[MacPorts] #15077: Document that installing other software in /usr/local can break ports

[MacPorts]

#15077: Document that installing other software in /usr/local can break ports
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 Reporter:  ryandesign at macports.org  |       Owner:  markd at macports.org     
     Type:  enhancement              |      Status:  new                    
 Priority:  Normal                   |   Milestone:  Website & Documentation
Component:  guide                    |     Version:                         
 Keywords:                           |  
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 We often field questions on the mailing lists regarding some port that
 doesn't install with some obscure error, and this is often the result of
 rogue software installed in /usr/local. readline is a frequent culprit but
 any software installed there is a bad idea. The Guide should recommend not
 having anything installed in /usr/local. Note that having things installed
 in /usr/local/anything is not a problem at all. For example, having
 /usr/local/mysql is fine. However having things directly in /usr/local is
 a problem because the compiler looks there by default and will find
 libraries that are installed there. So having things in /usr/local/bin and
 /usr/local/lib for example are problematic and not supported. Users who
 experience problems and who have the directory /usr/local are advised as a
 troubleshooting step to rename it (e.g. to /usr/local-off), clean the
 affected port, and retry the installation. If it succeeds, the software in
 /usr/local was the culprit. Users are advised to install whatever software
 they need using MacPorts and remove it from /usr/local.

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Ticket URL: <http://trac.macosforge.org/projects/macports/ticket/15077>
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