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Question 106:
A system administrator needs to find all files larger than 100MB in the /var directory. Which command accomplishes this task?
A) find /var -size +100M
B) locate /var -size 100M
C) grep -r size 100M /var
D) du -h /var | awk ‘$1>100’
Answer: A
Explanation:
The find command with the -size option and +100M parameter correctly locates all files larger than 100 megabytes in the /var directory. The find command is specifically designed for searching files based on various criteria including size, modification time, permissions, and ownership. The -size option accepts numerical values with unit specifiers where M represents megabytes, and the plus sign indicates greater than the specified value.
When executing this command, find recursively traverses the /var directory and all subdirectories, evaluating each file against the size criterion. Files exceeding 100 megabytes are printed to standard output with their full paths. This recursive behavior makes find ideal for comprehensive searches across directory hierarchies without requiring manual navigation through subdirectories.
The size option supports multiple unit specifiers including c for bytes, k for kilobytes, M for megabytes, and G for gigabytes. The plus or minus prefix modifies the comparison operation where plus means greater than, minus means less than, and no prefix means exactly equal to the specified size. This flexibility allows precise file size filtering for various administrative tasks.
Find can combine multiple criteria in a single command enabling complex searches. For example, combining size constraints with file type filters, modification time ranges, or permission checks helps administrators locate specific files efficiently. The command also supports actions like -delete, -exec, or -print0 for processing found files.
System administrators commonly use find for disk space management, identifying large log files, locating temporary files for cleanup, and auditing file systems. The ability to search based on size helps identify files consuming excessive disk space that may require archival or deletion to free resources.
The locate command searches a pre-built database of filenames rather than performing real-time filesystem searches. While locate is faster than find for simple name searches, it does not support size-based filtering and does not accept the -size option. The locate database must be regularly updated using updatedb to reflect current filesystem state.
The grep command is designed for searching text content within files rather than searching for files based on attributes. Grep cannot filter files by size and the syntax shown is not valid for any grep operation. Grep searches for patterns within file contents not filesystem metadata.
The du command displays disk usage for directories and files but does not filter based on size thresholds. While the shown command attempts to use awk for filtering, du output format varies and this approach is unreliable compared to find. Additionally, du reports directory sizes including all contained files making it unsuitable for finding individual large files.
Question 107:
Which file contains the system’s hostname configuration that persists across reboots on most modern Linux distributions?
A) /etc/hosts
B) /etc/hostname
C) /proc/sys/kernel/hostname
D) /var/lib/hostname
Answer: B
Explanation:
The /etc/hostname file contains the persistent hostname configuration on most modern Linux distributions including Ubuntu, Debian, CentOS, RHEL, and Fedora. This file stores a single line containing the system’s hostname without any additional information. When the system boots, initialization processes read this file and set the kernel hostname accordingly ensuring the configured name persists across reboots.
Editing /etc/hostname with a text editor and rebooting applies the new hostname permanently. Alternatively, administrators can use the hostnamectl command on systemd-based systems to modify this file and immediately apply changes without rebooting. The hostnamectl set-hostname command updates /etc/hostname and sets the running kernel hostname in a single operation.
The /etc/hostname file is part of the standard filesystem hierarchy on modern distributions replacing older methods that stored hostname configuration in distribution-specific locations. This standardization simplifies hostname management across different Linux variants and provides consistent administrative procedures.
Proper hostname configuration is essential for network identification, certificate validation, clustering, and many services that rely on consistent system naming. The hostname should follow DNS naming conventions using lowercase letters, numbers, and hyphens while avoiding spaces and special characters. Fully qualified domain names can be used in /etc/hostname though many systems store only the short hostname here.
System administrators should ensure hostname configuration aligns with DNS records and /etc/hosts entries to prevent name resolution issues. Mismatched hostnames can cause service failures, authentication problems, and network connectivity issues particularly in environments with strict naming requirements.
The /etc/hosts file maps IP addresses to hostnames for local name resolution but does not store the system’s own hostname configuration. While /etc/hosts typically includes entries for localhost and the system’s hostname, it is not the authoritative source for the system’s hostname. Changes to /etc/hosts do not affect the kernel hostname.
The /proc/sys/kernel/hostname file represents the currently running hostname as maintained by the kernel but this is not persistent storage. The /proc filesystem is virtual and regenerated at each boot. Writing to /proc/sys/kernel/hostname changes the running hostname immediately but the change is lost upon reboot.
The path /var/lib/hostname does not exist as a standard hostname configuration location. The /var/lib directory typically contains variable state information for applications but hostname configuration is stored in /etc as part of system configuration rather than variable application data.
Question 108:
A user needs to compress a directory containing multiple files and subdirectories into a single archive. Which command creates a compressed tar archive named backup.tar.gz?
A) tar -cvf backup.tar.gz /home/user/documents
B) tar -czvf backup.tar.gz /home/user/documents
C) gzip -r /home/user/documents > backup.tar.gz
D) compress -cf backup.tar.gz /home/user/documents
Answer: B
Explanation:
The command tar -czvf backup.tar.gz /home/user/documents correctly creates a compressed tar archive. The tar command with these specific options creates an archive, compresses it with gzip, operates verbosely, and specifies the output filename. Each option serves a distinct purpose in the archiving process making this combination the standard approach for creating compressed archives.
The -c option instructs tar to create a new archive rather than extract or list an existing one. This is the primary operation mode for generating backup archives. The -z option applies gzip compression to the archive, significantly reducing file size while maintaining data integrity. Gzip compression is widely supported and provides good compression ratios with reasonable processing speed.
The -v option enables verbose output, displaying each file as it is added to the archive. This feedback helps administrators verify that intended files are being archived and provides progress indication during lengthy operations. While optional, verbose mode is commonly used for interactive operations to ensure transparency.
The -f option specifies the filename for the archive. This option must be followed by the desired archive name and should typically be the last option before the source directory. The .tar.gz extension conventionally indicates a gzip-compressed tar archive, though .tgz is also commonly used as a shorter alternative.
Tar handles directory hierarchies efficiently by recursively processing all subdirectories and preserving directory structure within the archive. File attributes including permissions, ownership, and timestamps are preserved by default, enabling accurate restoration of archived content. This makes tar ideal for system backups and file distribution.
The combination of tar and gzip compression provides an efficient archiving solution. Tar packages multiple files into a single stream while gzip compression reduces overall size. This two-step process wrapped into a single command with the -z option simplifies archive creation and is standard practice in Linux environments.
The command tar -cvf backup.tar.gz creates an uncompressed tar archive despite the .tar.gz extension. The -z option is missing so gzip compression is not applied. While the file is named with a .tar.gz extension suggesting compression, the actual content would be an uncompressed tar archive leading to confusion and wasted disk space.
The gzip command compresses individual files but does not inherently handle directories or create tar archives. The -r option is not a standard gzip option and the syntax shown does not produce a valid tar archive. Gzip must be combined with tar to archive directories, typically through tar’s -z option rather than piping operations.
The compress command is an older compression utility largely replaced by gzip. It does not accept -cf options and cannot create tar archives. The syntax shown is invalid and would not produce the desired result. Modern Linux systems predominantly use gzip or bzip2 for compression rather than the legacy compress utility.
Question 109:
An administrator needs to change the ownership of all files in a directory and its subdirectories to user john and group developers. Which command accomplishes this?
A) chown john:developers /home/project
B) chown -R john:developers /home/project
C) chmod john:developers /home/project/*
D) chgrp -R john:developers /home/project
Answer: B
Explanation:
The command chown -R john:developers /home/project correctly changes ownership of the directory and all its contents recursively. The chown command modifies file and directory ownership, and the -R option enables recursive operation through directory hierarchies. The syntax user:group specifies both the new owner and group in a single operation, making this the most efficient approach for comprehensive ownership changes.
The -R or –recursive option instructs chown to descend into directories and apply ownership changes to all contained files and subdirectories. Without this option, only the specified directory itself would have its ownership modified while contents retain their original ownership. Recursive operation is essential when entire directory trees require ownership changes.
The user:group syntax allows simultaneous modification of both owner and group ownership. Alternatively, the user.group notation is supported on some systems. If only user ownership requires changes, the colon and group name can be omitted. If only group ownership requires changes, the syntax :group or .group applies changes only to group ownership.
Ownership changes typically require root privileges or sudo access because allowing arbitrary ownership changes would enable users to bypass disk quotas and permission restrictions. Users can change group ownership of files they own to groups they belong to, but changing user ownership requires elevated privileges.
Proper ownership configuration is critical for security and access control. Files and directories should be owned by appropriate users and groups that reflect organizational structure and access requirements. Incorrect ownership can prevent legitimate access or grant unintended permissions creating security vulnerabilities.
After changing ownership, administrators should verify that permissions remain appropriate. Ownership and permissions work together to control access, and changes to ownership may require corresponding permission adjustments to maintain intended access patterns. The ls -l command displays ownership and permissions for verification.
The command chown john:developers /home/project without the -R option changes ownership only for the /home/project directory itself. Files and subdirectories within /home/project retain their original ownership. This limited scope is insufficient when comprehensive ownership changes are required across directory hierarchies.
The chmod command modifies permissions not ownership. Chmod cannot change user or group ownership regardless of options or syntax used. The syntax shown is invalid for chmod which expects permission specifications like 755 or u+rwx rather than user and group names.
The chgrp command changes group ownership but cannot modify user ownership. While chgrp -R could change the group to developers recursively, it cannot set the user ownership to john. Two separate commands would be required using both chown and chgrp which is less efficient than using chown alone with the user:group syntax.
Question 110:
Which command displays the last 20 lines of a log file and continues to display new lines as they are appended?
A) tail -n 20 /var/log/syslog
B) tail -f -n 20 /var/log/syslog
C) head -20 /var/log/syslog
D) cat -n 20 /var/log/syslog
Answer: B
Explanation:
The command tail -f -n 20 /var/log/syslog displays the last 20 lines of the log file and continues monitoring for new content. The tail command is designed to display the end of files, and combining the -f and -n options provides both initial display of trailing lines and continuous monitoring of new content. This combination is essential for real-time log monitoring and troubleshooting.
The -f option activates follow mode where tail continues running and displays new lines as they are appended to the file. This live monitoring capability makes tail indispensable for observing log files generated by active services. The command continues until interrupted with Ctrl+C, providing persistent visibility into ongoing events.
The -n option specifies how many lines from the end of the file to display initially. The number 20 indicates the last 20 lines should be shown when the command starts. Without -n, tail defaults to displaying the last 10 lines. Combining -n with -f shows historical context from recent log entries before switching to live monitoring mode.
Follow mode works by periodically checking the file for changes and displaying new content as it appears. Tail efficiently handles log rotation and file truncation on many systems, continuing to display new content even when log files are rotated by logrotate or similar utilities. This robustness makes tail suitable for production monitoring.
System administrators use tail -f extensively for troubleshooting service issues, monitoring application behavior, and observing system events in real time. The ability to see log entries as they are generated helps identify problems immediately and understand event sequences that might be unclear when reviewing static logs.
Multiple options can enhance tail functionality including -F for following files even after rotation, –retry to keep trying if the file is inaccessible, and –pid to automatically exit when a specific process terminates. These options extend tail’s usefulness for various monitoring scenarios.
The command tail -n 20 /var/log/syslog without the -f option displays the last 20 lines but exits immediately. The output is static showing the file state at command execution time. New lines appended after tail completes are not displayed, requiring the command to be run again to see updates.
The head command displays lines from the beginning of files not the end. Head -20 shows the first 20 lines and does not provide live monitoring capabilities. Head is useful for previewing file contents but unsuitable for monitoring log files where recent entries are most relevant.
The cat command does not accept a -n option for displaying a specific number of lines. Cat concatenates and displays entire file contents without line count filtering or live monitoring. While cat can display files, it lacks the targeted display and follow capabilities required for efficient log monitoring.
Question 111:
A system administrator needs to schedule a script to run every day at 2:30 AM. Which cron time format is correct?
A) 30 2 * * * /path/to/script.sh
B) 2 30 * * * /path/to/script.sh
C) * * 2 30 * /path/to/script.sh
D) 30 2 1 * * /path/to/script.sh
Answer: A
Explanation:
The cron time format 30 2 * * * correctly schedules the script to run every day at 2:30 AM. Cron uses a five-field time specification followed by the command to execute. The fields represent minute, hour, day of month, month, and day of week in that specific order. Understanding this sequence is essential for accurate cron scheduling.
The first field specifies minutes and accepts values 0 through 59. The value 30 indicates the job runs at 30 minutes past the hour. The second field specifies hours in 24-hour format accepting values 0 through 23. The value 2 represents 2 AM. Together, these first two fields precisely define the 2:30 AM execution time.
The remaining three fields use asterisks indicating every possible value. The third field for day of month uses an asterisk meaning every day. The fourth field for month uses an asterisk meaning every month. The fifth field for day of week uses an asterisk meaning every day of the week. This combination ensures daily execution regardless of date.
Cron evaluates day of month and day of week fields with OR logic rather than AND logic. If either field is not an asterisk, the job runs when either condition matches. Using asterisks in both fields ensures the job runs every day without weekday or date restrictions.
System administrators configure cron jobs by editing crontab files using the crontab -e command. Each user has a personal crontab, and the system has a root crontab for administrative tasks. Cron jobs run with the privileges of the crontab owner, so root crontab entries execute with root permissions.
Cron provides no built-in notification when jobs complete successfully. Output from cron jobs is typically emailed to the crontab owner or redirected to log files. Adding redirection to commands like >> /var/log/script.log 2>&1 captures both standard output and errors for later review.
The format 2 30 * * * would schedule execution at 30 hours and 2 minutes, which is invalid since hours only range 0-23. This demonstrates the importance of correct field ordering. Reversing minute and hour fields is a common error that prevents jobs from running.
The format * * 2 30 * places values in the wrong fields. This attempts to specify day of month as 2 and month as 30, which is invalid since months range only 1-12. The asterisks in minute and hour positions would cause execution every minute of every hour on invalid dates.
The format 30 2 1 * * schedules execution at 2:30 AM only on the first day of each month. The 1 in the day of month field restricts execution to monthly rather than daily. This does not meet the requirement for daily execution at 2:30 AM.
Question 112:
Which command shows all currently mounted filesystems along with their mount points and filesystem types?
A) df -h
B) mount
C) lsblk
D) fdisk -l
Answer: B
Explanation:
The mount command without arguments displays all currently mounted filesystems with comprehensive information including device name, mount point, filesystem type, and mount options. This output provides complete visibility into the system’s filesystem topology showing exactly what storage devices and partitions are accessible and where they are mounted in the directory hierarchy.
Mount output includes critical information for system administration and troubleshooting. Each line shows the device or resource being mounted, the mount point directory where it is accessible, the filesystem type such as ext4 or xfs, and mount options like read-only or read-write status. This comprehensive view helps administrators understand storage configuration.
The mount command reveals various filesystem types including local filesystems on disk partitions, network filesystems like NFS or CIFS, pseudo-filesystems like proc and sysfs, and temporary filesystems like tmpfs. This diversity reflects the rich filesystem ecosystem in Linux where different filesystem types serve different purposes.
Mount points shown in the output represent directories where filesystems are attached to the directory tree. The root filesystem mounts at /, while additional filesystems mount at various points like /home, /var, or /mnt. Understanding the mount point hierarchy is essential for navigating storage and managing disk space.
Mount options displayed in the output affect filesystem behavior including whether files can be executed, whether devices are recognized, whether access times are updated, and numerous other characteristics. These options significantly impact security, performance, and functionality of mounted filesystems.
The mount command is also used to mount new filesystems with syntax like mount /dev/sdb1 /mnt/data, but when run without arguments it operates in query mode displaying current mounts. This dual purpose makes mount essential for both mounting operations and system inspection.
The df command displays disk space usage for mounted filesystems including total size, used space, available space, and percentage used. While df -h shows human-readable sizes, it focuses on space utilization rather than comprehensive mount information. Df does not display mount options or all filesystem types shown by mount.
The lsblk command lists block devices showing their relationships and mount points but presents information in a tree structure focused on device hierarchy. While lsblk shows which devices are mounted where, it does not provide complete mount options or all filesystem types. Lsblk complements mount but does not replace it.
The fdisk -l command lists partition tables showing how disks are divided into partitions. Fdisk displays partition sizes, types, and boundaries but does not show which partitions are currently mounted or where. Fdisk is a partitioning tool rather than a mount query tool.
Question 113:
An administrator needs to find which package installed a specific file on a Debian-based system. Which command identifies the package that owns /usr/bin/vim?
A) dpkg -S /usr/bin/vim
B) apt-cache search /usr/bin/vim
C) dpkg -L /usr/bin/vim
D) apt-file find vim
Answer: A
Explanation:
The command dpkg -S /usr/bin/vim searches installed packages to identify which package owns the specified file. The -S or –search option queries the dpkg database of installed packages looking for files matching the given pattern. This reverse lookup functionality helps administrators understand package contents and dependencies.
Dpkg maintains a comprehensive database of all installed packages and their file lists. When searching for file ownership, dpkg scans this database to find which package installed the specified file. The output shows the package name followed by a colon and the matching file path, clearly identifying the relationship.
This capability is invaluable for troubleshooting when administrators need to understand which package provides a particular command, library, or configuration file. Knowing file ownership helps determine which package to reinstall if files are corrupted, which package to update for security patches, or which package to remove if files are no longer needed.
The search pattern can be a complete path like /usr/bin/vim or a pattern that matches multiple files. Dpkg -S accepts partial paths and wildcards, finding all packages that own matching files. This flexibility enables both specific queries and broader searches across the filesystem.
Dpkg operates on installed packages only, searching files that exist on the system. For finding which available package contains a file before installation, tools like apt-file provide similar functionality by querying package contents databases for repositories.
System administrators frequently use dpkg -S when investigating unfamiliar files, determining which package to reinstall after file corruption, or understanding dependencies between packages. The ability to trace files back to their source packages provides essential visibility into system composition.
The apt-cache search command queries package descriptions and names in repositories rather than file ownership. It searches for packages whose descriptions contain search terms but does not identify which package owns specific files. Apt-cache search is useful for finding packages by functionality but not for file ownership queries.
The dpkg -L command lists files installed by a specified package, performing the opposite operation of dpkg -S. While dpkg -L shows what files a package contains, it requires knowing the package name first. The syntax dpkg -L /usr/bin/vim is invalid because -L expects a package name not a file path.
The apt-file find command searches package contents across repositories including uninstalled packages. While apt-file provides similar functionality to dpkg -S for available packages, it requires separate installation and database updates. Dpkg -S is the standard tool for searching installed package files.
Question 114:
Which file contains user password hashes on a modern Linux system with shadow passwords enabled?
A) /etc/passwd
B) /etc/shadow
C) /etc/security
D) /var/lib/shadow
Answer: B
Explanation:
The /etc/shadow file stores user password hashes on Linux systems with shadow password functionality enabled. This file contains sensitive authentication information separated from the publicly readable /etc/passwd file to enhance security. Shadow passwords prevent unprivileged users from accessing password hashes that could be subject to offline cracking attempts.
The /etc/shadow file contains one line per user with colon-separated fields including username, password hash, last password change date, minimum password age, maximum password age, password warning period, password inactivity period, account expiration date, and a reserved field. This comprehensive information enables sophisticated password aging and account expiration policies.
Password hashes in /etc/shadow use modern cryptographic algorithms such as SHA-256 or SHA-512 rather than legacy DES encryption. The hash field begins with an identifier indicating the algorithm, such as 66 6 for SHA-512. These strong hash algorithms resist brute force attacks significantly better than older methods.
File permissions on /etc/shadow restrict access to root only with typical permissions of 0640 or 0600. This protection prevents non-privileged users from reading password hashes. Only authentication services and administrative tools running with root privileges can access shadow password data.
Shadow password implementation separates security-sensitive information from general user account data in /etc/passwd. This separation allows /etc/passwd to remain world-readable for username lookups and UID mapping while keeping authentication credentials secure. The shadow password system is standard on modern Linux distributions.
System administrators should never edit /etc/shadow directly. Tools like passwd, usermod, and chage safely modify shadow file contents with proper locking and validation. Direct editing risks corrupting the file format or introducing inconsistencies that could lock users out of the system.
The /etc/passwd file historically stored password hashes but modern systems use an x placeholder in the password field indicating actual hashes are in /etc/shadow. The /etc/passwd file remains world-readable for user information lookups but contains no sensitive authentication data on shadow-enabled systems.
The /etc/security directory or file does not store password hashes. While /etc/security may contain security-related configurations on some systems, password hashes specifically reside in /etc/shadow. The /etc/security location is not a standard password storage mechanism.
The path /var/lib/shadow does not exist as a password storage location. The /var/lib directory contains variable state data for applications but authentication credentials are stored in /etc as system configuration. Shadow passwords specifically use /etc/shadow following filesystem hierarchy standards.
Question 115:
A user wants to run a command in the background and ensure it continues running after logging out. Which command syntax accomplishes this?
A) command &
B) nohup command &
C) bg command
D) command && exit
Answer: B
Explanation:
The syntax nohup command & runs a command in the background and protects it from hangup signals that occur when a user logs out. The nohup utility prevents the SIGHUP signal from terminating the process, while the ampersand runs the command in the background. This combination ensures the command continues executing even after the terminal session ends.
When users log out of a shell session, the system sends SIGHUP signals to all processes associated with that session. Without protection, these signals terminate running jobs. Nohup intercepts SIGHUP signals preventing process termination, while redirecting standard output and standard error to a file named nohup.out by default.
The ampersand operator places the command in the background immediately, returning control to the shell and allowing the user to continue working or log out. Background execution combined with SIGHUP protection creates persistent processes that survive session termination. This is essential for long-running tasks that must complete without maintaining an active login.
Nohup automatically redirects output because background processes cannot interact with a terminal that may disappear. By default, output goes to nohup.out in the current directory or the user’s home directory if the current directory is not writable. Users can explicitly redirect output to specific files for better organization.
Alternative approaches to persistent background execution include using screen or tmux terminal multiplexers, systemd user services, or at command for scheduled execution. Each method has advantages depending on requirements for interaction, monitoring, and control of background processes.
System administrators use nohup for tasks like data processing, file transfers, compilation, or script execution that must complete regardless of session status. The ability to disconnect from systems while jobs continue running enables efficient resource utilization and flexible work patterns.
The syntax command & runs a command in the background but does not protect it from SIGHUP signals. When the user logs out, the background job receives SIGHUP and typically terminates. This approach works for short background tasks completed before logout but fails for persistent execution.
The bg command resumes suspended jobs in the background but does not provide SIGHUP protection. Jobs resumed with bg remain associated with the terminal session and terminate upon logout. The bg command is useful for managing job control within a session but insufficient for persistent execution.
The syntax command && exit runs a command in the foreground and exits the shell only if the command succeeds. The command does not run in the background and the exit occurs immediately after command completion. This provides no mechanism for persistent execution after logout.
Question 116:
Which command displays the kernel version and system architecture information?
A) uname -a
B) cat /proc/version
C) lsb_release -a
D) hostnamectl
Answer: A
Explanation:
The command uname -a displays comprehensive system information including kernel name, hostname, kernel version, kernel release date, machine hardware architecture, processor type, hardware platform, and operating system. The -a option combines all available information flags providing complete system identification in a single command. This makes uname -a the standard command for quickly gathering system details.
Kernel version information is critical for troubleshooting compatibility issues, verifying patch levels, determining driver availability, and assessing security vulnerabilities. Different kernel versions support different features and hardware, making version identification essential for system administration and support.
System architecture information shown by uname indicates whether the system is 32-bit or 64-bit and the specific processor architecture such as x86_64, i686, aarch64, or armv7l. This information determines which software packages are compatible and what hardware can be supported.
The uname command retrieves information directly from the running kernel through system calls, providing authoritative current system state. This differs from reading files that may not reflect the actual running environment, especially on systems with multiple kernel versions installed.
Individual uname options provide specific information subsets including -s for kernel name, -r for kernel release, -m for machine hardware name, and -p for processor type. The -a option conveniently combines all these into comprehensive output suitable for system documentation and support requests.
System administrators include uname -a output when reporting bugs, requesting support, or documenting system configurations. The complete system identification helps support personnel understand the environment and provide appropriate guidance or solutions.
The cat /proc/version command displays kernel version information from the /proc virtual filesystem. While this provides kernel details, the output format differs from uname and may include compiler information. Both commands show kernel version but uname -a provides more structured comprehensive output.
The lsb_release -a command displays Linux distribution information including distributor ID, description, release number, and codename. While useful for identifying the distribution, lsb_release focuses on distribution version rather than kernel version and architecture. Distribution version and kernel version are related but distinct concepts.
The hostnamectl command on systemd-based systems displays hostname and related system information including operating system, kernel, and architecture. While hostnamectl provides comprehensive output, it is specific to systemd systems. Uname is more universal and traditional across all Linux systems.
Question 117:
An administrator needs to check which ports are currently listening for connections on the system. Which command displays listening ports along with the associated process?
A) netstat -tuln
B) netstat -tulnp
C) ifconfig -a
D) route -n
Answer: B
Explanation:
The command netstat -tulnp displays all listening TCP and UDP ports with associated process information. The combination of options provides comprehensive network listening status essential for security auditing, troubleshooting connectivity issues, and understanding which services are active. Each option contributes specific functionality to the output.
The -t option displays TCP connections and listening sockets. TCP is connection-oriented and used by many services including web servers, SSH, and database servers. Monitoring TCP listening ports reveals which services accept incoming TCP connections.
The -u option includes UDP sockets in the output. UDP is connectionless and used by services like DNS, DHCP, and many streaming applications. Including UDP information provides complete visibility into network service availability.
The -l option filters output to show only listening sockets rather than established connections. This focus on listening ports identifies what services are waiting for incoming connections, which is most relevant for security audits and service verification.
The -n option displays numeric addresses and port numbers instead of attempting hostname and service name resolution. Numeric output avoids delays from DNS lookups and displays exact IP addresses and port numbers useful for firewall configuration and security analysis.
The -p option displays the process ID and process name associated with each listening socket. This critical information links network listeners to specific applications enabling administrators to identify which program opened each port. Root privileges are required for full process information visibility.
Together, these options create a powerful network diagnostic command showing exactly what services listen on which ports and which processes own those services. System administrators use this information to verify expected services are running, identify unexpected listeners that may indicate malware, and troubleshoot connectivity problems.
The command netstat -tuln without the -p option displays listening ports but omits process information. While showing TCP and UDP listeners numerically, the lack of process association makes it harder to identify which application owns each port. Adding -p provides essential context for each listener.
The ifconfig -a command displays network interface configuration including IP addresses, MAC addresses, and interface statistics. Ifconfig manages network interfaces rather than displaying listening ports or services. It shows network connectivity but not service availability.
The route -n command displays the kernel routing table showing how packets are forwarded to different networks. Route information determines network reachability but does not show which ports are listening or which services are active. Routing and listening services are separate network administration concerns.
Question 118:
Which command changes a user’s default login shell to /bin/zsh?
A) usermod -s /bin/zsh username
B) chsh -s /bin/zsh username
C) passwd -s /bin/zsh username
D) useradd -s /bin/zsh username
Answer: A
Explanation:
The command usermod -s /bin/zsh username changes the specified user’s default login shell to /bin/zsh. The usermod command modifies existing user account properties, and the -s option specifically updates the login shell field in the user’s /etc/passwd entry. This administrative command requires root privileges to modify other users’ accounts.
Login shell configuration determines which shell program executes when a user logs in through console, SSH, or other authentication methods. Different shells offer varying features, syntax, and customization options. Common shells include bash, zsh, fish, tcsh, and dash, each with distinct capabilities and user communities.
The shell specified must exist on the system and be listed in /etc/shells for security. The /etc/shells file contains paths to valid login shells, preventing users from specifying arbitrary programs as shells which could create security vulnerabilities. Administrators add new shells to /etc/shells when installing alternative shell packages.
Usermod provides numerous options for modifying user accounts including changing home directories, user IDs, group membership, account expiration, and locking accounts. The -s option specifically targets shell modification, leaving other account properties unchanged. This focused modification reduces risk of unintended account changes.
When changing shells, administrators should verify the new shell is installed and functional before making changes. Configuring a non-existent or malfunctioning shell as the default can lock users out of their accounts. Testing shells in non-login contexts before setting them as default shells prevents accessibility issues.
Users can change their own shell using the chsh command without root privileges, though this may be restricted by system policy. Administrators use usermod to change other users’ shells or to enforce shell policies across accounts.
The chsh command can change login shells but requires different syntax. While chsh -s /bin/zsh changes the current user’s shell, changing another user’s shell with chsh typically requires running as that user or using administrative tools. Usermod provides more direct administrative shell modification.
The passwd command manages user passwords including setting, changing, and configuring password policies. Passwd does not modify login shells. The -s option for passwd relates to password status reporting, not shell configuration. Shell and password management are separate administrative functions.
The useradd command creates new user accounts and can specify initial shell with -s during account creation. However, useradd cannot modify existing accounts. For changing the shell of an existing user, usermod is the appropriate command. Useradd and usermod serve complementary but distinct account management purposes.
Question 119:
An administrator needs to view the last 50 commands executed in the current shell session. Which command accomplishes this?
A) history 50
B) cat ~/.bash_history | tail -50
C) last -50
D) fc -l -50
Answer: A
Explanation:
The command history 50 displays the last 50 commands from the current shell’s command history. The history command accesses the shell’s in-memory command list showing recently executed commands with line numbers. Specifying a number limits output to that many most recent entries, providing focused access to recent command history without overwhelming output.
Shell command history enables users to review past commands, repeat previous operations, and recall complex command syntax without retyping. This functionality significantly improves productivity by allowing quick access to frequently used commands and reducing typing errors when executing similar commands repeatedly.
The history command maintains sequential numbering for each command, and users can execute previous commands by number using syntax like !123 to run command number 123. This reference capability combined with searching enables efficient command recall and execution.
History is maintained in memory during the session and written to a history file typically ~/.bash_history for bash shells when the session ends. The size of history is configurable through environment variables like HISTSIZE for in-memory history and HISTFILESIZE for the history file.
Users can search command history interactively using Ctrl+R for reverse incremental search, allowing quick location of previously executed commands by typing partial matches. This search capability makes history an interactive tool beyond simple listing.
The history command supports various options including -c to clear history, -d to delete specific entries, and -a to append current session commands to the history file immediately. These options provide control over history content and persistence.
The command cat ~/.bash_history | tail -50 displays the last 50 lines from the bash history file but shows the saved history from previous sessions, not necessarily the current session’s recent commands. The history file is typically updated only when the shell exits, so current session commands may not appear. The history command shows live current session data.
The last command displays login history showing which users logged in, from where, and when. While named similarly to history, last serves entirely different purposes related to user authentication auditing rather than command history. Last -50 would show recent logins, not shell commands.
The fc command provides history functionality but with different syntax. While fc -l lists history and supports ranges, the syntax -50 is invalid. The fc command uses ranges like fc -l -50 -1 to show the last 50 commands, but history 50 provides simpler syntax for this common operation.
Question 120:
Which file system type is specifically designed for flash-based storage devices like USB drives and SD cards?
A) ext4
B) XFS
C) FAT32
D) Btrfs
Answer: C
Explanation:
FAT32 is specifically designed for removable flash-based storage devices like USB drives, SD cards, and memory sticks. The File Allocation Table filesystem uses simple structures well-suited to flash media characteristics and provides broad compatibility across operating systems including Windows, Linux, macOS, and embedded devices. This universal compatibility makes FAT32 the de facto standard for removable media.
FAT32’s design accommodates flash memory characteristics including limited write cycles and simple wear leveling requirements. The filesystem’s straightforward structure with minimal metadata reduces write operations compared to journaling filesystems, potentially extending flash device lifespan. However, modern flash controllers implement wear leveling regardless of filesystem choice.
The primary advantage of FAT32 is cross-platform compatibility. Removable media formatted with FAT32 works seamlessly across different operating systems without requiring additional drivers or software. This interoperability is essential for portable storage used to exchange files between diverse systems.
FAT32 limitations include maximum file size of 4GB and maximum volume size of 2TB in most implementations. These restrictions can be problematic for modern use cases involving large video files or high-capacity storage. The exFAT filesystem addresses these limitations while maintaining cross-platform compatibility.
Linux systems fully support FAT32 through native kernel drivers, enabling reading and writing FAT32 filesystems without additional software. Users can format flash devices with FAT32 using mkfs.vfat or mkfs.fat commands, and mount them like any other filesystem.
For removable media used exclusively with Linux systems, administrators might choose ext4 for features like permissions and journaling. However, such media would not be readable on Windows or macOS without additional software, limiting portability.
The ext4 filesystem is designed for hard drives and SSDs in Linux systems, providing features like journaling, large file support, and extensive metadata. While ext4 works on flash media, it is not specifically designed for removable flash devices and lacks the universal compatibility of FAT32 across operating systems.
XFS is a high-performance journaling filesystem designed for large files and high-capacity storage in Linux environments. XFS excels on server systems and large storage arrays but is not designed specifically for flash media or removable drives. XFS is not natively supported on non-Linux systems limiting removable media utility.
Btrfs is a modern copy-on-write filesystem for Linux with advanced features like snapshots, checksumming, and built-in RAID. While Btrfs works on flash media and includes features potentially beneficial for SSDs, it is not designed specifically for removable flash devices and lacks the broad cross-platform compatibility essential for portable media.