i did update my machine with pacman -Syu. after rebooting, i cannot login. i con see this error Failed to start Virtual Console Setup a tiny second right before log in screen. i had to capture it in slow mo to able to read it. i attach the image below.
and on the login, after i enter my username and hit enter it just hangs for a while without asking the password and asks for username again. it acts like when you enter wrong password.
Fix
turns out /bin some how got messed up. thanks to @wwwgem, i looked into system logs (journalctl) and fixed it
Today, my nixos took 50gb of drive space to update itself. I allocated 60gb for my root partition and nixos itself takes 20 already. Nixos is hot garbage in that regard. Nixos is stable but bloaty, arch is sleek but wonky.
An equivalent arch install took only 8gb.