Magento: 500 Internal server error

I have PHP as CGI installed server with magento.

I keep getting the 500 internal server error on some specific pages.-

1. When someone add items to cart and say checkout the error comes up on the screen and the page url is /checkout/onepage.

2. When I login into admin site once again the error is there.

I have given the 755 permission to all the required fil开发者_运维百科es and folders of magento.

I can fix this error temporary by giving the permission to the root index.php file to 755. But after some time the error is still there and again I have give the permission of root index.php file to 755 to access the pages.

How can I resolve this error permanently?

My hosting server is 1and1.com

Thanks.

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.htaccess by default in Magento has this options disabled that are specific to 1and1 hosting, I would try enabling them:

############################################
## this line is specific for 1and1 hosting

    #AddType x-mapp-php5 .php
    #AddHandler x-mapp-php5 .php

You may also want to read over:

http://www.magentocommerce.com/boards/viewthread/2019/

http://www.magentocommerce.com/boards/viewthread/199907/

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A nice article with various solutions http://www.techjam.gr/2012/magento/solve-magento-500-internal-server-errors/

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I found that copying php.ini.sample to php.ini stopped the 500 errors.

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This can be memory_limit issue.

For shared hosting, 1and1.com only has around 80M memory_limit.

Increasing memory_limit can solve this problem.

Magento System Requirements states that Memory_limit should be no less than 256Mb (http://www.magentocommerce.com/system-requirements). Otherwise, you might get this kind of errors time to time.

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In my case when I faced 500 internal error on moving the Magento application to development server, the index.php file was missing in the Magento root directory.Once I replaced this with default one.The error was not coming again.