LPI Linux Essentials key terms

A copyleft software license that lets anyone run, study, modify, and redistribute a program, provided derivative works are distributed under the same terms and source code is made available.

Software that grants users four freedoms: to run it for any purpose, study and change its source code, redistribute copies, and distribute modified versions. The term emphasizes user liberty rather than price.

A nonprofit organization that maintains the Open Source Definition and approves licenses meeting its criteria, which include free redistribution, access to source code, and no discrimination against persons or fields of use.

The human-readable instructions written by a programmer in a programming language. It is compiled or interpreted into machine-executable form, and access to it is what allows software to be studied and modified.

The core program of a Linux system. It manages memory, schedules processes, handles device drivers, and provides system calls that let applications use hardware without addressing it directly.

A complete installable operating system built around the Linux kernel, bundling a package manager, utilities, libraries, and often a desktop environment. Examples include Debian, Fedora, and Ubuntu.

A command interpreter that reads typed commands, expands them, and asks the kernel to run programs. Bash is the most common on Linux, and it also offers scripting, variables, and pipelines.

The text a shell prints to signal it is ready for input. It commonly shows the user name, host name, and current directory, and ends with a character such as $ for regular users or # for root.

A file location written from the root of the directory tree, always starting with a slash, such as /etc/hosts. It identifies the same file regardless of the current working directory.

A file location interpreted from the current working directory rather than from the root, such as docs/notes.txt or ../bin. It depends on where the user currently is.

The directory a shell session is currently operating in. Relative paths resolve against it, and the pwd command prints its absolute path.

The default data stream a program reads from, usually the keyboard in a terminal. It can be redirected from a file or fed from another command through a pipe.

The default stream where a program writes normal results, usually the terminal screen. It can be redirected to a file or connected to another command's input.

Changing where a command's input or output goes, using operators such as > to overwrite a file, >> to append, and < to read from a file. Error output can be redirected separately.

A chain of commands joined by the pipe symbol, where the standard output of one command becomes the standard input of the next, letting small tools be combined to process data.

A command that reads input, transforms or selects from it, and writes output, making it useful in pipelines. Common examples are grep, sort, cut, and uniq.

A pattern language for matching text. Tools such as grep, sed, and editors use it to find lines or strings that fit rules like character classes, anchors, and repetition.

A command that searches input line by line and prints lines matching a pattern, which may be a plain string or a regular expression. Options control case sensitivity, inversion, and line numbers.

A separate output stream for error and diagnostic messages, so they do not mix with normal results. It is usually shown on the terminal but can be redirected independently.

The superuser account with unrestricted access to the system. It can read or change any file, install software, and manage devices, so routine work should be done as a normal user.

A command that runs a single program with elevated privileges, typically as root, after checking the user's password and the policy in the sudoers configuration.

An identity on the system with a user name, numeric user ID, home directory, and login shell. Files and processes are owned by and run under accounts.

A named collection of user accounts with its own numeric ID, used to grant a set of people the same access to files and devices without assigning permissions individually.

The read, write, and execute rights assigned separately to a file's owner, its group, and everyone else. They determine who may view, modify, or run a file.

A command that changes a file's permission bits, either symbolically such as u+x or numerically with octal digits such as 644, which encode read, write, and execute for each class.

A command that changes which user and group own a file. Only the root user can normally give ownership to another account.

A tool that installs, upgrades, and removes software from repositories while resolving dependencies. Examples are apt on Debian-based systems and dnf on Fedora-based systems.

A server or local collection of software packages and metadata that a package manager queries to find, verify, and download installable software and its dependencies.

A running instance of a program, with its own memory, open files, and numeric process ID. The kernel schedules processes and lets them be listed, paused, or stopped.

A short asynchronous message the kernel delivers to a process, such as SIGTERM asking it to stop or SIGKILL forcing it to end. Programs may catch or ignore some signals.

A background process that runs without a controlling terminal and usually provides a service, such as scheduling, logging, or network handling. Names often end in d.

The default init and service manager on most Linux distributions. It starts services at boot, supervises them, and provides tools to enable, start, and inspect units.

Attaching a filesystem, such as a disk partition or network share, to a directory in the existing tree so its contents become accessible at that point.

The structure and rules an operating system uses to organize files on storage, including directories, file metadata, and free space. Common Linux types include ext4 and XFS.

The top of the Linux directory tree, written as a single slash. Every other directory and file is reached by a path descending from it.

A program that translates source code written in a language such as C into machine code or an intermediate form that the system can execute.

A named value stored in a process's environment that programs can read, such as PATH listing directories searched for commands. Child processes inherit them from their parent.