LFCS Essential Commands Practice Test 6 — 15 Questions

Question 1

A user needs to view the contents of a large text file one screen at a time. Which command is best for this?

Accepted Answer

less file.txt. `less` is a terminal pager that allows forward and backward navigation through a file, making it ideal for viewing large text files one screen at a time. Unlike `more`, `less` supports scrolling both up and down, and it does not load the entire file into memory, which is efficient for large files.

Answer

nl file.txt

Answer

more file.txt

Answer

cat file.txt

Question 2

A cron job runs a script every hour but sometimes fails because the script cannot find commands like 'tar' and 'gzip'. The script works when run manually from a terminal. What is the best fix?

Accepted Answer

Use absolute paths for all commands in the script.. Cron jobs run in a minimal environment with a restricted PATH (often just /usr/bin:/bin). When the script uses commands like 'tar' and 'gzip' without absolute paths, the shell cannot locate them. Using absolute paths (e.g., /bin/tar, /bin/gzip) ensures the script always finds the commands regardless of the environment.

Answer

Run the cron job as root.

Answer

Modify the script to source the user's .bashrc.

Answer

Add a PATH statement to the cron job definition.

Question 3

Which THREE commands can change the priority of an already running process?

Accepted Answer

top (press 'r'). Option B (top, press 'r') is correct because within the interactive top utility, pressing 'r' prompts for a PID and a new nice value, allowing you to renice an already running process on the fly. Option C (chrt) is correct because chrt sets or changes the scheduling policy and real-time priority of a running process by PID (e.g., chrt -p -f 10 ), directly altering its priority attributes. Option E (renice) is correct because renice is specifically designed to change the nice value of one or more running processes (renice -n 5 -p ), which adjusts their CPU scheduling priority. Option A (kill -STOP) is incorrect because it only suspends a process with SIGSTOP and does not modify its priority. Option D (nice) is incorrect because nice only launches a new command with a specified nice value; it cannot change the priority of an already running process.

Answer

kill -STOP

Answer

nice

Question 4

Which TWO commands can display the current environment variables?

Accepted Answer

env. The `env` command (option C) is correct because it prints all current environment variables and their values to standard output when run without arguments. The `printenv` command (option E) is also correct because it displays the values of all environment variables (or a specified one) in the current shell environment. Option A, `set`, is not marked correct because although it lists shell variables, it also includes shell functions and local variables, not strictly the environment variables. Option B, `echo $HOME`, is not marked correct because it only displays the value of the single HOME variable rather than the current environment variables as a whole. Option D, `export`, is not marked correct because it is used to mark variables for export to child processes, not to display the environment.

Answer

set

Answer

echo $HOME

Answer

export

Question 5

Refer to the exhibit. The output of 'ps aux' shows a process named 'process_hog' with PID 1234 consuming 99.5% CPU. The process is stuck in an infinite loop and does not respond to SIGTERM. Which signal should be used to forcefully terminate it?

Accepted Answer

kill -9 1234. SIGKILL (signal 9) cannot be caught, blocked, or ignored by a process, making it the only reliable way to terminate a process that is stuck in an infinite loop and unresponsive to SIGTERM. Since the process does not respond to SIGTERM (signal 15), a forceful kill with kill -9 is necessary.

Answer

kill -2 1234

Answer

kill -15 1234

Answer

kill -19 1234

Question 6

Refer to the exhibit. The /var partition is 100% full. Which command can be used to find the largest files in /var/log to free up space?

Accepted Answer

du -ah /var/log | sort -rh | head. It uses `du -ah` to list all files and directories in /var/log with human-readable sizes, pipes the output to `sort -rh` to sort them in reverse numerical order (largest first), and then uses `head` to display only the top entries. This combination efficiently identifies the largest files consuming space, allowing the administrator to target specific files for cleanup.

Answer

ls -lS /var/log

Answer

find /var/log -size +100M

Answer

df -h /var/log

Question 7

A DevOps engineer wants to measure how long a specific command takes to execute. Which command should be used?

Accepted Answer

time. The `time` command is specifically designed to measure the execution duration of a command, reporting real time, user CPU time, and system CPU time. It wraps the target command and tracks the elapsed wall-clock time and resource usage, making it the precise tool for benchmarking command performance.

Answer

date

Answer

uptime

Answer

wall

Question 8

An administrator runs 'ls -la' and sees the following entry for a file: 'lrwxrwxrwx 1 root root 24 Jan 10 12:00 link -> /etc/passwd'. If the target file /etc/passwd is deleted, what happens to the link file?

Accepted Answer

The link becomes a broken symbolic link. The entry 'lrwxrwxrwx' indicates a symbolic link (symlink), which stores a path to the target file rather than sharing its inode. When the target /etc/passwd is deleted, the symlink still exists but points to a non-existent path, making it a broken (dangling) symlink. Accessing it will result in a 'No such file or directory' error.

Answer

The link becomes a hard link to the deleted file's inode

Answer

The link becomes a regular file with the same content

Answer

The link is automatically deleted

Question 9

To compress a file while preserving the original file, which command should be used?

Accepted Answer

gzip -k file.txt. The `-k` (or `--keep`) flag in `gzip` instructs the utility to compress the file while retaining the original uncompressed file. By default, `gzip` replaces the original file with a compressed version (appending `.gz`), so `-k` is the explicit option to preserve the source file.

Answer

gzip file.txt

Answer

gzip -d file.txt.gz

Answer

gzip -1 file.txt

Question 10

A system administrator wants to display a list of all currently running processes with their parent process IDs. Which command is most appropriate?

Accepted Answer

ps -ef. (ps -ef) is correct because the 'ps' command with the '-e' flag displays all processes, and the '-f' flag provides a full-format listing that includes the PPID (parent process ID) in the output. This directly meets the requirement to list all currently running processes with their parent process IDs.

Answer

pstree

Answer

jobs

Answer

top

Question 11

To display the first 10 lines of a file named 'log.txt', which command is correct?

Accepted Answer

head log.txt. The `head` command is designed to display the first 10 lines of a file by default. Running `head log.txt` outputs the first 10 lines of the file without any additional options, making it the correct choice for this task.

Answer

less log.txt

Answer

tail log.txt

Answer

cat log.txt

Question 12

A user is unable to write to a file. The output of 'ls -l file' shows '-r--r--r--'. Which command will grant write permission to the owner?

Accepted Answer

chmod u+w file. The file's permissions are '-r--r--r--', meaning the owner has only read permission. The 'chmod u+w file' command adds write permission for the owner (u) because 'u' refers to the user/owner. This directly addresses the owner's lack of write access.

Answer

chmod o+w file

Answer

chmod a+w file

Answer

chmod g+w file

Question 13

A system administrator needs to change the group ownership of a file to 'developers' and set the setgid bit on a directory. Which two commands accomplish these tasks? (Choose two.)

Accepted Answer

chmod g+s dir. Option A, 'chmod g+s dir', is correct because the g+s symbolic mode sets the setgid bit on the directory, causing new files and subdirectories created inside it to inherit the directory's group ownership. Option D, 'chown :developers file', is correct because omitting the user and specifying only ':developers' changes the file's group ownership to the 'developers' group while leaving the owner unchanged. Option B, 'chmod u+s dir', is wrong because u+s sets the setuid bit on the owner, not the setgid bit, and setuid on a directory is generally ignored on Linux. Option C, 'chown developers: file', is wrong because it sets the user owner to 'developers' rather than the group owner. Option E, 'chmod g+s file', is wrong because the task requires setting setgid on a directory, not on a file.

Answer

chmod u+s dir

Answer

chown developers: file

Answer

chmod g+s file

Question 14

A user wants to view the contents of a compressed file file.txt.gz without decompressing it permanently. Which two commands can be used? (Choose two.)

Accepted Answer

gunzip -c file.txt.gz. Option A, gunzip -c file.txt.gz, is correct because the -c (--stdout) flag writes the decompressed output to standard output, allowing the user to view the contents while leaving the original .gz file intact on disk. Option B, zcat file.txt.gz, is correct because zcat is functionally equivalent to gunzip -c, decompressing the gzip file to stdout without removing or modifying the compressed file. Option C, gzip -l file.txt.gz, only lists metadata such as compressed size, uncompressed size, and ratio, so it does not show the file's contents. Option D, gzip -d file.txt.gz, actually decompresses and deletes the .gz file, which is a permanent decompression, not a view-only operation. Option E, gzip -k file.txt.gz, compresses a file while keeping the original, so it does not display the contents of an already compressed file.

Answer

gzip -l file.txt.gz

Answer

gzip -d file.txt.gz

Answer

gzip -k file.txt.gz

Question 15

A DevOps engineer wants to list all running processes sorted by memory usage in descending order. Which command should be used?

Accepted Answer

ps aux --sort=-%mem. `ps aux` lists all running processes, and `--sort=-%mem` sorts them by memory usage in descending order (the minus sign indicates descending). This is the standard way to identify memory-heavy processes for troubleshooting or resource monitoring.

Answer

ps aux --sort=%mem

Answer

ps aux --sort=+mem

Answer

ps aux --sort=-%cpu