This question already has an answer here:
so I needed to chown a folder and I accidently wrote
chown -R admin:admin /
And that chmowned all files for ~5sec then came up an error that it can not chown something and I stopped.
After I noticed I can not login in VestaCP, I changed password for VestaCP, but still could not log in.
So I checked the pass with somekind of Vestatool + standard login and it worked, so I understood this issue is because of the chmod - VestaCP cant' probably create a session file or something. Where should I look to set correct permissions? I checked most folders abd can not find any fault with them, comparing to my other server. Everything else seems working, also did a restart - booted up and running.