user_guide_src/source/installation/upgrade_301.rst
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Upgrading from 3.0.0 to 3.0.1
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Before performing an update you should take your site offline by
replacing the index.php file with a static one.
Step 1: Update your CodeIgniter files
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Replace all files and directories in your *system/* directory.
.. note:: If you have any custom developed files in these directories,
please make copies of them first.
Step 2: Update your CLI error templates
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Replace all files under your *application/views/errors/cli/* directory.