[ubuntu] How to take Hard Disk backup into external USB drive ?

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http://ubuntuforums.org – hi, I am using squid server on my Ubuntu box. I want to take full backup of my hard disk (All partitions & Data) into the externel usb drive.The reason is in case of crash of data I just roolback my ubuntu with its partitions and data. Is there any builtin command in linux ? Thanks, honey (Hardware)