rename, renameat, renameat2 - change the name or location of a file
#include <stdio.h>
int rename(const char *oldpath, const char *newpath);
#include <fcntl.h> /* Definition of AT_* constants */
#include <stdio.h>
int renameat(int olddirfd, const char *oldpath,
int newdirfd, const char *newpath);
int renameat2(int olddirfd, const char *oldpath,
int newdirfd, const char *newpath, unsigned int flags);Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
rename() renames a file, moving it between
directories if required. Any other hard links to the file (as created
using link(2)) are unaffected. Open file descriptors
for oldpath are also unaffected.
Various restrictions determine whether or not the rename operation succeeds: see ERRORS below.
If newpath already exists, it will be atomically replaced,
so that there is no point at which another process attempting to access
newpath will find it missing. However, there will probably be a
window in which both oldpath and newpath refer to the
file being renamed.
If oldpath and newpath are existing hard links
referring to the same file, then rename() does nothing,
and returns a success status.
If newpath exists but the operation fails for some reason,
rename() guarantees to leave an instance of
newpath in place.
oldpath can specify a directory. In this case,
newpath must either not exist, or it must specify an empty
directory.
If oldpath refers to a symbolic link, the link is renamed;
if newpath refers to a symbolic link, the link will be
overwritten.
The renameat() system call operates in exactly the same way as rename(), except for the differences described here.
If the pathname given in oldpath is relative, then it is
interpreted relative to the directory referred to by the file descriptor
olddirfd (rather than relative to the current working directory
of the calling process, as is done by rename() for a
relative pathname).
If oldpath is relative and olddirfd is the special
value AT_FDCWD, then oldpath is interpreted
relative to the current working directory of the calling process (like
rename()).
If oldpath is absolute, then olddirfd is
ignored.
The interpretation of newpath is as for oldpath,
except that a relative pathname is interpreted relative to the directory
referred to by the file descriptor newdirfd.
See openat(2) for an explanation of the need for renameat().
renameat2() has an additional flags
argument. A renameat2() call with a zero flags
argument is equivalent to renameat().
The flags argument is a bit mask consisting of zero or more
of the following flags:
Atomically exchange oldpath and newpath. Both
pathnames must exist but may be of different types (e.g., one could be a
non-empty directory and the other a symbolic link).
Don't overwrite newpath of the rename. Return an error if
newpath already exists.
RENAME_NOREPLACE can't be employed together with RENAME_EXCHANGE.
RENAME_NOREPLACE requires support from the underlying filesystem. Support for various filesystems was added as follows:
ext4 (Linux 3.15);
btrfs, tmpfs, and cifs (Linux 3.17);
xfs (Linux 4.0);
Support for many other filesystems was added in Linux 4.9, including ext2, minix, reiserfs, jfs, vfat, and bpf.
This operation makes sense only for overlay/union filesystem implementations.
Specifying RENAME_WHITEOUT creates a "whiteout" object at the source of the rename at the same time as performing the rename. The whole operation is atomic, so that if the rename succeeds then the whiteout will also have been created.
A "whiteout" is an object that has special meaning in union/overlay filesystem constructs. In these constructs, multiple layers exist and only the top one is ever modified. A whiteout on an upper layer will effectively hide a matching file in the lower layer, making it appear as if the file didn't exist.
When a file that exists on the lower layer is renamed, the file is first copied up (if not already on the upper layer) and then renamed on the upper, read-write layer. At the same time, the source file needs to be "whiteouted" (so that the version of the source file in the lower layer is rendered invisible). The whole operation needs to be done atomically.
When not part of a union/overlay, the whiteout appears as a character device with a {0,0} device number. (Note that other union/overlay implementations may employ different methods for storing whiteout entries; specifically, BSD union mount employs a separate inode type, DT_WHT, which, while supported by some filesystems available in Linux, such as CODA and XFS, is ignored by the kernel's whiteout support code, as of Linux 4.19, at least.)
RENAME_WHITEOUT requires the same privileges as creating a device node (i.e., the CAP_MKNOD capability).
RENAME_WHITEOUT can't be employed together with RENAME_EXCHANGE.
RENAME_WHITEOUT requires support from the underlying filesystem. Among the filesystems that support it are tmpfs (since Linux 3.18), ext4 (since Linux 3.18), XFS (since Linux 4.1), f2fs (since Linux 4.2), btrfs (since Linux 4.7), and ubifs (since Linux 4.9).
On success, zero is returned. On error, -1 is returned, and
errno is set to indicate the error.