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Question 91
Which command displays the manual page for a specific Linux command?
A) help
B) man
C) info
D) guide
Answer: B
Explanation:
The man command displays the manual page for a specific Linux command, providing comprehensive documentation about command syntax, options, arguments, and usage examples. Manual pages are the primary source of command documentation on Linux systems, offering detailed reference information that helps users understand how to properly use commands and their various options. The man system organizes documentation into sections covering different types of content, making it an essential resource for both beginners and experienced users.
Using the man command is straightforward with the basic syntax man command_name, which displays the manual page for the specified command. For example, man ls shows documentation for the ls command including all available options, what each option does, and examples of common usage patterns. Manual pages are displayed in a pager program, typically less, allowing users to scroll through the documentation using arrow keys, Page Up and Page Down, or vim-style navigation keys. Pressing q quits the manual page and returns to the command prompt. The space bar advances one page at a time, while the slash key allows searching within the manual page for specific terms.
Manual pages are organized into numbered sections that categorize different types of documentation. Section 1 contains user commands and executable programs, the most commonly accessed section. Section 2 documents system calls or kernel functions. Section 3 covers library functions and programming interfaces. Section 4 describes special files like device files in /dev. Section 5 documents file formats and configuration files. Section 6 contains games and screensavers. Section 7 provides miscellaneous information including macro packages and conventions. Section 8 covers system administration commands typically requiring root privileges. When a term appears in multiple sections, specifying the section number like man 5 passwd displays the specific version, in this case the passwd file format rather than the passwd command.
Option A, help, is a shell builtin command that provides brief usage information for shell builtin commands. While useful for quick reference, help provides less comprehensive documentation than man pages and only works for shell builtins.
Option C, info, is an alternative documentation system providing more detailed, hyperlinked documentation for some GNU programs. While valuable, info is less universally used than man pages, and not all commands have info documentation.
Option D, guide, is not a standard Linux documentation command. While various GUI help systems might use guide in their names, it is not the command for accessing manual pages.
The man command is the standard, essential tool for accessing comprehensive command documentation on Linux systems.
Question 92
What is the purpose of the sudo command?
A) To shut down the system
B) To execute commands with superuser privileges
C) To switch user accounts permanently
D) To display system information
Answer: B
Explanation:
The sudo command allows authorized users to execute commands with superuser or root privileges without logging in as the root user directly. This approach provides better security and accountability compared to sharing the root password or staying logged in as root, as it allows granular control over who can execute which privileged commands and creates audit logs of all privileged operations. Understanding sudo is essential for performing administrative tasks on Linux systems while maintaining security best practices.
When a user executes a command with sudo, the system checks the /etc/sudoers configuration file to determine whether that user is authorized to run commands with elevated privileges. If authorized, sudo prompts for the user’s own password, not the root password, providing authentication that the person at the keyboard is indeed the authorized user. After successful authentication, sudo executes the specified command with root privileges. By default, sudo caches authentication for a short period, typically 15 minutes, so subsequent sudo commands within that timeframe do not require re-entering the password. This caching improves usability while maintaining reasonable security.
The sudoers configuration file controls precisely what each user or group can do with sudo. Basic configurations might grant full root access to specific users, while more sophisticated configurations can restrict users to specific commands or command patterns. For example, a help desk user might be permitted to reset passwords but not install software, while a database administrator might be allowed to restart database services but not modify network configurations. The visudo command must be used to edit the sudoers file, as it performs syntax checking to prevent configuration errors that could lock administrators out of the system. Common sudo usage includes sudo apt install package for installing software, sudo systemctl restart service for managing services, sudo nano /etc/config for editing system configuration files, and sudo -i for starting an interactive root shell when multiple administrative commands are needed.
Option A incorrectly suggests system shutdown as sudo’s purpose. While sudo can be used to execute shutdown commands like sudo shutdown or sudo reboot, shutdown is not sudo’s purpose but rather one of many privileged operations it can perform.
Option C describes permanent account switching, which is the su command’s function. While sudo can start a root shell with sudo -i or sudo su, its primary purpose is executing individual commands with privilege rather than switching accounts.
Option D suggests displaying system information, which various commands like uname or hostname do. Sudo’s purpose is privilege elevation, not information display.
The sudo command is fundamental to secure Linux system administration, enabling controlled privilege elevation with accountability.
Question 93
Which directory contains user home directories on a Linux system?
A) /usr
B) /var
C) /home
D) /root
Answer: C
Explanation:
The /home directory contains user home directories on a Linux system, providing personal workspace for each regular user account where they can store files, configuration settings, and personal data. Each user typically has a subdirectory under /home matching their username, such as /home/alice or /home/bob, which serves as that user’s home directory. Understanding the home directory structure is fundamental to Linux file organization and user management.
When users log into a Linux system, they start in their home directory by default. This directory is where users have full read, write, and execute permissions, allowing them to create files, directories, and manage their personal data without requiring administrative privileges. User-specific configuration files, often called dotfiles because they begin with a period and are hidden by default, reside in home directories. Examples include .bashrc for bash shell configuration, .bash_history storing command history, .ssh containing SSH keys and configuration, and application-specific directories like .config or .local storing program settings. These configuration files allow users to customize their environment, shell behavior, and application preferences independently from other users.
The home directory location for each user is specified in the /etc/passwd file, and while /home/username is standard, administrators can configure alternative locations if needed. The HOME environment variable always points to the current user’s home directory, and the tilde symbol serves as a shortcut representing the home directory in shell commands. For example, cd ~ changes to the home directory, ~/Documents refers to the Documents subdirectory within the home directory, and ~alice/file refers to a file in alice’s home directory. The home directory structure promotes multi-user operation by providing each user with isolated personal space while sharing the same underlying system and installed applications.
Option A, /usr, contains user programs, libraries, documentation, and other files that are shareable and read-only. Despite its name suggesting user files, /usr holds system software rather than user personal data.
Option B, /var, contains variable data that changes during system operation like log files, spool directories, and temporary files. It does not contain user home directories.
Option D, /root, is specifically the home directory for the root user, the system administrator account. While /root is a home directory, it is not the location of regular user home directories which reside in /home.
The /home directory is the standard location providing personal workspace for regular user accounts on Linux systems.
Question 94
What does the ls -l command display?
A) Only file names
B) Detailed file information including permissions, owner, size, and modification time
C) Only hidden files
D) Only directory names
Answer: B
Explanation:
The ls -l command displays detailed file information in long format, showing file permissions, number of hard links, owner name, group name, file size in bytes, modification timestamp, and filename for each file and directory. This long listing format provides comprehensive information about files that is essential for understanding file attributes, ownership, and properties. The -l option transforms the simple filename list produced by ls alone into a detailed table of file metadata.
Each line of ls -l output represents one file or directory with columns providing specific information. The first column shows file type and permissions using a ten-character string. The first character indicates file type: dash for regular files, d for directories, l for symbolic links, c for character devices, b for block devices, and other letters for special file types. The remaining nine characters represent permissions in three groups of three: owner permissions, group permissions, and other permissions, each showing read, write, and execute permissions as r, w, x or dashes if not granted. The second column shows the hard link count, indicating how many directory entries point to this file’s inode. The third and fourth columns display the owner username and group name respectively. The fifth column shows file size in bytes. The sixth column shows the last modification date and time, displaying month, day, and either time if recent or year if older. The final column displays the filename.
Understanding ls -l output enables important file management decisions. Permission columns determine who can read, modify, or execute files. Owner and group information shows who controls the file. Size information helps identify large files consuming disk space. Timestamps indicate when files were last modified, useful for finding recent changes or old files. Additional ls options can be combined with -l for enhanced functionality: ls -la includes hidden files starting with periods, ls -lh displays file sizes in human-readable format like KB or MB instead of raw bytes, ls -lt sorts by modification time with newest first, and ls -lS sorts by file size with largest first. These combinations make ls -l a powerful tool for examining file systems.
Option A describes basic ls output without options, which shows only filenames in a simple list. The -l option specifically adds the detailed information that distinguishes it from simple filename listing.
Option C incorrectly suggests only hidden files are shown. The -a option shows hidden files; -l shows long format. Combining them as ls -la shows both hidden files and detailed information.
Option D suggests only directories are displayed. The -d option would show directories themselves rather than their contents, but -l shows long format for whatever files or directories match the given arguments.
The ls -l command is essential for viewing detailed file information necessary for effective Linux file management.
Question 95
Which command creates a new directory?
A) touch
B) mkdir
C) create
D) newdir
Answer: B
Explanation:
The mkdir command creates new directories in the Linux filesystem, establishing new locations where files and subdirectories can be stored. Directory creation is a fundamental file management operation, and mkdir provides the standard method for creating directory structures. Understanding mkdir and its options is essential for organizing files and building directory hierarchies on Linux systems.
The basic mkdir syntax is straightforward: mkdir directory_name creates a single directory with the specified name in the current working directory. Paths can be specified to create directories in other locations, such as mkdir /home/user/projects creating a projects directory in the specified location. Multiple directories can be created with a single command by listing multiple names: mkdir dir1 dir2 dir3 creates three separate directories. The newly created directories inherit permissions based on the umask setting, typically resulting in permissions like 755 or rwxr-xr-x allowing the owner full access and others read and execute access.
The -p option is particularly useful for creating directory hierarchies in a single command. Without -p, attempting to create a nested directory structure like mkdir /home/user/projects/2024/reports fails if the parent directories projects or 2024 do not exist. Using mkdir -p /home/user/projects/2024/reports creates all necessary parent directories in the path, eliminating the need to create each level separately. This option also prevents errors if the directory already exists, making mkdir -p safe to use in scripts that should not fail if directories already exist. The -m option allows specifying permissions at creation time: mkdir -m 700 private creates a directory with permissions accessible only to the owner. The -v or verbose option makes mkdir report each directory created, useful for confirming operations in scripts or interactive use.
Option A, touch, creates empty files or updates timestamps on existing files. While important for file creation, touch does not create directories.
Option C, create, is not a standard Linux command for directory creation. While some applications might have create functions, there is no create command in the standard Linux shell.
Option D, newdir, similarly is not a standard Linux command. The mkdir command is the established, universal method for directory creation across all Linux distributions.
The mkdir command is the fundamental tool for creating directory structures and organizing the Linux filesystem.
Question 96
What does the pwd command do?
A) Changes the current directory
B) Prints the current working directory
C) Creates a new directory
D) Removes a directory
Answer: B
Explanation:
The pwd command prints the current working directory, displaying the absolute path of the directory where the user is currently positioned in the filesystem hierarchy. This simple but essential command helps users maintain awareness of their location within the directory structure, preventing confusion about where commands will operate and where files will be created. Understanding pwd is fundamental to navigating the Linux filesystem effectively.
The pwd command operates without requiring any arguments in typical usage. Simply typing pwd and pressing enter causes the shell to display the full absolute path from the root directory to the current location. For example, if a user is in their Documents directory, pwd might display /home/alice/Documents. This absolute path representation starts from the root directory indicated by the leading forward slash and includes every directory in the hierarchy down to the current location. The information provided by pwd is particularly valuable when navigating complex directory structures or when the shell prompt does not display the full current path.
While pwd appears simple, it has a couple of options that handle special filesystem situations. The -L option, which is typically the default, prints the logical current working directory including any symbolic links in the path. The -P option prints the physical directory location, resolving all symbolic links to show the actual filesystem path. This distinction matters when working with symbolic links where the logical path might show a convenient shortcut while the physical path reveals the actual location in the filesystem. Many users customize their shell prompt to include pwd output or an abbreviated current directory, reducing the need to explicitly run pwd while still maintaining location awareness. The PWD environment variable always contains the current working directory path and can be referenced in scripts or commands.
Option A describes the cd command which changes the current directory. While pwd and cd are often used together, pwd displays the location while cd changes it.
Option C refers to the mkdir command which creates new directories. Pwd does not create anything but simply displays information about the current location.
Option D describes the rmdir command which removes empty directories. Pwd is purely informational and does not modify the filesystem.
The pwd command is essential for maintaining awareness of your location while navigating the Linux filesystem.
Question 97
Which command is used to copy files in Linux?
A) mv
B) cp
C) copy
D) duplicate
Answer: B
Explanation:
The cp command is used to copy files and directories in Linux, creating duplicates of the source files in the specified destination location while leaving the original files unchanged. File copying is a fundamental file management operation, and cp provides comprehensive capabilities for duplicating individual files, multiple files, or entire directory trees. Understanding cp and its various options is essential for effective file management on Linux systems.
The basic cp syntax follows the pattern cp source destination, where source specifies the file to be copied and destination specifies where the copy should be created. For example, cp document.txt backup.txt creates a copy of document.txt named backup.txt in the current directory. When the destination is a directory, the source file is copied into that directory with its original name: cp document.txt /home/user/backups/ copies the file into the backups directory. Multiple source files can be specified with a directory as the final destination: cp file1.txt file2.txt file3.txt /destination/ copies all three files to the destination directory. Wildcards work with cp to copy multiple files matching patterns: cp *.txt /backups/ copies all files ending in .txt.
Several cp options modify copying behavior for different scenarios. The -r or -R option enables recursive copying, essential for copying directories and their entire contents including subdirectories: cp -r /source/directory /destination/ copies the entire directory tree. The -i option enables interactive mode, prompting before overwriting existing files, preventing accidental data loss. The -p option preserves file attributes like ownership, permissions, and timestamps in the copy, useful for backups where maintaining original metadata matters. The -v option enables verbose output, displaying each file as it is copied, helpful for monitoring long copy operations. The -u option performs update copying, only copying files that are newer than the destination or that do not exist in the destination, efficient for incremental backups. Combining options like cp -rp provides powerful directory copying while preserving all attributes.
Option A, mv, moves or renames files, which changes the file location rather than creating a duplicate. While mv can also rename, it does not leave the original file in place like cp does.
Option C, copy, is not a standard Linux command. While copy is used in some other operating systems, Linux uses the abbreviated cp command.
Option D, duplicate, is not a standard command for file copying. The cp command is the established tool for file duplication on Linux systems.
The cp command is the fundamental tool for duplicating files and directories on Linux systems.
Question 98
What does the rm command do?
A) Renames files
B) Removes or deletes files
C) Moves files
D) Creates files
Answer: B
Explanation:
The rm command removes or deletes files and directories from the Linux filesystem, permanently eliminating them from storage. Unlike some operating systems that provide a recycle bin or trash folder with recovery options, rm typically deletes files immediately and irreversibly, making it a powerful but potentially dangerous command that requires careful use. Understanding rm and its options, particularly safety considerations, is critical for Linux file management.
The basic rm syntax is simple: rm filename deletes the specified file. Multiple files can be deleted in a single command: rm file1 file2 file3 removes all three files. Wildcards enable pattern-based deletion: rm *.txt deletes all files ending in .txt in the current directory, while rm * would delete all files in the current directory. By default, rm does not delete directories; attempting rm directory produces an error message. The command operates silently on success, providing no confirmation that files were deleted unless errors occur. This silent operation, combined with immediate permanent deletion, makes rm a command that demands careful attention to avoid unintended data loss.
Several rm options modify deletion behavior and provide safety mechanisms. The -i option enables interactive mode, prompting for confirmation before deleting each file, providing a safety mechanism against accidental deletions. The -r or -R option enables recursive deletion, allowing rm to delete directories and all their contents: rm -r directory removes the directory and everything inside it, making this combination particularly dangerous if used carelessly. The -f option forces deletion without prompting, overriding interactive mode and suppressing error messages about non-existent files. The combination rm -rf is extremely powerful and dangerous, recursively deleting directories and all contents without any confirmation, capable of destroying entire filesystem trees in seconds if misused. The -v option provides verbose output, displaying each file as it is deleted, useful for monitoring what rm is doing. Many users create aliases like alias rm=’rm -i’ to make interactive mode default, reducing accidental deletion risks.
Option A describes file renaming, which is accomplished with the mv command. While mv can rename files by moving them to a new name, rm specifically deletes files.
Option C refers to moving files, also accomplished with mv. The rm command does not relocate files but rather deletes them entirely from the filesystem.
Option D suggests file creation, which is done with commands like touch, echo with redirection, or text editors. The rm command destroys files rather than creating them.
The rm command is the standard file deletion tool, requiring careful use due to its immediate and irreversible nature.
Question 99
Which command displays the contents of a text file?
A) cat
B) show
C) display
D) view
Answer: A
Explanation:
The cat command displays the contents of text files by reading the file and outputting its contents to standard output, typically the terminal screen. The name cat is short for concatenate, as the command can also combine multiple files, but its most common use is simply displaying file contents. Understanding cat and when to use it versus alternative commands is important for viewing and working with text files on Linux systems.
The basic cat usage involves specifying one or more filenames: cat filename displays the contents of the specified file. When multiple files are specified like cat file1 file2 file3, cat displays them sequentially, concatenating their contents into a single output stream. This concatenation capability makes cat useful for combining files: cat file1 file2 > combined creates a new file containing the contents of both source files. The cat command processes the entire file immediately and displays it all at once, which works well for short files but can be problematic for large files where the content scrolls past too quickly to read.
For viewing longer files where immediate full output is impractical, alternative commands provide better solutions. The less command displays file contents one page at a time with navigation controls, allowing scrolling forward and backward through the file. The more command provides similar functionality with simpler controls. The head command displays only the first lines of a file, useful for previewing file contents: head -n 20 filename shows the first 20 lines. The tail command shows the last lines, useful for examining log files: tail -f logfile even follows files as new content is appended, essential for monitoring active log files. Despite these alternatives, cat remains valuable for quickly viewing short files, combining files, and redirecting file contents to other commands through pipes.
Option B, show, is not a standard Linux command for displaying file contents. While some applications might have show commands, there is no built-in show command in the Linux shell.
Option C, display, is not a standard text file viewing command. The display command exists in ImageMagick for viewing images, not text files.
Option D, view, can refer to the vim editor’s read-only mode, but it is not primarily a command for simply displaying file contents. The cat command is the standard tool for this purpose.
The cat command is the quick, simple tool for displaying text file contents and concatenating files on Linux systems.
Question 100
What is the purpose of the cd command?
A) To create directories
B) To change the current working directory
C) To delete directories
D) To copy directories
Answer: B
Explanation:
The cd command changes the current working directory, allowing users to navigate through the Linux filesystem hierarchy by moving from one directory to another. Navigation is fundamental to working with files and directories, and cd is the primary tool for moving around the filesystem. Understanding cd and its various usage patterns is essential for efficient Linux command line operation.
The basic cd syntax specifies the target directory: cd /path/to/directory changes to the specified directory using an absolute path starting from the root. Relative paths work as well: cd Documents changes to the Documents subdirectory within the current location. Special directory references provide convenient navigation shortcuts. The tilde symbol represents the home directory, so cd ~ or simply cd with no arguments changes to the user’s home directory from anywhere in the filesystem. The double-dot reference represents the parent directory: cd .. moves up one level in the directory hierarchy, while cd ../.. moves up two levels. The single-dot reference represents the current directory, rarely used with cd but important in other contexts. The dash symbol represents the previous directory: cd – switches back to the directory you were in before the last cd command, useful for toggling between two locations.
Effective cd usage often combines with other commands for efficient filesystem navigation. The pwd command confirms the current location after changing directories. Tab completion helps navigate by automatically completing directory names when the tab key is pressed, reducing typing and preventing errors. Directory stacks managed by pushd and popd provide another navigation mechanism for managing multiple locations. Understanding that cd operates within the current shell session is important: changes made with cd affect only that shell and do not persist when the shell exits. Scripts that change directories only affect their own execution environment, not the shell that invoked them. Environment variables like CDPATH can customize cd behavior by defining additional search paths for directory names.
Option A describes mkdir which creates directories. The cd command navigates to directories but does not create them.
Option C refers to rmdir or rm -r which delete directories. The cd command only changes location and does not remove directories.
Option D suggests cp -r which copies directories. The cd command moves your working position within the filesystem but does not copy anything.
The cd command is the essential tool for navigating the Linux filesystem and changing your working location.
Question 101
Which key combination typically interrupts a running command in the Linux terminal?
A) Ctrl+C
B) Ctrl+D
C) Ctrl+Z
D) Ctrl+X
Answer: A
Explanation:
The Ctrl+C key combination interrupts a running command in the Linux terminal by sending a SIGINT signal to the foreground process, causing most programs to terminate immediately. This keyboard interrupt is one of the most frequently used terminal control sequences, providing a quick way to stop commands that are taking too long, producing unwanted output, or were started by mistake. Understanding terminal control sequences like Ctrl+C is essential for effective command line use and process management.
When Ctrl+C is pressed while a command is running, the terminal driver sends the SIGINT signal, typically signal number 2, to all processes in the foreground process group. Most programs handle SIGINT by performing minimal cleanup and then terminating, though programs can choose to catch the signal and handle it differently or even ignore it. For example, text editors might catch SIGINT to prevent accidental data loss, while shell scripts might use signal traps to perform cleanup operations before exiting. Interactive programs like less or top that normally respond to keyboard input usually exit cleanly when receiving SIGINT, returning control to the shell prompt.
Ctrl+C is particularly useful in several common scenarios. When a command is taking longer than expected or appears to be stuck, Ctrl+C provides immediate termination rather than waiting for completion or timeout. When accidentally starting a wrong command or with wrong arguments, Ctrl+C prevents unwanted operations from completing. When commands produce excessive output filling the screen, Ctrl+C stops the flow before more output accumulates. Programs running in loops or waiting for input can be interrupted rather than waiting indefinitely. Understanding that Ctrl+C may not always work is important: some programs block or ignore SIGINT, requiring stronger signals like SIGTERM or SIGKILL sent through the kill command. Programs running with elevated privileges or in certain system states may also not respond to Ctrl+C.
Option B, Ctrl+D, sends an end-of-file signal rather than interrupting. Ctrl+D is used to signal no more input, such as exiting a shell or completing input to a program reading from standard input.
Option C, Ctrl+Z, suspends a running process, sending SIGTSTP rather than terminating it. The suspended process can be resumed later with fg or bg commands, different from Ctrl+C’s termination.
Option D, Ctrl+X, is not a standard terminal control sequence for interrupting commands. While used in some text editors for specific functions, it does not interrupt running commands.
The Ctrl+C key combination is the standard, essential method for interrupting and terminating commands in the Linux terminal.
Question 102
What does the echo command do?
A) Displays text or variable values to standard output
B) Repeats the last command
C) Creates sound alerts
D) Checks network connectivity
Answer: A
Explanation:
The echo command displays text or variable values to standard output, typically the terminal screen, making it useful for printing messages, displaying variable contents, creating simple text output, and generating input for other commands through pipes or redirection. Echo is a simple but versatile command that appears frequently in shell scripts for providing user feedback, debugging, and creating formatted output. Understanding echo is fundamental to shell scripting and command line operations.
The basic echo usage involves providing text as arguments: echo “Hello World” displays the text Hello World on the screen. Multiple arguments are separated by spaces in the output: echo one two three displays one two three. Echo automatically adds a newline character at the end of its output, moving the cursor to the next line after displaying the text. Variables can be included in echo output by prefixing them with a dollar sign: echo HOME displays the value of the HOME environment variable, while echo “Your username is $USER” incorporates variable values into messages. Single quotes prevent variable expansion, so echo ‘ HOME’ literally displays $HOME rather than the variable value, useful when displaying literal text containing dollar signs.
Several echo options modify output behavior. The -n option suppresses the trailing newline, keeping the cursor on the same line after output, useful for prompts or creating output without line breaks. The -e option enables interpretation of backslash escape sequences, allowing special characters in output. Common escape sequences include \n for newline, \t for tab, \ for literal backslash, and ” for double quote. For example, echo -e “Line1\nLine2” displays text on two separate lines. Echo is frequently used with output redirection to create or append to files: echo “Log entry” >> logfile appends text to a file, while echo “New content” > file overwrites a file with the text. In shell scripts, echo provides user messages, debugging output showing variable values, and formatted report generation.
Option B suggests repeating the last command, which is done with !! in bash or through command history mechanisms, not echo. Echo displays specified text rather than repeating previous commands.
Option C mentions sound alerts, which might be produced with the beep command or system bell, not echo. Echo produces text output rather than audio.
Option D refers to network connectivity testing, typically done with ping or similar network diagnostic tools. Echo displays text rather than testing network connections.
The echo command is the standard tool for displaying text and variable values in the Linux terminal and shell scripts.
Question 103
Which command shows the first few lines of a file?
A) top
B) head
C) first
D) start
Answer: B
Explanation:
The head command shows the first few lines of a file, by default displaying the first 10 lines of the specified file. This command is useful for previewing file contents, examining file headers, checking file formats, and quickly viewing the beginning of log files or data files without processing the entire file. Understanding head and its counterpart tail provides efficient ways to examine specific portions of files.
The basic head usage specifies a filename: head filename displays the first 10 lines of the file to standard output. The number of lines displayed can be controlled with the -n option: head -n 20 filename shows the first 20 lines, while head -n 5 filename shows only the first 5 lines. A shorthand syntax head -20 filename works equivalently to head -n 20 filename for specifying line counts. Multiple files can be specified, with head displaying the first lines of each and separating them with filename headers to identify which output corresponds to which file. This makes head useful for comparing the beginnings of multiple files.
The head command provides several practical applications. When working with large data files, head allows quick examination of file structure and format without loading the entire file into an editor. For log files, head shows the oldest entries when files are written chronologically from beginning to end. For comma-separated value files or other structured data, head reveals column headers and the first few data rows, useful for understanding file structure before processing. Head can also display specific numbers of bytes rather than lines using the -c option: head -c 100 filename shows the first 100 bytes, useful for examining binary file headers. Combining head with pipes enables processing only the beginning of command output: ps aux | head shows the first few processes from the process list. Together with tail for viewing file ends and grep for searching, head forms part of the essential toolkit for text file examination.
Option A, top, is a system monitoring command displaying active processes and resource usage. While named similarly, top shows process information rather than file lines.
Option C, first, is not a standard Linux command for displaying file contents. While the concept matches, the actual command is head.
Option D, start, is not a standard command for viewing file beginnings. The head command is the established tool for this purpose.
The head command is essential for quickly previewing the beginning of files without viewing their entire contents.
Question 104
What is the purpose of file permissions in Linux?
A) To compress files
B) To control who can read, write, or execute files
C) To determine file types
D) To set file creation dates
Answer: B
Explanation:
The purpose of file permissions in Linux is to control who can read, write, or execute files, implementing security and access control at the filesystem level. Permissions define three types of access for three categories of users, creating a flexible system that protects data privacy, prevents unauthorized modifications, and controls program execution. Understanding file permissions is fundamental to Linux security and multi-user system operation.
Linux file permissions use a three-by-three matrix defining access rights. The three types of access are read, write, and execute. Read permission allows viewing file contents or listing directory contents. Write permission allows modifying files or creating and deleting files within directories. Execute permission allows running files as programs or entering directories. These three permission types apply to three categories of users: the file owner who created or owns the file, the group associated with the file allowing permissions for a set of users, and others representing all users not covered by owner or group. Each category can have any combination of the three permissions, providing granular control over file access.
Permissions are displayed in the first column of ls -l output using a ten-character string. The first character indicates file type, while the remaining nine characters show permissions in three groups of three representing owner, group, and others. Each group uses r for read, w for write, x for execute, or dash if the permission is not granted. For example, rwxr-xr-x means the owner has full access, while group and others can read and execute but not write. Permissions are modified with the chmod command using either symbolic notation like chmod g+w filename adding group write permission or numeric notation like chmod 755 filename setting specific permission combinations. Understanding ownership via the chown command and group membership complements permission management. Proper permission configuration prevents unauthorized access, protects against accidental modifications, and enables secure multi-user collaboration on shared systems.
Option A refers to file compression, accomplished with commands like gzip or tar, unrelated to permissions. Permissions control access rather than storage format.
Option C suggests determining file types, which is done through file extensions, the file command, or the file type character in ls -l output, not through the permission system.
Option D mentions file creation dates, which are metadata stored separately from permissions and displayed in file listings, not controlled by the permission system.
File permissions are the fundamental access control mechanism protecting data and controlling operations on Linux systems.
Question 105
Which command displays the manual page for a specific command?
A) help
B) info
C) man
D) guide
Answer: C
Explanation:
The man command displays the manual page for a specific command in Linux. Manual pages, commonly called man pages, are the primary form of documentation for commands, system calls, library functions, and configuration files in Linux and Unix systems.
When you type man followed by a command name, the system retrieves and displays the comprehensive documentation for that command using a pager program, typically less. Man pages follow a standardized format that includes sections such as NAME for the command name and brief description, SYNOPSIS showing command syntax, DESCRIPTION providing detailed explanation, OPTIONS listing available command-line options, EXAMPLES demonstrating usage, and SEE ALSO referencing related commands.
The man system organizes documentation into numbered sections. Section 1 contains user commands, section 2 covers system calls made available by the kernel, section 3 documents library functions, section 4 describes special files, section 5 explains file formats and conventions, section 6 contains games and screensavers, section 7 provides miscellaneous information, and section 8 covers system administration commands. You can specify a section number like man 5 passwd to view specific documentation.
Man pages support navigation using keyboard commands inherited from the less pager. You can scroll down with the space bar or down arrow, scroll up with b or up arrow, search for text by typing forward slash followed by a search term, and quit by pressing q. The ability to quickly access and navigate man pages is a critical skill for Linux users.
The help command or –help flag provides brief usage information but not comprehensive manual pages.
The info command provides documentation in a different format called info pages, which are hyperlinked and more detailed than man pages but less commonly used.