sudo tar czf /backup.tar.gz \

    --exclude=/backup.tar.gz \

    --exclude=/dev \

    --exclude=/mnt \

    --exclude=/proc \

    --exclude=/sys \

    --exclude=/tmp \

    --exclude=/media \

    --exclude=/lost+found \

    /

​

Add more --exclude= parameters if you need to.

​

It will create an archive of all your files at /backup.tar.gz, which should be copied to another computer or drive.

​

To restore your files when the system goes pear-shaped, use a Live CD. Mount the bad system under /media or /mnt and then run tar xf /path/to/drive/with/backup.tar.gz -C /mnt (or /media).

​