So, the problem got solved when I use root user. So, probably the 'steam' user have some permission issue that I don't know how to fix yet. So check out using root user when setting up the server.
BTW, the 'steam' user is one I created using "useradd steam" command. I forgot where I saw such usage, but anyway, that user doesn't work very well. So for now, I am using root user, and it works.
Sorry, I misunderstood that you had similar issue. My bad. And yeah, as I said, I fixed this issue with using root user instead of 'steam' user I created before.