After upgrading php from 5.1 to 5.2.10, I got the following warnings when php -v:
    # php -v
    PHP Warning:  PHP Startup: fileinfo: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: mcrypt: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: memcache: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: mhash: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: mssql: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: readline: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP Warning:  PHP Startup: tidy: Unable to initialize module
    Module compiled with module API=20050922, debug=0, thread-safety=0
    PHP    compiled with module API=20060613, debug=0, thread-safety=0
    These options need to match
     in Unknown on line 0
    PHP 5.2.10 (cli) (built: Nov 13 2009 11:24:03)
    Copyright (c) 1997-2009 The PHP Group
    Zend Engine v2.2.0, Copyright (c) 1998-2009 Zend Technologies
How can I fix it? Thanks!
Looks like you haven't upgraded PHP modules, they are not compatible.
Check extension_dir directive in your php.ini. It should point to folder with 5.2 modules. 
Create and open a phpinfo file and search for extension_dir to find the path.
Since you did upgrade, there is a chance that you are using old php.ini that is pointing to 5.1 modules
try to upgrade each of those modules using pecl command
# pecl upgrade fileinfo
# pecl upgrade memcache
# pecl upgrade mhash
# pecl upgrade readline
etc...
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