Where Is server.cfg on a Rust Server?

The Rust server configuration file belongs in the identity-specific configuration directory:

rust/server/<server.identity>/cfg/server.cfg

Find the server identity

Check the server's startup command for the +server.identity parameter:

+server.identity "server1"

This parameter sets the server's internal identity and determines the directory used for its files. With an identity of server1, the configuration file belongs at:

rust/server/server1/cfg/server.cfg

Create server.cfg if it is missing

If the file does not exist, create a file named server.cfg in the identity's cfg directory.

On Shockbyte-managed servers, note the Server Identity shown under Config > Rust Server Settings, then open the corresponding directory under:

server/<identity>/cfg

Shockbyte's control panel allows a missing server.cfg to be created in that directory with the New File option.

Add server settings

Entries in server.cfg omit the + and - prefixes used by startup parameters. The Facepunch Rust Wiki provides this example:

server.maxplayers 10
server.hostname "Tom Server"
hackablelockedcrate.requiredhackseconds 600

For example:

Startup parameter: +server.maxplayers 10
server.cfg entry:  server.maxplayers 10

Apply the configuration

The server reads server.cfg at startup, so restart the server after saving changes. Settings in this file take priority over values supplied on the command line. The server does not update server.cfg automatically; changes must be made manually.

Sources

See the Facepunch Rust server guide and Shockbyte's server.cfg guide.