Merge old rootfs with fresh installation without copying permissions

Question

Recently, my Raspberry Pi's permissions were butchered. I am now accessing the Pi's file system through a USB drive running Ubuntu. This is great, but my next step is to return to working on the Pi again with a fresh install of Raspbian OS (and fresh permissions). Also, I cannot edit some of the directories' files as they are read only (the Ubuntu user is not the owner).

What is the most efficient way to go about this and what are the steps involved?
The way I see it, I need to move the files to the fresh OS installation without copying:

• messed up permissions
• broken sudo
• broken SSH
• etc.

I imagine there's multiple ways to do this, some much better than others...

If any clarification is needed, please ask! :)

I can move this question to a different community if necessary...there's a lot of overlap, so I wasn't sure which was most appropriate.

Answer 1

While I am not able to help with changing the messed up permissions, I believe I can help with an efficient restore process. Bear in mind that you'll need to perform most of the backup either AS root, or from a live cd/USB.

First, as far as I know, there is no way to keep the permissions from copying over. This seems bad at first, but think about what you really need to copy over. Do you really need to copy over everything to get a working system, or can you copy over just your configuration files? Do you not even need the config files? Maybe it's just one directory (/home, /usr, etc) that you need. If that's the case, copy just that directory over. The key here is to shrink down the amount of work you'll end up doing when it comes time to restore files.

Once you have your backup ready, do a reinstall of the base system. If you have config files that need to be restored, use echo to send the contents of the old files to the new files on the system.

echo <oldfile> > /etc/new/config/file

This should overwrite the new files with the contents of the old without changing the permissions to 777.

For any files that are staying in your home directory, place them in a folder and run

chown -R 644 <foldername> 
(Or chown -R 640 <foldername>) 

to make the permissions a little more sane. If they end up being owned by root, use chown to give yourself access to them again.

chown -R <username>:<group> <foldername>

If there are additional files/folders that need to be restored, check the permissions on the new filesystem and get them to match.