UNLINK(2)

💅 UNLINK(2) — remove directory entry

okay so bestie, you've stumbled into the unlink(2) manual page from the System Calls Manual, section 2 (the system-call girlies) 🎀 stay a while, this one's actually so useful.

---

✨ NAME ✨

unlink, unlinkat, funlinkat — remove directory entry 🗑️✨

📚 LIBRARY 📚

Standard C Library (libc, -lc) — yeah she's built in, no cap.

🧚 SYNOPSIS 🧚

#include <unistd.h>

int
unlink(const char *path);

int
unlinkat(int dfd, const char *path, int flag);

int
funlinkat(int dfd, const char *path, int fd, int flag);

---

💖 DESCRIPTION 💖

unlink() — the main character 🫶

The unlink() system call removes the link named by path from its directory and decrements the link count of the file which was referenced by the link. literally decrementing her link count, iconic.

If that decrement reduces the link count of the file to zero, and no process has the file open, then all resources associated with the file are reclaimed 🔥 the file is gone gone.

If one or more process have the file open when the last link is removed, the link is removed, but the removal of the file is delayed until all references to it have been closed 😴 she's just chilling until everyone's done with her.

⚠️ the path argument may not be a directory. do not try it. she said no.

unlinkat() — the deluxe version ✨

The unlinkat() system call is equivalent to unlink() or rmdir() except in the case where path specifies a relative path 🙈 in that case, the directory entry to be removed is determined relative to the directory associated with the file descriptor dfd instead of the current working directory. so instead of "wherever I'm standing rn" it's "wherever dfd is pointing" 💅

The values for flag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h> 🎀

• AT_REMOVEDIR — Remove the directory entry specified by fd and path as a directory, not a normal file. she's a directory girlie now.
• AT_RESOLVE_BENEATH — Only walk paths below the directory specified by the fd descriptor. See the description of the O_RESOLVE_BENEATH flag in the open(2) manual page. no climbing out the window 🚪✨

If unlinkat() is passed the special value AT_FDCWD in the fd parameter, the current working directory is used and the behavior is identical to a call to unlink or rmdir respectively, depending on whether or not the AT_REMOVEDIR bit is set in flag. cute little shortcut 🫶

funlinkat() — the paranoid baddie 👑

The funlinkat() system call can be used to unlink an already-opened file, unless that file has been replaced since it was opened 😤 it's equivalent to unlinkat() in the case where path is already open as the file descriptor fd. Otherwise, the path will not be removed and an error will be returned — no sneaky swaps on her watch, periodt.

The fd can be set the FD_NONE. In that case funlinkat() behaves exactly like unlinkat() 🌈 lowkey just a flex flag at that point.

---

🦋 RETURN VALUES 🦋

The unlink() function returns the value 0 if successful 🎉 otherwise the value -1 is returned and the global variable errno is set to indicate the error 💀 classic.

---

💀 ERRORS 💀

The unlink() succeeds unless:

• [ENOTDIR] — A component of the path prefix is not a directory.
• [EISDIR] — The named file is a directory. ma'am that's a folder.
• [ENAMETOOLONG] — A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters. girl why is your filename a novel 😭
• [ENOENT] — The named file does not exist. nothing there bestie.
• [EACCES] — Search permission is denied for a component of the path prefix.
• [EACCES] — Write permission is denied on the directory containing the link to be removed.
• [ELOOP] — Too many symbolic links were encountered in translating the pathname. 🌀 it's loops all the way down.
• [EPERM] — The named file is a directory.
• [EPERM] — The named file has its immutable, undeletable or append-only flag set, see the chflags(2) manual page for more information. locked down 🔒
• [EPERM] — The parent directory of the named file has its immutable or append-only flag set.
• [EPERM] — The directory containing the file is marked sticky, and neither the containing directory nor the file to be removed are owned by the effective user ID. sticky situation, truly.
• [EIO] — An I/O error occurred while deleting the directory entry or deallocating the inode.
• [EINTEGRITY] — Corrupted data was detected while reading from the file system. 🫠
• [EROFS] — The named file resides on a read-only file system. she's frozen, can't touch her.
• [EFAULT] — The path argument points outside the process's allocated address space.
• [ENOSPC] — On file systems supporting copy-on-write or snapshots, there was not enough free space to record metadata for the delete operation of the file. yes even deleting can run out of space, I know 😭

In addition to the errors returned by the unlink(), the unlinkat() may fail if:

• [EBADF] — The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for searching.
• [ENOTEMPTY] — The flag parameter has the AT_REMOVEDIR bit set and the path argument names a directory that is not an empty directory, or there are hard links to the directory other than dot or a single entry in dot-dot. clean your room first 🧹
• [ENOTDIR] — The flag parameter has the AT_REMOVEDIR bit set and path does not name a directory.
• [EINVAL] — The value of the flag argument is not valid.
• [ENOTDIR] — The path argument is not an absolute path and fd is neither AT_FDCWD nor a file descriptor associated with a directory.
• [ENOTCAPABLE] — path is an absolute path, or contained a ".." component leading to a directory outside of the directory hierarchy specified by fd, and the process is in capability mode or the AT_RESOLVE_BENEATH flag was specified. 🚫 no escaping the sandbox, bestie.

In addition to the errors returned by unlinkat(), funlinkat() may fail if:

• [EDEADLK] — The file descriptor is not associated with the path. 👻 she doesn't know that file.

---

🌸 SEE ALSO 🌸

chflags(2), close(2), link(2), rmdir(2), symlink(7) — go read the whole friend group, iykyk 💜

⭐ STANDARDS ⭐

The unlinkat() system call follows The Open Group Extended API Set 2 specification. certified, standardized, slay 💅

👑 HISTORY 👑

• The unlink() function appeared in Version 1 AT&T UNIX 🦕 the OG.
• The unlinkat() system call appeared in FreeBSD 8.0.
• The funlinkat() system call appeared in FreeBSD 13.0 ✨ the newest baby.

The unlink() system call traditionally allows the super-user to unlink directories which can damage the file system integrity. This implementation no longer permits it. 🚨 like fr fr do not do that, that was a whole era of chaos and we're not going back.

---

🎀 and that's the whole page, bestie — unlink(2), straight from the Debian build dated February 23, 2021. go delete things responsibly, mwah 💖🦋