it was... but unfortunatelly after this command i lost sound firstly, than internet...then i rebooted and stuck with this image on screen. Also there were a lot of messages that changing failed, but not for every raw that appeared in terminal....so...something was changed

I might, but i very sure that i did it without -R.. i'm close to "shoked" condition right now....What options do i have?

Yep. I did -R. Updated picture of your "log" will add to post

Added log screenshot to main topick body. I understand that i'm in really big deeeeeeep trouble. Any instruction is highly uppreciated

Please, help with any step by step possibilities of mine... a lot of user data on this system is very important. There are some uncommited important changes in projects and files. And I don't know how to reinstall ubuntu if i have windows near it on boot.

I agree with @user535733, It is easiest and fastest to backup your personal files (everything that you cannot afford to lose), and after that re-install your Ubuntu system (a fresh installation).

What is a way of making backup? I'm ready for reinstall, but how to make backup

The straightforward way is to copy all those important files (directories and files) to another drive, an external drive or network drive or to some location on the 'internet cloud'. There are also special application programs; it should be discussed in a separate question. Check until you are sure, that the backup is good (and can be used).

How to start copying files... in terminal?

It is probably easiest, if you boot from a live drive, a USB pendrive or DVD disk with Ubuntu and use the full desktop environment, that comes with that system. But it is possible in a text screen too. Have you got a USB pendrive and an external hard disk drive?

I do have USB bootable ubuntu flash drive, but at home. And i have one or two flash drive or hard drives to store data...at home again. Will i see files if i would boot in bootable OS?

I tried to check home directory in terinal

and it was empty

Windows might have problems to see them, but an Ubuntu boot drive runs Ubuntu, and can see files in the internal drive.

i tried in terminal of recovery mode

of linux

i hope that it was just because of recovery mode that hides user data

Which home directory did you look at? Root's home directory might be empty.

but that is just a gues

i mean /home

of root

total home))

If you boot from a USB drive, your internal drive will probably automount. If not, you can mount it manually. Then you can see its content via the mountpoint.

sudo lsblk -f

and

sudo lsblk -m

will show the partitions and mountpoints (for the mounted partitions).

oh

this stuf with partitions was a black side of linux for me)

so

this commands are for mounting drives to usb OS

What is the output of the command (when running the system as you do now)

ls -l /

There is a small but ...huge trouble

ell ess space minus ell space slash

i'm now on windows

i'm now on windos that is in paralell with those linux

OK, I see. Then I suggest that you create a USB boot drive with Ubuntu

i have it at home, ok. Whats next>?

I've stuck in office now, but will continu at home. what are my options with bootable drive?

Unfortunately it is getting late here, so I cannot wait while you are doing that. But I can help you tomorrow (or someone else can help, if our time schedules do not match). Anyway good luck and good night :-)

Thats ok

Hope to see you or anyone tomorrow

Certain files or folders of files it can be best to compress them before transferring to a usb drive. Also if need be while using a live session to look thru your borked install you can, in the live session, create a new user using the exact same name as the borked user. Then log out from live session > to newly created user.