What methods can be used to estimate memory usage in the Linux operating system?

In Linux, several tools can be used to estimate memory usage:

• free — shows total, used, and free memory.
• top or htop — display real-time memory usage by processes.
• vmstat — provides virtual memory statistics.
• Viewing the contents of /proc/meminfo — detailed memory information.

For example, the command free -h will display information in a human-readable format:

free -h