How to make yourself admin on a Rust server (ownerid)

Quick answer: in the server console (the window RustDedicated.exe runs in) or over RCON, type ownerid <your SteamID64> "YourName" "owner". You are admin straight away, with no reconnect, and the server keeps it after a restart. Then press F1 in game for the admin console.

ownerid 76561198000000000 "Drizzza" "owner"

Find your SteamID64

Your SteamID64 is a 17 digit number that starts with 7656. Three ways to get it:

In Steam, open your profile. If you never set a custom profile URL, the number is at the end of the address.
In Steam, open Account details: it shows your Steam ID under your account name.
Join the server, then type status or users in the server console. Both list everyone connected with their ID.

Owner or moderator

Command	What it gives
`ownerid <steamid> "name" "note"`	Owner: full admin.
`moderatorid <steamid> "name" "note"`	Moderator: admin powers in game, but cannot add owners.
`removeowner <steamid>`	Takes owner away.
`removemoderator <steamid>`	Takes moderator away.

Each one works at once if the player is online, and the server saves it by itself. The name and note are only for your own records.

The first admin

Nobody is admin on a new server, so the first ownerid has to come from the server console or from RCON. After that, an owner can add more owners and moderators from the F1 console in game.

Where admins are saved

Owners and moderators go in users.cfg, in the server’s cfg folder (server/<identity>/cfg/, next to RustDedicated.exe). A full wipe deletes that folder, so add yourself again after one; see how to wipe a Rust server.

In Crucible Local Server

Crucible Local Server does this with one box: the Add ownerid card in the Quick view while the server is Live, and the owners list in the Config tab. See make yourself an admin.

How to kick, ban and unban players
Rust admin commands, every command an admin can run
Rust server.cfg example