Ubuntu Manpage: rename, renameat, renameat2 - change the name or location of a file

NAME

       rename, renameat, renameat2 - change the name or location of a file

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #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)):

       renameat():
           Since glibc 2.10:
               _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_SOURCE

       renameat2():
           _GNU_SOURCE

DESCRIPTION

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.

renameat()
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()
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:

RENAME_EXCHANGE
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).

RENAME_NOREPLACE
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.

RENAME_WHITEOUT (since Linux 3.18)
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).

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set to indicate  the
       error.

ERRORS

EACCES Write permission is denied for the directory containing oldpath or newpath, or,
search permission is denied for one of the directories in the path prefix of
oldpath or newpath, or oldpath is a directory and does not allow write permission
(needed to update the .. entry). (See also path_resolution(7).)

EBUSY The rename fails because oldpath or newpath is a directory that is in use by some
process (perhaps as current working directory, or as root directory, or because it
was open for reading) or is in use by the system (for example as a mount point),
while the system considers this an error. (Note that there is no requirement to
return EBUSY in such cases—there is nothing wrong with doing the rename anyway—but
it is allowed to return EBUSY if the system cannot otherwise handle such
situations.)

EDQUOT The user's quota of disk blocks on the filesystem has been exhausted.

EFAULT oldpath or newpath points outside your accessible address space.

EINVAL The new pathname contained a path prefix of the old, or, more generally, an attempt
was made to make a directory a subdirectory of itself.

EISDIR newpath is an existing directory, but oldpath is not a directory.

ELOOP Too many symbolic links were encountered in resolving oldpath or newpath.

EMLINK oldpath already has the maximum number of links to it, or it was a directory and
the directory containing newpath has the maximum number of links.

ENAMETOOLONG
oldpath or newpath was too long.

ENOENT The link named by oldpath does not exist; or, a directory component in newpath does
not exist; or, oldpath or newpath is an empty string.

ENOMEM Insufficient kernel memory was available.

ENOSPC The device containing the file has no room for the new directory entry.

ENOTDIR
A component used as a directory in oldpath or newpath is not, in fact, a directory.
Or, oldpath is a directory, and newpath exists but is not a directory.

ENOTEMPTY or EEXIST
newpath is a nonempty directory, that is, contains entries other than "." and "..".

EPERM or EACCES
The directory containing oldpath has the sticky bit (S_ISVTX) set and the process's
effective user ID is neither the user ID of the file to be deleted nor that of the
directory containing it, and the process is not privileged (Linux: does not have
the CAP_FOWNER capability); or newpath is an existing file and the directory
containing it has the sticky bit set and the process's effective user ID is neither
the user ID of the file to be replaced nor that of the directory containing it, and
the process is not privileged (Linux: does not have the CAP_FOWNER capability); or
the filesystem containing oldpath does not support renaming of the type requested.

EROFS The file is on a read-only filesystem.

EXDEV oldpath and newpath are not on the same mounted filesystem. (Linux permits a
filesystem to be mounted at multiple points, but rename() does not work across
different mount points, even if the same filesystem is mounted on both.)

The following additional errors can occur for renameat() and renameat2():

EBADF oldpath (newpath) is relative but olddirfd (newdirfd) is not a valid file
descriptor.

ENOTDIR
oldpath is relative and olddirfd is a file descriptor referring to a file other
than a directory; or similar for newpath and newdirfd

The following additional errors can occur for renameat2():

EEXIST flags contains RENAME_NOREPLACE and newpath already exists.

EINVAL An invalid flag was specified in flags.

EINVAL Both RENAME_NOREPLACE and RENAME_EXCHANGE were specified in flags.

EINVAL Both RENAME_WHITEOUT and RENAME_EXCHANGE were specified in flags.

EINVAL The filesystem does not support one of the flags in flags.

ENOENT flags contains RENAME_EXCHANGE and newpath does not exist.

EPERM RENAME_WHITEOUT was specified in flags, but the caller does not have the CAP_MKNOD
capability.

STANDARDS

       rename()
              C11, POSIX.1-2008.

       renameat()
              POSIX.1-2008.

       renameat2()
              Linux.

HISTORY

       rename()
              4.3BSD, C89, POSIX.1-2001.

       renameat()
              Linux 2.6.16, glibc 2.4.

       renameat2()
              Linux 3.15, glibc 2.28.

   glibc notes
       On older kernels where renameat() is unavailable, the glibc wrapper function falls back to
       the  use  of  rename().  When oldpath and newpath are relative pathnames, glibc constructs
       pathnames based on the symbolic links in /proc/self/fd that correspond to the olddirfd and
       newdirfd arguments.

BUGS

       On  NFS  filesystems,  you  can  not assume that if the operation failed, the file was not
       renamed.  If the server does the rename operation and then crashes, the retransmitted  RPC
       which  will be processed when the server is up again causes a failure.  The application is
       expected to deal with this.  See link(2) for a similar problem.