Which command is used to change the group owner of a file?

The command used to change the group owner of a file is 'chgrp'. This command specifically targets the group ownership aspect of a file or directory, allowing the user to change the group associated with the specified file or directory to a different group.

For example, if you wanted to change the group ownership of a file named "example.txt" to a group named "developers", you would use the command chgrp developers example.txt. This command is straightforward and is designed exclusively for this purpose, making it the most appropriate choice for changing the group owner.

While 'chown' is also related to file ownership, it is used to change both the user owner and the group owner of a file. 'chmod' is utilized for changing the file permissions, and 'setfacl' is relevant for setting Access Control Lists, which provide more granular permissions than traditional Unix file permissions. Therefore, 'chgrp' is specifically the correct tool for changing the group owner.