LFA key terms

The core program of a Linux system that manages memory, CPU scheduling, devices, and filesystems, and exposes hardware resources to user-space programs through system calls.

A command-line interpreter such as Bash that reads commands from a terminal or script, expands variables and wildcards, and asks the kernel to run the resulting programs.

A standard layout that defines where Linux systems place directories such as /etc for configuration, /var for changing data, and /usr for installed software.

A filesystem metadata record describing one file: its owner, permissions, timestamps, size, and pointers to data blocks. Names in directories map to inode numbers.

A special file that stores a path to another file or directory. Following the link resolves that path, so the link can point across filesystems and can become broken.

Nine mode bits on each file that grant read, write, and execute rights separately to the owner, group, and others, usually shown as rwx triples or octal numbers.

Three predefined channels every process inherits: standard input for data read, standard output for normal results, and standard error for diagnostics, each numbered 0, 1, and 2.

A shell operator, written as |, that connects one command's standard output to the next command's standard input, letting small tools be combined into processing chains.

A named value held in a process's environment, such as PATH or HOME, that programs read for configuration and that child processes inherit from their parent.

A configuration file describing something systemd manages, such as a service, mount, timer, or socket, including how to start, stop, and order it.

The systemd logging service that collects messages from the kernel, services, and applications into a structured, indexed journal queried with journalctl rather than plain text files.

A daemon that runs scheduled commands defined in crontab files, using five time fields for minute, hour, day of month, month, and day of week.

A program that lets a permitted user run a specific command as another user, commonly root, according to rules in /etc/sudoers and with each use logged.

The /etc/fstab file lists filesystems to mount at boot, giving the device, mount point, filesystem type, and options; mistakes can prevent a system from booting cleanly.

A storage layer that pools physical volumes into volume groups and carves logical volumes from them, allowing resizing and snapshots without repartitioning disks.

A tool such as apt or dnf that installs, upgrades, and removes software from repositories while tracking dependencies and recording installed versions in a local database.

Numeric identifiers the kernel uses for accounts and groups. The UID 0 is root; file ownership and permission checks use these numbers, not the displayed names.

A complete guest operating system running on emulated or virtualized hardware under a hypervisor, isolated from other guests but heavier than a container.

A process isolated with Linux namespaces and cgroups that shares the host kernel and carries its own filesystem image, giving fast startup and consistent dependencies.

A service that stores data as objects in flat buckets, accessed by HTTP APIs with keys and metadata rather than by block device or filesystem path; suited to backups and static assets.

A private, logically isolated network in a cloud provider where you define subnets, route tables, and gateways, and control which resources can reach the internet.

A cloud feature that adds or removes instances based on metrics such as CPU load or request count, keeping capacity matched to demand within configured minimum and maximum limits.

A service that spreads incoming requests across several backend servers, performs health checks, and removes failing targets, improving availability and smoothing traffic spikes.

The practice of giving users, services, and processes only the permissions needed for their tasks, reducing the damage possible if an account or credential is compromised.

A protocol that encrypts and authenticates traffic between clients and servers, typically on HTTPS, using certificates to prove server identity and keys to protect data in transit.

A scheme using a key pair: the public key can be shared and verifies signatures or encrypts, while the private key stays secret and decrypts or signs.

A filter on network traffic that allows or blocks packets by rules matching addresses, ports, and protocols, implemented in Linux by nftables or iptables or by cloud security groups.

A publicly catalogued identifier for a specific disclosed vulnerability, with a description and references, used to track affected software and available fixes.

A one-way function that maps data to a fixed-length digest; the same input always gives the same digest, and small changes alter it completely. Used for integrity checks, not decryption.

Storing and distributing credentials such as API keys, passwords, and certificates in a controlled vault or service, with access control, auditing, and rotation instead of hard-coding them.

An automated sequence that builds, tests, and delivers code changes, usually triggered by commits, so that integration and deployment happen consistently and repeatedly.

A distributed version control system that records snapshots of files as commits, supports branches and merges, and lets every clone hold the full history.

An immutable, layered filesystem plus metadata used to start containers, built from instructions and stored in a registry with tags identifying versions.

An orchestration platform that schedules containers across a cluster of nodes, restarts failed ones, and manages networking, scaling, and configuration through declarative manifests.

Managing infrastructure through versioned definition files that tools apply to create and change resources, making environments reproducible and reviewable like application code.

The ability to understand a system's internal state from its outputs, chiefly metrics, logs, and traces, so operators can detect and diagnose failures in production.

A defined contract that lets one program call another, specifying available operations, input formats, and responses, often over HTTP in web services.

An architectural style for web APIs using stateless HTTP requests, resource-oriented URLs, and standard methods such as GET, POST, PUT, and DELETE, usually exchanging JSON.

A server that accepts client requests and forwards them to backend applications, adding TLS termination, caching, path routing, or load balancing while hiding internal hosts.

A probe, such as an HTTP endpoint or TCP connection test, that reports whether an instance is ready to serve traffic, letting load balancers and orchestrators route around failures.