Solution after sudo/su is ruined or sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set
1. Restart your system, press SHIFT/Esc key while Ubuntu is booting.
2. This will bring you up the boot menu.
3. Go to Advanced Options. Select recovery mode and press Enter.
4. It will bring you up another screen. Now select “Drop to root shell prompt” and press Enter.
5. It will load a command line at the bottom of the screen.
Now run each of the following commands:
1. mount -o remount,rw /
2. mount –all
3. chown root:root /usr/bin/sudo
4. chmod 4755 /usr/bin/sudo
Note: If not able to restart then write exit and press Enter. Come out of recovery mode and restart your system.
=> Check it by writing sudo su in your command prompt.
Feel free to share your inputs/ feedbacks.