Just a quick question:
I'ld like to format a portable HDD to ext4 for backup purposes.
Which rights should I give so I can use it on any of my machines? 777?
FAT/NTFS don't ask those questions.... 
You have two ways to go.
1. Set permissions to 777, but this means anybody can write to or delete your files.
2. Mount the partition somewhere, then as
root use the
chown command to give ownership of the partition to your user.
[root@localhost ~]# chown -R <user>:<user> <mount-point-directory>Replace
<user> with your actual user name, and
<mount-point-directory> with the directory where the partition is mounted. You will then personally own the partition, wherever it is mounted in the future, and can, as your
normal user, give read/write access to other users, as you see fit.
