path: root/man-pages-posix-2013/man3p/symlink.3p

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.TH SYMLINK "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
symlink, symlinkat
\(em make a symbolic link relative to directory file descriptor
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>
.P
int symlink(const char *\fIpath1\fP, const char *\fIpath2\fP);
int symlinkat(const char *\fIpath1\fP, int \fIfd\fP, const char *\fIpath2\fP);
.fi
.SH DESCRIPTION
The
\fIsymlink\fR()
function shall create a symbolic link called
.IR path2
that contains the string pointed to by
.IR path1
(\c
.IR path2
is the name of the symbolic link created,
.IR path1
is the string contained in the symbolic link).
.P
The string pointed to by
.IR path1
shall be treated only as a character string and shall not be validated
as a pathname.
.P
If the
\fIsymlink\fR()
function fails for any reason other than
.BR [EIO] ,
any file named by
.IR path2
shall be unaffected.
.P
If
.IR path2
names a symbolic link,
\fIsymlink\fR()
shall fail and set
.IR errno
to
.BR [EEXIST] .
.P
The symbolic link's user ID shall be set to the process' effective
user ID. The symbolic link's group ID shall be set to the group
ID of the parent directory or to the effective group ID of the
process. Implementations shall provide a way to initialize the symbolic
link's group ID to the group ID of the parent directory. Implementations
may, but need not, provide an implementation-defined way to initialize the
symbolic link's group ID to the effective group ID of the calling process.
.P
The values of the file mode bits for the created symbolic link are
unspecified. All interfaces specified by POSIX.1\(hy2008 shall behave as if the
contents of symbolic links can always be read, except that the value of
the file mode bits returned in the
.IR st_mode
field of the
.BR stat
structure is unspecified.
.P
Upon successful completion,
\fIsymlink\fR()
shall mark for update the last data access, last data modification,
and last file status change timestamps of the symbolic link. Also,
the last data modification and last file status change timestamps of
the directory that contains the new entry shall be marked for update.
.P
The
\fIsymlinkat\fR()
function shall be equivalent to the
\fIsymlink\fR()
function except in the case where
.IR path2
specifies a relative path. In this case the symbolic link is created
relative to the directory associated with the file descriptor
.IR fd
instead of the current working directory. If the file descriptor was
opened without O_SEARCH, the function shall check whether directory
searches are permitted using the current permissions of the directory
underlying the file descriptor. If the file descriptor was opened with
O_SEARCH, the function shall not perform the check.
.P
If
\fIsymlinkat\fR()
is passed the special value AT_FDCWD in the
.IR fd
parameter, the current working directory shall be used and the behavior
shall be identical to a call to
\fIsymlink\fR().
.SH "RETURN VALUE"
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return \(mi1 and set
.IR errno
to indicate the error.
.SH ERRORS
These functions shall fail if:
.TP
.BR EACCES
Write permission is denied in the directory where the symbolic link is
being created, or search permission is denied for a component of the
path prefix of
.IR path2 .
.TP
.BR EEXIST
The
.IR path2
argument names an existing file.
.TP
.BR EIO
An I/O error occurs while reading from or writing to the file system.
.TP
.BR ELOOP
A loop exists in symbolic links encountered during resolution of the
.IR path2
argument.
.TP
.BR ENAMETOOLONG
.br
The length of a component of the pathname specified by the
.IR path2
argument is longer than
{NAME_MAX}
or the length of the
.IR path1
argument is longer than
{SYMLINK_MAX}.
.TP
.BR ENOENT
A component of the path prefix of
.IR path2
does not name an existing file or
.IR path2
is an empty string.
.TP
.BR ENOSPC
The directory in which the entry for the new symbolic link is being
placed cannot be extended because no space is left on the file system
containing the directory, or the new symbolic link cannot be created
because no space is left on the file system which shall contain the
link, or the file system is out of file-allocation resources.
.TP
.BR ENOTDIR
A component of the path prefix of
.IR path2
names an existing file that is neither a directory nor a symbolic link
to a directory.
.TP
.BR EROFS
The new symbolic link would reside on a read-only file system.
.P
The
\fIsymlinkat\fR()
function shall fail if:
.TP
.BR EACCES
.IR fd
was not opened with O_SEARCH and the permissions of the directory
underlying
.IR fd
do not permit directory searches.
.TP
.BR EBADF
The
.IR path2
argument does not specify an absolute path and the
.IR fd
argument is neither AT_FDCWD nor a valid file descriptor open for reading
or searching.
.TP
.BR ENOTDIR
The
.IR path2
argument is not an absolute path and
.IR fd
is a file descriptor associated with a non-directory file.
.P
These functions may fail if:
.TP
.BR ELOOP
More than
{SYMLOOP_MAX}
symbolic links were encountered during resolution of the
.IR path2
argument.
.TP
.BR ENAMETOOLONG
.br
The length of the
.IR path2
argument exceeds
{PATH_MAX}
or pathname resolution of a symbolic link in the
.IR path2
argument produced an intermediate result with a length that exceeds
{PATH_MAX}.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
Like a hard link, a symbolic link allows a file to have multiple
logical names. The presence of a hard link guarantees the existence of
a file, even after the original name has been removed. A symbolic link
provides no such assurance; in fact, the file named by the
.IR path1
argument need not exist when the link is created. A symbolic link can
cross file system boundaries.
.P
Normal permission checks are made on each component of the symbolic
link pathname during its resolution.
.SH RATIONALE
The purpose of the
\fIsymlinkat\fR()
function is to create symbolic links in directories other than the
current working directory without exposure to race conditions. Any part
of the path of a file could be changed in parallel to a call to
\fIsymlink\fR(),
resulting in unspecified behavior. By opening a file descriptor for
the target directory and using the
\fIsymlinkat\fR()
function it can be guaranteed that the created symbolic link is located
relative to the desired directory.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIfdopendir\fR\^(\|)",
.IR "\fIfstatat\fR\^(\|)",
.IR "\fIlchown\fR\^(\|)",
.IR "\fIlink\fR\^(\|)",
.IR "\fIopen\fR\^(\|)",
.IR "\fIreadlink\fR\^(\|)",
.IR "\fIrename\fR\^(\|)",
.IR "\fIunlink\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<unistd.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

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