FHLINK(2)

📦 version 15.1, in freebsd 14.5, freebsd 15.1

okay so bestie, this is a System Calls Manual page for fhlink and fhlinkat — the make a hard file link duo. yes, it's giving "niche but iconic." let's get into it 🎀

✨ NAME ✨

fhlink, fhlinkat — make a hard file link. that's the whole vibe. 🫶

📚 LIBRARY 📚

Standard C Library (libc, -lc). the classics, always.

🌸 SYNOPSIS 🌸

#include <unistd.h>

int
fhlink(fhandle_t *fhp, const char *to);

int
fhlinkat(fhandle_t *fhp, int tofd, const char *to);

look at those signatures. impeccable. no notes. 💅

💫 DESCRIPTION 💫

so the fhlink() system call atomically creates the specified directory entry (hard link) to with the attributes of the underlying object pointed at by fhp. like, it's one clean motion — no half-links, no messy in-betweens. we love atomic behavior 💖

if the link is successful:

  • the link count of the underlying object is incremented ✨
  • fhp and to share equal access and rights to the underlying object 🤝

and if fhp is removed? important: the file to is not deleted, and the link count of the underlying object is decremented. so don't panic. it's fine. it's fine. 😌

the object pointed at by the fhp argument must exist for the hard link to succeed, and both fhp and to must be in the same file system. also fhp may not be a directory. sorry directory girlies, not today 🙈

fhlinkat() is equivalent to fhlink except in the case where to is a relative path. in that case, a relative path to is interpreted relative to the directory associated with the file descriptor tofd instead of the current working directory. it's giving "context-aware" 💫

if fhlinkat() is passed the special value AT_FDCWD in the tofd parameter, the current working directory is used for the to argument. and if tofd has value AT_FDCWD, the behavior is identical to a call to link(). unless flag contains the AT_SYMLINK_FOLLOW flag, if fhp names a symbolic link, a new link is created for the symbolic link fhp and not its target. no cap. 🔥

🌈 RETURN VALUES 🌈

the link() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. the classic 0-or-meltdown situation. 😭

💀 ERRORS 💀

the fhlink() system call will fail and no link will be created if:

  • [ENOTDIR] — a component of to prefix is not a directory.
  • [ENAMETOOLONG] — a component of to exceeded 255 characters, or entire length of to name exceeded 1023 characters. like bestie that's so long 🫠
  • [ENOENT] — a component of to prefix does not exist.
  • [EOPNOTSUPP] — the file system containing the file pointed at by fhp does not support links. rude honestly.
  • [EMLINK] — the link count of the file pointed at by fhp would exceed 32767. that's a lot of links but okay.
  • [EACCES] — a component of to prefix denies search permission.
  • [EACCES] — the requested link requires writing in a directory with a mode that denies write permission.
  • [ELOOP] — too many symbolic links were encountered in translating one of the pathnames. it's loops all the way down 😵‍💫
  • [ENOENT] — the file pointed at by fhp does not exist.
  • [EEXIST] — the link named by to does exist. already taken, babe.
  • [EPERM] — the file pointed at by fhp is a directory.
  • [EPERM] — the file pointed at by fhp has its immutable or append-only flag set, see the chflags(2) manual page for more information.
  • [EPERM] — the parent directory of the file named by to has its immutable flag set.
  • [EXDEV] — the link named by to and the file pointed at by fhp are on different file systems. long distance relationship = not happening 💔
  • [ENOSPC] — the directory in which the entry for the new link is being placed cannot be extended because there is no space left on the file system containing the directory.
  • [EDQUOT] — the directory in which the entry for the new link is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted.
  • [EIO] — an I/O error occurred while reading from or writing to the file system to make the directory entry.
  • [EINTEGRITY] — corrupted data was detected while reading from the file system. 🚨
  • [EROFS] — the requested link requires writing in a directory on a read-only file system.
  • [EFAULT] — one of the pathnames specified is outside the process's allocated address space.
  • [ESTALE] — the file handle fhp is no longer valid.

in addition to the errors returned by the fhlink(), the fhlinkat() system call may fail if:

  • [EBADF] — the fhp or to argument does not specify an absolute path and the tofd argument, is not AT_FDCWD nor a valid file descriptor open for searching.
  • [EINVAL] — the value of the flag argument is not valid.
  • [ENOTDIR] — the fhp or to argument is not an absolute path and tofd is not AT_FDCWD nor a file descriptor associated with a directory.
lowkey the error list is long but honestly these all just mean "the link did not happen, here's why." read the bracket, fix the thing, try again. you got this 💪

🦋 SEE ALSO 🦋

the whole file-handle friend group. go say hi 👋

👑 HISTORY 👑

the fhlink() and fhlinkat() system calls first appeared in FreeBSD 12.1. vintage-ish. we stan a documented origin story ✨

and that's the page!! mwah 💋 this edition was brought to you by Debian, dated November 30, 2022, filed under FHLINK(2) — go create some hard links responsibly, bestie 🍓💜

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