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.
18.9.1. Troubleshooting NFS and portmap
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
The following is sample output from this command:
program vers proto port
100000 2 tcp 111 portmapper
100000 2 udp 111 portmapper
100021 1 udp 32774 nlockmgr
100021 3 udp 32774 nlockmgr
100021 4 udp 32774 nlockmgr
100021 1 tcp 34437 nlockmgr
100021 3 tcp 34437 nlockmgr
100021 4 tcp 34437 nlockmgr
100011 1 udp 819 rquotad
100011 2 udp 819 rquotad
100011 1 tcp 822 rquotad
100011 2 tcp 822 rquotad
100003 2 udp 2049 nfs
100003 3 udp 2049 nfs
100003 2 tcp 2049 nfs
100003 3 tcp 2049 nfs
100005 1 udp 836 mountd
100005 1 tcp 839 mountd
100005 2 udp 836 mountd
100005 2 tcp 839 mountd
100005 3 udp 836 mountd
100005 3 tcp 839 mountd
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 18.5, “Starting and Stopping NFS”.
Other useful options are available for the rpcinfo command. Refer to the rpcinfo man page for more information.
