A JSON Web Token is a compact, URL-safe string that encodes a set of claims about a subject. It is defined by RFC 7519 as a representation format “intended for space constrained environments such as HTTP Authorization headers and URI query parameters” . The token is not encrypted by default. Its three parts—header, payload, and…
Every API request that touches protected data must answer one question before it does anything else: who is making this request? Authentication is the mechanism that answers it. The three methods in this chapter—API keys, HTTP Basic authentication, and Bearer tokens—represent three different answers to that question, and they are not interchangeable. An API key…
systemd is the init system and service manager that replaced SysVinit and Upstart on most modern Linux distributions. It is not just a boot script runner. It is a dependency-aware, parallel-starting, socket-activated service manager that also handles device management, mount points, timers, and resource control. The core abstraction is the unit: a resource that systemd…
A signal is a limited form of inter-process communication: a notification delivered to a process by the kernel or by another process. It interrupts whatever the process is doing and invokes one of three dispositions—the default action, an ignore, or a handler function that the process installed. The default action is signal-specific. SIGTERM terminates the…
A shell session ends when the terminal closes or the SSH connection drops. Every process that was started from that shell receives a SIGHUP (hang-up signal), and unless the process is specifically designed to survive it, it terminates. This is the default behavior, and for a quick command it is correct. For a long-running task—a…
A shell session is not limited to running one command at a time. Job control is the mechanism that lets you start a process in the background, suspend a foreground process, resume it later, and list everything the shell is managing. The ampersand (&) starts a command asynchronously, returning the prompt immediately while the process…
Every process on a Linux system competes for CPU time, and the scheduler decides who gets the processor and for how long. The nice value is the user-space lever for influencing that decision. It is an integer from -20 to 19, where -20 is the highest priority and 19 is the lowest . The name…
A Vue component does not exist in isolation. It reads from a Pinia store, navigates with Vue Router, and fetches data asynchronously. A test that mounts the component without providing these dependencies fails with an injection error, a missing $router, or an assertion that runs before the data arrives. The three dependencies require three different…
A Vue component is a black box from the outside. It receives props, renders output, and emits events. The test should assert on those three things—what goes in, what comes out, and what the user sees—rather than on the internal refs, computed properties, or methods. Vue Test Utils is the library that mounts the component…
Vue components and native Web Components are two different component models that solve overlapping problems. Vue’s component model is framework-specific: a Vue component is a plain object or function that the Vue runtime knows how to mount and update. A Web Component is a browser primitive: a class that extends HTMLElement and is registered with…