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Question 121
Which command displays the manual page for a specific Linux command?
A) help
B) info
C) man
D) doc
Answer: C
Explanation:
The man command displays the manual page for a specific Linux command, providing comprehensive documentation about command usage, options, arguments, and examples. Manual pages are the primary documentation system in Linux and Unix systems, organized into numbered sections covering different types of documentation. When you type man followed by a command name, the system retrieves and displays the formatted documentation for that command in a pager allowing you to scroll through the content. This built-in documentation is essential for learning command syntax and understanding available options without needing internet access.
Manual pages follow a standard structure that makes them easy to navigate and understand. The NAME section provides a brief description of the command. The SYNOPSIS section shows the command syntax including required and optional parameters. The DESCRIPTION section explains what the command does in detail. The OPTIONS section lists all available command-line options with explanations. Additional sections may include EXAMPLES showing practical usage, FILES listing related configuration files, SEE ALSO referencing related commands, and BUGS describing known issues. This consistent organization helps users quickly find the information they need.
The man system organizes documentation into numbered sections representing different types of content. Section 1 contains user commands, section 2 covers system calls, section 3 documents library functions, section 4 describes special files, section 5 explains file formats and conventions, section 6 contains games, section 7 covers miscellaneous topics, and section 8 documents system administration commands. When multiple manual pages exist for the same name in different sections, you can specify the section number like man 5 passwd to view the password file format instead of man 1 passwd which shows the passwd command documentation.
The help command is a bash built-in that provides brief usage information for shell built-in commands but does not display full manual pages. The info command accesses the GNU Info documentation system which provides more detailed hyperlinked documentation but is separate from manual pages. The doc command is not a standard Linux documentation command. Only the man command provides access to the comprehensive manual page system that documents commands, system calls, configuration files, and other aspects of the Linux system.
Question 122
Which directory contains user home directories in a standard Linux filesystem?
A) /root
B) /users
C) /home
D) /usr
Answer: C
Explanation:
The /home directory contains user home directories in a standard Linux filesystem hierarchy. Each regular user typically has a subdirectory under /home named after their username, such as /home/john or /home/alice. These home directories provide personal workspace where users can store their files, customize their environment, and maintain privacy from other users. When users log in, they are automatically placed in their home directory as their current working directory, and shell configuration files in the home directory customize their environment with preferences for prompt appearance, command aliases, and environment variables.
Home directories serve multiple important purposes in Linux systems. They provide private storage space where users can organize documents, downloads, and personal files with permissions that prevent other users from accessing them by default. They contain user-specific configuration files called dotfiles that begin with a period like .bashrc, .profile, and application-specific settings that customize the user’s environment and application behavior. They allow users to install software locally without requiring administrative privileges when system-wide installation is not available. They enable quota enforcement to limit disk space usage per user preventing any single user from consuming all available storage.
The filesystem permissions and ownership of home directories follow security best practices. Each home directory is typically owned by the user it belongs to with group ownership matching the user’s primary group. Default permissions are usually set to 755 or 700, where 755 allows other users to list directory contents but not read files, and 700 provides complete privacy preventing other users from even listing the directory. Files within home directories inherit appropriate ownership and permissions, with newly created files typically defaulting to user-only write permissions while allowing read access to the group and others unless umask settings change this behavior.
The /root directory is the home directory specifically for the root superuser account, not for regular users. The /users directory is not a standard Linux directory and does not exist in typical installations. The /usr directory contains user programs and data but not individual user home directories; it holds system-wide programs, libraries, and documentation available to all users. Only /home provides the standard location for regular user home directories in the Linux filesystem hierarchy.
Question 123
What does the Linux kernel do?
A) Provides the graphical user interface
B) Manages hardware resources and provides core system services
C) Runs application software
D) Stores user files and data
Answer: B
Explanation:
The Linux kernel manages hardware resources and provides core system services that enable the operating system to function. The kernel is the fundamental component of Linux that operates at the lowest software level, directly interfacing with computer hardware including processors, memory, storage devices, and peripherals. It provides essential services that applications and users depend on including process management, memory management, device drivers, filesystem access, and network communication. The kernel creates an abstraction layer that allows software to interact with hardware through standardized interfaces without needing to understand specific hardware details.
Process management is one of the kernel’s primary responsibilities, controlling how programs execute on the system. The kernel creates and destroys processes, allocates CPU time through scheduling algorithms that determine which processes run when, manages process states like running, sleeping, or stopped, and handles inter-process communication allowing processes to exchange data. Memory management ensures efficient use of system RAM by allocating memory to processes as needed, implementing virtual memory that uses disk space to extend available memory, managing memory protection so processes cannot access each other’s memory, and handling page swapping when physical memory becomes scarce.
Device drivers are kernel components that enable communication with hardware devices. The kernel includes drivers for storage controllers, network interfaces, graphics cards, USB devices, and many other peripherals. These drivers translate generic kernel requests into hardware-specific commands that devices understand. The kernel also manages filesystems, providing the structures and operations that allow reading and writing files on disks. Network functionality including TCP/IP protocols, routing, firewalling, and socket interfaces all operate within the kernel, providing the foundation for network communication.
The graphical user interface is provided by display servers and window managers running in user space, not by the kernel itself. Application software runs on top of the kernel using services it provides but the kernel does not directly run applications. User files and data are stored on filesystems that the kernel manages, but storage is provided by physical disks and the kernel only coordinates access. The kernel’s core role is managing hardware resources and providing the essential system services that make everything else possible.
Question 124
Which command creates a new directory in Linux?
A) makedir
B) newdir
C) mkdir
D) createdir
Answer: C
Explanation:
The mkdir command creates new directories in Linux, with the name standing for “make directory.” This essential file management command accepts one or more directory names as arguments and creates them in the filesystem. When executed, mkdir creates directories with default permissions determined by the current umask setting, typically resulting in permissions that allow the owner full access while restricting others. The command is fundamental to organizing files in a hierarchical structure by creating the folder containers needed to logically group related files.
The mkdir command supports several useful options that extend its functionality. The -p option creates parent directories as needed, allowing you to create an entire directory path in a single command even if intermediate directories do not exist. For example, mkdir -p /home/user/documents/work/projects creates all necessary directories in the path regardless of which ones already exist. The -m option sets specific permissions on the newly created directory, overriding default umask behavior. The -v option provides verbose output, displaying a message for each directory created, which is helpful in scripts or when creating multiple directories.
Understanding directory creation is important for effective filesystem organization and system administration. Directories provide logical containers for grouping related files, making them easier to find and manage. Proper directory structure improves system organization, whether creating personal document folders, organizing software projects, or setting up server directory hierarchies. Directory permissions control who can access contents, create files within, or modify the directory itself, making proper directory creation with appropriate permissions important for security.
The makedir command is not a standard Linux command and would not create directories. The newdir command also does not exist as a standard Linux utility. The createdir command is not part of the standard Linux command set. Only mkdir is the correct and standard command for directory creation in Linux and Unix systems, having been part of these operating systems since their earliest versions.
Question 125
Which file contains user account information including usernames and user IDs in Linux?
A) /etc/shadow
B) /etc/passwd
C) /etc/group
D) /etc/users
Answer: B
Explanation:
The /etc/passwd file contains user account information including usernames, user IDs, group IDs, home directories, and default shells. This text file is one of the fundamental configuration files in Linux systems, with each line representing one user account. The file is readable by all users because many system utilities need to look up user information like converting user IDs to usernames in file listings. However, for security reasons, actual password hashes are stored in the separate /etc/shadow file that only root can read, while /etc/passwd historically contained password hashes as indicated by its name.
Each line in /etc/passwd follows a specific format with seven colon-separated fields. The first field is the username used for login. The second field historically contained the encrypted password but now typically contains an “x” indicating the password is in /etc/shadow. The third field is the numeric user ID that the system uses internally to identify the user. The fourth field is the primary group ID. The fifth field is the GECOS field containing optional user information like full name and contact details. The sixth field specifies the user’s home directory path. The seventh field defines the user’s login shell, such as /bin/bash.
Understanding /etc/passwd structure is important for system administration and troubleshooting. User IDs below 1000 typically indicate system accounts used by services and daemons rather than human users. The UID 0 always belongs to the root superuser account. Normal user accounts usually start at UID 1000 or 1001 depending on the distribution. The file can be edited directly by root but tools like useradd, usermod, and userdel should be used instead to ensure consistency with related files like /etc/shadow and /etc/group.
The /etc/shadow file contains encrypted password hashes and password policy information but not the basic account details like username and UID. The /etc/group file defines group memberships and group IDs but not individual user account information. The /etc/users file is not a standard Linux configuration file and does not exist on typical systems. Only /etc/passwd serves as the central database of user account information in Linux systems.
Question 126
Which command shows the current working directory?
A) cwd
B) pwd
C) dir
D) where
Answer: B
Explanation:
The pwd command shows the current working directory, displaying the absolute path from the root of the filesystem to your current location. PWD stands for “print working directory” and is one of the most basic and frequently used commands in Linux. When you execute pwd, it outputs the full directory path, helping you understand your location in the filesystem hierarchy. This is particularly useful after navigating through multiple directories or when working with relative paths, as it provides context about where commands will operate and where relative paths will be resolved from.
The current working directory is an important concept in Linux filesystem navigation. Every process including your shell session has a current working directory that serves as the reference point for relative paths. When you specify a filename or path without a leading slash, the system interprets it relative to the current working directory. Commands like ls without arguments list the contents of the current directory, and commands like cd with relative paths navigate relative to the current position. Knowing your current location through pwd helps prevent mistakes like creating files in wrong directories or accidentally modifying files in unexpected locations.
The pwd command supports options although they are rarely needed for typical usage. The -L option displays the logical current directory including any symbolic links in the path, which is the default behavior. The -P option displays the physical directory path, resolving all symbolic links to show the actual directory location. This distinction matters when you have navigated through symbolic links and want to see either the path as you traversed it or the actual physical location on disk.
The cwd command is not a standard Linux command for displaying the current directory. The dir command exists on some systems as an alias for ls but does not display the current directory path. The where command is not a standard command for showing current location. Only pwd provides the standard functionality for displaying the current working directory path in Linux systems.
Question 127
What is the purpose of the sudo command?
A) To switch to another user account permanently
B) To execute a command with superuser or another user’s privileges
C) To create a new user account
D) To change file ownership
Answer: B
Explanation:
The sudo command allows authorized users to execute commands with superuser or another user’s privileges temporarily. The name stands for “superuser do” and it provides a controlled way for regular users to perform administrative tasks without logging in as root or knowing the root password. When you prefix a command with sudo, the system checks if you are authorized in the /etc/sudoers configuration file, prompts for your own password to verify your identity, and then executes the command with elevated privileges. This approach improves security by limiting who can perform administrative actions and creating audit trails of privileged command execution.
The sudo system provides fine-grained access control through its configuration file. The /etc/sudoers file defines which users or groups can run which commands as which other users. Administrators can grant specific users permission to run only certain commands rather than all commands, implementing the principle of least privilege. For example, a user might be granted permission to restart web services but not modify system configuration files. The configuration can require password entry, allow passwordless execution for specific commands, or set timeout periods for cached authentication. This flexibility enables secure delegation of administrative tasks to trusted users.
Using sudo instead of logging in as root provides several security benefits. It creates audit logs showing who executed which privileged commands and when, enabling accountability and security investigations. It reduces risk from typos or mistakes because you explicitly invoke sudo for each privileged command rather than operating continuously with full root access. It allows granular permission control rather than all-or-nothing superuser access. It protects the root password by not requiring users to know it, and it can be configured differently across different systems to match their specific security requirements.
Switching to another user account permanently is accomplished with the su command, not sudo. Creating new user accounts is done with useradd or adduser commands, not sudo, though you would need sudo to run those commands with proper privileges. Changing file ownership uses the chown command, again requiring sudo for files you don’t own. The sudo command itself is specifically designed to execute individual commands with elevated or different user privileges rather than performing these other specific tasks.
Question 128
Which environment variable contains the search path for executable commands?
A) HOME
B) PATH
C) SHELL
D) USER
Answer: B
Explanation:
The PATH environment variable contains the search path for executable commands, consisting of a colon-separated list of directories that the shell searches when you type a command name without a full path. When you execute a command like ls or grep, the shell looks through each directory listed in PATH in order until it finds an executable file with that name. This mechanism allows you to run commands by name from any location without needing to specify their full path or be in the same directory as the executable. Understanding PATH is essential for troubleshooting why commands might not be found and for customizing your command environment.
The PATH variable typically includes standard system directories containing executable programs. Common directories in PATH include /usr/local/bin for locally installed software, /usr/bin for most user commands, /bin for essential system binaries, /usr/local/sbin and /usr/sbin for system administration commands, and sometimes user-specific directories like ~/bin for personal scripts. The order of directories in PATH matters because the shell stops searching as soon as it finds a matching executable, meaning earlier directories take precedence over later ones. This ordering allows local installations to override system commands or user scripts to override system utilities.
You can view your current PATH by typing echo PATH,andyoucanmodifyitbyaddingdirectoriestosuityourneeds.TemporaryPATHmodificationscanbemadewithexportPATH=PATH, and you can modify it by adding directories to suit your needs. Temporary PATH modifications can be made with export PATH= PATH,andyoucanmodifyitbyaddingdirectoriestosuityourneeds.TemporaryPATHmodificationscanbemadewithexportPATH=PATH:/new/directory which appends a new directory to the existing PATH for the current shell session. Permanent changes are made by editing shell configuration files like .bashrc or .bash_profile in your home directory, adding the export statement so it executes each time you log in. Some applications and development environments add their own directories to PATH during installation or activation.
The HOME environment variable contains the path to your home directory, not the command search path. The SHELL variable identifies which shell program you are using like /bin/bash. The USER variable contains your username. While these are all important environment variables, only PATH determines where the system searches for executable commands when you type command names without full paths.
Question 129
Which command displays the first 10 lines of a text file?
A) head
B) top
C) first
D) begin
Answer: A
Explanation:
The head command displays the first 10 lines of a text file by default, providing a quick way to preview the beginning of file contents. This utility is commonly used to examine the start of log files, check file headers, verify file contents, or extract the first few lines of data files. When executed with a filename as an argument, head reads and outputs the specified number of initial lines then exits. The command is particularly useful for large files where displaying entire contents would be impractical or when you only need to see how a file begins.
The head command accepts options that modify its behavior and output. The -n option followed by a number specifies how many lines to display instead of the default 10, such as head -n 20 file.txt to show the first 20 lines. The option can be shortened to just a hyphen and number like head -20 file.txt. The -c option displays a specific number of bytes instead of lines, useful for binary files or when working with fixed-width data. Multiple files can be specified, and head will display the first lines of each with headers identifying which file each output section comes from.
The head command is frequently used in combination with other commands through pipes to process data streams. For example, ls -l | head shows the first few files in a directory listing, or dmesg | head displays the first kernel messages. In scripts, head extracts header rows from CSV files, samples the beginning of log files for analysis, or retrieves top results from command output. Understanding head alongside its counterpart tail which shows the end of files provides powerful tools for text file examination and processing.
The top command is a system monitoring tool that displays running processes and resource usage, not file contents. The first command is not a standard Linux utility for displaying file contents. The begin command also does not exist as a standard Linux command. Only head provides the functionality to display the first lines of text files in Linux systems.
Question 130
Which symbol is used to redirect standard output to a file, overwriting the file if it exists?
A)
B) >
C) >>
D) |
Answer: B
Explanation:
The greater-than symbol redirects standard output to a file, overwriting the file if it already exists. This fundamental shell redirection operator takes output that would normally appear on the screen and writes it to a file instead. When you execute a command like ls > filelist.txt, the directory listing that would typically display on your terminal is instead written to filelist.txt. If filelist.txt already exists, its previous contents are completely replaced with the new output. If it does not exist, the shell creates it. This capability is essential for saving command output, creating files from command results, and building data processing pipelines.
Output redirection is part of the shell’s standard stream manipulation system. Linux processes have three standard streams: standard input for reading data, standard output for normal output, and standard error for error messages. The > operator specifically redirects standard output, which is file descriptor 1. Error messages still appear on screen unless separately redirected. To redirect both standard output and standard error, you can use &> or redirect them separately with 1> for output and 2> for errors. Understanding these distinctions helps control where different types of output go.
Redirection operators enable powerful command combinations and automation. You can chain operations like command1 > temp.txt followed by command2 < temp.txt to pass data between commands through files. You can suppress output entirely by redirecting to /dev/null, a special file that discards everything written to it. You can create simple logs by redirecting command output to files, though the overwriting behavior means you lose previous contents unless you use append mode. The ability to redirect output is fundamental to shell scripting and command-line productivity.
The less-than symbol < redirects standard input, reading from a file instead of keyboard. The double greater-than >> redirects output while appending to the file instead of overwriting it, preserving existing contents. The pipe symbol | connects the output of one command to the input of another command for chaining operations. Only the single > operator redirects standard output while overwriting any existing file contents.
Question 131
What does the chmod command do?
A) Changes file ownership
B) Changes file permissions
C) Changes file location
D) Changes file timestamps
Answer: B
Explanation:
The chmod command changes file permissions in Linux, controlling who can read, write, or execute files and directories. The name stands for “change mode” where mode refers to the permission settings that determine access rights. Permissions in Linux are divided into three categories: owner permissions for the file owner, group permissions for members of the file’s group, and other permissions for everyone else. Each category can have read, write, and execute permissions enabled or disabled. The chmod command allows you to modify these permissions to control access according to security requirements.
Linux file permissions can be specified using either symbolic or numeric notation with chmod. Symbolic notation uses letters like chmod u+x file to add execute permission for the owner, or chmod go-w file to remove write permission for group and others. The letters u, g, and o represent owner, group, and others, while r, w, and x represent read, write, and execute. Numeric notation uses octal values where read equals 4, write equals 2, and execute equals 1, combined to create three-digit codes like chmod 755 file which sets rwxr-xr-x permissions.
Understanding when and how to change permissions is important for security and functionality. Execute permission is required to run programs and scripts, and to access contents of directories. Write permission allows modifying or deleting files. Read permission enables viewing file contents or listing directory contents. Improper permissions can prevent legitimate access or allow unauthorized access. Common permission patterns include 644 for regular files (owner can write, all can read), 755 for directories and executables (owner can write, all can read and execute), and 600 for private files (only owner can access).
The chown command changes file ownership, not permissions. The mv command changes file location by moving or renaming files. The touch command can change file timestamps. While you might need appropriate permissions to use these commands, chmod specifically modifies the permission bits that control access rights. Understanding the distinction between ownership, location, timestamps, and permissions is important for effective Linux file management and security.
Question 132
Which directory contains temporary files that are typically deleted on system reboot?
A) /var/tmp
B) /tmp
C) /temp
D) /cache
Answer: B
Explanation:
The /tmp directory contains temporary files that are typically deleted on system reboot, providing a location for applications and users to store data that is only needed for short periods. This directory serves as temporary workspace for programs that need to create intermediate files during processing, store temporary downloads, maintain session data, or cache information briefly. The automatic cleanup on reboot ensures that /tmp does not accumulate old temporary files that consume disk space unnecessarily. Users can freely create files in /tmp without worrying about cleaning them up, though they should not store anything important there since it will be lost on restart.
The /tmp directory has specific characteristics that make it suitable for temporary storage. It is typically world-writable with the sticky bit set, meaning any user can create files there, but users can only delete their own files, preventing users from maliciously deleting others’ temporary files. On many modern Linux distributions, /tmp is mounted as a tmpfs filesystem in RAM rather than on disk, providing very fast access speeds but limiting capacity to available memory. This RAM-based storage makes /tmp excellent for frequently accessed temporary data while reinforcing its temporary nature since contents are lost not only on reboot but also if the tmpfs becomes full.
Different distributions handle /tmp cleanup differently. Some distributions delete /tmp contents on every boot, while others use systemd-tmpfiles or similar tools to age out old files based on access times rather than strictly on reboot. Some systems maintain separate /tmp directories that persist across reboots but clean old files periodically. Understanding your system’s /tmp handling is important when deciding whether to use it for specific temporary storage needs. For temporary files that should survive reboots, /var/tmp is the appropriate location.
The /var/tmp directory is for temporary files that should persist across reboots, with files typically retained for 30 days before automatic cleanup. The /temp directory is not a standard Linux directory and does not exist in typical filesystem hierarchies. The /cache directory is also not a standard top-level directory, though /var/cache exists for persistent cache files. Only /tmp provides the standard temporary storage location with automatic cleanup on reboot.
Question 133
What is the default shell for most Linux distributions?
A) sh
B) csh
C) bash
D) zsh
Answer: C
Explanation:
Bash is the default shell for most Linux distributions, serving as the command-line interpreter that processes user commands and executes scripts. Bash stands for “Bourne Again Shell” and is an enhanced replacement for the original Bourne shell. It provides a text-based interface where users type commands, an environment for running programs and scripts, command history allowing recall and editing of previous commands, powerful scripting capabilities with variables and flow control, and extensive customization through configuration files. Bash’s widespread adoption as the default shell means most Linux documentation and tutorials assume bash is being used.
Bash provides numerous features that make it powerful and user-friendly for both interactive use and scripting. Command completion with the Tab key automatically fills in command names, file paths, and arguments, reducing typing and preventing errors. Command history accessed through arrow keys allows recalling and editing previous commands. Aliases enable creating shortcuts for frequently used commands. Job control allows running multiple programs concurrently and switching between foreground and background processes. Scripting capabilities including variables, conditionals, loops, and functions enable automation of complex tasks.
The bash configuration files control shell behavior and customize the user environment. System-wide configuration in /etc/bash.bashrc or /etc/profile affects all users. User-specific configuration in ~/.bashrc executes for non-login interactive shells, while ~/.bash_profile or ~/.profile executes for login shells. These files set environment variables like PATH, define aliases and functions, customize the command prompt appearance, and configure shell options. Understanding how bash reads these configuration files and in what order helps troubleshoot environment issues and customize the shell effectively.
The sh shell refers to the original Bourne shell or a POSIX-compliant shell, but it is not typically the default interactive shell. The csh shell uses C-like syntax and was popular on BSD systems but is not the default on Linux distributions. The zsh shell is a powerful alternative with advanced features but is not yet the default on most distributions, though it is default on macOS. Bash remains the most common default shell for Linux distributions due to its balance of power, compatibility, and ease of use.
Question 134
Which command searches for files in a directory hierarchy based on various criteria?
A) search
B) locate
C) find
D) grep
Answer: C
Explanation:
The find command searches for files in a directory hierarchy based on various criteria including name patterns, file types, sizes, modification times, permissions, and ownership. Find is an extremely powerful and flexible utility that recursively traverses directory trees starting from specified paths and tests each file against the criteria you specify. When files match the specified conditions, find can display them, execute commands on them, or perform various actions. This makes find essential for locating specific files, performing bulk operations on groups of files, and system maintenance tasks.
The find command uses a sophisticated syntax where you specify a starting directory path followed by test expressions and actions. Basic usage like find /home -name “*.txt” searches the /home directory tree for files ending in .txt. Tests can be combined with logical operators where -and is implicit between tests, -or provides alternative conditions, and ! negates conditions. Common tests include -name for filename patterns, -type for file types like files or directories, -size for file size ranges, -mtime for modification time, -user for ownership, and -perm for permission patterns.
Find can perform actions on matched files beyond just displaying their paths. The -exec option executes commands on each found file, using {} as a placeholder for the filename and requiring ; to terminate the command. The -delete option removes matched files. The -print action explicitly displays paths and is the default when no action is specified. The -ok option is like -exec but prompts for confirmation before each action. These capabilities make find powerful for bulk file operations like finding and deleting old log files, changing permissions on specific file types, or locating files owned by particular users.
The search command is not a standard Linux utility for finding files. The locate command searches a pre-built database of filenames rather than actively searching the filesystem, making it faster but potentially showing outdated results. The grep command searches for text patterns within file contents rather than searching for files themselves. Only find provides comprehensive real-time filesystem searching based on file attributes and metadata with the flexibility to perform actions on found files.
Question 135
Which file would you edit to permanently add a directory to your PATH for your user account?
A) /etc/environment
B) ~/.bashrc
C) /etc/passwd
D) ~/.profile
Answer: B
Explanation:
The ~/.bashrc file is the most common location to permanently add a directory to your PATH for your user account in most Linux distributions. This file executes every time you start a new interactive bash shell, making it ideal for setting environment variables, defining aliases, and customizing your shell environment. To add a directory to PATH, you would add a line like export PATH=$PATH:/new/directory to your ~/.bashrc file. The $PATH variable references the current PATH value, and :/new/directory appends the new directory to the end. After saving the file, you can either log out and back in or run source ~/.bashrc to apply the changes immediately.
Understanding the different bash configuration files and when they execute helps choose the right location for customizations. The ~/.bash_profile or ~/.profile files execute for login shells when you initially log in to the system. The ~/.bashrc file executes for non-login interactive shells, which includes most terminal windows you open in graphical environments. Many distributions configure ~/.bash_profile to source ~/.bashrc so that settings apply to both login and non-login shells. For PATH modifications and most environment customizations, ~/.bashrc is typically the best choice because it applies to all your interactive shells.
When modifying PATH, the order matters and different addition methods have different effects. Using export PATH=PATH:/new/directoryappendstotheend,meaningexistingpathsaresearchedfirst.UsingexportPATH=/new/directory:PATH:/new/directory appends to the end, meaning existing paths are searched first. Using export PATH=/new/directory: PATH:/new/directoryappendstotheend,meaningexistingpathsaresearchedfirst.UsingexportPATH=/new/directory:PATH prepends to the beginning, giving the new directory priority over system directories. Be careful when modifying PATH because incorrect changes can make commands unavailable or cause wrong versions to execute. Always preserve the existing PATH value by including $PATH in your modification rather than completely replacing it. If you make a mistake, you can usually recover by opening a new terminal or logging out and back in.
The /etc/environment file sets system-wide environment variables but requires root access and affects all users. The ~/.profile file works for login shells but is not always sourced by graphical terminal emulators. The /etc/passwd file contains user account information but should never be edited for PATH modifications. For user-specific PATH changes that apply to everyday terminal usage, ~/.bashrc is the standard and most appropriate location.