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NAME

       link - link to a file

SYNOPSIS

       #include <unistd.h>

       int link(const char *path1, const char *path2);

DESCRIPTION

       The link() function shall create a new link (directory entry) for the existing file, path1.

       The path1 argument points to a pathname naming an existing file.  The path2 argument points to a pathname
       naming the new directory entry to be created. The link() function shall atomically create a new link  for
       the existing file and the link count of the file shall be incremented by one.

       If  path1  names  a  directory,  link()  shall fail unless the process has appropriate privileges and the
       implementation supports using link() on directories.

       Upon successful completion, link() shall mark for update the  st_ctime  field  of  the  file.  Also,  the
       st_ctime and st_mtime fields of the directory that contains the new entry shall be marked for update.

       If link() fails, no link shall be created and the link count of the file shall remain unchanged.

       The implementation may require that the calling process has permission to access the existing file.

RETURN VALUE

       Upon  successful  completion,  0  shall  be  returned.  Otherwise,  -1 shall be returned and errno set to
       indicate the error.

ERRORS

The link() function shall fail if:

EACCES A component of either path prefix denies search permission, or the requested link requires writing
in a directory that denies write permission, or the calling process does not have permission to
access the existing file and this is required by the implementation.

EEXIST The path2 argument resolves to an existing file or refers to a symbolic link.

ELOOP A loop exists in symbolic links encountered during resolution of the path1 or path2 argument.

EMLINK The number of links to the file named by path1 would exceed {LINK_MAX}.

ENAMETOOLONG
The length of the path1 or path2 argument exceeds {PATH_MAX} or a pathname component is longer
than {NAME_MAX}.

ENOENT A component of either path prefix does not exist; the file named by path1 does not exist; or path1
or path2 points to an empty string.

ENOSPC The directory to contain the link cannot be extended.

ENOTDIR
A component of either path prefix is not a directory.

EPERM The file named by path1 is a directory and either the calling process does not have appropriate
privileges or the implementation prohibits using link() on directories.

EROFS The requested link requires writing in a directory on a read-only file system.

EXDEV The link named by path2 and the file named by path1 are on different file systems and the
implementation does not support links between file systems.

EXDEV path1 refers to a named STREAM.

The link() function may fail if:

ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path1 or path2
argument.

ENAMETOOLONG
As a result of encountering a symbolic link in resolution of the path1 or path2 argument, the
length of the substituted pathname string exceeded {PATH_MAX}.

The following sections are informative.

EXAMPLES

   Creating a Link to a File
       The following example shows how to create a link to  a  file  named  /home/cnd/mod1  by  creating  a  new
       directory entry named /modules/pass1.

              #include <unistd.h>

              char *path1 = "/home/cnd/mod1";
              char *path2 = "/modules/pass1";
              int   status;
              ...
              status = link (path1, path2);

   Creating a Link to a File Within a Program
       In  the following program example, the link() function links the /etc/passwd file (defined as PASSWDFILE)
       to a file named /etc/opasswd (defined as SAVEFILE), which is used to  save  the  current  password  file.
       Then, after removing the current password file (defined as PASSWDFILE), the new password file is saved as
       the current password file using the link() function again.

              #include <unistd.h>

              #define LOCKFILE "/etc/ptmp"
              #define PASSWDFILE "/etc/passwd"
              #define SAVEFILE "/etc/opasswd"
              ...
              /* Save current password file */
              link (PASSWDFILE, SAVEFILE);

              /* Remove current password file. */
              unlink (PASSWDFILE);

              /* Save new password file as current password file. */
              link (LOCKFILE,PASSWDFILE);

APPLICATION USAGE

       Some implementations do allow links between file systems.

RATIONALE

       Linking to a directory is restricted to the superuser in most  historical  implementations  because  this
       capability  may produce loops in the file hierarchy or otherwise corrupt the file system.  This volume of
       IEEE Std 1003.1-2001 continues that philosophy by prohibiting link() and unlink() from doing this.  Other
       functions could do it if the implementor designed such an extension.

       Some  historical  implementations  allow linking of files on different file systems. Wording was added to
       explicitly allow this optional behavior.

       The exception for cross-file system links is intended to apply only to links  that  are  programmatically
       indistinguishable from "hard" links.

FUTURE DIRECTIONS

       None.

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc and The Open Group. 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.opengroup.org/unix/online.html .