I've been trying with my Konsole to type sudo command or su - root, but it won't accept what I'm told is the default root password of 1234. I'm on Nexus 5, and have tried with both the neon and arch build.

Have you tried first to setup password for user with

passwd

command? It's described here: https://community.kde.org/Plasma/Mobile/FAQ#I.27ve_installed_Plasma_Mobile.2C_what_is_login_password.3F

Same problem here using the intel-based amd64 ISO (neon-pm-devedition-gitunstable-20180305-1543-amd64.iso, boot from USB Stick):

Due to password prompt I cannot install any application from discover or execute anything using sudo as always it prompts for a password.
Also calamares would not work as it also asks for a password.

I tried no password at all or 1234: Everything raises the typical password mismatch reply.
Then tried using the "passwd" command in some combinations from console (e.g. fpr phablet user) yet it keeps prompting me for a password before doing anything and raises password mismatch reply on any tested input so far.
Yet maybe I am using the command wrongly (im kinda new to Ubuntu).

Can you specify what exactly to enter to set a password, e.g. "test", so I can provide a password thatwill work for sudo (and discover, and calamares)?
Thanks a lot in advance!

fkander wrote:Same problem here using the intel-based amd64 ISO (neon-pm-devedition-gitunstable-20180305-1543-amd64.iso, boot from USB Stick):

I somehow doubt that you have the same problem as the OP. Their problem initially appears to be specific to Konsole (an installed environment) whereas yours is more related to whatever Linux distribution you grabbed than KDE itself.

fkander wrote:Yet maybe I am using the command wrongly (im kinda new to Ubuntu).

So you grabbed the Ubuntu live CD I assume? But if you wanted KDE why not grab Kubuntu instead (there's a difference there)?

Also: although I don't recognize the name of the image you used it might be a better idea not to rely on developer snapshots, because - generally speaking - they could contain bugs resulting in a product which doesn't work as intended.

Now, it's been quite a while since I messed with Linux but are you sure you actually need sudo? Some distributions, especially in a live CD, will drop you into a root environment straight away. Try using "id" and pay close attention to your userID.