What does the command mount --bind do?

The command mount --bind is used to make the contents of one directory available in another directory within the filesystem. This means that any files or subdirectories within the source directory can be accessed from the target directory as if they were located there. This is particularly useful for creating alternative views of a filesystem or for making certain directories available at specific locations without duplicating data.

For example, if you have a directory /source/dir and you execute mount --bind /source/dir /target/dir, then accessing /target/dir will show the same files and directories as /source/dir. This functionality is commonly employed in scenarios involving containerization, chroot environments, or when setting up specific user permissions for a certain set of files.

The other options do not accurately describe the purpose of the --bind option in the mount command, focusing instead on broader or different functionalities that do not convey the specific operation of making a source directory viewable from a target directory.