From a sysadmin pov, suits are for interviews, funerals and weddings. Shorts and cargos are for home/non-business wear. Smart-ish trousers or jeans, sneakers/trainers or better and T-shirt (no hoodies, sweatshirts etc.) for everyday workwear, replace the T-shirt with a shirt when customers are in.
If you're a sysadmin (and I mean practical, hands dirty sysadmin, not a management middle-man) and you're wearing a tie, then one day you're going to choke yourself when it gets caught while you're crawling/hauling/fixing something. Even if you have people who are supposed to do all that, we all know that sometimes if you want something done right, you've just got to do it yourself.