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.

SEE ALSO

       symlink() , unlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <unistd.h>

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 .