NFS Daemons

To support NFS activities, several daemons are started when a system goes into run-level 3 or multiuser mode. Two of these daemons (mountd and nfsd) are run on systems that are NFS servers. The automatic startup of the server daemons depends on the existence of entries labeled with the NFS file-system type in /etc/dfs/sharetab.

The other two daemons (lockd and statd) are run on NFS clients to support NFS file locking. These daemons must also run on the NFS servers.

lockd

This daemon supports record-locking operations on NFS files. It will send locking requests from the client to the NFS server. On the NFS server, it will start local locking. The daemon is normally started without any options. You can use three options with this command (see the lockd(1M) man page).

The -g graceperiod option selects the number of seconds that the clients have to reclaim locks after a server reboot. During this time, the NFS server will only process reclaims of old locks. All other requests for service must wait until the grace period is over. This option affects the NFS server-side response, so can be can be changed only on an NFS server. The default value for graceperiod is 45 seconds. Reducing this value means that NFS clients can resume operation more quickly after a server reboot, but it increases the chances that a client might not be able to recover all its locks.

The -t timeout option selects the number of seconds to wait before retransmitting a lock request to the remote server. This option affects the NFS client-side service. The default value for timeout is 15 seconds. Decreasing the timeout value can improve response time for NFS clients on a noisy network, but it can cause additional server load by increasing the frequency of lock requests.

The nthreads option specifies the maximum number of concurrent threads that the server will handle per connection. Base the value for nthreads should on the load expected on the NFS server. The default value is 20. Since each NFS client using TCP uses a single connection with the NFS server, each TCP client will be granted the ability to use up to 20 concurrent threads on the server. All NFS clients using UDP will share a single connection with the NFS server. Under these conditions it might be necessary to increase the number of threads available for the UDP connection. A minimum calculation would be to allow for two threads for each UDP client, but this is specific to the workload on the client, so two threads per client might not be sufficient. The disadvantage to using more threads is that when the threads are used, more memory will be used on the NFS server, but if the threads are never used increasing nthreads will have no effect.

mountd

This is a remote procedure call (RPC) server that handles file system mount requests from remote systems and provides access control. It checks /etc/dfs/sharetab to determine which file systems are available for remote mounting and which systems are allowed to do the remote mounting. Two options might be used with this command (see the mountd(1M) man page).

The -v option runs the command in verbose mode. Each time an NFS server determines the access a client should get, a message will be printed on the console. The information generated can be useful when trying to determine why a client can not access a file system.

The -r option rejects all future mount requests from clients. This does not affect clients that already have a file system mounted.

nfsd

This daemon handles other client file-system requests. You can use several options with this command. See the nfsd(1M) man page for a complete listing.

The -l option sets the connection queue length for the NFS/TCP over connection-oriented transports. The default value is 32 entries.

The -c #_conn option selects the maximum number of connections per connection-oriented transport. The default value for #_conn is unlimited.

The nservers option is the maximum number of concurrent requests that a server can handle. The default value for nservers is 1, but the startup scripts select 16.

Unlike older versions of this daemon, nfsd does not spawn multiple copies to handle concurrent requests. Checking the process table with ps only shows one copy of the daemon running.

statd

This daemon works with lockd to provide crash and recovery functions for the lock manager. It keeps track of the clients that hold locks on an NFS server. If a server crashes, upon rebooting statd on the server contacts statd on the client. The client statd can then attempt to reclaim any locks on the server. The client statd also informs the server statd when a client has crashed, so that the client's locks on the server can be cleared. There are no options to select with this daemon. For more information see the statd(1M) man page.