safe_mode is a feature of php. It is always prefferable to keep it ON due to security resaons. But for the working of some scripts it need to be turned off , in that case also dont turn it off server wide as it is a potential vulnerability.
How to turn off safe_mode for a particular domain.
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First thing we need to check is whether php is compiled as modular or cgi
If modular then we can do it via .htaccess in his public_html
If cgi then we can do it via php.ini in his publichtml
Via .htaccess
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Add the following line
php_value safe_mode 0ff
or
php_flag safe_mode Off
If it is php 5 then add it inside the if module like
php_flag safe_mode off
via php.ini
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Just make a file called php.ini in his public_html then just add the line
safe_mode Off
Via hhtpd.conf
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Add the following line and use ifmodule if needed
php_admin_flag safe_mode Off