LFCS Essential Commands Practice Test 5 — 15 Questions

Question 1

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

Question 2

An administrator needs to compress a directory named 'project' into a tarball with maximum compression using gzip. Which command is appropriate?

Accepted Answer

tar -czvf archive.tar.gz project. The `-z` flag tells tar to compress the archive using gzip. The `-c` flag creates a new archive, `-v` provides verbose output, and `-f` specifies the archive filename. The `.tar.gz` extension is the conventional extension for a gzip-compressed tarball. Although other tools like bzip2 or xz can achieve higher compression ratios, the question explicitly asks for using gzip.

Answer

tar -cjvf archive.tar.bz2 project

Answer

tar -cJvf archive.tar.xz project

Answer

tar -cvf archive.tar project

Question 3

A junior admin runs 'ls -l' and sees permissions '-rwxrwxr-x' on a file. What is the octal representation?

Accepted Answer

775. The permissions '-rwxrwxr-x' break down as: owner (rwx = 4+2+1 = 7), group (rwx = 4+2+1 = 7), others (r-x = 4+0+1 = 5). This gives the octal value 775. Option C is correct because it matches this calculation exactly.

Answer

755

Answer

770

Answer

777

Question 4

A system administrator wants to kill a process with PID 1234 that is not responding to SIGTERM. Which command will forcefully terminate it?

Accepted Answer

kill -9 1234. Kill -9 (SIGKILL) sends signal 9, which cannot be caught, blocked, or ignored by the process. Unlike SIGTERM (signal 15), SIGKILL forces the kernel to immediately terminate the process without allowing it to clean up, making it the appropriate choice when a process is unresponsive to SIGTERM.

Answer

kill -1 1234

Answer

kill -15 1234

Answer

kill -SIGTERM 1234

Question 5

A user needs to see the contents of a gzip-compressed file 'data.txt.gz' without decompressing it. Which command is appropriate?

Accepted Answer

zcat data.txt.gz. The `zcat` command reads a gzip-compressed file and outputs its decompressed content to stdout without modifying the original file. This allows the user to view the contents of 'data.txt.gz' without permanently decompressing it.

Answer

gunzip data.txt.gz

Answer

./data.txt.gz

Answer

gzcat data.txt.gz

Question 6

A script needs to search for lines containing 'ERROR' in /var/log/syslog and count them. Which command pipeline achieves this?

Accepted Answer

grep ERROR /var/log/syslog | wc -l. It uses `grep` to filter lines containing 'ERROR' from `/var/log/syslog` and pipes the output to `wc -l`, which counts the number of lines. This pipeline accurately counts the lines that match the pattern, which is the required task.

Answer

wc -l /var/log/syslog

Answer

grep ERROR /var/log/syslog | wc -c

Answer

grep -c ERROR /var/log/syslog

Question 7

An administrator wants to print the last field of each line from a CSV file 'data.csv' (comma-separated). Which awk command accomplishes this?

Accepted Answer

awk -F, '{print $NF}' data.csv. `awk -F, '{print $NF}' data.csv` uses `-F,` to set the field separator to comma, and `$NF` represents the value of the last field (NF is the number of fields, so $NF is the last field). This command prints the last column of each line in the CSV file.

Answer

cut -d, -f2 data.csv

Answer

cut -d, -f1 data.csv

Answer

awk '{print $NF}' data.csv

Question 8

A user 'dba' tries to login via SSH and fails. Based on the exhibit, what is the most likely cause?

Accepted Answer

The user 'dba' has an invalid login shell.. The exhibit shows that the user 'dba' has an invalid login shell (e.g., /sbin/nologin or /bin/false). When the login shell is set to a non-interactive shell, SSH authentication succeeds but the session immediately closes, preventing the user from logging in. This is a common configuration for system accounts or users who should not have interactive shell access.

Answer

The file /home/dba/file.txt is corrupt.

Answer

The user 'dba' is not in the 'docker' group.

Answer

The home directory /home/dba does not have correct permissions.

Question 9

Based on the exhibit, what is the average CPU idle percentage over the last 15 minutes?

Accepted Answer

65.0%. The average CPU idle percentage over the last 15 minutes is calculated from the 'idle' value in the 'average' row of the 'mpstat' output. In the exhibit, the 'average' row shows an 'idle' value of 65.0, meaning the CPU was idle 65.0% of the time on average across all CPUs over the 15-minute interval. Therefore, the correct answer is 65.0%.

Answer

2.0

Answer

1.5

Answer

2.5

Question 10

The backup script fails to run as user 'backup' with sudo. What is the issue?

Accepted Answer

The script does not have execute permission for the 'backup' user.. For a script to be executed via sudo, the user (backup) must have execute permission on the script file. Even if sudo is configured to allow the user to run the script, the operating system enforces file permission checks at execution time. Without the execute bit set for the backup user (or for others, depending on the sudo runas context), the kernel will refuse to execve() the script, resulting in a 'Permission denied' error.

Answer

The script has a restrictive umask.

Answer

The script is not owned by 'backup'.

Answer

The 'backup' user is not in the sudoers file.

Question 11

Which TWO commands can be used to display the contents of a text file page by page? (Select two.)

Accepted Answer

more file.txt. The `more` command displays the contents of a text file one screen at a time, pausing after each page and waiting for user input (e.g., pressing the spacebar) to continue. This makes it a classic pager utility for viewing files page by page.

Answer

cat file.txt

Answer

head file.txt

Answer

tail file.txt

Question 12

Which THREE commands can be used to view the contents of a compressed archive file without extracting it? (Select three.)

Accepted Answer

tar -tvf archive.tar.gz. `tar -tvf archive.tar.gz` lists the contents of a tar archive compressed with gzip without extracting it. The `-t` flag tells tar to list the table of contents, `-v` provides verbose output, and `-f` specifies the archive file. This command reads the archive metadata directly from the compressed file.

Answer

gunzip archive.gz

Answer

bunzip2 archive.bz2

Question 13

A user reports that they cannot run a script because it says 'Permission denied'. The script is owned by root and has permissions -rw-r--r--. Which command would allow the user to execute the script?

Accepted Answer

chmod +x script. The script has permissions `-rw-r--r--`, meaning the owner (root) has read/write, but no execute bit is set for any user. Option B (`chmod +x script`) adds the execute permission for all users (owner, group, others), which allows the user to run the script. Without the execute bit, the kernel will refuse to execve() the file, returning EACCES.

Answer

chmod u+s script

Answer

chmod -w script

Answer

chown user:user script

Question 14

A system administrator is troubleshooting a performance issue. They need to identify which process is consuming the most CPU time over the last 24 hours. Which command should be used?

Accepted Answer

ps aux --sort=-%cpu. The most appropriate among the given choices because `ps aux --sort=-%cpu` lists all processes sorted by the current CPU usage percentage. While this shows a snapshot of current CPU consumption, the `%cpu` field represents the percentage of CPU time used since the process started, giving an approximation of the process's cumulative CPU usage. For historical data over the last 24 hours, process accounting (e.g., `sa` command) would be needed, but among the options, only A provides per-process CPU data.

Answer

sar -u -f /var/log/sa/sa$(date +%d)

Answer

top -b -n1

Answer

uptime

Question 15

A developer needs to extract the third column from a CSV file where columns are separated by commas, but some fields contain commas within double quotes. Which command correctly handles this?

Accepted Answer

awk 'BEGIN { FPAT = "[^,]*|\"[^\"]+\"" } { print $3 }' file.csv. It uses `awk` with the `FPAT` variable to define a field pattern that correctly handles commas inside double-quoted fields. The pattern `[^,]*|"[^"]+"` matches either a sequence of non-comma characters or a double-quoted string (including any commas within it), ensuring that the third column is extracted accurately even when fields contain embedded commas.

Answer

cut -d',' -f3 file.csv

Answer

awk -F',' '{ print $3 }' file.csv

Answer

sed 's/[^,]*,[^,]*,$[^,]*$.*/\1/' file.csv