In a typical Linux system, which command is most commonly used specifically to display a summary of memory usage such as total, used, and free RAM and swap?

Introduction / Context:
System administrators and developers working on Linux often need a quick view of how much RAM and swap space is available and how much is currently in use. Several tools can reveal memory information, but some are more specialized than others. This question asks which command is specifically used to display a summary of memory usage in a simple table form, rather than focusing primarily on processes or unrelated tasks.

Given Data / Assumptions:

• We are working in a shell on a Linux or similar Unix like system.
• We want an overview of total, used, and free memory and swap.
• The command should be a standard, commonly available utility.
• We distinguish between tools that have memory columns and tools dedicated to summarizing memory.

Concept / Approach:
The free command is designed to display a concise summary of memory usage. Running free or free minus m prints tables that show total, used, and free memory, buffers, cache, and swap. The top command also shows memory information, but its main purpose is to monitor running processes. Buffer and swap as written here are not standard commands for memory display, and echo simply prints text. Therefore, free is the best match for a direct answer to the question.

Step-by-Step Solution:
Step 1: Recall that typing free on a Linux command line outputs lines labeled Mem and Swap with corresponding numeric values. Step 2: Recognize that this is exactly the information the question asks about: a summary of memory usage including total, used, and free values. Step 3: Compare free with top. While top does include memory at the top of its display, it is focused on process monitoring and is not the standard answer in many exam questions. Step 4: Check the other options and note that buffer and swap are not standard standalone commands for this purpose, and echo does not show memory statistics by default. Step 5: Conclude that option b, free, is the correct choice.

Verification / Alternative check:
On an actual Linux machine, running free minus h will show human readable memory units. You will see total, used, free, shared, buff cache, and available columns for both memory and swap. This is exactly the type of summary described in the question. Although top and related tools can also show memory information, they are not primarily memory summary commands.

Why Other Options Are Wrong:
Option a, top, is primarily a process viewer and is not as focused on a simple memory summary. Option c and option d mention commands that do not exist as generic memory tools on standard systems. Option e refers to echo, which only prints whatever text you supply; it does not automatically provide memory statistics.

Common Pitfalls:
Candidates sometimes confuse tools that incidentally display memory with tools built specifically for that purpose. They may recall that top shows memory and select it, overlooking that the standard exam answer for a dedicated memory summary is free. Remembering the association free for memory overview helps you choose correctly in such questions.

Final Answer:
The Linux command most commonly used to display a concise summary of memory usage is free, so option b is correct.