Successfully running CA on Android device

[whitedavidp]

I have been successful in running CA on an Android device. CA actually runs under a chroot'ed Ubuntu which runs simultaneously with Android (sharing the Android kernel). This opens up the possibility of using old Android phones or TV computer boxes for this purpose!

Before you bother to do this, you need to have success in connecting your USB modem to your Android device - at least to the extent that the modem is "seen" by the Android kernel. I found that, at least on the devices I have tested so far, my USR modem, when connected to USB (on typical phones, via an OTG (on the go) cable like this - which also allows the phone to charge at the same time), the stock kernels have "seen" the modem and, after connecting, there is a /dev/ttyACM0 (can be seen without root in a terminal window). If you do NOT see this (or a different entry if your modem is NOT USR like mine), then it would seem that the Android kernel in the device does not know how to deal with the modem and you may be out of luck when using that device - but perhaps a different modem might help?

To do this, it MAY be needed to have a rooted Android device. I got Ubuntu installed via an app called Linux Deploy and its matching Busybox - both of which need root access. I used these tools mostly because I had previous experience with them over the years and they worked great. However, I have become aware of a highly-rated, alternate tool called [UserLand](https://play.google.com/store/apps/details?id=tech.ula&hl=en) which claims to do the same sort of thing without need for root. So that might be worthwhile looking into.

Once you get a Linux distribution (I used Ubuntu Focal as that was the latest - but still would work fine with the latest CA - that did not use tar and zst compression which the Busybox's tar command could not handle) installed, you should be able to access it via ssh, vnc, etc - depending on the options given by the deploying app. And from there, the install and configure of CA should be very straight forward.

I have noted that, at least on the Android TV computer with Focal that I just completed, there is no support for systemd due to the chroot'ed Linux. That MIGHT differ using the UserLand approach but I have not checked it out. So I ended up using the sysv support, that does work, to control CA start/stop. This requires a script be written and placed in the right place (/etc/init.d) and then symlink'ed into /etc/rc3.d, etc. I am not an expert in this so I will not offer all the details here. But I was able to get it running, stopping, and logging the console to a file (with time stamps, thanks to Royce).

I am able to connect to the Ubuntu from any computer on my LAN via ssh or vnc,. And, after installing Team Viewer Host on Android, I also Android ssh and vnc clients to enable connection from there as well. This all opens up a ton of possibilities for those who have old or spare Android devices lying around.

Feel free to ask specific questions.

Best

[whitedavidp]

BTW - I found my USR modem is "seen" by the kernel on a Samsung S6 running Android 7 but NOT on a Samsung Note3 running Android 4.x. And I also found the modem "seen" on an Android TV computer running Android 5. So it may be that newer Android (or at least newer kernels) are required.

[thess]

Depends on whether the kernel on these devices supports USB Host (OTG) mode or not.

https://android.stackexchange.com/questions/36887/how-can-i-determine-if-my-device-has-usb-host-mode-otg-support
https://www.mobitrix.com/android-support/android-version-compatible-with-usb-otg.html

... and as usual IMMV.

[whitedavidp]

Well, you are totally correct on that. But OTG support is NOT the entire story. For example the Note3 I mentioned does indeed support OTG. But the kernel is still not recognizing the USR modem with an entry in /dev. Of course the S6 also supports OTG and it does see the modem. The Android TV computer has 3 "normal" PC-style USB ports and so OTG is not needed there.

Yet, it is also a function of the list of kernel features compiled into the kernel in use. For example, I have found that all of the Android kernels I have worked with do NOT support USB->Serial adapters. But if you supply an appropriate kernel model that includes USB->Serial and load it (requires root, I believe), your device can indeed recognize and work with such adapters. I have managed to USB->Serial kernel modules for 3 different Android TV boxes (each requiring different compilation). It was no fun for me. But I managed eventually.

I am certainly no expert in this. But when readying a kernel for compile, if you run make menuconfig, go into Device Drivers->USB Support there is a USB Modem (CDC ACM) Support entry that needs to be enabled. I had to do similar when building my kernel modules. So it might be possible to build kernel modules for kernels that lack built-in USB Modem support. Needless to say, I was thrilled to plug my USR modem into several devices and see the kernel had support enabled without my having to do anything!