141 lines
11 KiB
HTML
141 lines
11 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
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<meta name="security" content="public" />
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<meta name="Robots" content="index,follow" />
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<meta http-equiv="PICS-Label" content='(PICS-1.1 "http://www.icra.org/ratingsv02.html" l gen true r (cz 1 lz 1 nz 1 oz 1 vz 1) "http://www.rsac.org/ratingsv01.html" l gen true r (n 0 s 0 v 0 l 0) "http://www.classify.org/safesurf/" l gen true r (SS~~000 1))' />
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Link" />
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<meta name="abstract" content="A link is a named connection between a directory and an object. A user or a program can tell the server where to find an object by specifying the name of a link to the object. A link can be used as a path name or as part of a path name." />
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<meta name="description" content="A link is a named connection between a directory and an object. A user or a program can tell the server where to find an object by specifying the name of a link to the object. A link can be used as a path name or as part of a path name." />
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<meta name="DC.subject" content="link, what is it?, why use" />
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<meta name="keywords" content="link, what is it?, why use" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxbasics.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxhardlnk.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxsymlnk.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxrootlinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxopenlink.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxudfslink.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxliblinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxiasplinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxqdlslinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxoptlinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxntlinks.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxos4links.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxnfslink.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxsymlink_type2.htm" />
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<meta name="DC.Relation" scheme="URI" content="rzaaxqnetlinks.htm" />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1999, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1999, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Identifier" content="rzaaxlinkifs" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Link</title>
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</head>
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<body id="rzaaxlinkifs"><a name="rzaaxlinkifs"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Link</h1>
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<div><p>A <dfn class="term">link</dfn> is a named connection
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between a directory and an object. A user or a program can tell the server
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where to find an object by specifying the name of a link to the object. A
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link can be used as a path name or as part of a path name.</p>
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<p>For users of directory-based file systems, it is convenient to think of
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an object, such as a file, as something that has a name that identifies it
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to the server. In fact, it is the directory path to the object that identifies
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it. You can sometimes access an object by giving just the object's <span class="q">"name"</span>.
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You can do this only because the system is designed to assume the directory
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part of the path under certain conditions. The idea of a link takes advantage
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of the reality that it is the directory path that identifies the object.
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The name is given to the link rather than the object.</p>
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<p>After you get used to the idea that the link has the name
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rather than the object, you begin to see possibilities that were hidden before.
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There can be multiple links to the same object. For example, two users can
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share a file by having a link from each user's home directory to the file
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(see <a href="rzaaxhomedir.htm#rzaaxhomedir">Home directory</a>). Certain types of
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links can cross file systems, and can exist without an object existing.</p>
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<p>There are two types of links: Hard link and Symbolic link. When using path
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names in programs, you have a choice of using a hard link or a symbolic link.
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Each type of link has advantages and disadvantages. The conditions under which
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one type of link has an advantage over the other type is as follows:</p>
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<div class="tablenoborder"><a name="rzaaxlinkifs__rzaaxlinkcmp"><!-- --></a><table cellpadding="4" cellspacing="0" summary="" id="rzaaxlinkifs__rzaaxlinkcmp" width="100%" frame="border" border="1" rules="all"><caption>Table 1. Comparison of
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hard link and symbolic link</caption><thead align="left"><tr><th align="left" valign="bottom" width="33.429394812680115%" id="d0e84">Item</th>
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<th align="left" valign="bottom" width="33.429394812680115%" id="d0e86">Hard link</th>
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<th align="left" valign="bottom" width="33.14121037463977%" id="d0e88">Symbolic link</th>
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</tr>
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</thead>
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<tbody><tr><td align="left" valign="top" width="33.429394812680115%" headers="d0e84 ">Name resolution</td>
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<td align="left" valign="top" width="33.429394812680115%" headers="d0e86 ">Faster. A hard link contains a
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direct reference to the object.</td>
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<td align="left" valign="top" width="33.14121037463977%" headers="d0e88 ">Slower. A symbolic link contains
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a path name to the object, which must be resolved to find the object.</td>
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</tr>
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<tr><td align="left" valign="top" width="33.429394812680115%" headers="d0e84 ">Object existence</td>
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<td align="left" valign="top" width="33.429394812680115%" headers="d0e86 ">Required. An object must exist
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in order to create a hard link to it.</td>
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<td align="left" valign="top" width="33.14121037463977%" headers="d0e88 ">Optional. A symbolic link can
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be created when the object it refers to does not exist.</td>
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</tr>
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<tr><td align="left" valign="top" width="33.429394812680115%" headers="d0e84 ">Object deletion</td>
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<td align="left" valign="top" width="33.429394812680115%" headers="d0e86 ">Restricted. All hard links to
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an object must be unlinked (removed) to delete the object.</td>
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<td align="left" valign="top" width="33.14121037463977%" headers="d0e88 ">Unrestricted. An object can be
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deleted even if there are symbolic links referring to it.</td>
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</tr>
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<tr><td align="left" valign="top" width="33.429394812680115%" headers="d0e84 ">Static objects (attributes do
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not change)</td>
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<td align="left" valign="top" width="33.429394812680115%" headers="d0e86 ">Faster. For a static object, name
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resolution is the primary performance concern. Name resolution is faster
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when hard links are used.</td>
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<td align="left" valign="top" width="33.14121037463977%" headers="d0e88 ">Slower. Name resolution is slower
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when symbolic links are used.</td>
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</tr>
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<tr><td align="left" valign="top" width="33.429394812680115%" headers="d0e84 ">Scope</td>
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<td align="left" valign="top" width="33.429394812680115%" headers="d0e86 ">Restricted. Hard links cannot
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cross file systems.</td>
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<td align="left" valign="top" width="33.14121037463977%" headers="d0e88 ">Unrestricted. Symbolic links can
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cross file systems.</td>
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</tr>
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</tbody>
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</table>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="rzaaxhardlnk.htm">Hard link</a></strong><br />
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A <dfn class="term">hard link</dfn>, which is sometimes
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just called a link, cannot exist unless it is linked to an actual object.</li>
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<li class="ulchildlink"><strong><a href="rzaaxsymlnk.htm">Symbolic link</a></strong><br />
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A <dfn class="term">symbolic link</dfn>,
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which is also called a soft link, is a path name contained in a file. </li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaaxbasics.htm" title="This topic introduces the basic concepts of integrated file system, such as directory, link, path name, stream file, name continuity, extended attributes, and scanning support.">Integrated file system concepts</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="rzaaxrootlinks.htm" title="Multiple hard links to the same object are allowed in the root (/) file system. Symbolic links are fully supported.">Links in the "root" (/) file system</a></div>
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<div><a href="rzaaxopenlink.htm" title="Multiple hard links to the same object are allowed in the QOpenSys file system. Symbolic links are fully supported.">Links in the QOpenSys file system</a></div>
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<div><a href="rzaaxudfslink.htm" title="A user-defined file system (UDFS) allows multiple hard links to the same object and fully supports symbolic links.">Links in an integrated file system user-defined file system</a></div>
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<div><a href="rzaaxliblinks.htm" title="Symbolic links cannot be created or stored in the QSYS.LIB file system.">Links in the QSYS.LIB file system</a></div>
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<div><a href="rzaaxiasplinks.htm" title="Symbolic links cannot be created or stored in the Independent ASP QSYS.LIB file system.">Links in the independent ASP QSYS.LIB file system</a></div>
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<div><a href="rzaaxqdlslinks.htm" title="Symbolic links cannot be created or stored in the QDLS file system.">Links in the QDLS file system</a></div>
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<div><a href="rzaaxoptlinks.htm" title="The QOPT file system supports only one link to an object. Symbolic links cannot be created or stored in QOPT.">Links in the QOPT file system</a></div>
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<div><a href="rzaaxntlinks.htm" title="The QNTC file system supports only one link to an object. You cannot create or store symbolic links in QNTC.">Links in the QNTC file system</a></div>
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<div><a href="rzaaxos4links.htm" title="The QFileSvr.400 file system supports only one link to an object.">Links in the QFileSvr.400 file system</a></div>
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<div><a href="rzaaxnfslink.htm" title="Generally, multiple hard links to the same object are allowed in the Network File System.">Links in the Network File System</a></div>
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<div><a href="rzaaxsymlink_type2.htm" title="Symbolic links are objects within the integrated file system that contain a path to another object.">Tips: Symbolic link</a></div>
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<div><a href="rzaaxqnetlinks.htm" title="The QNetWare file system supports only one link to an object. Symbolic links cannot be created or stored in QNetWare.">Links in the QNetWare file system</a></div>
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</div>
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</div>
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</body>
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</html>
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