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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 18] 18.7 Linking Directories </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly &amp; Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly &amp; Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:39:03Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch18_01.htm"TITLE="18. Linking, Renaming, and Copying Files"><LINKREL="prev"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "><LINKREL="next"HREF="ch18_08.htm"TITLE="18.8 Showing the Actual Filenames for Symbolic Links "></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 18.6 Stale Symbolic Links "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 18<BR>Linking, Renaming, and Copying Files</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_08.htm"TITLE="18.8 Showing the Actual Filenames for Symbolic Links "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 18.8 Showing the Actual Filenames for Symbolic Links "BORDER="0"></A></TD></TR></TABLE>&nbsp;<HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-9009">18.7 Linking Directories </A></H2><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-20545"></A><ACLASS="indexterm"NAME="AUTOID-20548"></A><ACLASS="indexterm"NAME="AUTOID-20551"></A>One feature of <SPANCLASS="link">symbolic links (<ACLASS="linkend"HREF="ch18_04.htm"TITLE="More About Links ">18.4</A>)</SPAN>(a.k.a. <EMCLASS="emphasis">symlinks</EM>) is that unlike hard links, you can use symbolic links to link directories as well as files.Since symbolic links can span between filesystems, this can becomeenormously useful.</P><PCLASS="para">For example, sometimes administrators want to install a packagein a directory tree that's different from where users and other programs expect it to be.On our site, we like to keep <EMCLASS="emphasis">/usr/bin</EM> pure&nbsp;- that is, we like tobe sure that all the programs in <EMCLASS="emphasis">/usr/bin</EM> came with theoperating system.That way, when we install a new OS, we know forsure that we can overwrite the entirety of <EMCLASS="emphasis">/usr/bin</EM>and not lose any &quot;local&quot; programs.We install all local programs in <EMCLASS="emphasis">/usr/local</EM>.</P><PCLASS="para">The<SPANCLASS="link">X11 (<ACLASS="linkend"HREF="ch01_31.htm"TITLE="The X Window System ">1.31</A>)</SPAN>package poses a problem, though.X11 programs are expected to be installed in <EMCLASS="emphasis">/usr/bin/X11</EM>.But X isn't distributedas part of our OS, so we'd prefer not to put it there.Instead, weinstall X programs in <EMCLASS="emphasis">/usr/local/X11/bin</EM>, and create a symboliclink named <EMCLASS="emphasis">/usr/bin/X11</EM>.We do the same for <EMCLASS="emphasis">/usr/include/X11</EM>and <EMCLASS="emphasis">/usr/lib/X11</EM>:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen"># <CODECLASS="userinput"><B>ln -s /usr/local/X11/bin /usr/bin/X11</B></CODE># <CODECLASS="userinput"><B>ln -s /usr/local/X11/lib /usr/lib/X11</B></CODE># <CODECLASS="userinput"><B>ln -s /usr/local/X11/include /usr/include/X11</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para">By using symlinks, we can have it both ways: we installed the packagewhere we wanted to, but kept it invisible to anyusers or programs that expected the X programs, libraries, or includefiles to be in the standard directories.</P><PCLASS="para">Directory links can result in some unexpected behavior, however.For example, let's suppose I want to look at files in<EMCLASS="emphasis">/usr/bin/X11</EM>.I can just <EMCLASS="emphasis">cd</EM> to <EMCLASS="emphasis">/usr/bin/X11</EM> even though the files are really in <EMCLASS="emphasis">/usr/local/X11/bin</EM>:</P><PCLASS="para"><TABLECLASS="screen.co"BORDER="1"><TR><THVALIGN="TOP"><PRECLASS="calloutlist">&#13;<ACLASS="co"HREF="ch16_12.htm"TITLE="16.12 Useful ls Aliases ">-F</A> &#13;</PRE></TH><TDVALIGN="TOP"><PRECLASS="screen">% <CODECLASS="userinput"><B>cd /usr/bin/X11</B></CODE>% <CODECLASS="userinput"><B>ls -F</B></CODE>       mkfontdir*      xcalc*          xinit*          xset*   ...</PRE></TD></TR></TABLE></P><PCLASS="para">But when I do a <EMCLASS="emphasis">pwd</EM>, I see that I'm really in <EMCLASS="emphasis">/usr/local/X11/bin</EM>.If I didn't know about the symlink, this might be confusing for me:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>pwd</B></CODE>/usr/local/X11/bin</PRE></BLOCKQUOTE></P><PCLASS="para">Now suppose I want to look at files in <EMCLASS="emphasis">/usr/bin</EM>.Since I did a <EMCLASS="emphasis">cd</EM> to <EMCLASS="emphasis">/usr/bin/X11</EM>, I might think I can just goup a level.But that doesn't work:</P><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">% <CODECLASS="userinput"><B>cd ..</B></CODE>% <CODECLASS="userinput"><B>ls -F</B></CODE>bin/     include/     lib/% <CODECLASS="userinput"><B>pwd</B></CODE>/usr/local/X11</PRE></BLOCKQUOTE></P><PCLASS="para">What happened?Remember that a symbolic link is just a<EMCLASS="emphasis">pointer</EM> to another file or directory.So when I wentto the <EMCLASS="emphasis">/usr/bin/X11</EM> directory, my current working directorybecame the directory <EMCLASS="emphasis">/usr/bin/X11</EM> points to,<EMCLASS="emphasis">/usr/local/X11/bin</EM>.</P><TABLECLASS="para.programreference"BORDER="1"><TR><THVALIGN="TOP"><ACLASS="programreference"HREF="examples/index.htm"TITLE="lndir">lndir</A><BR></TH><TDVALIGN="TOP"><ACLASS="indexterm"NAME="AUTOID-20605"></A><ACLASS="indexterm"NAME="AUTOID-20607"></A>As a solution to this problem and others, the X distribution provides a program called <EMCLASS="emphasis">lndir</EM>.<EMCLASS="emphasis">lndir</EM> is also provided on ourCD-ROM.<EMCLASS="emphasis">lndir</EM> makes symlinks between directories by creating links for each individual file.It's cheesy, but it works.We can use <EMCLASS="emphasis">lndir</EM> instead of <EMCLASS="emphasis">ln -s</EM>:</TD></TR></TABLE><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen"># <CODECLASS="userinput"><B>lndir /usr/local/X11/bin /usr/bin/X11</B></CODE># <CODECLASS="userinput"><B>ls -F /usr/bin/X11</B></CODE>X@       mkfontdir@      xcalc@          xinit@          xset@   ...</PRE></BLOCKQUOTE></P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">LM</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_06.htm"TITLE="18.6 Stale Symbolic Links "><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 18.6 Stale Symbolic Links "BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch18_08.htm"TITLE="18.8 Showing the Actual Filenames for Symbolic Links "><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 18.8 Showing the Actual Filenames for Symbolic Links "BORDER="0"></A></TD></TR><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172">18.6 Stale Symbolic Links </TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="index"HREF="index/idx_0.htm"TITLE="Book Index"><IMGSRC="gifs/index.gif"SRC="gifs/index.gif"ALT="Book Index"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172">18.8 Showing the Actual Filenames for Symbolic Links 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