Revisiting the Android, UserLAnd app.

One of the facts which I had reported some time ago was, that a handy, easy-to-use Android app exists, which is called ‘UserLAnd‘, and, that I had installed it on my Google Pixel C Tablet. As the tooltip suggests, this is an Android app that will allow people to install a basic Linux system, without requiring ‘root’. Therefore, it mounts the apparent, local Linux file system with ‘proot’ – which is similar in how it works to ‘chroot’, except that ‘proot’ does not require root by the host system to set up – and any attempts to obtain root within this Linux system really fail to change the userid, of the app that the files belong to, or of the processes running. Yet, becoming root within this sandboxed version of Linux will convince Linux, for the purpose of installing or removing packages via ‘apt-get’.

In the meantime, I have uninstalled the ‘UserLAnd’ Linux guest system from my Pixel C Tablet, in order to free up storage. But, I have set up something like this again, on my Samsung Galaxy Tab S6 Tablet, which has 256GB of internal storage. Therefore, I have a few observations to add, about how this app runs under Android 10.

Through no fault of the developer of this Android app, the user is more restricted in what he can run, because Android 10 places new restrictions on regular processes. Specifically, none of the major LISP Interpreters that were designed to run under Debian 10 / Buster will run. (:1) What the Linux developers did was, to make the garbage collection of their LISP Interpreters more aggressive, through a strategy that changes the memory protection bits of memory-maps, to read-only if they belong to the state of the machine, and then, ~to try deleting as much of the bytecode as can still be deleted~. Pardon me, if my oversimplification gets some of it wrong.

Well, Android 10 no longer allows regular apps to change the protected memory state of any pages of RAM, for which reason none of the affected LISP Interpreters will run. And for that reason, neither “Maxima” nor anything that depends on Maxima can be made to run.

Yet, certain other Linux applications, notably “LibreOffice” and “Inkscape”, run just fine… So does “GIMP”…

Screenshot_20200912-171020_VNC Viewer

Also, the way in which files can be shared between theĀ  Android Host and the Linux Guest System has been changed, as the following two screen-shots show:

Screenshot_20200912-155032_VNC Viewer

Screenshot_20200912-155144_File Manager

Here, the file ‘Text-File.txt’ has been shared between Android and Linux. Larger files can also be shared in the same way, and the folder bookmarked under Linux. (:2)

In many ways, the Linux applications behave as described before, with the unfortunate exceptions I just named, and I intend to keep using this app.

Technically, a Host app that just sandboxes a Guest Application in this way, does not count as a Virtual Machine. A real VM allows processes to obtain root within the Guest System, without endangering the Host System. Also, ‘a real VM’ provides binary emulation, that makes no specific assumptions about the Guest System, other than, usually, what CPU is being used. Emulation that includes non-native CPU emulation is still a somewhat special type of emulation.

Therefore, the ability of Debian 10 / Buster to run under ‘UserLAnd’ depends, in this case, on the Linux package maintainers having cross-compiled the packages, to run on an ‘ARM-64′ CPU…

 

(Updated 9/13/2020, 21h30… )

Continue reading Revisiting the Android, UserLAnd app.

I now have Linux installed on my Samsung Galaxy Tab S.

A fact which I had lamented about, was that my Samsung Galaxy Tab S, First Generation – Android tablet – had essentially crashed. Its behavior had gotten so unstable as to make it unusable.

What this also did – given that I have a working Pixel C – was make the software / firmware -installation on the Tab S expendable, which meant that as soon as I was over the loss, I found myself willing to experiment with it.

So I did a factory reset, which made it stable again, at the expense of deleting all my user-data and separately-installed apps from Google Play. Essentially, the tablet had crashed while I was doing a routine update of apps, for which reason the FS corruption was limited to the ‘/sdcard’ partition, where user-installed apps are stored, as well as perhaps, to the ‘/data’ partition, where application data is stored. The factory reset empties those, and, because no system software update was taking place at the time of the crash, the ‘/system’ and ‘/boot’ partitions probably did not suffer from any corruption.

Then, I installed Linux on that tablet, using the Google Play store app named “GNURoot“, as well as using the Google Play store app named “XSDL“. When we install Linux on Android-capable hardware, we need to have a working Android system on that as well, because only the Android software can really provide the display drivers, and the I/O.

XSDL is an Android app which emulates a Linux X-server, which Linux sessions could connect to, as long as the Linux sessions can be persuaded not to try launching their own X-server instance, which their packages tend to depend on.

GNURoot is an app for Android 6+ that allows Debian / Jessie packages to be installed directly to the Android File System, and which runs those packages as though it was Linux. Remarkably, it does not require the device be rooted. It also uses the Android kernel. With the correct packages installed, it’s possible to get a proper desktop-session going between ‘GNURoot’ and ‘XSDL’. But the process is not user-friendly.

At first I had tried to install a system of ~400 packages, that provide ‘XFCE’, only to find that this desktop-manager could not connect to the ‘XSDL’, X-server, at least in any way I could get working. But then I tried uninstalling ‘GNURoot’, reinstalling ‘GNURoot’, and then installing the packages for ‘LXDE’, which is a lightweight, yet better desktop manager than the older XFCE would have been. This time, doing so required I patiently install ~600 packages.

Apparently, LXDE could be told to connect to an ‘XSDL’ instance quite well, and I obtained a working desktop-session. I also installed “GIMP” and “Blender”, which both ran fine – even on my Android tablet !

screenshot_2017-09-24-06-00-25

screenshot_2017-09-24-05-59-53

There was one caveat to using this configuration however, which is that I absolutely needed to connect an external, Bluetooth mouse, as well as an external Keyboard. Apparently, the ability of ‘XSDL’ to provide virtual replacements for those, just wasn’t up to snuff.

(Updated 8/31/2019, 12h10 … )

Continue reading I now have Linux installed on my Samsung Galaxy Tab S.