FreeTDS User Guide: A Guide to Installing, Configuring, and Running FreeTDS
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What it does

The interfaces file aliases a dataserver name to the hostname and port number of the dataserver's machine. When FreeTDS receives a request to connect to a database server, it looks up the dataserver name in interfaces. There, it finds the machine name (or address) and port number to connect to, that is, the port where the database server is listening.

Tip

How's that again?

The interfaces file sometimes trips people up. It seems innocuous enough, but it's also a pretty good example of "it's easy if you know how". Keep in mind:

  • The dataserver name is the name of the database server. When a database client specifies the "name of the server" to connect to, it's the dataserver name that is used.

  • The host name is the name of the host (machine) where the database server is running. It has an IP address, and in almost any environment, you can ping the machine name to see if you've got it right. After it uses the dataserver name to look up the host name, FreeTDS will do the same thing ping does to get the IP address of the machine to connect to.

  • Finally, the port number is frequently overlooked. From the network's point of view, knowing the IP address without the port number is a little like knowing the address of an apartment building without knowing the apartment number. In both cases, it will be hard to find what you came for. Make sure you know the port number, and that it's correctly entered in the interfaces file.

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