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.\"     @(#)unlink.2	8.1 (Berkeley) 6/4/93
.\"
.Dd June 4, 1993
.Dt UNLINK 2
.Os BSD 4
.Sh NAME
.Nm unlink ,
.Nm unlinkat
.Nd remove directory entry
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fo unlink
.Fa "const char *path"
.Fc
.Ft int
.Fn unlinkat "int fd" "const char *path" "int flag"
.Sh DESCRIPTION
The
.Fn unlink
function
removes the link named by
.Fa path
from its directory and decrements the link count of the
file which was referenced by the link.
If that decrement reduces the link count of the file
to zero,
and no process has the file open, then
all resources associated with the file are reclaimed.
If one or more process have the file open when the last link is removed,
the link is removed, but the removal of the file is delayed until
all references to it have been closed.
.Pp
The
.Fn unlinkat
system call is equivalent to
.Fn unlink
or
.Fn rmdir
except in the case where
.Fa path
specifies a relative path.
In this case the directory entry to be removed is determined
relative to the directory associated with the file descriptor
.Fa fd
instead of the current working directory.
.Pp
The values for
.Fa flag
are constructed by a bitwise-inclusive OR of flags from the following list,
defined in
.In fcntl.h :
.Bl -tag -width AT_SYMLINK_NOFOLLOW_ANY
.It Dv AT_REMOVEDIR
Remove the directory entry specified by
.Fa fd
and
.Fa path
as a directory, not a normal file.
.El
.Bl -tag -width AT_SYMLINK_NOFOLLOW_ANY
.It Dv AT_SYMLINK_NOFOLLOW_ANY
If
.Fa path
contains a symbolic link in any intermediate directory of the path, it is not
followed and an error is returned instead.
.El
.Bl -tag -width AT_SYMLINK_NOFOLLOW_ANY
.It Dv AT_RESOLVE_BENEATH
If
.Fa path
does not reside in the hierarchy beneath the starting directory,
an error is returned.
.El
.Bl -tag -width AT_SYMLINK_NOFOLLOW_ANY
.It Dv AT_NODELETEBUSY
If
.Fa path
refers to a file with any open file descriptors, an error is returned.
.El
.Bl -tag -width AT_SYMLINK_NOFOLLOW_ANY
.It Dv AT_UNIQUE
If
.Fa path
resolves to a vnode with multiple hard links,
an error is returned.
.El
.Pp
If
.Fn unlinkat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is
identical to a call to
.Fa unlink
or
.Fa rmdir
respectively, depending on whether or not the
.Dv AT_REMOVEDIR
bit is set in flag.
.Sh RETURN VALUES
Upon successful completion, a value of 0 is returned.
Otherwise, a value of -1 is returned and
.Va errno
is set to indicate the error.
.Sh ERRORS
The
.Fn unlink
system call will fail if:
.Bl -tag -width Er
.\" ===========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ===========
.It Bq Er EACCES
Write permission is denied on the directory containing the link
to be removed.
.\" ===========
.It Bq Er EBUSY
The entry to be unlinked is the mount point for a
mounted file system.
.\" ===========
.It Bq Er EBUSY
The file named by the
.Fa path
argument cannot be unlinked
because it is being used by the system or by another process.
.\" ===========
.It Bq Er EBUSY
The flag parameter has the AT_NODELETEBUSY bit set and the file referred to by
.Fa path
has one or more open file descriptors.
.\" ===========
.It Bq Er EFAULT
.Fa Path
points outside the process's allocated address space.
.\" ===========
.It Bq Er EIO
An I/O error occurs while deleting the directory entry
or deallocating the inode.
.\" ===========
.It Bq Er ELOOP
Too many symbolic links are encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ===========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeds
.Dv {NAME_MAX}
characters, or an entire path name exceeds
.Dv {PATH_MAX}
characters (possibly as a result of expanding a symlink).
.\" ===========
.It Bq Er ENOENT
The named file does not exist.
.\" ===========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ===========
.It Bq Er EPERM
The named file is a directory and the effective user ID
of the process is not the super-user.
.\" ===========
.It Bq Er EPERM
The directory containing the file is marked sticky,
and neither the containing directory nor the file to be removed
are owned by the effective user ID.
.\" ===========
.It Bq Er EROFS
The named file resides on a read-only file system.
.El
.Pp
In addition to the errors returned by the
.Fn unlink ,
the
.Fn unlinkat
may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er ENOTEMPTY
The
.Fa flag
parameter has the
.Dv AT_REMOVEDIR
bit set and the
.Fa path
argument names a directory that is not an empty directory,
or there are hard links to the directory other than dot or
a single entry in dot-dot.
.It Bq Er ENOTDIR
The
.Fa flag
parameter has the
.Dv AT_REMOVEDIR
bit set and
.Fa path
does not name a directory.
.It Bq Er EINVAL
The value of the
.Fa flag
argument is not valid.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.It Bq Er ELOOP
The
.Fa flag
parameter has the
.Dv AT_SYMLINK_NOFOLLOW_ANY
bit set and one of the intermediate directories in the
.Fa path
argument is a symbolic link.
.It Bq Er ENOTCAPABLE
The flag parameter has the
.Dv AT_RESOLVE_BENEATH
bit set and
.Fa path
does not reside in the directory hierarchy beneath the starting directory.
.It Bq Er ENOTCAPABLE
The flag parameter has the
.Dv  AT_UNIQUE
bit set and
.Fa path
resolves to a vnode with multiple links.
.El
.Sh SEE ALSO
.Xr close 2 ,
.Xr link 2 ,
.Xr rmdir 2 ,
.Xr symlink 7
.Sh STANDARDS
The
.Fn unlinkat
system call is expected to conform to POSIX.1-2008 .
.Sh HISTORY
An
.Fn unlink
function call appeared in 
.At v6 .
The
.Fn unlinkat
system call appeared in OS X 10.10