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version 1.28, 2005/05/22 18:00:10 version 1.29, 2006/05/30 02:58:00
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 you will need for generated files during a build, i.e. compiling the sources.  you will need for generated files during a build, i.e. compiling the sources.
   
 <p>  <p>
 If you just get the source tree, you will need to deal with local  
 modifications.  One way to do this is to use the <b>union</b> filesystem,  
 (see <a href="http://www.openbsd.org/cgi-bin/man.cgi?query=mount_union&amp;sektion=8">mount_union(8)</a>)  
 although there have been reports that the <b>union</b> filesystem can be  
 unstable if both the upper and lower layers reside on the same physical  
 filesystem.  If you place your upper and lower layers on separate  
 filesystems you should have no problems.  A sample of this is as follows:  
   
 <p>  
 Suppose your CTM-updated tree is in <tt><b>/usr/src-ctm</b></tt>, and  
 your real source tree, the one you make your modifications to and do  
 your builds from, is in <tt><b>/usr/src</b></tt>.  
 <tt><b>/usr/src</b></tt> should be initially an empty directory.  The  
 following command will set up the union mount:  
   
 <pre>  
         mount -t union -o -b /usr/src-ctm /usr/src  
 </pre>  
   
 <p>  
 Modifications made to files in <tt><b>/usr/src</b></tt> will become a  
 file contained within <tt><b>/usr/src</b></tt>, hiding the one in  
 <tt><b>src-ctm</b></tt>.  If changes are made via CTM to the  
 underlying <tt><b>src-ctm</b></tt> tree, those changes will <b>not</b>  
 be seen if there is a file in the upper layer hiding it.  
   
 <p>  
 You should periodically unmount the  
 union and search for files which are local to the union filesystem.  
   
 <pre>  
         umount /usr/src  
         find /usr/src -type f  
 </pre>  
   
 <p>  
 The commands <tt><b>ls -W</b></tt> and <tt><b>rm -W</b></tt> will be  
 useful too, as objects named "whiteouts" in <tt><b>/usr/src</b></tt>  
 will also hide files in <tt><b>src-ctm</b></tt>.  
   
 <p>  
 If you get the CVS repository, you can use the <tt><b>cvs checkout</b></tt>  If you get the CVS repository, you can use the <tt><b>cvs checkout</b></tt>
 command to check out a source tree from it.  Each time you update  command to check out a source tree from it.  Each time you update
 with CTM you can use the <tt><b>cvs update</b></tt> command to  with CTM you can use the <tt><b>cvs update</b></tt> command to
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