How to use the command 'free' (with examples)

The ‘free’ command is used to display the amount of free and used memory in the system. It provides information about the memory allocation and usage in various units. This command is useful for monitoring system memory and identifying any potential memory issues.

Use case 1: Display system memory

Code:

free

Motivation: This use case is helpful when you want to quickly check the overall memory usage of your system. By running the ‘free’ command without any arguments, you will get a summary of the total memory, used memory, free memory, shared memory, and buffers/cache.

Explanation: Running the ‘free’ command without any arguments provides a summary of the system memory. It shows the total memory available, the memory used by the system, the free memory, the shared memory, and the memory used for buffers and cache.

Example output:

             total       used       free     shared    buffers     cache
Mem:       8192000    2526000    5666000      53000     270000    1294000
-/+ buffers/cache:     961000    7231000
Swap:            0          0          0

Use case 2: Display memory in Bytes/KB/MB/GB

Code:

free -b

or

free -k

or

free -m

or

free -g

Motivation: In certain scenarios, it may be important to view the memory usage in specific units, such as Bytes, Kilobytes, Megabytes, or Gigabytes. Displaying the memory in different units allows for a better understanding of the memory allocation and usage.

Explanation: The ‘-b’ option shows the memory utilization in Bytes, ‘-k’ shows it in Kilobytes, ‘-m’ in Megabytes, and ‘-g’ in Gigabytes. By specifying the desired unit, the output of the ‘free’ command will be displayed accordingly.

Example output:

             total       used       free     shared    buffers     cache
Mem:    8388608000  2573519360  5815088640   62617600  282066688  1357298176
-/+ buffers/cache:  933153496  7455454504
Swap:    2147483648          0  2147483648

Use case 3: Display memory in human-readable units

Code:

free -h

Motivation: The ‘-h’ option makes the ‘free’ command output more human-readable by automatically choosing suitable units (e.g., Gigabytes, Megabytes, etc.) based on the memory size.

Explanation: By using the ‘-h’ option, the ‘free’ command automatically selects the most appropriate unit (e.g., G, M) based on the memory size. This makes the output easier to read and understand.

Example output:

             total       used       free     shared    buffers     cache
Mem:           7.9G       2.4G       5.5G       161M       271M       1.3G
-/+ buffers/cache:       900M       6.9G
Swap:            0B         0B         0B

Use case 4: Refresh the output every 2 seconds

Code:

free -s 2

Motivation: In some situations, you might need to monitor the memory usage in real-time. The ‘-s’ option allows you to refresh the output at a specified interval, enabling you to observe any changes in memory usage over time.

Explanation: By using the ‘-s’ option, followed by the interval in seconds, the ‘free’ command updates the memory usage output at the specified frequency. This allows you to continuously monitor the memory utilization and detect any fluctuations.

Example output:

             total       used       free     shared    buffers     cache
Mem:       8192000    2526316    5665684      53000     270000    1294032
-/+ buffers/cache:     961284    7230716
Swap:            0          0          0

             total       used       free     shared    buffers     cache
Mem:       8192000    2523804    5668196      53000     270020    1293692
-/+ buffers/cache:     959092    7232908
Swap:            0          0          0

Conclusion:

The ‘free’ command is a powerful tool for monitoring system memory usage. By using different options, you can customize the output to suit your needs, such as displaying memory in specific units or refreshing the output at regular intervals. Understanding memory allocation and utilization is crucial for maintaining optimal system performance.