What command is used to check the memory usage of a system?

The command that is used to check the memory usage of a system is indeed "free." This command provides a quick overview of the system's memory status, including total memory, used memory, free memory, shared memory, buffer/cache, and available memory. By default, it displays these values in kilobytes, making it easy to see how much memory is currently in use and what is available for new applications.

The command presents valuable information for system monitoring and resource management. When executed, "free" gives a snapshot view that helps administrators understand the current memory load and make decisions regarding applications or processes to run or potentially terminate.

This command is typically preferred for a straightforward memory check and is faster and simpler than other options, which may provide a more detailed and complex view of system performance. For instance, while "top" offers real-time updates of running processes, including their memory usage, it can be more overwhelming for those just looking for a quick memory check. "df" is used specifically for checking disk space rather than memory, and "memstat" is not a standard command in Linux, which could lead to confusion.