19.9. NFS and portmap

19.9. NFS and portmap


The following section only applies to NFSv2 or NFSv3 implementations that require the portmap service for backward compatibility.

The portmapper maps RPC services to the ports they are listening on. RPC processes notify portmap when they start, registering the ports they are listening on and the RPC program numbers they expect to serve. The client system then contacts portmap on the server with a particular RPC program number. The portmap service redirects the client to the proper port number so it can communicate with the requested service.

Because RPC-based services rely on portmap to make all connections with incoming client requests, portmap must be available before any of these services start.

The portmap service uses TCP wrappers for access control, and access control rules for portmap affect all RPC-based services. Alternatively, it is possible to specify access control rules for each of the NFS RPC daemons. The man pages for rpc.mountd and rpc.statd contain information regarding the precise syntax for these rules.

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