libc/sys/link.2

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.\"     @(#)link.2	8.3 (Berkeley) 1/12/94
.\"
.Dd July 20, 2024
.Dt LINK 2
.Os
.Sh NAME
.Nm link
.Nd make a hard file link
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn link "const char *name1" "const char *name2"
.In fcntl.h
.Ft int
.Fn linkat "int fd1" "const char *name1" "int fd2" "const char *name2" "int flags"
.Sh DESCRIPTION
The
.Fn link
function call
atomically creates the specified directory entry (hard link)
.Fa name2
with the attributes of the underlying object pointed at by
.Fa name1 .
If the link is successful: the link count of the underlying object
is incremented;
.Fa name1
and
.Fa name2
share equal access and rights
to the
underlying object.
.Pp
If
.Fa name1
is removed, the file
.Fa name2
is not deleted and the link count of the
underlying object is
decremented.
.Pp
.Fa name1
must exist for the hard link to
succeed and
both
.Fa name1
and
.Fa name2
must be in the same file system.
.Fa name1
may not be a directory.
.Pp
.Fn linkat
works the same way as
.Fn link
except if
.Fa name1
(resp.
.Fa name2 )
is relative.
In that case, it is looked up from a directory whose file
descriptor was passed as
.Fa fd1
(resp.
.Fa fd2 ) .
Search permission is required on the directories named by
.Fa fd1
and
.Fa fd2 .
.\"    (These alternatives await a decision about the semantics of O_SEARCH)
.\" Search permission is required on the directories named by
.\" .Fa fd1
.\" and
.\" .Fa fd2
.\" unless they were opened with the
.\" .Dv O_SEARCH
.\" flag.
.\"    - or -
.\" The directories named by
.\" .Fa fd1
.\" and
.\" .Fa fd2
.\" must have been opened with the
.\" .Dv O_SEARCH
.\" flag.
.Fa fd1
or
.Fa fd2
can be set to
.Dv AT_FDCWD
in order to specify the current directory.
.Pp
When operating on a symlink,
.Fn link
resolves the symlink and creates a hard link on the target.
.Fn linkat
will do the same if
.Dv AT_SYMLINK_FOLLOW
is set in
.Fa flags ,
but it will link on the symlink itself if the flag is clear.
.Sh RETURN VALUES
.Rv -std link linkat
.Sh ERRORS
.Fn link
and
.Fn linkat
will fail and no link will be created if:
.Bl -tag -width Er
.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 EDQUOT
The directory in which the entry for the new link
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 EEXIST
The link named by
.Fa name2
does exist.
.It Bq Er EFAULT
One of the pathnames specified
is outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to
the file system to make the directory entry.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating one of the pathnames.
.It Bq Er EMLINK
The link count of the file named by
.Fa name1
would exceed
.Brq Dv LINK_MAX .
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
A component of either path prefix does not exist, or the file named
by
.Fa name1
does not exist.
.It Bq Er ENOSPC
The directory in which the entry for the new link is being placed
cannot be extended because there is no space left on the file
system containing the directory.
.It Bq Er ENOTDIR
A component of either path prefix is not a directory.
.It Bq Er EOPNOTSUPP
The file system containing the file named by
.Fa name1
does not support links.
.It Bq Er EPERM
The file named by
.Fa name1
is a directory.
.It Bq Er EROFS
The requested link requires writing in a directory on a read-only file
system.
.It Bq Er EXDEV
The link named by
.Fa name2
and the file named by
.Fa name1
are on different file systems.
.El
.Pp
In addition,
.Fn linkat
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
.Fa name1
or
.Fa name2
does not specify an absolute path and
.Fa fd1
or
.Fa fd2 ,
respectively, is neither
.Dv AT_FDCWD
nor a valid file descriptor open for reading or searching.
.It Bq Er ENOTDIR
.Fa name1
or
.Fa name2
is not an absolute path and
.Fa fd1
or
.Fa fd2 ,
respectively, is a file descriptor associated with a non-directory file.
.El
.Sh SEE ALSO
.Xr symlink 2 ,
.Xr unlink 2
.Sh STANDARDS
The
.Fn link
function conforms to
.St -p1003.1-90 .
.Fn linkat
conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn link
function appeared in
.At v1 .