What is the primary function of the 'sync' command?

The primary function of the 'sync' command is to flush file system buffers. When data is written to a file, it is often temporarily held in memory (or buffer) before being written to the disk. This buffering improves performance by reducing the number of direct write operations to the disk, which can be a slower process.

The 'sync' command forces the system to write all buffered changes to the disk. This is particularly important in scenarios where data integrity is crucial, such as before shutting down a system or unmounting a filesystem. By ensuring that all data in the buffers is written to disk, 'sync' helps prevent data loss or corruption.

Other options pertain to different functionalities that are unrelated to the purpose of 'sync'. For example, deleting unused files or stopping running processes does not relate to flushing or managing file system buffers, while synchronizing file times typically involves adjusting timestamps on files, rather than managing buffer states.