LCA ICT Specialism key terms

A convention that defines where directories such as /etc, /var, /home, and /usr live on Linux systems, so configuration, variable data, and user files appear in predictable locations regardless of distribution.

A file location written from the root directory, beginning with a forward slash, so it resolves to the same target no matter what the current working directory is.

A file location interpreted from the shell's current working directory, using names, dots, and double dots rather than a leading slash, so its meaning changes as the working directory changes.

The directory a shell process currently treats as its base for relative paths; the pwd command prints it, and cd changes it for that shell session only.

The three default channels every Linux process gets: standard input for reading data, standard output for normal results, and standard error for diagnostics, each separately redirectable to files or pipes.

A shell operator that connects the standard output of one command to the standard input of the next, letting small tools be chained into a processing pipeline without temporary files.

Shell syntax that sends a command's standard output or error to a file or device, or feeds a file into standard input, using operators such as >, >>, 2>, and <.

A text search utility that prints lines matching a pattern, commonly used with pipes to filter command output or log files, with options for case-insensitive and regular-expression matching.

A pattern language for describing text, using anchors, character classes, and quantifiers, so one expression can match many related strings during search, filtering, or validation.

The command interpreter that reads typed or scripted commands, expands variables and wildcards, and launches programs on behalf of the user, with bash being the most common default on Linux.

A named value held in a process's environment, such as PATH or HOME, that programs read at runtime and that child processes inherit from their parent unless explicitly changed.

A text file of shell commands executed in sequence by an interpreter, typically starting with a shebang line, used to automate repetitive administration tasks with variables, conditionals, and loops.

A time-based scheduler that runs commands or scripts at specified minutes, hours, days, and months according to entries in a crontab file owned by a user or the system.

A configuration file describing something systemd manages, such as a service, mount, or timer, including how to start it, its dependencies, and its restart behaviour.

The command-line client for controlling systemd, used to start, stop, enable, disable, and inspect services and to query the overall state of the init system.

A unique number the kernel assigns to each running process, used to signal, monitor, prioritise, or terminate that specific process rather than others.

A software interrupt delivered to a process to request an action, such as SIGTERM asking it to shut down cleanly or SIGKILL forcing immediate termination without cleanup.

A process that has finished executing but still has an entry in the process table because its parent has not yet collected its exit status.

A moving average of the number of processes runnable or waiting on disk I/O over one, five, and fifteen minutes, useful for judging whether a system is overloaded relative to its CPU count.

An existing directory where a filesystem is attached into the single Linux directory tree, making the filesystem's contents appear beneath that path until it is unmounted.

The system file listing filesystems and their mount options, mount points, and dump and check settings, consulted at boot and by mount so devices attach consistently.

A filesystem data structure holding a file's metadata, such as ownership, permissions, size, and pointers to data blocks, but not its name, which lives in a directory entry.

An additional directory entry pointing to the same inode as an existing file, so both names refer to identical content and removing one leaves the data accessible through the other.

A special file containing a path to another file or directory, resolved at access time, which can cross filesystems and becomes broken if its target is removed.

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

The read, write, and execute flags set separately for a file's owner, its group, and all other users, controlling who may view, modify, or run it.

The command that changes a file's permission bits, accepting either symbolic notation such as u+x or octal notation such as 640 to set owner, group, and other access.

A per-process mask of permission bits that are removed from the default mode when new files and directories are created, shaping the access they receive automatically.

A utility that lets a permitted user run a command as another user, usually root, according to policy rules, with each invocation logged for accountability.

The security principle of granting each user, process, or service only the access strictly needed for its task, limiting the damage that a compromise or mistake can cause.

An SSH login method where the client proves possession of a private key matching a public key stored on the server, avoiding password transmission and enabling non-interactive automation.

A filter that inspects network traffic against rules and allows or blocks packets, typically configured on Linux with nftables or firewalld to expose only intended services.

The layered protocol suite underlying most networking, where IP addresses and routes deliver packets between hosts and TCP provides ordered, reliable, connection-oriented streams.

A bit pattern that separates the network portion of an IP address from the host portion, determining which addresses are local and which must be reached through a gateway.

The router address a host sends traffic to when the destination is not on any directly connected subnet, serving as the exit point from the local network.

The process of translating a hostname into an IP address by querying name servers, whose failure typically leaves name-based connections broken while numeric addresses still work.

A software-defined computer with virtual CPU, memory, disk, and network devices, running a full guest operating system under a hypervisor on shared physical hardware.

The software layer that creates and runs virtual machines, allocating physical resources among guests and isolating them from one another, either directly on hardware or atop a host OS.

An isolated process environment sharing the host kernel, packaged with its dependencies as an image, which starts quickly and uses fewer resources than a full virtual machine.

A structured investigation that moves past the visible symptom to identify the underlying reason an incident occurred, so the fix prevents recurrence rather than merely restoring service.

The documented handover of an unresolved issue to a more specialised or authorised support tier, including the symptoms observed, steps already taken, and their results.

A recorded support request capturing the reporter, symptoms, priority, actions taken, and resolution, forming the auditable history that teams rely on for handovers and reporting.

A chronological record of modifications made to a system, including what changed, who changed it, when, and why, used to correlate faults with recent configuration work.