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

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:
               _XOPEN_SOURCE >= 700 || _POSIX_C_SOURCE >= 200809L
           Before glibc 2.10:
               _ATFILE_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.

If newpath already exists, it will be atomically replaced (subject to a few conditions; see ERRORS
below), so that there is no point at which another process attempting to access newpath will find it
missing.

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.

However, when overwriting there will probably be a window in which both oldpath and newpath refer to the
file being renamed.

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_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.

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
provide that support are shmem (since Linux 3.18), ext4 (since Linux 3.18), and XFS (since Linux
4.1).

RETURN VALUE

       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

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 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 pathname 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 olddirfd or 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.

VERSIONS

       renameat() was added to Linux in kernel 2.6.16; library support was added to glibc in version 2.4.

       renameat2() was added to Linux in kernel 3.15.

CONFORMING TO

       rename(): 4.3BSD, C89, C99, POSIX.1-2001, POSIX.1-2008.

       renameat(): POSIX.1-2008.

       renameat2() is Linux-specific.

NOTES

   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.

COLOPHON

       This page is part of release 4.04 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       http://www.kernel.org/doc/man-pages/.