Sophos installation on a server without internet connection
The Sophos scan engine must be connected to Sophos Central in order to function correctly. To protect servers without a direct internet connection, you can turn an existing server with an internet connection into an "Update and Message Relay" server, as described in the Sophos online help at https://support.sophos.com/support/s/article/KB-000035498?language=en_US#How-do-I-set-up-an-Update-Cache-and-a-Message-Relay.
This server can then be used by others as a proxy. During operation, these servers are automatically found by the engine, but during an initial installation, you must tell Setup once which server it should use to download the installation data.
The setup is simply downloaded as normal in Sophos Central under "Protect devices" and copied to the target server.
The subsequent command line for an installation directly via the update cache looks like this (under Windows):
.\SophosSetup.exe --messagerelays=<Servername/IP>:
8190
For instructions on how to install a Linux system using the update cache, see.: https://support.sophos.com/support/s/article/KB-000039204?language=en_US