Gentoo Stage4 (or backup whole system)
The basic rule is to run this, assuming the root filesystem to compress
is in /mnt/gentooroot (or mounted there as would be more likely):
cd /mnt/gentooroot
tar -cpP -j --ignore-failed-read --xattrs-include='*.*' --numeric-owner \
-f destination.tar.bz2 .
when your system is not live... naturally you can exclude directories when you perform this task on a live system.