Linux
First hours on a Linux VPS
Updates, a sudo user, SSH hardening — without turning the guide into a distro wiki.
Update
On Ubuntu/Debian: apt update && apt upgrade. Reboot if a kernel update requires it. Do this before you expose extra ports.
Unprivileged user
Create a user with sudo, copy your SSH key to that account, confirm you can log in, then disable root password login. Keep root key login only if you have a reason.
Firewall and fail2ban
Enable a host firewall as in Firewall basics. fail2ban on SSH reduces credential stuffing; it is not a substitute for keys.
Time and logs
Set timezone and enable NTP. Logs fill disks; configure logrotate. A full disk is a frequent cause of “the site is down but ping works”.