Solving permission problems when using external EXT4 hard disk with multiple linux installs

The simplest solution is to make sure your Ubuntu & Fedora user accounts have the same user id (UID).

I think Fedora starts user accounts at 500 by default, while Debian & Ubuntu start them at 1000, so it's very likely that in one OS you are user number 500 and in the other you are user number 1000. The file system uses this UID number to keep track of permissions, so if you make sure they have the same UID, they will be considered the same user, and no permission issues will happen.

I think the best you can do is make them both UID = 1000, so change the UID in the Fedora system, then make sure all files on the external disk and in the user's $HOME in the Fedora install are owned by UID 1000. After that you should have no permission problems anymore.

Lame though it may be of me, I'm going to have to answer the question with another question. If all we're talking about is for one OS, then it would be either

sudo chown -R (user name) /dev/(device name)

(ubuntu)

or just

chown -R (user name) /dev/(device name)

fedora - no sudo, just run the command from root.

The noodle scratcher part, and the part I don't have any good answers for, is how to make it so you don't have to manually retype when you go back and forth between distros. I'd almost be tempted to add the line to my ~/.bashrc, but there's probably a better way I don't know or haven't thought of yet.

In /etc/fstab you could put uid=1000 (in Ubuntu -- it's 500 in Fedora) for the drive to be owned by your user (assuming you're the first user, yada yada yada... if not, your user's uid from id) and umask=000 if you wanted all users to have access (or 077 for just the one specified by uid= -- it's a mask, so you put the opposite of what you'd chmod as)

For more info on using /etc/fstab: http://ubuntulinuxtipstricks.blogspot.com/2008/02/fun-with-etcfstab.html