unlink

Unlink is a function and system call used to remove a directory entry that names a file in Unix-like and other operating systems. In POSIX systems, the unlink operation removes a link to a file as identified by a pathname. If this was the last link to the file and no process has the file open, the filesystem frees the associated inode and data blocks; otherwise the storage remains allocated until all references are closed.

When a file has multiple hard links, unlink only removes one link entry. The file continues to exist under any remaining links. If the pathname refers to a symbolic link, unlink deletes the link itself, not the target file. Directories are generally not unlinkable; attempting to unlink a directory typically fails, and directory removal is performed with rmdir (or appropriate variants on certain systems).

Platform and language variations exist. In POSIX, unlink is declared in unistd.h and returns zero on success or -1 on error with errno set. Some environments provide unlinkat to unlink using a directory file descriptor. In high-level languages or frameworks, similar concepts may be exposed under names like remove, delete, or unlink, with behavior that often mirrors the underlying system call.

Common failure modes include non-existent paths (ENOENT), permission issues (EACCES or EPERM), attempts to unlink directories (EISDIR), and attempts to unlink files that are in use or locked in certain contexts. Understanding unlink’s semantics is important for correct file lifecycle management, particularly in applications that create, rename, or manage temporary files.