Personal experience: When I've been new to something that's gone wrong, I've found that when people told me "it is your fault", it was usually because, well, er, it was surprisingly, unexpectedly, unprecedentedly, novelly, shockingly... my fault. Imagine that. Who'da thunk?
Coarse crass crash course in basic permissions:
(u)ser (g)roup (o)ther -- The who (not the band)
(r)ead (w)rite e(x)ecute -- The what
Ownership is expressed as 2 values, thus:
user:group
Each user belongs to multiple supplementary groups, but their primary group is (normally) unique to them and bears their name (generated when creating new users. So user "marty" will normally belong to the grouo "marty", which is his unique/private group. He may also belong to the groups "audio", "cdrom", "delorean", and others, allowing him permission to use certain devices.
Example: /dev/boombox is a device node for a boombox and may be owned by the group "audio". Thus "marty" can access it. But what he can do is determined by these lovelies: rwx. The rwx specified for the group "audio". Now let's say we want people in "audio" to be able to use it typically as a boombox, i.e. listening to music, changing casettes, etc., they need group (r)ead and (w)rite capabilities. So the boombox permissions will look like this:
user: rwx
group: rw-
other: ---
(other will depend on file type and security defaults)
Anyway, that's the gist.
Now the soft and creamy center: Every user and group has a numeric id; uid and gid respectively. The default uid and gid for users beings at 1000 for most systems. So your system will be along the lines of:
you: 1000
yourgroup: 1000
Okay, now the filesystems that support ownership like EXT, XFS, BTRFS, et al, do not store files' ownership as names, only numbers. So "marty" creates a file called "todo.txt", automatically it is owned as marty:marty which means that tge filesystem records "todo.txt" as belonging to 1000:1000.
Okay putting it together? Yes? No? Maybe (could you repet the question)?
Hypotheyical:
OS1: your main account is "terrance"(uid 1000) and "terrance" (gid).
OS2: your main account is "phillip" (uid 1000) and "phillip" (gid 1000)
Any documents made by "terrance" will belong to 1000:1000 by default and saved to the flashdrive with 1000:1000 ownernship.
So, when "phillip" gets the drive, it will appear as if he owns it since his uid and gid are 1000:1000 as well.
That's what I meant.
As for your problem, I'm guessing now it's at time of mount. Issue this:
Code:
sudo -i
// Find the flashdrive partition's UUID and
// note it down... I'll use 123-456 as a substitute.
blkid
// Now we create a permanent mountpoint
// with loose permissions. This is inelegant
// but still.
mkdir -p /media/flashdrive01
chown 1000:1000 /media/flashdrive01
chmod u+rwx /media/flashdrive01
// I'm ssuming the usb stick is EXT4, correct
// that to whatever it is as with the UUID.
echo "UUID=124-456 /media/flashdrive01 ext4 defaults,user,noauto,exec 0 0" >> /etc/fstab
// A *buntu bug from ages back, you may
// not need this step, but it won't hurt.
mount -a
chown -R 1000:1000 /media/flashdrive01
chmod -R u+rwx /media/flashdrive01
umount /media/flashdrive01
// Overkill, but whatevs
reboot
Okay, once you've rebooted and logged in, whenever you plug in your flashdrive, it should appear in your filebrowser's device list (usually left pane). Click to mount it, right-click+umount to unmount it. Solved.
* In your spare time, do some reading and see why what I told you is hacky and why LABEL= is better than UUID= in fstab and correct the fstab entry by means of self-study.
Edit: Probably a few other few minor glitches. I typed it on my phone.