## Pursuing the question of, whether a Linux subsystem, that runs under Android, due to the UserLAnd app, can be used for Web development.

It was a subject which I wrote about several months, or years ago, that I had installed the “UserLAnd” app on my Google Pixel C Tablet, so that I could install Debian Linux on it. And a question which one reader had asked me was, whether such an arrangement could be used, to carry out Web development. In fact, some question existed, as to whether proprietary software could be made to run, and my answer was, that it would be preferred to run only Free, Open-Source Software.

In the meantime, I’ve uninstalled Linux from the Pixel C, and installed it on my Samsung Galaxy Tab S6, which has 256GB of internal storage, so that this question can be examined more seriously.

The answer I’d give to this question is, that Web-development can be done in this way, as long as the developer accepts some severe restrictions.

• Successful development of any kind will depend on whether the user has a real keyboard to type on.
• The Open-Source application “Bluefish” runs out-of-the box, which is more than I can say for any sort of Python IDE.
• Because there is little possibility to run a Web-server on the tablet, the features which Bluefish would normally have, to edit PHP Scripts as well, will simply need to be ignored. The ability to preview the Web-pages written, depends on the Guest System’s Firefox browser following the ‘prooted’ Guest System’s Filename-Paths, so that, when Bluefish opens Firefox, the HTML File will essentially be opened as if from the hard drive. And the feature works…

The main reason I would say, not to invest in paid-for software on this platform, is, because its full potential will not be realized.

The HTML and CSS Files created in this way will next need to be transferred to an actual Web-server, and some of the ways in which Bluefish would be set up on a real Linux box, would make this easier.

(Updated 10/03/2020, 4h00: )

## Certain things which the almighty CMake utility cannot do.

CMake happens to be a friend of mine. On my Linux computers, if I need to custom-compile some software, and, if that software does not come with the older ‘./configure’ scripts…, then chances are, that source tree has a ‘CMakeLists.txt’ file in its root directory. On an ‘amd64′, or an ‘i386′ -based computer, this is usually all that I need to create Makefiles, and then to compile the project.

But, I have recently run into a situation where this utility became useless to me. It was an ‘aarch64-linux-gnu’, aka, an ‘arm64′ -based Guest System, running within ‘TightVNC’, running within an Android Host System, via the ‘UserLAnd’ Android app, that uses ‘proot’ to sandbox the Linux Guest System. I tried to use CMake as usual (not really trying to cross-compile anything), and was startled by what this utility next told me: That my C++ compiler was broken, because CMake could not compile a test program, that CMake, in turn, generally tests compilers with.

What I found out was, that it was not the compiler’s fault, but rather, the apparent magic that allows CMake to find the libraries, not working when run on this platform. Hence, the compiler was failing its test, because CMake could not even discern a single library’s location, nor any other variables, that would ultimately have been relevant to the project. The compiler’s test was not even being linked to ‘libstdc++.so’.

I basically had to give up on using CMake on that platform, as well as, on custom-compiling many software projects, that would have been written by other programmers.

What I have learned however is the apparent fact, that when true experts write the ‘CMakeLists.txt’ file to do so, they can even get it to cross-compile their projects to the same platform. But those would be their projects, and not my own project.

Dirk

## Trying to turn an ARM-64 -based, Android-hosted, prooted Linux Guest System, into a software development platform.

In a preceding posting I described, how I had used an Android app that does not require or benefit from having ‘root’, to install a Linux Guest System on a tablet, that has an ARM-64 CPU, which is referred to more precisely as an ‘aarch64-linux-gnu’ architecture. The Android app sets up a basic Linux system, but the user can use apt-get to extend it – if he chose a Debian 10 / Buster -based system as I did. And then, for the most part, the user’s ability to run software depends on how well the Debian package maintainers cross-compiled their packages to ‘AARCH64′. Yet, on some occasions, even in this situation, a user might want to write and then run his own code.

To make things worse, the main alternative to a pure text interface, is a VNC Session, based on ‘TightVNC’, by the choice of the developers of this app. On a Chromebook, I chose differently, by setting up a ‘TigerVNC’ desktop instead, but on this tablet, the choice was up to the Android developers alone. What this means is, that the Linux applications are forced to render purely in software mode.

Many factors work against writing one’s own code, that include, the fact that executables will result, that have been compiled for the ‘ARM’ CPU, and linked against Linux libraries!

But one of the immediate handicaps could be, that the user might want to program in Python, but can’t get any good IDEs to run. Every free IDE I could try would segfault, and I don’t even believe that these segfaults are due to problems with my Python libraries. The IDEs were themselves written in Python, using Qt5, Gtk3 or wxWidgets modules. These types of libraries are as notorious as the Qt5 Library, for relying on GPU acceleration, which is nowhere to be found, and one reason I think this is most often the culprit, is the fact that one of the IDE’s – “Eric” – actually manages to report with a gasp, that it could not create an OpenGL rendering surface – and then Segfaults. (:3)

(Edit 9/15/2020, 13h50: )

I want to avoid any misinterpretations of what I just wrote. This does not happen out of nowhere, because an application developer decided to build his applications using ‘python3-pyqt5′ etc… When I give the command:


# apt install eric



Doing so pulls in many dependencies, including an offending package. (:1) Therefore, the application developer who wrote ‘Eric’ not only chose to use one of the Python GUI libraries, but chose to use OpenGL as well.

Of course, after I next give the command to remove ‘eric’, I also follow up with the command:


# apt autoremove



Just so that the offending dependencies are no longer installed.

(End of Edit, 9/15/2020, 13h50.)

Writing convoluted code is more agreeable, if at the very least we have an IDE in front of us, that can highlight certain syntax errors, and scan includes for code completion, etc. (:2)

Well, there is a Text Editor cut out for that exact situation, named “CudaText“. I must warn the reader though, that there is a learning curve with this text editor. But, just to prove that the AARCH64-ported Python 3.7 engine is not itself buggy, the text editor’s plug-in framework is written in Python 3, and as soon as the user has learned his first lesson in how to configure CudaText, the plug-in system comes to full life, and without any Segfaults, running the Guest System’s Python engine. I think CudaText is based on Gtk2.

This might just turn out to be the correct IDE for that tablet.

(Updated 9/19/2020, 20h10… )

## 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”…

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

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… )