System resource monitoring (free, uptime, vmstat) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What does the command free -m output?

You run free -m on a Linux system. What does the Mem: line show?

Linux CLI

free -m

A CPU usage percentages for user, system, and idle

B Memory usage in megabytes including total, used, free, shared, buff/cache, and available

C Disk space usage in megabytes for all mounted filesystems

D Network interface statistics including packets sent and received

💡 Hint

Think about what 'free' command is designed to show about system memory.

The free -m command shows memory usage in megabytes. The Mem: line lists total memory, used memory, free memory, shared memory, buffers/cache, and available memory.

💻 Command Output

intermediate

What does the uptime command output?

You run uptime on a Linux system. Which of the following best describes the output?

Linux CLI

uptime

A Network connections and their states

B List of running processes with CPU and memory usage

C Current time, system uptime, number of users logged in, and load averages for 1, 5, and 15 minutes

D Disk usage statistics for mounted filesystems

💡 Hint

Think about what 'uptime' means for a system.

The uptime command shows how long the system has been running, current time, how many users are logged in, and the system load averages over 1, 5, and 15 minutes.

💻 Command Output

advanced

What does the vmstat 1 2 command output show?

You run vmstat 1 2. What does the second line of output represent?

Linux CLI

vmstat 1 2

A System performance statistics averaged over the last 1 second interval

B Initial system statistics since boot time

C Disk usage summary for the last 2 seconds

D Network packet statistics for the last 1 second

💡 Hint

The first line of vmstat output is a summary since boot, the next lines are interval samples.

The first line of vmstat output shows averages since boot. The second line shows statistics for the last 1 second interval, which is the sampling period.

❓ Troubleshoot

advanced

Why does free -m show low free memory but high available memory?

You notice free -m shows low free memory but high available memory. What is the most likely explanation?

A Linux uses free memory for cache and buffers, which can be freed when needed

B The system is running out of memory and will soon crash

C There is a memory leak in the kernel causing incorrect reporting

D The command is showing swap memory instead of RAM

💡 Hint

Think about how Linux manages memory for performance.

Linux uses free memory to cache files and buffers to speed up access. This memory is counted as used but can be freed quickly, so available memory is a better indicator of free memory.

✅ Best Practice

expert

Which command combination gives a real-time view of CPU, memory, and process info?

You want to monitor CPU usage, memory usage, and running processes in real-time on a Linux system. Which command or combination is best?

A Run <code>free -m</code> repeatedly in a loop

B Check <code>uptime</code> every minute

C Use <code>vmstat 5</code> alone without any other tool

D Use <code>top</code> command which shows CPU, memory, and process info live

💡 Hint

Think about a tool that shows multiple system stats live in one place.

The top command provides a live, interactive view of CPU usage, memory usage, and running processes, making it ideal for real-time monitoring.

Practice

1. What does the free command primarily display on a Linux system?

easy

A. System uptime and load average

B. Disk usage statistics

C. CPU temperature

D. Memory usage and availability

Solution

1. Step 1: Understand the purpose of free

   The free command shows information about the system's memory usage, including total, used, free, and available memory.

2. Step 2: Compare with other commands

   uptime shows system running time and load, vmstat shows detailed CPU and memory stats, but free focuses on memory.

3. Final Answer:

   Memory usage and availability -> Option D

4. Quick Check:

   free = Memory info [OK]

Hint: Remember: free = memory info, uptime = running time [OK]

Common Mistakes:

• Confusing free with uptime output
• Thinking free shows CPU or disk info
• Mixing vmstat details with free

2. Which of the following is the correct syntax to display memory usage in megabytes using the free command?

easy

A. free -k

B. free -m

C. free -g

D. free --bytes

Solution

1. Step 1: Identify the option for megabytes

   The -m option in free shows memory in megabytes.

2. Step 2: Check other options

   --bytes shows bytes, -g shows gigabytes, -k shows kilobytes. So -m is correct for MB.

3. Final Answer:

   free -m -> Option B

4. Quick Check:

   free -m = megabytes [OK]

Hint: Use -m for MB, -k for KB, -g for GB in free [OK]

Common Mistakes:

• Using -k expecting MB output
• Confusing --bytes with -m
• Using wrong option like -g for MB

3. What output will the command uptime produce on a system that has been running for 3 days, 4 hours, 12 minutes with load averages 0.15, 0.10, 0.05?

medium

A. 10:30:00 up 3 days, 4:12, 1 user, load average: 0.15, 0.10, 0.05

B. 3 days, 4 hours, 12 minutes uptime with load 0.15, 0.10, 0.05

C. uptime: 3d 4h 12m, load: 0.15 0.10 0.05

D. System up for 3 days 4 hours 12 minutes, load averages: 0.15 0.10 0.05

Solution

1. Step 1: Understand uptime output format

   The uptime command shows current time, system uptime in days and hours:minutes, number of users, and load averages.

2. Step 2: Match given data to output style

   The correct format includes current time, "up 3 days, 4:12", user count, and load averages separated by commas.

3. Final Answer:

   10:30:00 up 3 days, 4:12, 1 user, load average: 0.15, 0.10, 0.05 -> Option A

4. Quick Check:

   uptime shows time, up, users, load [OK]

Hint: Look for 'up' and load averages format in uptime output [OK]

Common Mistakes:

• Expecting uptime to print in verbose sentences
• Missing commas or user count in output
• Confusing uptime with other commands

4. You run vmstat 1 3 but get an error saying "command not found". What is the most likely cause?

medium

A. vmstat is not installed on the system

B. The interval must be greater than 1 second

C. The command syntax is incorrect; count must be last

D. You need to run vmstat as root user

Solution

1. Step 1: Verify vmstat syntax

   vmstat 1 3 uses correct syntax: 1-second delay, 3 samples.

2. Step 2: Analyze the error

   "command not found" means vmstat (from procps package) is not installed.

3. Final Answer:

   vmstat is not installed on the system -> Option A

4. Quick Check:

   command not found = not installed [OK]

Hint: vmstat missing? Install procps package [OK]

Common Mistakes:

• Assuming syntax error for missing command
• Thinking root needed for vmstat
• Believing interval too small

5. You want to monitor CPU and memory usage every 2 seconds for 5 samples using vmstat. Which command will correctly do this and what will be the total monitoring time?

hard

A. vmstat 2 5; total time 10 seconds

B. vmstat 5 2; total time 10 seconds

C. vmstat 2 5; total time 8 seconds

D. vmstat 5 2; total time 8 seconds

Solution

1. Step 1: Understand vmstat interval and count

   vmstat 2 5 runs vmstat every 2 seconds, 5 times total.

2. Step 2: Calculate total monitoring time

   vmstat prints the first line immediately, then 4 intervals of 2 seconds each, so total time = 2 * (5 - 1) = 8 seconds.

3. Final Answer:

   vmstat 2 5; total time 8 seconds -> Option C

4. Quick Check:

   Total time = interval * (count - 1) [OK]

Hint: Total time = interval x (count - 1) for vmstat [OK]

Common Mistakes:

• Multiplying interval by count instead of count-1
• Swapping interval and count values
• Assuming total time equals interval x count