I quess,adb,is not,recognized sometimes

sudo ubuntu-device-flash --server=http://system-image.ubports.com touch --device=turbo --channel=ubports-touch/16.04/rc --wipe

thank you for your explanations

By restoring the Backup 16.04 stable with TWRP, just download it, unpack it and then restore it. Afterwards, you'll only need to flash Ubuntu Recovery with fastboot.
But, the future updates (OTA-stable, rc, devel ) might fail due the size of the .cache (if you don't resize it before) , otherwise you should be able to use Ubports installer.

And second query, if I turn everything except TWRP, will it work with "ubports-installer" or I would still have to increase the cache?

thank you in advance

Furthermore, can anyone list the exact metrics of their sda41 through sda44 partitions after a succesful resize on a 64GB model? The start and end points, the size, etc?

Note: I came back to edit this message because the browser on my M10 often cuts out because of too many tabs, so I didn't want to lose it and made it a work in progress.

I actually went and manually downloaded the partition images for 16.04 and (carefully) extracted them on the phone and that worked also. I'm now happily running UBports 16.04 development with Anbox. I can't believe what I'm seeing. What the UBports team has achieved is amazing!

I'm currently fighting with the UBports Installer and ubuntu-device-flash to try to get actual flashing of UBports system images to the device working (still the only working system has arisen from your TWRP backup). I've no idea what's wrong, but am wondering if there's an ADB authorization problem preventing the installers/flashers from working. I may try getting a UBports 16.04 image and manually transferring files from it to partitions on the device using the TWRP terminal...

/dev/block/sda42 720896 797700 76805 300M Linux filesystem
/dev/block/sda43 851968 983039 131072 512M Microsoft basic data
/dev/block/sda44 983040 7633914 6650875 25.4G Microsoft basic data

and increase the size of partition 43(sda43) (cache)

I decreased the 42 to 300M and increased 43 to 700 (-ish) and 16.04 installed without any issue then

In your case the partitions start and end block will be different as you have 64Gb version of PRO5, but that's not an issue.

Just follow the instrucions ;

reboot to TWRP,
In terminal on your PC write;

mount /dev/block/sda41 /system
mount -t proc proc /system/proc
mount -t sysfs sys /system/sys
mount -o bind /dev /system/dev
chroot /system /bin/bash

type: fdisk
type: fdisk /dev/block/sda

type: m
Now you should be in the menu of FDISK utility,

have a look at the commands.

type: p

the output should be your phone partition table, copy it and save it to Libre Office writer or whatever you want( gedit...etc)

Now you can see your partitions 42 and 43 which are of your interest.
You need to decrease the size of 42 and increase 43.
About 725M for partition of 43 would suffice, but you can give it more if you'd like.
Remember what you add to 43 you need to take from 42.

Here is my table for comparison only:

Device Start End Sectors Size Type
/dev/block/sda1 1024 1279 256 1M Microsoft basic data
/dev/block/sda2 1280 1343 64 256K Microsoft basic data
/dev/block/sda3 1344 1407 64 256K Microsoft basic data
/dev/block/sda21 2048 3071 1024 4M Microsoft basic data
/dev/block/sda22 3072 5119 2048 8M Microsoft basic data
/dev/block/sda23 5120 5631 512 2M Microsoft basic data
/dev/block/sda24 5632 6655 1024 4M Microsoft basic data
/dev/block/sda25 6656 7679 1024 4M Microsoft basic data
/dev/block/sda26 7680 13823 6144 24M Microsoft basic data
/dev/block/sda27 13824 22015 8192 32M Microsoft basic data
/dev/block/sda28 22016 30207 8192 32M Microsoft basic data
/dev/block/sda29 30208 35327 5120 20M Microsoft basic data
/dev/block/sda30 35328 40447 5120 20M Microsoft basic data
/dev/block/sda31 40448 45567 5120 20M Microsoft basic data
/dev/block/sda32 45568 50687 5120 20M Microsoft basic data
/dev/block/sda33 50688 55807 5120 20M Microsoft basic data
/dev/block/sda41 65536 720895 655360 2.5G Microsoft basic data
/dev/block/sda42 720896 797700 76805 300M Microsoft basic data
/dev/block/sda43 797952 983039 185088 723M Microsoft basic data
/dev/block/sda44 983040 7633914 6650875 25.4G Microsoft basic data

NOW, delete the 42 partition by typing: d
it should ask you the number of partition
Command (m for help): d
Partition number (1-3,21-33,41-44, default 44): 42

Partition 42 has been deleted.

Now you need to create a new 42 partition with smaller size
type: n
it will ask you for a partition number and you'll type 42
now it's asking for a first sector and you'll need to calculate the size as your 64Gb phone has a different partition table as mine 32Gb.

the first sector should stay the same, just press enter on keyboard,
the end sector you'll need to try to guess it. I've used end sector of 790000 instead of 810000, thus gaining some space for partition 43, but you'll need to try it on you own.
NO WORRIES, unless you save it, it won't be set, you can try it again and again, just by pressing q and enter
Then again typing: fdisk /dev/block/sda
and you'll be in the fdisk menu again, without any changes to the partition table, you can verify this by typing: p
I know it's a good game to try to guess the partition size, I've gone through that as well.

Anyway, when you finally manage to set the right end sector of partition 42, you'll need to change the partition type as at the moment is LINUX FILE SYSTEM and we nee a MICROSOFT BASIC DATA ( or type 6 )
In order to do that, type command : t
It will ask you for a partition No, you type: 42
Now it will ask for a type of the partition 42
type in: l
It will list all known file types, as you can see we need the No. 6 or MICROSOFT basic data
type: 6
Changed type of partition 'Linux filesystem' to 'Microsoft basic data'.

Now go back and verify that by typing: p

it should list again the partition table with changed 42 partition size and file type.

You'll need to verify this by typing: v

See something like this?
Command (m for help): v
No errors detected.
Header version: 1.0
Using 20 out of 128 partitions.
A total of 11386 free sectors is available in 3 segments (the largest is 38 MiB).
So it's verified.

Now type: x
It will take you to expert menu/mode.
You'll need to change the name of the partition 42 to ''custom''
To do that, type: m

This should appear on you Terminal:

Expert command (m for help): m

Help (expert commands):

GPT
i change disk GUID
n change partition name
u change partition UUID
M enter protective/hybrid MBR

A toggle the legacy BIOS bootable flag
B toggle the no block IO protocol flag
R toggle the required partition flag
S toggle the GUID specific bits

Generic
p print the partition table
v verify the partition table
d print the raw data of the first sector from the device
D print the raw data of the disklabel from the device
f fix partitions order
m print this menu

Save & Exit
q quit without saving changes
r return to main menu

O.K ,type: n
type:42

Give it a new name as prompted.
Type: custom

Now type: r
it takes you back to main menu of FDISK utility.

Type: w
it writes the changes and saves them.
Now you should be back in adb shell as root@localhost #
Good,
you'll need to format the newly created partition of 42, by typing:
mke2fs -t ext4 -m 0 /dev/block/sda42

This should look the output like:

root@localhost:/# mke2fs -t ext4 -m 0 /dev/block/sda42
mke2fs 1.42.12 (29-Aug-2014)
/dev/block/sda42 contains a ext4 file system
created on Fri Jan 26 19:09:44 2018
Proceed anyway? (y,n) y
Discarding device blocks: done
Creating filesystem with 76805 4k blocks and 76896 inodes
Filesystem UUID: f7f0db2f-b0e9-4bf7-bf94-ae843a409094
Superblock backups stored on blocks:
32768

Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

Now to verify if the partition 42 has been decreased in size, reboot the phone to TWRP recovery and again do this steps:

adb shell

mount /dev/block/sda41 /system
mount -t proc proc /system/proc
mount -t sysfs sys /system/sys
mount -o bind /dev /system/dev
chroot /system /bin/bash

Now go back to fdisk utility by typing: fdisk /dev/block/sda

and verify the changes in partition 42 by typing: p

You should see the partition 42( sda42) decreased in size
If true, congratulation, now to increase the partition 43 (sda43) which is our main interest off course.

Go back and do the same steps for partition 43 ,delete it, create it, increase the size, change the name to ''cache'', save it, then format it, verify , just like with the partition 42.

I guess you'll be busy today Have fun.

I hope you don't mind, but I'd love to get a little more guidance from you, if you are willing. I want to get this machine up to 16.04/devel.

After using TWRP to restore your image, I flashed the Ubuntu recovery image and then, just to test it out, tried to see if the Ubuntu update facility in the settings would be able to update the system. Unfortunately something isn't quite working here and I'm getting the "Update failed, contact support." message from the Ubuntu recovery. Perhaps this is partition-related.

Anyway, now I'm thinking about changing the partitions to prepare the machine for 16.04/devel. I can see that you had some success on this here. Would you be able to tell me the commands you used?