.\"	$NetBSD: rename.2,v 1.19 2003/04/16 13:34:55 wiz Exp $
.\"
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.\"     @(#)rename.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt RENAME 2
.Os
.Sh NAME
.Nm rename
.Nd change the name of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdio.h
.Ft int
.Fn rename "const char *from" "const char *to"
.Sh DESCRIPTION
.Fn rename
causes the link named
.Fa from
to be renamed as
.Fa to .
If
.Fa to
exists, it is first removed.
Both
.Fa from
and
.Fa to
must be of the same type (that is, both directories or both
non-directories), and must reside on the same file system.
.Pp
.Fn rename
guarantees that an instance of
.Fa to
will always exist, even if the system should crash in
the middle of the operation.
.Pp
If the final component of
.Fa from
is a symbolic link,
the symbolic link is renamed,
not the file or directory to which it points.
.Pp
If both
.Fa from
and
.Fa to
are pathnames of the same existing file in the file system's name space,
.Fn rename
returns successfully and performs no other action.
.Sh RETURN VALUES
A 0 value is returned if the operation succeeds, otherwise
.Fn rename
returns -1 and the global variable
.Va errno
indicates the reason for the failure.
.Sh ERRORS
.Fn rename
will fail and neither of the argument files will be
affected if:
.Bl -tag -width Er
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv {NAME_MAX}
characters, or an entire path name exceeded
.Dv {PATH_MAX}
characters.
.It Bq Er ENOENT
A component of the
.Fa from
path does not exist,
or a path prefix of
.Fa to
does not exist.
.It Bq Er EACCES
A component of either path prefix denies search permission, or
the requested link requires writing in a directory with a mode
that denies write permission.
.It Bq Er EPERM
The directory containing
.Fa from
is marked sticky,
and neither the containing directory nor
.Fa from
are owned by the effective user ID.
Or the
.Fa to
file exists,
the directory containing
.Fa to
is marked sticky,
and neither the containing directory nor
.Fa to
are owned by the effective user ID.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating either pathname.
.It Bq Er ENOTDIR
A component of either path prefix is not a directory, or
.Fa from
is a directory, but
.Fa to
is not a directory.
.It Bq Er EISDIR
.Fa to
is a directory, but
.Fa from
is not a directory.
.It Bq Er EXDEV
The link named by
.Fa to
and the file named by
.Fa from
are on different logical devices (file systems).
Note that this error code will not be returned if the implementation
permits cross-device links.
.It Bq Er ENOSPC
The directory in which the entry for the new name is being placed
cannot be extended because there is no space left on the file
system containing the directory.
.It Bq Er EDQUOT
The directory in which the entry for the new name
is being placed cannot be extended because the
user's quota of disk blocks on the file system
containing the directory has been exhausted.
.It Bq Er EIO
An I/O error occurred while making or updating a directory entry.
.It Bq Er EROFS
The requested link requires writing in a directory on a read-only file
system.
.It Bq Er EFAULT
.Em Path
points outside the process's allocated address space.
.It Bq Er EINVAL
.Fa from
is a parent directory of
.Fa to ,
or an attempt is made to rename
.Ql \&.
or
.Ql \&.. .
.It Bq Er ENOTEMPTY
.Fa to
is a directory and is not empty.
.El
.Sh SEE ALSO
.Xr open 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn rename
function deviates from the semantics defined in
.St -p1003.1-90 ,
which specifies that if both
.Fa from
and
.Fa to
.Em link
to the same existing file,
.Fn rename
shall return successfully and performs no further action, whereas this
implementation will remove the file specified by
.Fa from
unless both
.Fa from
and
.Fa to
are pathnames of the same file in the file system's name space.
.Pp
To retain conformance, a compatibility interface is provided by the
.Lb libposix
which is also be brought into scope if any of the
.Dv _POSIX_SOURCE ,
.Dv _POSIX_C_SOURCE
or
.Dv _XOPEN_SOURCE
preprocessor symbols are defined at compile-time:
the
.Fn rename
function conforms to
.St -p1003.1-90
and
.St -xpg4.2 .
.Sh BUGS
The system can deadlock if a loop in the file system graph is present.
This loop takes the form of an entry in directory
.Ql Pa a ,
say
.Ql Pa a/foo ,
being a hard link to directory
.Ql Pa b ,
and an entry in
directory
.Ql Pa b ,
say
.Ql Pa b/bar ,
being a hard link
to directory
.Ql Pa a .
When such a loop exists and two separate processes attempt to
perform
.Ql rename a/foo b/bar
and
.Ql rename b/bar a/foo ,
respectively,
the system may deadlock attempting to lock
both directories for modification.
Hard links to directories should be
replaced by symbolic links by the system administrator.