After repeated trouble with my NTFS formatted backup/media hard drive (undeletable files, etc.), I decided to reformat it with a unix file system (ext4 preferred).

I do not intend to use it from a Windows machine, but it should be accessible from other Linux systems (e.g. live cd, after system reinstallation or change of computer).

Could I run into trouble because of user/group permissions?

Is there a way to minimize these (e.g. by chosing a more appropriate file system than ext4 or parameters in /etc/fstab)? Recursive chowns do not seem very elegant or efficient to me.

  • For more information about uid/gid mappings and pitfalls, see here and here (the same concepts will apply to files on the external drive as to those in a tar archive; read from "However, there is a catch...").
    – goldilocks
    Commented Mar 25, 2014 at 12:51

3 Answers 3


Whether you may encounter permission problems with external media depends on whether all your machines share the same password and group database (the username-UID and group-GID mappings). Ownership on an ext4 filesystem is stored as UID and GID numbers.

A more appropriate but somewhat experimental filesystem you could try is UDF. It has the benefit of being theoretically cross-platform. You can mount a UDF filesystem with uid=… and gid=… options, which may help you if you don't have a unified user database among your machines.


The id of the user that owns the files needs to be present on all machines. That is if you want to access the files as the same user.

Root will read anything from anywhere.

If you give proper permissions to the files you will need only the same group id all systems. The user accessing the files will need to be in this group.


You should not have any problem with standard distros, since most of them start user ids from 1000 on and most probably there will always be a user 1000 in every system.

By the way, you can use those HDs on Windows. Check this out.

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