I use Drupal and I run debian6 on linode 512,and I want to know how to set up ftp access.

You'd be better off updating it manually, ftp requires installing a ftp server and ftp is inherently insecure.

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Or setup something like SuPHP/SuExec/php-fpm with user owning files running PHP too. You will then be able to to this automaticly (at least on Wordpress this is case)