An inode can be safely deleted when its link count reaches zero, ensuring no file system entries refer to it and it is not in use by any processes, allowing the system to reclaim its space.
An inode on a filesystem refers to a data structure that stores information about a file except its name or its actual data. In a Unix-like operating system, an inode can be safely deleted when there are no links (either hard links or directory entries) pointing to it. When the inode's link count drops to zero, which indicates that no file system entries (such as filenames) refer to it, the inode and the disk space it refers to are freed and can be reused by the system.
The system will typically handle this process automatically when the last reference to the file is removed, such as when the rm command is used to delete a file, and all file descriptors that had the file open are closed.
So, an inode can be deleted safely when the link count is zero and there are no processes holding the file open. This ensures that the file is not in use, and its allocation can be reclaimed without causing file system inconsistencies or data loss.