問題文
A team wants to allow every user to drop files into a shared upload directory, but a user must not be able to delete a file that another user placed there. Which mechanism addresses this requirement?
選択肢
- Removing the write bit from the directory for all but the owner, which still lets users add files because creating a file only requires read access.
- Making the directory read-only for all users, leaving every existing file exactly as it is today.
- Setting the set-user-ID bit on the directory so that every file created inside it is owned by the directory's owner and keeps that ownership from then on.
- Setting the restricted deletion flag, also called the sticky bit, on the directory so that only the owner of a file or of the directory can remove or rename it.