And alternatively i just saw an other thread that could help you with terminal inside uTouch.
I'll quote here :

@craig said in How to install PIA VPN on UT (Working!):

When running the script, you may get a message that the script was not able to write to /etc/openvpn. If so, do this before you execute the script:

sudo -i
sudo mount -o remount,rw /
sudo chmod 777 /etc/openvpn
exit

After you run the script, set permission back:

sudo chmod 755 /etc/openvpn

You could try the chmod 777 with \system folder.

If enough people were interested in such a device I could prototype a PCB. The major cost from where I live though would be shipping. I could have thousands of tiny PCBs made for a couple of dollars and components would be pennies a piece but shipping to me makes that cost jump by 2000%. Then shipping each one would cost $20+ each to ship to someone outside my country using reliable traceable shipping.

So if anyone lives in a manufacturing hub with good outgoing shipping systems that make it easy for small businesses to ship you may want to look into making these.

Have you simply tried to put the file where you expect it to be even if it doesn't already exist? It may be that it looks in multiple locations for the file and it will work from where you expect it to be?

Yes i did adb push gpio-keys.kl /system/usr/keylayout/
It created the different directories and pushed the file but after a reboot on UT, the /system was exactly the same.
I wonder if there is a /system used by TWRP and a /system used by UT.
I don't know, I may not fully understand what I've done through these 4 days.
Anyways I learnt a lot of things playing with ROMS and recovery imgs. And the result is ... I 'm giving up Ubuntu touch for now but I have a fully fonctionning e/OS where I can lock / unlock the screen with my volume buttons. I did not reach my original goal but I am already satisfied with what I have done
This is thanks to you guys.

Have you simply tried to put the file where you expect it to be even if it doesn't already exist? It may be that it looks in multiple locations for the file and it will work from where you expect it to be?

I have a canonical MX4, made for utouch, with bootloader unlocked (unlike ALL others MX4, wich bootloader is quite un-unlockable), and specific custom recovery (not the same as flyme one).

In this canonical custom uTouch MX4 recovery, nothing else than adb is possible.

I will not try to do anything to this phone software, other than updating uTouch, i don't want to mess with it.

Anyway, we're going off topic.

TWRP stands for Team Win Recovery Project and they have a recovery for almost every Android device out there. You download the correct TWRP for your device (Check XDA for recommended one) then while in fastboot from the command line you run

# change path and TWRP to match your file location and name
fastboot boot path/to/TWRP.img

It will boot the device into TWRP recovery where you can do all kinds of stuff like flash new roms or edit files or wipe directories. (DO NOT install TWRP when it asks you to. that is for Android only)

EDIT: These are the versions of TWRP for hammerhead but you will likely need a certain one that was made for the Android version your UT is based on and by the look of this Halium page. it is Android 5.1 . This where you need to check XDA to find out which one goes with Android 5.1.

We'll see when he answers ^^

Edit : if i refer to thread and Dobey, \system is part of androïd stuff.

That I why I gave instructions for doing it via the file manager in TWRP. Because in TWRP everything can be written over.

First sorry i misreaded you and though you were asking him to do that with uTouch file manager.

Second, are you sure he will be able to do that without enabling dev mode first?

@antidroid
Go to \system with file manager, after image made writable with UTTT, then check infos for folders and files in here : all is read only, you will not be able to paste anything here, you can copy files from, then paste in writable folder like "downloads", but that's all.

That I why I gave instructions for doing it via the file manager in TWRP. Because in TWRP everything can be written over.

@dobey In recovery mode, the /system directory contains only a lost+found directory and i can't find the file /system/usr/keylayout/gpio-keys.kl

Did you try acces this file with ADB from recovery after enabling Developer Mode from system settings under Ubuntu Touch? (System settings -> About -> Developer mode -> enable -> adb reboot recovery -> adb shell)

adb push path/to/new/file /sdcard

from your host to get the new file on the device and then use the file manager under advanced in TWRP to replace the one that keeps being over written with the one you placed in /sdcard?

If anyone has a tip to help me set the /system partition writable or replace this file one way or another. If it is not possible, what i'm going to do next is probably go try paranoid android to play with in the next few days / weeks.

Is it possible to get a zip with the ubuntu touch ROM for NEXUS 5, so i can install it through twrp like i did with the other android systems ?

Thank you all for your help and keep up the good work.

I bought 2 replacement buttons on the internet. I tried to do it myself first... it was a total disaster Then I brought it to a local repair shop. It cost me 35€. And it worked 2-3 months and broke again...
So now I just want to have a usable phone to play with UT.

Ok i understand :disappointed_face:

However, i must tell, never again go to those so-called "phone repair shops" that pop up from here and there, they're 99% owned by incompetents, always go to real electronician repair shop (hard to find i know).

Hope you will succeed in software workaround.

@dobey Ok, I managed to flash my Nexus with an android rom. I could edit the files and it worked perfectly as expected. Then I reinstalled Ubuntu touch. I did not check the "wipe system" checkbox hoping the /system files would stay but unfortunately they have been replaced. I'm trying again tomorrow.
Thank you and good night

It's just a proposal if he feels he can do it (and have tools for that), or know someone that can do it for him.

Beyond that, I'm not sure.

@creuzdos Can't you simply repair harware?

It can be repaired, but I would hardly use the word simply to describe the act.