Here are two commands to backup your wordpress site.

First you need to backup database:

mysqldump -uUSER -h127.0.0.1 -pPASSWORD DB_NAME > database.sql

Now you can archive www root folder:

tar -chvzf www.tar.gz /var/site.com/www

After this manipulations you can copy this two files to the same place.

How to Restore WordPress Site