Followed by this tutorial: https://www.digitalocean.com/community/tutorials/how-to-configure-secure-updates-and-installations-in-wordpress-on-ubuntu
I have a 64bit Debian 7 installed on my VPS(LEMP stack with php-fpm), this tutorial works well as long as I don't set passphrase to the generated ssh2 keys, with password I get error "Public and Private keys incorrect for user".