLE) networking
- A low-power version of Bluetooth for short-range links to sensors, beacons and wearables.
- Board bring-up hardware
- The process of getting a new board to boot for the first time: power, clocks, memory, bootloader, then the kernel.
- Boot loop reliability
- A device repeatedly restarting without ever reaching a working state, often after a bad update or corrupted storage.
- Boot process software
- The sequence from power-on to a running system: ROM code, bootloader stages, kernel, init and services.
- Boot ROM software
- Code permanently stored in the SoC that runs first. It finds and loads the next-stage bootloader from storage such as SD, eMMC or SPI flash.
- Boot time tooling
- How long a device takes from power-on to being usable. Trimming services and using a lean init shortens it.
- Bootloader software
- The first software that runs when a device powers on. It initialises basic hardware, then loads the kernel into memory and starts it. U-Boot is a common one on embedded boards.
- Botnet security
- A network of compromised devices controlled by an attacker, often built from poorly secured routers and cameras.
- Bricking reliability
- Rendering a device unusable, typically through a failed or wrong firmware flash, so that it no longer boots. Recovery may need special tools.
- Brute-force attack security
- Trying many passwords or keys until one works. Rate limiting and strong credentials defeat it.
- BSP (Board Support Package) software
- The bundle of code that makes an operating system work on a specific board: bootloader, kernel configuration, device tree and drivers.
- Btrfs storage
- A copy-on-write filesystem with snapshots, checksums and compression.
- Build system (embedded) software
- A toolchain that generates a custom Linux image from source for a target device, instead of installing a ready-made distribution. Buildroot and Yocto are the two widely used ones.
- Buildroot software
- A tool that generates embedded Linux systems through cross-compilation, producing the toolchain, root filesystem, kernel image and bootloader from one configuration.
- BusyBox software
- A single small executable that provides simplified versions of many common Unix tools (ls, cp, grep, a shell…). It is a staple of minimal and embedded systems.
- BusyBox init software
- A minimal init included in BusyBox, configured through /etc/inittab. Common in tiny embedded images.
- CAN bus hardware
- Controller Area Network: a robust multi-device bus originally for vehicles, now also common in industrial machines and embedded systems.
- Canary release tooling
- Deploying a change to a few devices to detect problems before it reaches everyone.
- Carrier board hardware
- The board that a SoM plugs into, providing connectors, power and product-specific interfaces.
- CBOR protocols
- A compact binary data format similar in structure to JSON, suited to constrained devices.
- Certificate authority security
- An organisation trusted to issue certificates by signing them.
- cgminer mining
- A widely used open-source mining program and codebase that many miner firmwares are derived from.
- cgroups software
- Control groups: a kernel feature that limits and accounts for the CPU, memory and I/O used by groups of processes. It underpins containers.
- Chain of trust security
- Each boot stage verifies the next, starting from an unchangeable root of trust, so trust extends from hardware up to the running system.
- Checksum software
- A short value computed from a file’s contents, used to detect corruption or tampering after download or flashing.
- CI/CD tooling
- Continuous Integration and Delivery: automatically building, testing and releasing software on every change.
- cloud-init tooling
- A tool that configures an instance at first boot from user-supplied data, used on cloud images and some SBC images.
- CMake software
- A cross-platform build-configuration tool that generates build files for make, Ninja and others.
- CoAP protocols
- The Constrained Application Protocol: a REST-like protocol over UDP designed for very small devices and lossy networks.
- Code signing security
- Signing firmware or software releases so devices can verify they come from the legitimate publisher and are unmodified.
- Coinbase transaction mining
- The special first transaction in a block that pays the miner the block reward. Unrelated to the exchange of the same name.
- Compression (gzip, xz, zstd) software
- Reducing file size. xz compresses most but is slower; zstd offers a good speed/size balance; gzip is the widespread baseline. Choice affects image size and boot time.
- Configuration management tooling
- Describing a system’s desired state as code and applying it consistently across many machines.
- Console software
- The text interface through which the kernel prints messages and you can log in, often a serial port on embedded boards.
- Container tooling
- A packaged application and its dependencies run in isolation using kernel features such as namespaces and cgroups, sharing the host’s kernel.
- Control board mining
- The board that runs the miner’s Linux firmware, talks to the hashboards, network and pool, and serves the web interface.
- Copy-on-write storage
- Instead of overwriting data in place, changes are written to new blocks. This enables cheap snapshots and safer updates.
- Copyleft concepts
- Licensing that requires derived works to be shared under the same terms, as opposed to permissive licences.
- Core dump tooling
- A snapshot of a crashed program’s memory, saved so developers can analyse the failure with a debugger.
- Cortex-A hardware
- The ARM core line designed for ‘application’ processors that can run a full operating system such as Linux, with an MMU and virtual memory.
- Cortex-M hardware
- The ARM core line for microcontrollers. These cores usually have no MMU and run bare-metal code or an RTOS rather than Linux.
- CPU hardware
- The Central Processing Unit: the part of a chip that executes program instructions. On small devices it is usually one or more cores inside a SoC.
- CPU cache hardware
- Small, very fast memory inside or next to the CPU that keeps recently used data close, hiding the slowness of main RAM.
- cron software
- A scheduler that runs commands at fixed times or intervals.
- Cross-compilation software
- Building software on one type of machine (for example an x86 PC) to run on another (for example an ARM board). Embedded build systems rely on it because small devices are too slow to build on.
- Curtailment mining
- Reducing or pausing mining, for instance when electricity is expensive or the grid requests demand reduction.
- CVE security
- Common Vulnerabilities and Exposures: a public catalogue assigning unique IDs, like CVE-2024-12345, to known security flaws.
- CVSS security
- The Common Vulnerability Scoring System rates the severity of a vulnerability from 0 to 10.
- D-Bus software
- A message bus that lets desktop and system services talk to each other. It adds weight, so minimal images often omit it.
- Daemon software
- A background process that provides a service, such as an SSH server or a web server.
- dash software
- A fast, minimal POSIX shell used as the system shell on Debian and Ubuntu for scripts.
- dd storage
- A command that copies raw data between files and devices, commonly used to write images to SD cards. Choosing the wrong target can destroy data.
- DEB package software
- The package format used by Debian, Ubuntu and derivatives, handled by apt and dpkg.
- Default credentials security
- Factory usernames and passwords left unchanged. A leading cause of compromised IoT devices and routers.
- defconfig software
- A minimal saved kernel or build configuration listing only the options that differ from defaults, used as a reproducible starting point for a board.
- Dependency software
- Software that another piece of software needs in order to build or run. Managing dependencies is the main job of a package manager.
- Determinism concepts
- A system behaving the same way, with the same timing, every time. Valued in control and industrial applications.
- Device shadow protocols
- A cloud-held copy of a device’s last reported and desired state, letting apps interact even when the device is offline.
- Device tree software
- A data structure describing the hardware of a board (CPU, memory, buses, peripherals) so the kernel can configure it without hard-coding each board.
- devtmpfs software
- A kernel-managed filesystem mounted on /dev that automatically creates device nodes as hardware appears.
- DHCP networking
- A protocol that automatically gives devices an IP address and network settings when they join a network.
- Difficulty mining
- A measure of how hard it is to find a valid block. Bitcoin adjusts it every 2016 blocks to keep the block interval near ten minutes.
- Digital certificate security
- A signed document binding a public key to an identity such as a domain or device, used by TLS.
- Digital signature security
- A value produced with a private key that anyone with the public key can verify, proving who made data and that it was not altered.
- Digital twin protocols
- A software model that mirrors the state of a physical device, so it can be monitored and simulated remotely.
- DIN rail hardware
- A standard metal mounting rail used in industrial cabinets. DIN-rail gateways and computers clip onto it.
- Distribution (distro) software
- A packaged operating system built around the Linux kernel: kernel, libc, init system, tools, a package manager and a release process. Examples are Alpine and Debian.
- dm-verity security
- A kernel feature that verifies a read-only block device against a hash tree at read time, detecting any tampering with the system partition.
- dmesg software
- A command that prints the kernel’s message buffer: hardware detection, driver messages and errors. The first place to look when hardware misbehaves.
- DNS networking
- The Domain Name System translates names like example.org into IP addresses.
- Docker tooling
- A popular platform for building and running containers. Many Alpine-based images exist because of their small size.
- Documentation stripping software
- Removing man pages, docs and locales from an image to shrink it, a common footprint-trimming step.
- DRAM hardware
- Dynamic RAM, the main memory type in most computers and boards. It must be refreshed constantly and is cheaper per bit than SRAM.
- Driver software
- Software that lets the kernel talk to a specific piece of hardware. Missing or poor drivers are the most common reason a device does not work with a mainstream kernel.
- Dropbear software
- A small SSH server and client designed for low-memory systems, the default SSH on OpenWrt.
- DSP hardware
- A Digital Signal Processor: a processor specialised in fast maths on streams of samples such as audio, radio or sensor data.
- Dynamic DNS networking
- A service that keeps a hostname pointed at an address that changes, such as a home connection’s public IP.
- Dynamic linking software
- Programs load shared libraries at run time. It saves disk space when many programs share a library, but requires the right libraries to be present.
- Edge AI protocols
- Performing AI inference on the local device or gateway, reducing latency, bandwidth and data leaving the site.
- Edge computing concepts
- Running processing close to where data is produced (a gateway, a local server) instead of sending everything to a distant data centre. Edge nodes are often small machines running a lean Linux.
- Efficiency (J/TH) mining
- Energy used per terahash. Lower is better, and it is the main figure for comparing miners.
- Electrum server mining
- A service that indexes the blockchain so lightweight wallets can query balances quickly from your own node.
- ELF software
- Executable and Linkable Format, the standard binary file format for programs and libraries on Linux.
- Elliptic-curve cryptography security
- Public-key cryptography that achieves strong security with much smaller keys than RSA, well suited to constrained devices.
- Embedded Linux concepts
- A Linux system built for one specific device or purpose, usually with only the components that device needs. It is often assembled with a build system rather than installed from a general-purpose distribution.
- Embedded system concepts
- A computer built into a product to do a dedicated job, such as a router, meter or miner control board, rather than serve as a general-purpose PC.
- eMMC hardware
- Flash storage soldered onto a board, packaged with its own controller. It is generally sturdier and more consistent than removable SD cards.
- Encryption security
- Transforming data so only someone with the right key can read it, protecting it in transit and at rest.
- End of life (EOL) concepts
- The point after which a product or software version no longer receives updates or security fixes.
- EROFS storage
- Enhanced Read-Only File System: a fast, compressed read-only filesystem, an alternative to SquashFS.
- Ethernet networking
- The standard wired local-network technology. Boards and gateways use it for reliable, low-latency connections compared with Wi-Fi.
- exFAT storage
- A lightweight filesystem for flash drives and cards that supports files larger than 4 GB.
- ext4 storage
- The default journaling filesystem on most Linux distributions, reliable and well supported.
- F2FS storage
- A filesystem designed for flash storage that reduces write amplification, used on some SD cards and phones.
- Factory reset reliability
- Restoring a device’s settings and data to its original state.
- Fail2ban security
- A tool that watches logs and temporarily blocks addresses showing repeated failed logins.
- Failover concepts
- Automatically switching to a standby component when the primary fails.
- Fanless design hardware
- A device cooled passively by heatsinks and enclosure, with no moving parts. It avoids fan failure and dust but limits sustained power.
- FAT32 storage
- A simple, universally readable filesystem. Boards often use a small FAT partition for boot files.
- Fault tolerance concepts
- A system’s ability to keep working, perhaps in a reduced way, when parts fail.
- Firewall security
- A system that filters network traffic according to rules, allowing or blocking connections.
- Firmware software
- Software stored on a device that controls its hardware. On many ASIC miners and routers, the firmware is a full embedded Linux image, and third-party firmware can replace the stock one.
- Firmware update reliability
- Replacing a device’s firmware with a newer version to add features or fix bugs. Interrupted updates are a leading cause of failures.
- First-boot setup tooling
- Initialisation that runs only the first time a device starts, such as expanding the filesystem or generating keys.
- Fixed release concepts
- A distribution model with discrete versions on a schedule, each stable and supported for a defined period.
- Flash wear hardware
- Flash storage (SD cards, eMMC, NAND) survives a limited number of write cycles. Heavy logging or swapping can wear it out, so embedded systems limit or redirect writes.
- Flashing storage
- Writing a firmware or system image to a device’s storage.
- Fleet management tooling
- Tracking, configuring and updating many devices as a group.
- Footprint concepts
- How much of a device’s resources a system uses: storage for the image, RAM at runtime, and sometimes CPU and boot time. A small footprint lets the OS run on cheaper or older hardware.
- Fork concepts
- A copy of a project that continues on its own path, sometimes to maintain it after the original stops.
- Form factor concepts
- The physical size, shape and connector layout of a board or device.
- FOSS concepts
- Free and open-source software: software whose source is available and licensed to be used, modified and shared.
- FPGA hardware
- A Field-Programmable Gate Array: a chip whose logic can be reconfigured after manufacture. Used for custom hardware acceleration and protocol handling.
- FreeRTOS software
- A widely used open-source real-time kernel for microcontrollers, offering tasks, queues and timers in a very small footprint.
- fsck storage
- A tool that checks and repairs filesystem errors, typically run after an unclean shutdown.
- fstab storage
- The file /etc/fstab listing which filesystems to mount at boot and with which options, such as read-only or noatime.
- Full node mining
- Software that downloads and independently validates all of a blockchain’s rules and blocks, rather than trusting someone else. Running one on a small computer is a common use of lightweight Linux.
- Gateway networking
- A device that connects networks that speak different protocols or sit in different places. An IoT gateway links local sensors to the cloud.
- GCC software
- The GNU Compiler Collection, the standard compiler for Linux and embedded C and C++ work.
- GDB tooling
- The GNU debugger, able to debug programs on the device itself or remotely from another machine.
- Git tooling
- The distributed version-control system used by nearly all open-source embedded projects, including the Linux kernel.
- glibc software
- The GNU C Library, the default libc on most mainstream Linux distributions. It is feature-rich and widely compatible, and larger than some alternatives.
- GNU coreutils software
- The standard set of basic command-line tools (ls, cp, mv, cat…) on most full Linux distributions. Larger than BusyBox’s equivalents.
- Golden image tooling
- A prepared, tested system image used as the template that every device is flashed with.
- GPIO hardware
- General-Purpose Input/Output: pins a program can set high or low or read, used to drive LEDs, relays and read switches.
- GPL concepts
- The GNU General Public License: a copyleft licence requiring that distributed modifications and derived works stay under the same licence, with source available. The Linux kernel uses GPLv2.
- GPT storage
- The GUID Partition Table: a modern scheme supporting many partitions and large disks, used with UEFI.
- GPU hardware
- A Graphics Processing Unit. On embedded boards it accelerates display output and sometimes general compute. Headless devices often never use it.
- Graceful degradation concepts
- Continuing to provide core functions with reduced capability when something fails, instead of stopping entirely.
- Grafana tooling
- A dashboard tool for visualising metrics from sources like Prometheus and InfluxDB.
- gRPC protocols
- A remote-procedure-call framework using Protocol Buffers over HTTP/2, efficient for service-to-service communication.
- GRUB software
- A bootloader widely used on x86 systems that lets you choose an operating system or kernel at start-up.
- Halving mining
- The scheduled event, every 210,000 blocks (about four years), that halves Bitcoin’s block subsidy.
- Hard real-time concepts
- Real-time where missing a deadline is a failure, for example in braking systems. Needs an RTOS or specialised setup.
- Hardening security
- Reducing a system’s vulnerabilities by removing unused services and software, tightening permissions and changing insecure defaults.
- Hardware errors (HW) mining
- Invalid results produced by a miner’s chips, often from heat, voltage or aging. A rising rate signals a problem.
- Hardware revision hardware
- A numbered version of a board design. Different revisions of the same product may need different firmware, device trees or drivers.
- Hash function security
- A one-way function that turns any input into a fixed-size fingerprint. Even a tiny change in input produces a completely different output.
- Hashboard mining
- A circuit board carrying many ASIC chips. A miner usually holds several hashboards driven by one control board.
- Hashrate mining
- How many hash calculations a miner performs per second, the standard measure of mining speed.
- HAT / add-on board hardware
- An expansion board that attaches to an SBC’s header to add features such as PoE, sensors, radios or extra I/O.
- Headless hardware
- A device run without a monitor, keyboard or mouse, managed over the network or a serial console. Most IoT and mining systems are headless.
- Headroom concepts
- Spare capacity in CPU, memory or storage beyond what the system needs at normal load, allowing for peaks and future growth.
- High availability concepts
- Designing so a service keeps running despite failures, usually with redundancy and automatic failover.
- Hotplug software
- Connecting or removing hardware while the system is running, such as plugging in a USB stick, and having the system react.
- HSM security
- A Hardware Security Module: dedicated hardware that generates and guards cryptographic keys, used for example to sign firmware releases.
- HTTP / HTTPS protocols
- The protocol of the web. HTTPS is HTTP inside TLS encryption.
- I²C hardware
- A two-wire serial bus (data and clock) connecting a controller to many low-speed peripherals such as sensors and small displays, each with its own address.
- IDS / IPS security
- Intrusion Detection and Prevention Systems watch network traffic for malicious patterns, alerting (IDS) or blocking (IPS).
- IMA security
- The Integrity Measurement Architecture measures or checks files against known-good values as they are used.
- Image software
- The final flashable file or set of files containing bootloader, kernel and root filesystem for a device.
- Immersion cooling mining
- Cooling miners by submerging them in a non-conductive liquid, allowing higher density and often quieter operation.
- Immutable system tooling
- A system whose base is never modified in place; updates replace the whole image, which makes state predictable.
- Industrial grade concepts
- Hardware rated for harsher conditions such as wide temperature ranges, vibration and long product lifetimes.
- InfluxDB tooling
- A database optimised for time-series data such as sensor readings.
- Init system software
- The first process started by the kernel (PID 1). It brings up services and supervises them. Common examples are systemd, OpenRC and BusyBox init.
- Initial block download (IBD) mining
- The first sync of a new node, in which it downloads and verifies the entire blockchain. Slow on weak CPUs and storage.
- initramfs software
- A small filesystem loaded into RAM at boot. It prepares the system — for example finding and mounting the real root filesystem — before handing control over.
- IoT (Internet of Things) hardware
- Physical devices — sensors, gateways, meters, cameras — that connect to a network and exchange data. They often have small CPUs, little RAM and flash storage, which is why lightweight operating systems matter.
- IPK package software
- The package file format used by opkg, a small archive of files plus metadata.
- IPsec networking
- A suite of protocols that secures IP traffic, widely used for site-to-site VPNs between networks.
- iptables security
- The long-standing command-line tool for configuring Linux packet filtering, now being replaced by nftables.
- IPv4 networking
- The older Internet addressing scheme with 32-bit addresses such as 192.168.1.10. Addresses are scarce, which is why NAT is widespread.
- IPv6 networking
- The newer addressing scheme with 128-bit addresses, giving every device room for a public address without NAT.
- JFFS2 storage
- An older journaling filesystem for raw flash, still used on small NOR chips, with slow mount times on larger ones.
- Jitter networking
- Variation in latency between packets. High jitter harms real-time audio, video and control traffic.
- journald tooling
- systemd’s logging service, storing structured logs that are read with journalctl.
- Journaling storage
- A filesystem records intended changes in a log first, so after a crash it can recover to a consistent state quickly.
- JSON protocols
- A text data format of objects and arrays, human-readable and the default for web APIs, though bulkier than binary formats.
- JTAG hardware
- A standard debug and test interface on chips. It allows halting the CPU, reading memory and programming flash even when the software is broken.
- K3s tooling
- A lightweight Kubernetes distribution designed for edge devices and small clusters.
- Kconfig software
- The configuration language and system used by the Linux kernel, Buildroot and others to declare options and their dependencies.
- Kernel command line software
- Text passed by the bootloader to the kernel to set options such as the root device, console and debug flags.
- Kernel module software
- A piece of kernel code, often a driver, that can be loaded or unloaded at runtime instead of being built into the kernel image.
- Kernel panic software
- A fatal error the kernel cannot recover from. The system halts or reboots, and the message usually points at a missing root filesystem or a driver fault.
- Kernel space vs userspace software
- Kernel space is where the kernel and drivers run with full hardware access; userspace is where ordinary programs run with restricted privileges and call into the kernel.
- kexec software
- A mechanism to load and start a new kernel from a running one, skipping firmware start-up. It speeds reboots and is used for crash dumps.
- Key management security
- Creating, storing, rotating and revoking cryptographic keys safely across their lifetime.
- KNX protocols
- An open standard for building automation such as lighting and blinds, often over twisted-pair cabling.
- Kubernetes tooling
- An orchestrator that schedules and manages containers across many machines.
- Latency networking
- The time a packet takes to travel from source to destination, usually measured in milliseconds.
- Layer (Yocto) software
- A collection of recipes and settings grouped by purpose, such as a board support layer. Layers stack to form a distribution.
- Least privilege security
- Giving each program and user only the access it needs, so a compromise does less damage.
- LGPL concepts
- A weaker copyleft licence mainly for libraries, allowing them to be linked from software under other licences with conditions.
- libc software
- The C standard library that almost every program depends on. Different systems use different ones, such as glibc, musl or uClibc-ng, and a binary built for one may not run on another.
- Lightning Network mining
- A layer built on Bitcoin for fast, low-fee payments through channels between nodes.
- Linux kernel software
- The core of the operating system. It manages hardware, memory and processes, and provides drivers. Everything else (libc, init, applications) runs on top of it.
- LLVM / Clang software
- A compiler infrastructure with the Clang C/C++ front end, an alternative to GCC that is also widely used for cross-compiling.
- Locale software
- Settings for language, character set and formatting. Minimal images often strip locale data to save space.
- Log rotation tooling
- Automatically archiving and deleting old logs so they do not fill storage.
- Logging tooling
- Recording events and errors from a system. On flash-based devices logs are often kept in RAM or shipped elsewhere to limit wear.
- LoRa networking
- A long-range, low-power radio modulation suited to small amounts of data sent over kilometres, such as remote sensors.
- LoRaWAN networking
- A network protocol built on LoRa that connects devices through gateways to a central network server.
- LPDDR hardware
- Low-Power DDR memory, a DRAM variant designed for battery-powered and compact devices such as phones and many SBCs.
- LSM (Linux Security Module) security
- The kernel framework that lets security systems such as SELinux and AppArmor hook into access decisions.
- LTS concepts
- Long-Term Support: a release maintained for an extended period with fixes but few new features.
- LTS kernel software
- A Long-Term Support kernel branch that receives bug and security fixes for years. Embedded products usually track one.
- Lua software
- A small, fast scripting language embedded in many devices; OpenWrt’s LuCI interface historically used it.
- LuCI software
- The web interface of OpenWrt, used to configure network, wireless and packages from a browser.
- LUKS / dm-crypt security
- The standard Linux disk-encryption system. dm-crypt does the encryption in the kernel and LUKS manages keys and metadata.
- LVM storage
- Logical Volume Manager: an abstraction letting you resize and combine storage volumes flexibly.
- LwM2M protocols
- Lightweight M2M: a device-management protocol from the Open Mobile Alliance for remote configuration and firmware updates of constrained devices.
- LXC tooling
- Linux Containers: lightweight system containers that behave more like a small virtual machine than a single app.
- Mainline kernel software
- The official Linux kernel tree maintained by Linus Torvalds. Hardware supported in mainline is easier to keep updated than hardware needing vendor patches.
- make / Makefile software
- A build tool that runs rules from a Makefile to compile only what has changed. The backbone of many embedded builds.
- Matter networking
- A smart-home connectivity standard designed so devices from different makers work together locally.
- MBR storage
- The classic partition scheme and boot sector format, limited to four primary partitions and 2 TB disks.
- MCU (microcontroller) hardware
- A small chip combining a processor, a little RAM and flash, and peripherals. It runs firmware directly or an RTOS and is far more limited than a Linux-capable SoC.
- mdev software
- A lightweight device manager built into BusyBox, used on small systems in place of udev.
- mDNS networking
- Multicast DNS: lets devices on a local network find each other by name (such as device.local) without a DNS server.
- Measured boot security
- Recording hashes of each boot component into a secure store such as a TPM so the boot state can later be checked or attested.
- Mempool mining
- The waiting area where a node keeps valid unconfirmed transactions until they are included in a block.
- Mesh network networking
- A network where nodes relay traffic for each other, extending coverage and providing alternative paths.
- Meson software
- A fast build system with a readable configuration language, used by many modern open-source projects.
- Message broker protocols
- The server that receives messages from publishers and delivers them to subscribers, as in MQTT.
- Metrics tooling
- Numeric measurements over time, such as temperature, memory use or hashrate.
- MicroPython software
- A compact implementation of Python 3 for microcontrollers, allowing scripting on very small devices.
- Miner hosting mining
- Paying a facility to house and power your miners, handling cooling, networking and electricity.
- minicom / picocom tooling
- Terminal programs for talking to a serial port, used to see boot logs and log in.
- Minimal Debian install software
- A Debian installation with only the base system and no desktop, a common starting point for small servers and SBC images.
- Mining pool mining
- A group of miners combining hashrate and sharing rewards in proportion to work submitted, giving steadier payouts than mining alone.
- Mining power supply mining
- The high-current power supply feeding a miner. Its quality and the electrical supply strongly affect stability and safety.
- MIPS hardware
- A RISC instruction set architecture long used in routers and consumer network gear. Many older OpenWrt-era devices are MIPS-based.
- MMU (Memory Management Unit) hardware
- Hardware that translates virtual addresses to physical ones and enforces memory protection between processes. Standard Linux needs an MMU.
- Modbus protocols
- A simple, decades-old industrial protocol for reading and writing device registers, running over serial (RTU) or TCP.
- Monitoring tooling
- Continuously collecting health and performance data from devices so problems are noticed early.
- Mount storage
- Attaching a filesystem to a directory so its files become accessible.
- MQTT protocols
- A lightweight publish/subscribe messaging protocol widely used in IoT. Devices publish to topics on a broker and others subscribe to them.
- MQTT QoS levels protocols
- Delivery guarantees in MQTT: 0 at most once, 1 at least once, 2 exactly once. Higher levels cost more bandwidth and time.
- MTBF concepts
- Mean Time Between Failures: an average predicted time between failures of a repairable component. It is a statistical estimate, not a guarantee.
- MTD storage
- Memory Technology Device: the Linux subsystem for raw flash chips, used with flash-specific filesystems.
- MTU networking
- Maximum Transmission Unit: the largest packet size a link carries without fragmenting. Mismatches, often with VPNs, cause odd connection stalls.
- Multi-factor authentication security
- Requiring more than one proof of identity, such as a password plus a one-time code or hardware key.
- musl software
- A lightweight libc implementation aimed at small size and simplicity. Alpine Linux uses it. Software built against glibc may need rebuilding to run on musl.
- Mutual TLS (mTLS) security
- TLS where both client and server present certificates, letting a service verify each device as well as the reverse.
- Namespaces software
- A kernel feature that gives processes an isolated view of resources such as network, process IDs or mounts. Together with cgroups it makes containers possible.
- NAND flash storage
- A dense, cheaper flash type used for larger storage. It has bad blocks and needs wear levelling and error correction.
- NAT networking
- Network Address Translation: a router rewrites addresses so many private devices share one public IP address.
- NB-IoT / LTE-M networking
- Cellular technologies designed for IoT: low power, wide coverage and small data volumes, using operator networks.
- Netfilter security
- The Linux kernel framework for packet filtering and NAT, on which iptables and nftables are built.
- Network bridge networking
- Joins two network segments so they behave as one, commonly linking a wired port and a wireless interface.
- nftables security
- The modern Linux packet-filtering framework that supersedes iptables with a single, more consistent rule language.
- Node-RED protocols
- A flow-based visual programming tool for wiring devices, APIs and services together, popular on Raspberry Pi and gateways.
- Nonce mining
- A number miners change on each attempt so the block’s hash differs, searching for one below the target.
- NOR flash storage
- A flash type allowing fast random reads and execute-in-place, used for small bootloaders and firmware, often over SPI.
- NPU hardware
- A Neural Processing Unit: a block designed to accelerate machine-learning inference at low power, found in some edge SoCs.
- NTP software
- Network Time Protocol: synchronises a device’s clock over the network. Important for logs, TLS certificates and devices without a battery-backed RTC.
- NVMe storage
- A fast storage protocol for flash drives over PCIe, much quicker than SATA. Some SBCs and mini PCs offer an M.2 NVMe slot.
- NX bit security
- A CPU feature marking memory as non-executable so injected data cannot be run as code.
- Observability tooling
- Being able to understand a system’s internal state from its outputs: logs, metrics and traces.
- OCI image tooling
- The Open Container Initiative standard for container images and runtimes, so images work across different tools.
- OPC UA protocols
- An industrial interoperability standard for exchanging structured machine data securely between systems.
- Open hardware concepts
- Hardware whose design files are published so others can study, modify and build it.
- OpenEmbedded software
- The build framework and metadata collection on which the Yocto Project is based.
- OpenRC software
- A dependency-based init system that is lighter than systemd. Alpine Linux uses it.
- OpenSSH software
- The standard full-featured SSH implementation on most Linux systems.
- OpenVPN networking
- A long-established, highly configurable open-source VPN that runs in userspace.
- opkg software
- A lightweight package manager for embedded Linux, long used by OpenWrt and other small embedded distributions.
- OTA update (over-the-air) reliability
- Delivering software updates to a device remotely over the network, without physical access. Reliable OTA needs a way to recover if the update fails.
- Overclocking mining
- Running chips faster than their default setting for more hashrate, at the cost of more heat, power and a higher error rate.
- Overlay network networking
- A virtual network built on top of another, giving devices private addresses and direct paths regardless of where they physically are.
- OverlayFS software
- A Linux filesystem that layers a writable area over a read-only base. It gives the appearance of a writable system while keeping the original image untouched.
- Package manager software
- The tool that installs, updates and removes software and resolves dependencies (for example apk on Alpine, or opkg on some embedded systems).
- Package repository software
- A server holding packages and an index that a package manager downloads from. Also called a feed on OpenWrt.
- Packet loss networking
- The share of packets that never arrive. Even small loss can noticeably slow TCP connections.
- Partition table storage
- The structure at the start of a disk describing how it is divided into partitions.
- Patch management security
- The process of tracking, testing and applying software updates that fix bugs and vulnerabilities.
- PCIe hardware
- PCI Express: a high-speed serial bus for expansion devices such as NVMe drives, network cards and accelerators. Some SBCs expose a lane or two.
- perf tooling
- The Linux profiling tool that shows where CPU time is spent in the kernel and applications.
- Permissive licence concepts
- A licence such as MIT, BSD or Apache 2.0 that allows reuse with few conditions, generally attribution.
- PID 1 software
- The first userspace process started by the kernel. It is responsible for starting services and for reaping orphaned processes.
- ping networking
- A tool that sends small ICMP echo requests to check whether a host is reachable and how long replies take.
- PKI security
- Public Key Infrastructure: the system of keys, certificates and authorities that manages digital identities.
- PMIC hardware
- A Power Management IC that generates and sequences the various voltages a board needs. Its configuration matters for power-up, sleep and stability.
- Podman tooling
- A daemonless container engine compatible with Docker images.
- PoE (Power over Ethernet) hardware
- Delivering electrical power to a device over its network cable, so one cable carries both data and power. Common for cameras, access points and gateways.
- Point release concepts
- A minor update within a stable release line, bundling fixes without changing the major version.
- Poky software
- The Yocto Project’s reference distribution and build environment, a starting point for custom distributions.
- Port forwarding networking
- A router rule that sends incoming connections on a given port to a specific device on the local network. Exposing devices this way increases attack surface.
- POSIX software
- A family of standards for Unix-like systems, defining shell behaviour and system interfaces so software is portable across them.
- Power-loss resilience reliability
- A device’s ability to survive sudden power cuts without corrupting its filesystem. Read-only system partitions and careful write handling are the usual techniques.
- PREEMPT_RT software
- A set of kernel changes, now largely merged into mainline, that makes Linux more predictable in response time for real-time workloads.
- procfs software
- A virtual filesystem (usually /proc) exposing process and kernel information as files, for example /proc/meminfo.
- Profiling tooling
- Measuring where a program spends time or memory in order to optimise it.
- Prometheus tooling
- An open-source monitoring system that scrapes metrics from targets and stores them as time series.
- Proof of work mining
- A consensus mechanism in which miners repeatedly hash block candidates until one meets a difficulty target, showing that computational effort was spent.
- Protocol Buffers protocols
- A compact, schema-based binary serialisation format from Google, often used with gRPC.
- Provisioning protocols
- Giving a new device its identity, credentials and configuration so it can join a system securely.
- Pruned node mining
- A node that validates everything but discards old block data to save disk space, keeping only recent blocks. It suits devices with limited storage.
- Publish/subscribe protocols
- A messaging pattern where senders publish to named channels and receivers subscribe to the ones they care about, without knowing each other.
- PWM hardware
- Pulse-Width Modulation: switching a pin on and off rapidly and varying the on-time to control things like LED brightness, motor speed or fan speed.
- QEMU tooling
- An emulator that can run a system for a different CPU architecture on your PC, handy for testing images before flashing hardware.
- QoS / SQM networking
- Quality of Service and Smart Queue Management prioritise traffic and reduce bufferbloat so a busy connection stays responsive.
- RAID storage
- Combining several drives for redundancy or speed. It protects against drive failure but is not a backup.
- RAM hardware
- Random-access memory: fast, volatile working memory holding running programs and data. Its size largely decides which operating systems a device can run.
- Raw disk image storage
- A byte-for-byte copy of a disk or card, such as a .img file, that can be written straight to storage.
- Read-only root filesystem reliability
- Mounting the system partition so it cannot be modified at runtime. It prevents corruption from sudden power loss and makes devices behave identically after every boot; changing data goes to a separate writable area.
- Real-time concepts
- Computing where correctness depends on responding within a time limit. It is about predictable timing, not raw speed.
- Recipe (Yocto) software
- A file describing how to fetch, configure, build and package one piece of software in the Yocto Project.
- Redundancy concepts
- Having spare components so one failure does not stop the system.
- Remote management tooling
- Administering devices from afar, through SSH, a web UI or a management platform.
- Reproducible builds security
- Building the same source so that anyone gets bit-for-bit identical output, making tampering detectable.
- Rescue / recovery mode reliability
- A minimal boot mode used to repair a broken system, reflash firmware or restore settings.
- REST protocols
- A style of web API using standard HTTP methods on resources identified by URLs, usually exchanging JSON.
- Retained message protocols
- An MQTT message the broker stores so new subscribers immediately receive the last known value on a topic.
- Reverse proxy networking
- A server that receives requests on behalf of other servers and forwards them, often adding TLS, caching or authentication.
- Right to repair concepts
- The principle that owners should be able to repair and modify their devices, including installing alternative firmware.
- RISC-V hardware
- An open instruction set architecture that anyone may implement without licence fees. Linux and several embedded distributions support it, with growing hardware choice.
- Rollback tooling
- Returning to a previous working version after a bad update.
- Rolling release concepts
- A distribution model with continuous updates and no discrete versions. Fresh, but changes constantly.
- Root filesystem (rootfs) software
- The filesystem mounted at “/”. It holds the system’s programs, libraries and configuration. On embedded systems it is often compact and sometimes read-only.
- Root of trust security
- The immutable hardware or ROM component that everything else’s trust is anchored to, typically holding a public key or key hash.
- Router networking
- A device that forwards packets between networks, typically linking a home or site network to the Internet.
- RPC interface mining
- A programmatic interface letting other software query and control a node, such as Bitcoin Core’s JSON-RPC.
- RS-485 hardware
- A robust serial standard for long cable runs and multiple devices on one bus, widely used in industrial and building automation, often carrying Modbus.
- RSA security
- A widely used public-key algorithm for signatures and key exchange, needing larger keys than elliptic-curve alternatives.
- RTC (real-time clock) hardware
- A small clock chip, usually battery-backed, that keeps the time while the device is powered off. Many boards lack one, so time is set from the network at boot.
- RTOS software
- A Real-Time Operating System designed to respond to events within guaranteed time limits. FreeRTOS and Zephyr are examples; typical on microcontrollers.
- runit software
- A small init and service supervision scheme where each service is a directory with a run script, used by Void Linux among others.
- Rust for embedded software
- Using the Rust language on small devices, valued for memory safety without a garbage collector. It can target both microcontrollers and Linux boards.
- s6 software
- A set of small tools for process supervision and init, valued for minimal size and reliability.
- Sandbox security
- An isolated environment that limits what a process can see or do, using mechanisms like namespaces, seccomp or containers.
- SATA storage
- A common interface for connecting hard drives and SSDs to a computer.
- SBC (Single-Board Computer) hardware
- A complete computer on one circuit board, with CPU, RAM, storage interfaces and I/O. Raspberry Pi–style boards are the best-known examples.
- SBOM security
- A Software Bill of Materials: a list of every component and version inside a firmware image, letting you check it against known vulnerabilities.
- SD / microSD card hardware
- Removable flash storage used as the boot and system drive on many SBCs. Cheap but prone to wear and corruption under heavy writes or power loss.
- SDK software
- A Software Development Kit: toolchain, libraries and headers packaged so developers can build software for a target device without building the whole system.
- seccomp software
- A kernel feature that restricts which system calls a process may make, shrinking the damage a compromised program can do.
- Secure Boot security
- A boot process that verifies each stage’s cryptographic signature before running it, so tampered firmware or kernels are rejected.
- Secure element security
- A tamper-resistant chip that protects secret keys and performs cryptography, used to give devices a hardware-backed identity.
- Seed phrase mining
- A list of words that can regenerate a wallet’s keys. Anyone who has it controls the funds, so it must be stored offline and never shared.
- SegWit mining
- Segregated Witness, a Bitcoin upgrade that separated signature data from transactions, fixing malleability and increasing effective capacity.
- SELinux security
- A mandatory access control system for Linux that enforces detailed policies on what each process may access.
- Semantic versioning concepts
- A version scheme of MAJOR.MINOR.PATCH where the number signals the kind of change: breaking, feature or fix.
- Serial console tooling
- Accessing a device’s console over a UART with a USB-serial adapter and a terminal program. It works even when the network or display does not.
- Service supervision software
- Automatically restarting a service when it crashes, done by init systems and supervisors like runit, s6 and systemd.
- SHA-256 security
- A widely used cryptographic hash producing a 256-bit value. Used to verify downloads, in signatures, and as the basis of Bitcoin’s proof-of-work.
- Shell software
- The program that reads commands and runs them. Minimal systems use lightweight shells like BusyBox ash; full systems use bash.
- SLC / MLC / TLC storage
- Flash cell types storing 1, 2 or 3 bits. More bits per cell means more capacity per cost but lower endurance and speed.
- Snapshot storage
- A point-in-time view of a filesystem or volume that can be rolled back to.
- SNMP protocols
- The Simple Network Management Protocol, used to monitor and configure network equipment such as switches and routers.
- SoC (System on Chip) hardware
- A single chip that integrates the CPU cores, memory controller and many peripherals (network, USB, storage, GPU) that would otherwise be separate chips. Most single-board computers, routers and IoT devices are built around one.
- Soft real-time concepts
- Real-time where occasional missed deadlines degrade quality but are tolerable, such as audio playback.
- Solo mining mining
- Mining without a pool, keeping the entire reward if a block is found but with very irregular chances of success.
- SoM (System on Module) hardware
- A small board carrying the SoC, RAM and storage, meant to be plugged into a product-specific carrier board.
- SPI hardware
- Serial Peripheral Interface: a fast, synchronous serial bus using separate lines for data in, data out, clock and chip-select. Often used for flash chips and displays.
- SquashFS software
- A compressed, read-only filesystem. It is popular in embedded images because it saves flash space; it is often combined with OverlayFS for writable changes.
- SRAM hardware
- Static RAM: faster and more power-hungry per bit than DRAM. Used for CPU caches and the small on-chip memory of microcontrollers.
- SSD storage
- A Solid-State Drive: flash-based storage with no moving parts, faster and more robust than a hard disk.
- SSH security
- Secure Shell: an encrypted protocol for remote login and file transfer, the standard way to administer headless Linux devices.
- SSH keys security
- A public/private key pair used instead of passwords for SSH login. Safer because the private key never crosses the network.
- SSH tunnel tooling
- Forwarding a network port through an SSH connection, reaching a device’s internal service securely without exposing it.
- SSID networking
- The name a Wi-Fi network broadcasts.
- Stack canary security
- A guard value placed on the stack that is checked before a function returns, detecting many buffer overflows.
- Staged rollout tooling
- Releasing an update to a small share of devices first, then widening if nothing goes wrong.
- Static Go binaries software
- Go programs compile to a single self-contained executable, which makes them easy to deploy on minimal systems and cross-compile for other CPUs.
- Static IP / DHCP reservation networking
- Making a device always use the same address, either configured on the device or reserved in the router. Useful for servers, miners and gateways.
- Static linking software
- Bundling libraries into the executable at build time. The binary is larger but self-contained, which simplifies deployment to minimal systems.
- strace tooling
- A tool that shows the system calls a program makes, useful for finding why it fails or hangs.
- Stratum mining
- The protocol miners use to talk to a mining pool: receiving work and submitting results.
- Stratum V2 mining
- The newer version of the Stratum mining protocol adding encryption and letting miners choose the transactions they mine.
- Stripping binaries software
- Removing debug symbols from executables and libraries to make them much smaller for production images.
- Supply-chain attack security
- Compromising software or hardware before it reaches the user, for example by tampering with a dependency or a build.
- Swap storage
- Disk space used as overflow when RAM is full. On flash storage heavy swapping causes wear, so it is often disabled or compressed in RAM.
- Switch networking
- A device that forwards Ethernet frames between connected machines on a local network.
- sysfs software
- A virtual filesystem (usually /sys) exposing kernel objects and device attributes as files, such as LED brightness or GPIO state.
- Syslog protocols
- A standard for sending log messages to a central collector.
- System call software
- The controlled entry point by which a userspace program asks the kernel to do something such as open a file or send data.
- systemd software
- A widely used init system and service manager with extensive features (service supervision, logging, timers). It is powerful but larger than minimal alternatives.
- systemd timer software
- A systemd unit that triggers a service on a schedule or event, an alternative to cron.
- systemd-analyze tooling
- A command that reports where boot time goes on a systemd system.
- SysVinit software
- The traditional init system that starts services from ordered shell scripts, simple and still found on small systems.
- Taproot mining
- A Bitcoin upgrade improving privacy and flexibility of scripts using Schnorr signatures.
- Tarball software
- A .tar archive, usually compressed (.tar.gz, .tar.xz), the traditional way of distributing source code and root filesystems.
- TCP/IP networking
- The family of protocols the Internet runs on. IP moves packets between machines; TCP adds reliable, ordered delivery on top.
- TDP (thermal design power) hardware
- A figure describing how much heat a chip is expected to produce under typical heavy load, used to size cooling. It is not the same as peak power draw.
- Telemetry protocols
- Measurements and status data a device sends back automatically, such as temperature, hashrate or uptime.
- Testnet / regtest / signet mining
- Separate Bitcoin networks for testing with worthless coins: testnet is public, regtest is a private local chain, signet is a signed public test chain.
- TH/s mining
- Terahashes per second, a unit of hashrate equal to one trillion hashes per second.
- Thermal throttling hardware
- Automatic reduction of CPU speed when temperature gets too high, protecting hardware at the cost of performance.
- Thread networking
- A low-power IPv6 mesh networking protocol for smart-home devices, on which Matter can run.
- Throughput networking
- The amount of data successfully transferred per second, distinct from the link’s theoretical bandwidth.
- TinyML protocols
- Running small machine-learning models directly on very low-power devices instead of in the cloud.
- TLS security
- Transport Layer Security: the protocol that encrypts and authenticates connections, such as HTTPS and secure MQTT.
- tmpfs storage
- A filesystem that lives in RAM. Frequently used for /tmp and logs on embedded systems to avoid flash writes.
- tmux tooling
- A terminal multiplexer that keeps sessions running after you disconnect and splits one terminal into several panes.
- Toolchain software
- The set of tools — compiler, linker, libc headers and utilities — used to build software for a target. A cross toolchain targets a different CPU from the one you build on.
- Topic protocols
- The hierarchical name (such as home/kitchen/temp) that messages are published to in MQTT.
- Total cost of ownership concepts
- The full cost of a device or system over its life, including power, maintenance and replacement, not just the purchase price.
- Toybox software
- A compact implementation of common Unix commands in a single binary, similar in spirit to BusyBox and used in Android.
- TPM security
- A Trusted Platform Module: a small secure chip that stores keys and measurements and performs cryptographic operations.
- traceroute networking
- A tool that shows the path packets take to a destination, hop by hop, to locate where delays or failures occur.
- Transaction index mining
- An optional node index allowing lookup of any transaction by ID, at the cost of extra disk space. Not available on pruned nodes.
- TRIM storage
- A command telling a flash drive which blocks are no longer used, helping it maintain performance and endurance.
- U-Boot software
- A very common open-source bootloader for embedded boards. It initialises hardware, can load the kernel from many sources and offers a small command shell.
- UART / serial port hardware
- A simple asynchronous serial interface. Embedded boards commonly expose one as a debug console showing boot messages and a login prompt.
- UBI storage
- Unsorted Block Images: a layer over raw NAND that handles wear levelling and bad blocks, on which UBIFS runs.
- UBIFS storage
- A flash filesystem for raw NAND built on UBI, offering good performance and reliability for large chips.
- UCI software
- The Unified Configuration Interface used by OpenWrt to store settings in simple text files and change them with one command-line tool.
- uClibc-ng software
- A small C library aimed at embedded Linux, a maintained descendant of uClibc, offered by Buildroot and used on some routers.
- udev software
- The device manager that reacts to hardware being added or removed and creates device nodes and runs rules. Minimal systems often use mdev instead.
- UDP networking
- A lightweight transport protocol with no delivery guarantee. Used where speed matters more than reliability, such as DNS queries and some IoT protocols.
- UEFI software
- The modern firmware interface on PCs that initialises hardware and starts the bootloader. It replaced BIOS and supports Secure Boot.
- Undervolting mining
- Lowering the voltage supplied to chips to cut power use and heat, improving efficiency when stable.
- UPnP networking
- A protocol that lets devices ask a router to open ports automatically. Convenient but a frequent security concern.
- Upstream / downstream concepts
- Upstream is the original project; downstream is a distribution or product that builds on it. Fixes accepted upstream reach all downstream users.
- Uptime concepts
- How long a system has been running without interruption, or the fraction of time it is available.
- USB hardware
- Universal Serial Bus, the common interface for peripherals and storage. Many miners, SBCs and gateways use USB for dongles, drives and radios.
- USB OTG hardware
- On-The-Go: lets a USB port act as either host or device. Boards use it to appear as a drive or network adapter to a PC, for example during flashing.
- Userland software
- Everything above the kernel: libc, shell, utilities, services and applications. Alpine, Debian and OpenWrt share the Linux kernel but differ in userland.
- UTXO mining
- An unspent transaction output: a coin-like record that can be spent once. A node tracks the full set of them.
- Valgrind tooling
- A tool that detects memory errors and leaks in programs by running them under instrumentation.
- Vendor kernel software
- A kernel fork supplied by a chip or board maker, often based on an older release and carrying patches not accepted upstream. Convenient to start, harder to maintain.
- Vendor lock-in concepts
- Depending so heavily on one supplier’s proprietary parts or formats that switching becomes costly.
- VLAN networking
- A Virtual LAN separates traffic on the same physical network into isolated groups, for example keeping IoT devices apart from computers.
- VPN networking
- A Virtual Private Network creates an encrypted tunnel between devices or networks, used for secure remote access.
- Vulnerability security
- A flaw in software or hardware that can be exploited to violate its security.
- Wallet mining
- Software or hardware that manages keys and creates transactions. Holding the keys is what controls the coins.
- Watchdog timer reliability
- A hardware or software timer that resets the device if the system stops responding. Unattended devices use it to recover from hangs.
- Wear levelling storage
- Spreading writes across all flash blocks so none wears out early. Handled by the controller in SD cards and eMMC, or by the filesystem on raw flash.
- WebSocket protocols
- A protocol giving a persistent two-way connection between browser and server, handy for live dashboards.
- Wi-Fi (IEEE 802.11) networking
- The family of wireless LAN standards. Different generations trade range, speed and power use.
- Wide-temperature range concepts
- Components rated to operate across a broader span than consumer parts, for example well below freezing to high heat.
- WireGuard networking
- A modern, compact VPN protocol built into the Linux kernel, known for simple configuration and good performance on small devices.
- WPA2 / WPA3 security
- Wi-Fi security standards that encrypt wireless traffic. WPA3 is the newer, stronger generation; open networks and WEP should be avoided.
- Write amplification storage
- When flash performs more physical writes than the data requested, shortening its life.
- x86 / x86-64 hardware
- The instruction set family used by most PCs and servers. x86-64 is its 64-bit form (also called amd64). Common in industrial PCs and mini PCs used as edge nodes.
- XFS storage
- A high-performance journaling filesystem good with large files and parallel workloads.
- Yocto Project software
- A framework and set of tools for building custom embedded Linux distributions. It is layer-based and aimed at products that need long-term maintenance and reproducible builds.
- Z-Wave networking
- A low-power wireless protocol for smart-home devices operating in sub-gigahertz bands.
- Zephyr software
- An open-source RTOS for resource-constrained devices, supported by many microcontroller boards and hosted by the Linux Foundation.
- Zero-day security
- A vulnerability unknown to the vendor, or with no fix yet available, so defenders have had no time to prepare.
- Zigbee networking
- A low-power mesh wireless standard widely used in smart-home devices such as sensors and lights.
- zram storage
- A kernel feature that creates a compressed block device in RAM, often used as swap to stretch limited memory without touching flash.
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