RENAME(3POSIX)

🦋 RENAME(3POSIX) 🦋

okay bestie, welcome to rename(3POSIX) from the POSIX Programmer's Manual — literally the blueprint for how renaming files works on POSIX systems. sit down, grab a boba, we're doing this 💅

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🌸 PROLOG 🌸

So this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. yeah. read that twice. no cap.

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✨ NAME ✨

rename, renameat — rename file. that's it. that's the whole vibe. 🎀

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👑 SYNOPSIS 👑

#include <stdio.h>

int rename(const char *old, const char *new);

#include <fcntl.h>

int renameat(int oldfd, const char *old, int newfd,
    const char *new);

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💖 DESCRIPTION 💖

okay so, for rename(): the functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1‐2017 defers to the ISO C standard. (translation: ISO C is the main character here, we're just respecting the canon 🫶)

The rename() function shall change the name of a file. The old argument points to the pathname of the file to be renamed. The new argument points to the new pathname of the file. If the new argument does not resolve to an existing directory entry for a file of type directory and the new argument contains at least one non-<slash> character and ends with one or more trailing <slash> characters after all symbolic links have been processed, rename() shall fail. (so like, trailing slashes on a non-directory? absolutely not, it's giving error 💀)

If either the old or new argument names a symbolic link, rename() shall operate on the symbolic link itself, and shall not resolve the last component of the argument. If the old argument and the new argument resolve to either the same existing directory entry or different directory entries for the same existing file, rename() shall return successfully and perform no other action. (it's a no-op, bestie, we love a chill function ✨)

If the old argument points to the pathname of a file that is not a directory, the new argument shall not point to the pathname of a directory. If the link named by the new argument exists, it shall be removed and old renamed to new. In this case, a link named new shall remain visible to other threads throughout the renaming operation and refer either to the file referred to by new or old before the operation began. Write access permission is required for both the directory containing old and the directory containing new.

If the old argument points to the pathname of a directory, the new argument shall not point to the pathname of a file that is not a directory. If the directory named by the new argument exists, it shall be removed and old renamed to new. In this case, a link named new shall exist throughout the renaming operation and shall refer either to the directory referred to by new or old before the operation began. If new names an existing directory, it shall be required to be an empty directory. (empty. i said what i said. no leftovers 🚫)

If either pathname argument refers to a path whose final component is either dot or dot-dot, rename() shall fail. like literally rename("a", ".")? nope. not happening. 🙈

If the old argument points to a pathname of a symbolic link, the symbolic link shall be renamed. If the new argument points to a pathname of a symbolic link, the symbolic link shall be removed.

The old pathname shall not name an ancestor directory of the new pathname. Write access permission is required for the directory containing old and the directory containing new. If the old argument points to the pathname of a directory, write access permission may be required for the directory named by old, and, if it exists, the directory named by new.

If the link named by the new argument exists and the file's link count becomes 0 when it is removed and no process has the file open, the space occupied by the file shall be freed and the file shall no longer be accessible. If one or more processes have the file open when the last link is removed, the link shall be removed before rename() returns, but the removal of the file contents shall be postponed until all references to the file are closed. (the classic "it's gone but actually not gone" energy 😭)

Upon successful completion, rename() shall mark for update the last data modification and last file status change timestamps of the parent directory of each file.

If the rename() function fails for any reason other than [EIO], any file named by new shall be unaffected. 🫶

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🌈 the renameat() era 🌈

The renameat() function shall be equivalent to the rename() function except in the case where either old or new specifies a relative path. If old is a relative path, the file to be renamed is located relative to the directory associated with the file descriptor oldfd instead of the current working directory. If new is a relative path, the same happens only relative to the directory associated with newfd. If the access mode of the open file description associated with the file descriptor is not O_SEARCH, the function shall check whether directory searches are permitted using the current permissions of the directory underlying the file descriptor. If the access mode is O_SEARCH, the function shall not perform the check. (she checks the vibes, but only when she has to 💅)

If renameat() is passed the special value AT_FDCWD in the oldfd or newfd parameter, the current working directory shall be used in the determination of the file for the respective path parameter. iconic behavior honestly.

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⭐ RETURN VALUE ⭐

Upon successful completion, the rename() function shall return 0. Otherwise, it shall return -1, errno shall be set to indicate the error, and neither the file named by old nor the file named by new shall be changed or created. (so if it flops, it flops cleanly — no half-done mess 🧚)

Upon successful completion, the renameat() function shall return 0. Otherwise, it shall return -1 and set errno to indicate the error.

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🔥 ERRORS 🔥

The rename() and renameat() functions shall fail if:

• EACCES — A component of either path prefix denies search permission; or one of the directories containing old or new denies write permissions; or, write permission is required and is denied for a directory pointed to by the old or new arguments.
• EBUSY — The directory named by old or new is currently in use by the system or another process, and the implementation considers this an error.
• [EEXIST] or [ENOTEMPTY] — The link named by new is a directory that is not an empty directory.
• EINVAL — The old pathname names an ancestor directory of the new pathname, or either pathname argument contains a final component that is dot or dot-dot.
• EIO — A physical I/O error has occurred.
• EISDIR — The new argument points to a directory and the old argument points to a file that is not a directory.
• ELOOP — A loop exists in symbolic links encountered during resolution of the path argument.
• EMLINK — The file named by old is a directory, and the link count of the parent directory of new would exceed {LINK_MAX}.
• ENAMETOOLONG — The length of a component of a pathname is longer than {NAME_MAX}.
• ENOENT — The link named by old does not name an existing file, a component of the path prefix of new does not exist, or either old or new points to an empty string.
• ENOSPC — The directory that would contain new cannot be extended.
• ENOTDIR — A component of either path prefix names an existing file that is neither a directory nor a symbolic link to a directory; or the old argument names a directory and the new argument names a non-directory file; or the old argument contains at least one non-<slash> character and ends with one or more trailing <slash> characters and the last pathname component names an existing file that is neither a directory nor a symbolic link to a directory; or the old argument names an existing non-directory file and the new argument names a nonexistent file, contains at least one non-<slash> character, and ends with one or more trailing <slash> characters; or the new argument names an existing non-directory file, contains at least one non-<slash> character, and ends with one or more trailing <slash> characters.
• EPERM or EACCES — The S_ISVTX flag is set on the directory containing the file referred to by old and the process does not satisfy the criteria specified in the Base Definitions volume of POSIX.1‐2017, Section 4.3, Directory Protection with respect to old; or new refers to an existing file, the S_ISVTX flag is set on the directory containing this file, and the process does not satisfy the criteria specified in the Base Definitions volume of POSIX.1‐2017, Section 4.3, Directory Protection with respect to this file.
• EROFS — The requested operation requires writing in a directory on a read-only file system.
• EXDEV — The links named by new and old are on different file systems and the implementation does not support links between file systems.

💜 In addition, the renameat() function shall fail if:

• EACCES — The access mode of the open file description associated with oldfd or newfd is not O_SEARCH and the permissions of the directory underlying oldfd or newfd, respectively, do not permit directory searches.
• EBADF — The old argument does not specify an absolute path and the oldfd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching, or the new argument does not specify an absolute path and the newfd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching.
• ENOTDIR — The old or new argument is not an absolute path and oldfd or newfd, respectively, is a file descriptor associated with a non-directory file.

🌸 The rename() and renameat() functions may fail if:

• EBUSY — The file named by the old or new arguments is a named STREAM.
• ELOOP — More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
• ENAMETOOLONG — The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.
• ETXTBSY — The file named by new exists and is the last directory entry to a pure procedure (shared text) file that is being executed.

ok the following sections are informative. just so you know. 👀

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🎀 EXAMPLES 🎀

🌟 Renaming a File

The following example shows how to rename a file named /home/cnd/mod1 to /home/cnd/mod2. literally so simple bestie:

#include <stdio.h>

int status;
...
status = rename("/home/cnd/mod1", "/home/cnd/mod2");

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girl, we're not done — more of this page is coming in part 2, so stay tuned 💖

🌸 APPLICATION USAGE 🌸

Okay bestie, here's the tea on timestamps, and it's giving chaos:

Some implementations mark for update the last file status change timestamp of renamed files, and some literally do not. So if your app is out here relying on that timestamp? It may behave differently with respect to renamed files unless it's designed to allow for either behavior. Design accordingly, or perish 💀

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💅 RATIONALE 💅

This rename() function is equivalent for regular files to the one defined by the ISO C standard, periodt. Its inclusion here expands that definition to include actions on directories, and it specifies behavior when the new parameter names a file that already exists. And that specification? It requires that the action of the function be atomic. No half-renames, no messy in-between states. Iconic behavior only ✨

One of the reasons for introducing this function was to have a means of renaming directories while permitting implementations to prohibit the use of link() and unlink() with directories, thus constraining links to directories to those made by mkdir(). Very demure, very mindful of the filesystem 🎀

The specification that if old and new refer to the same file is intended to guarantee that:

rename("x", "x");

does not remove the file. So like, renaming something to itself is a no-op, not self-destruction. We love a safe vibe check 🫶

Renaming dot or dot-dot is prohibited in order to prevent cyclical file system paths. Yeah. That's the whole reason. Do not come for . or .., they are booked and busy 🔥

See also the descriptions of [ENOTEMPTY] and [ENAMETOOLONG] in rmdir() and [EBUSY] in unlink(). For a discussion of [EXDEV], see link(). Cross-referencing queen 👑

The purpose of the renameat() function is to rename files in directories other than the current working directory without exposure to race conditions. Any part of the path of a file could be changed in parallel to a call to rename(), resulting in unspecified behavior. By opening file descriptors for the source and target directories and using the renameat() function, it can be guaranteed that that renamed file is located correctly and the resulting file is in the desired directory. It's giving atomic and unbothered 💅

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🦋 FUTURE DIRECTIONS 🦋

None.

That's it. Nothing. Nada. The future is a blank canvas, bestie 🌈

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🌟 SEE ALSO 🌟

• link()
• rmdir()
• symlink()
• unlink()

The Base Definitions volume of POSIX.1‐2017, Section 4.3, Directory Protection, <fcntl.h>, <stdio.h>

Go read those, fr fr. They're the supporting cast and they ate 📚✨

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👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

Important: if anything in this cute lil rewrite looks sus compared to the real Standard, the original IEEE and The Open Group Standard wins. It's the referee, this is just the commentary booth 🎤

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And that's the whole page, bestie!! 🎀 This one came from IEEE/The Open Group, dated 2017, and it lives under the name RENAME(3POSIX) — go forth and rename responsibly, you absolute Unix icon 💖🦋✨