Red Hat Summit21.9. NFS and portmap
Note
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.
21.9.1. Troubleshooting NFS and portmap
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Because
portmap provides coordination between RPC services and the port numbers used to communicate with them, it is useful to view the status of current RPC services using portmap when troubleshooting. The rpcinfo command shows each RPC-based service with port numbers, an RPC program number, a version number, and an IP protocol type (TCP or UDP).
To make sure the proper NFS RPC-based services are enabled for
portmap, issue the following command as root:
rpcinfo -p
rpcinfo -p
The following is sample output from this command:
If one of the NFS services does not start up correctly,
portmap is unable to map RPC requests from clients for that service to the correct port. In many cases, if NFS is not present in rpcinfo output, restarting NFS causes the service to correctly register with portmap and begin working. For instructions on starting NFS, refer to Section 21.5, “Starting and Stopping NFS”.
Other useful options are available for the
rpcinfo command. Refer to the rpcinfo man page for more information.
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