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…

 

Screenshot_20200924-052525_VNC Viewer

Screenshot_20200924-052618_VNC Viewer

 

The main reason I would say, not to invest in for-pay 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.

 

Dirk

 

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.

Major Problem when Upgrading a UserLAnd Linux Guest System via ‘apt-get’.

A fact which I had blogged about before was, that I had installed a Debian 10 Linux Guest System on the Android, Google Pixel C Tablet, using the Android app ‘UserLAnd’. This Debian 10 version was compiled by the package maintainers to run on an ARM-64 CPU.

Well, along with major updates to Debian 9 / Stretch, the Debian maintainers have just issued an update to Debian 10 / Buster, from version 10.0 to version 10.1 . The problem? When trying to perform the upgrade via ‘sudo apt-get’, the process hangs over the attempt to update or install ‘systemd’, and then configure it. Apparently, doing this requires full root privileges, because ‘systemd’ would normally control how services run in the background with ‘root’, but UserLAnd does not allow any part of its Guest System to run as ‘root’.

This could become a stumbling-block, in any future updates.

The ‘solution’ which I attempted to apply was, to remove everything that depends on ‘systemd’, and to re-apply the upgrade in total. But the net effect of that is, to remove many more packages than I intended to remove, including all things related to ‘Gtk 3′, ‘LXTerminal’, as well as key components that allow ‘LXDE’, the Lightweight Desktop Manager, to function at all.

Caution: This would have been a completely unsafe thing to do on a real computer, and was only plausible because the setup in question was virtual in some way, and also expendable. This would normally brick the computer…

When the makers of UserLAnd provided easy screen-shortcuts to install Debian and LXDE, they knew how to modify the installation script, to ignore whatever problems result from installing LXDE and its dependencies in a ‘proot’ed environment. But I don’t know those tricks. (:1) So at one point I had a partially gutted system, without LXDE really installed.

But the (Android) devs behind UserLAnd also provided a quick workaround for that problem. The next time I exited the corrupted session, and re-launched LXDE from the UserLAnd menu, this Android app recognized that LXDE was no longer installed, and simply reinstalled it for me, after which I could access it again.

Once I had done this, my wallpaper was a black background, and quite a few of the installed applications were no longer installed. And so what I needed to do next was, to run the equivalent of the following command:

 


$ sudo apt-get install gnome-backgrounds clipit evince wxmaxima gcl firefox-esr libpam-cracklib

 

After having done this, I was able to select a wallpaper again, from the file chooser, and to regain most of the abilities I already had before.

I might still be missing some of the applications I once had.

But what all this suggests is, that the Linux Guest System should only consist of a vest-pocket system, with a small number of applications, because in reality any and all Linux applications may simply need to be reinstalled at some point in time. But, there is a way in which users are not ‘hosed’ if this happens:

Linux still segregates its data into a system directory, and a user home directory. Even though we have no form of access control within a ‘proot’ed system, even if certain applications are removed from the system directory, and then reinstalled there, our home directory will remember all our personal settings and data.

So the solution can be as quick as the initial disaster was.

My Linux Guest System is now down to taking up 4.86GB of Android application-data.


 

(Updated 9/09/2019, 16h15 … )

(As of 9/07/2019, 20h00 : )

I think I’ve gotten closer to finding out, what went wrong…

Continue reading Major Problem when Upgrading a UserLAnd Linux Guest System via ‘apt-get’.

Problems Getting Synaptic To Work, On My Google Pixel C Tablet

One of the facts which I’ve blogged about was, that I had used an Android app (that does not require root) in order to install a Linux Guest System, on my Google Pixel C Tablet. The version of Linux it’s subscribed to is Debian 10 / Buster. And, the CPU of that tablet is an ARM-64. One of the considerations which need to be made, when setting up this Guest System, is that both RAM and Storage are scarce, the latter because the entire Linux Guest System consists of Application Data, belonging to this one Android app.

One idea which I was pursuing until last night was, to get the Synaptic GUI to work, where the ‘apt-get’ command-line does already work. Either would provide the main way to install software. But the GUI is much nicer, in allowing searches for packages to take place, instead of just package-names being burped on the command-line (blindly), and also, displaying lengthy descriptions of the packages first.

The way I’d need to launch Synaptic is like so:

 


$ xhost +
$ sudo synaptic

 

The first bug which needs to be dealt with, is This Bug. But, even when that bug has been dealt with, there are more problems facing the use of Synaptic under Debian / Buster. And they all have to do with the fact that the new Synaptic can no longer be used effectively, to search for packages.

First off, in order for the Search Field to display in the toolbar of Synaptic, one needs to install the following:

 


$ sudo apt-get install apt-xapian-index
$ sudo update-apt-xapian-index

 

This is a process that takes about an hour to complete, and when it has completed, its only result is that the Search Field displays in the Tool-Bar of Synaptic. By itself, this Search Field is useless because it only acts as a filter, on the actual search results, that we get when clicking on the Search Button. And, this process is not optimal in a ‘proot’ed environment, on an Android tablet, because the fully built database takes up more than 200MB.

The actual Search Button has been rendered useless. When told to search both the names and descriptions of packages, the resulting search takes about 20 minutes to complete, and does not become faster the second time, even when we have ‘apt-xapian-index’ installed and set up. The only other possibility is, only to search the names of packages, which defeats the entire purpose of using Synaptic.

I once had a (Debian 8 / Jessie) Linux Guest System installed the same way, on a Samsung Galaxy Tab S, first generation, and the searches within Synaptic were quick and painless.

(Updated 9/07/2019, 15h15 … )

Continue reading Problems Getting Synaptic To Work, On My Google Pixel C Tablet