Linux Overview

Practice flashcards covering Linux command structure, help systems, basic utilities, file permissions, and redirection based on the lecture notes.

Linux Command

An executable program that interacts with the operating system, including the kernel and shell, to perform requested functions.

Command Options

Optional switches, usually preceded by "-" or "--", that indicate the mode of operation for a command.

Command Arguments

Optional data used or manipulated by a command, such as a filename.

$$man$$

The manual pager used to find information about commands, organized into sections ($1$ to $9$).

$man$ Section 1

Contains documentation for executable programs or shell commands.

$man$ Section 2

Contains documentation for system calls.

$$info$$

The GNU info system used to find command information using logical nodes; keys include "n" (next), "p" (previous), and "t" (top).

$$ls$$

Command used to list directory contents.

$$pwd$$

Command that prints the name of the current working directory.

$$mkdir$$

Command used to create a new directory.

$$cp$$

Command used to copy a file or directory.

$$mv$$

Command used to move or rename a file or directory.

$$rm$$

Command used to remove a file or directory.

$$rmdir$$

Command used to remove an empty directory.

$$file$$

Command used to determine the file type of a specific file.

$$touch$$

Command used to change a file timestamp or create an empty file if it does not exist.

$$wc$$

Command that prints the number of lines, words, and characters in a file.

$$sort$$

Command used to sort lines of a file numerically or alphabetically.

$$ps$$

Command that prints a snapshot of current processes.

$$top$$

Command that displays a dynamic view of running processes.

$$netstat$$

Command used to print network statistics.

$$whoami$$

Command that prints the effective userid to identify the current user.

$$which$$

Command used to locate a command's executable path.

$$grep$$

Command that prints lines matching a pattern using regular expressions.

$$cat$$

Command used to concatenate files and print them to standard output.

$$less$$

A file viewer similar to "more" but with additional features for paging through text.

$$head$$

Command used to print the first $n$ lines of a file.

$$tail$$

Command used to print the last $n$ lines of a file.

$$diff$$

Command used to compare files line-by-line.

$$df$$

Command used to print file system disk space usage.

$$du$$

Command used to estimate file space usage for a directory and its subdirectories.

$$stdin$$

Standard input; the default file (keyboard) where a command reads its input from.

$$stdout$$

Standard output; the default file (terminal) where a command sends its output.

$$stderr$$

Standard error; the default file (terminal) where a command sends its error messages.

File Descriptor

A unique, non-negative integer used to identify open files on a per-process basis.

Permission Group: User

Often called the owner; applies exclusively to the owner of the file.

Permission Group: Others

Often referred to as "world"; applies to all other users in the system who are not the owner or in the assigned group.

Read Permission ($r$)

Indicates the capability to read the contents of a file; has a numeric value of $4$.

Write Permission ($w$)

Indicates the capability to write to a file or modify a directory; has a numeric value of $2$.

Execute Permission ($x$)

Indicates the capability to execute a file or view the contents of a directory; has a numeric value of $1$.

Hard Link

A directory entry that associates a name with a file; every file must have at least one.

Symbolic Mode

A method of setting permissions using letters: "u" (user), "g" (group), "o" (others), and "a" (all).

Absolute Mode

A method of representing permissions using three-digit octal values, where the first digit is for owner, second for group, and third for others.

$$chmod$$

Command used to change the access mode (permissions) of a file or directory.

$$chown$$

Command used to change the user owner of a file.

$$chgrp$$

Command used to change the group ownership of a file.

$$vim$$

An improved version of the original vi text editor available on Linux systems.

Input Redirection ($<$)

Syntax used to detach the keyboard from standard input and attach a file instead.

Output Redirection ($>$)

Syntax used to detach the display screen from standard output and attach an output file, overwriting existing content.

Appending Redirection ($>>$)

Syntax used to add output to the end of a file instead of overwriting it.

Pipe ($|$)

A method of interprocess communication (IPC) where the standard output of one command is used as the standard input for the next.