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Relatively new to Linux, this is probably a basic question.

I've just dual-booted Ubuntu alongside Windows 10. When on the desktop, in the task bar (if that's the right word for it) on the left, I can see a grey box with "SSD" in it. When I click on this I can see what I think is the entire Windows file system, and access the files in it from Ubuntu.

I've dual-booted alongside Windows 10 once before, and I couldn't see the Windows file system back then. I just want to understand why I'm able to see it now - could it be because both OSes might now be stored on the same disk or partition? Ideally I don't want to be able to access file systems of one OS from the other, and I'm willing to reinstall - I have nothing important on Ubuntu yet.

Thank you for your patience.

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    No, it's not related to the location of the OSes. It is related with Fast Startup in Windows being enabled or not or with Dynamic disk or whatever, a Microsoft proprietary technology that when enabled makes the partitions readable by Windows only.
    – ChanganAuto
    Aug 17, 2022 at 19:14
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    Windows and Ubuntu cannot be in the same partition. They use different partition types. Windows do not understand Ubuntu partition type. Ubuntu understands and can read from and write to Windows partition type. That's why you can see the Windows partition from within Ubuntu. It will not be mounted unless you click on the icon. You can right click on the icon and unmount it after you are done looking at it.
    – user68186
    Aug 17, 2022 at 19:15
  • When was it the "once before" when you dual-booted with Windows and couldn't see Windows files? Was it with the same installation? With the same Ubuntu release? What you describe is a pretty normal behaviour of Ubuntu desktop. It displays icons for all unmounted partitions that it finds on all disks, and by clicking on these icons you can mount these partitions and access files on them.
    – raj
    Aug 17, 2022 at 20:33
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    Count your blessings! Regularly (at least once a month), I transfer data between my Linux and Windows partitions. Some very useful software runs only under Windows and some runs only under Linux, so I find it very useful to be able to move my data back and forth. I can do this only using Linux (Ubuntu) because, as is pointed out below, Windows can not read data stored on a Linux-formatted partition. It is a Blessing to be able to be able to do this.
    – ve3oat
    Aug 17, 2022 at 21:56

2 Answers 2

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"Ideally I don't want to be able to access file systems of one OS from the other"

Actually, any operating system can see the files of any volume, including operating system files, unless the volume is encrypted.

Many people think that a good password will prevent someone with physical access from accessing the data on a device, but this is not true. Your Windows user password only protects the sign on and other restrictions from within the Windows OS. Someone with a live USB of Ubuntu or any other operating system would be able to read/write anything to the disk.

So in order to make it impossible for one OS to access the other, you need to utilize Full Disk Encryption for both operating systems. In Ubuntu, you can choose to encrypt the entire system during the system installation. The best way to do this is to reinstall the OS. You may be able to find methods to encrypt your system after the fact, but this is quite messy and requires some expertise or knowledge of how Ubuntu works "under the hood".

There are likely a number of ways to encrypt a Windows installation, but Microsoft's official full disk encryption option is called BitLocker.

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Linux will support as many filesystems as is possible. NTFS, FAT, and exFAT are the 3 main filesystems for Windows and all three are supported.

If a partition or disk is recognized and the mount is set to be done in /media or in /home/$USER/ a filemanager will show these in the dock with an icon. This is optional: each filemanager will have an option to disable this behaviour.

There is a simple method where you can set the partition/disk from within Ubuntu as inaccessible: see https://askubuntu.com/a/1423774/15811 for the details:

UUID={UUID} /mnt/{mountpoint} ntfs defaults,noauto,umask=777 0 0

This still allows mounting by an admin but is an easy fix. If you want the data to be secured too you need to encrypt it within Windows.

could it be because both OSes might now be stored on the same disk or partition?

Nope. Same partition is not possible: only 1 OS per partition.

A couple of things could be different between your experiences (not claiming it is a full list ;) ):

  • you told the filemanager to not show the icons
  • the partition/disk mountpoint is outside of /media or /home
  • in your old system you disabled a service related to this
  • you removed support for windows filesystems by deleting the ntfs driver.
  • you added the partition/disk to /etc/fstab and made it auto mount.
  • you added ntfs to /etc/modprobe.d/blacklist.conf and blacklisted it.

But as @raj stated: it is normal behaviour to add icons for partitions or disks to the dock (or to the desktop).

@ChanganAuto

It is related with Fast Startup in Windows being enabled or not or with Dynamic disk or whatever, a Microsoft proprietary technology that when enabled makes the partitions readable by Windows only.

I would believe that would still show an icon in the dock.

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    FYI: it is possible, but difficult, to install more than one OS on the same partition. xnux.eu/log/#014
    – user253751
    Aug 18, 2022 at 16:11
  • @user253751: I think it's possible to boot Windows too from btrfs, but it requires a LOT of "coercion" to do that.
    – Oskar Skog
    Aug 18, 2022 at 20:32
  • @OskarSkog Booting Linux from NTFS, on the other hand, is probably possible. With effort.
    – user253751
    Aug 18, 2022 at 20:38

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