I'm a multi-linux-distro/multi-boot guy. I always have more than one configured linux distro on my grub menu. Whenever I'm considering radical changes to one of my working linux I like to back it up. Quite some time ago I learned to do this with tar. For example I've got both Arch Linux and Xubuntu on this desktop pc. I've decided to attempt using a network upgrade process to upgrade the Xubuntu from Karmic to the current Lucid release. So first I boot Arch, mount a storage drive on /mnt/other, & mount the Xubuntu partition on /mnt/xubuntu. Then cd to /mnt/xubuntu. (with a root shell of course)

# tar -czf /mnt/other/xubuntu.tgz -p --numeric-owner .

And of course if it's necessary I can restore the backup to an empty partition with:

# tar -xzf /mnt/other/xubuntu.tgz -p --numeric-owner .

But I only partially understand the -p and --numeric-owner options. I do know that -p is supposed to be default for root but I like to make sure... I think I understand that the reason somebody told me (quite some time ago) to use --numeric-owner is because (in this example) Arch may have different user id numbers than Xubuntu which could have bad results if it tried to apply permissions based on user names (especially if it involves a "system account")...

What I don't know is if either of these options are necessary during the "tar -czf" operation, or if I only need to bother with them when/if I restore a file system with "tar -xzf" ???

I know it does work the way I expect it to when I use the options for both the "-czf" & the "-xzf" operations. And that I don't get any error messages from tar when I do it that way. But I don't know if using them for the "-czf" operation makes any difference or not.

Would someone be so kind as to set me straight on this???