System resource monitoring (free, uptime, vmstat) in Linux CLI - Step-by-Step Execution

Concept Flow - System resource monitoring (free, uptime, vmstat)

Run 'free' command

↓

Display memory usage

↓

Run 'uptime' command

↓

Show system uptime and load

↓

Run 'vmstat' command

↓

Show CPU, memory, IO stats

↓

End of monitoring snapshot

The flow shows running three commands one after another to get memory, uptime, and system stats snapshots.

Execution Sample

Linux CLI

free
uptime
vmstat 1 2

Runs free to show memory, uptime for system time/load, vmstat for CPU/memory stats twice with 1 second interval.

Execution Table

Step	Command	Output Summary	Details
1	free	Shows total, used, free memory and swap	Mem: total=8000MB, used=3000MB, free=5000MB; Swap: total=2000MB, used=0MB, free=2000MB
2	uptime	Shows system uptime and load averages	Uptime=5 days 3:20, Load averages=0.15, 0.10, 0.05
3	vmstat 1 2 (first)	First vmstat snapshot	r=1, b=0, swpd=0, free=5000, buff=200, cache=1000, si=0, so=0, bi=10, bo=5, in=100, cs=200, us=5, sy=3, id=90, wa=2, st=0
4	vmstat 1 2 (second)	Second vmstat snapshot after 1 second	r=0, b=0, swpd=0, free=4800, buff=250, cache=1100, si=0, so=0, bi=5, bo=3, in=90, cs=180, us=3, sy=2, id=95, wa=0, st=0
5	End	Monitoring snapshot complete	All commands executed, system stats captured

💡 All commands completed, system resource snapshot taken

Variable Tracker

Variable	Start	After free	After uptime	After vmstat 1	After vmstat 2	Final
Memory Used (MB)	unknown	3000	3000	3000	3000	3000
Memory Free (MB)	unknown	5000	5000	5000	4800	4800
System Uptime	unknown	unknown	5 days 3:20	5 days 3:20	5 days 3:20	5 days 3:20
CPU Usage User (%)	unknown	unknown	unknown	5	3	3
CPU Idle (%)	unknown	unknown	unknown	90	95	95

Key Moments - 3 Insights

Why does vmstat show two sets of data when we run 'vmstat 1 2'?

The first vmstat output shows stats since last reboot, the second is the real snapshot after 1 second interval (see rows 3 and 4 in execution_table).

What does the 'load average' in uptime mean?

Load average shows average system demand over 1, 5, and 15 minutes, indicating how busy the CPU is (see row 2 in execution_table).

Why is free memory different between free and vmstat outputs?

free shows memory including buffers/cache, vmstat separates free memory and buffers/cache (see variable_tracker Memory Free values).

Visual Quiz - 3 Questions

Look at the execution_table row 2, what is the system uptime shown by 'uptime'?

A 5 hours 3 minutes

B 5 days 3:20

C 3 days 5:20

D Unknown

💡 Hint

Check the 'Output Summary' and 'Details' columns in execution_table row 2.

At which vmstat snapshot does CPU idle percentage increase?

A Second snapshot

B First snapshot

C Both snapshots are equal

D CPU idle is not shown

💡 Hint

Compare 'CPU Idle (%)' in variable_tracker after vmstat 1 and vmstat 2.

If the system had more swap used, which command output would show it clearly?

A vmstat

B uptime

C free

D None of these

💡 Hint

Look at the 'free' command output in execution_table row 1 showing swap usage.

Concept Snapshot

System resource monitoring uses commands:
- free: shows memory and swap usage
- uptime: shows system running time and load averages
- vmstat: shows CPU, memory, IO stats in intervals
Run them sequentially for a snapshot of system health.

Full Transcript

This visual execution shows how to monitor system resources on Linux using three commands: free, uptime, and vmstat. First, 'free' displays memory and swap usage, telling how much RAM is used and free. Next, 'uptime' shows how long the system has been running and the load averages, which indicate CPU demand. Finally, 'vmstat' gives detailed CPU, memory, and IO statistics, showing two snapshots with a 1-second gap. The execution table traces each command's output step-by-step, and the variable tracker follows key values like memory used, free memory, uptime, and CPU usage. Key moments clarify common confusions like why vmstat shows two outputs and what load averages mean. The quiz tests understanding by asking about uptime, CPU idle changes, and swap usage visibility. This helps beginners see how these commands work together to give a clear picture of system health.

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