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.

automountd

This daemon handles the mount and unmount requests from the autofs service. The syntax of the command is:

automountd [ -Tnv ] [ -D name=value ]

where -T selects to display each RPC call to standard output, -n disables browsing on all autofs nodes, -v selects to log all status messages to the console, and -D name=value substitutes value for the automount map variable indicated by name. The default value for the automount map is /etc/auto_master. Use the -T option for troubleshooting.

lockd

This daemon supports record-locking operations on NFS files. It sends locking requests from the client to the NFS server. On the NFS server, it starts 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 only processes 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 it 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 a reduction 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 handles per connection. Base the value for nthreads on the load expected on the NFS server. The default value is 20. Because each NFS client using TCP uses a single connection with the NFS server, each TCP client is granted the ability to use up to 20 concurrent threads on the server. All NFS clients using UDP 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 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 is 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. You can use two options with this command (see the mountd(1M) man page): -v and -r.

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

nfslogd

This daemon provides operational logging. NFS operations against a server are logged based on the configuration options defined in /etc/default/nfslogd. When NFS server logging is enabled, records of all RPC operations on a selected file system are written into a buffer file by the kernel. Then nfslogd post-processes these requests. The name service switch is used to help map UIDs to logins and IP addresses to host names. The number is recorded if no match can be found through the identified name services.

Mapping of file handles to path names is also handled by nfslogd. The daemon keeps track of these mappings in a file-handle-to-path mapping table. One mapping table exists for each tag identified in /etc/nfs/nfslogd. After post-processing, the records are written out to ASCII log files.

statd

This daemon works with lockd to provide crash and recovery functions for the lock manager. It tracks the clients that hold locks on an NFS server. If a server crashes, on 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.

In the Solaris 7 release, the way that statd keeps track of the clients has been improved. In all earlier Solaris releases, statd created files in /var/statmon/sm for each client using the client's unqualified host name. This caused problems if you had two clients in different domains that shared a hos tname, or if there were clients that were not resident in the same domain as the NFS server. Because the unqualified host name only lists the host name, without any domain or IP-address information, the older version of statd had no way to differentiate between these types of clients. To fix this problem, the Solaris 7 statd creates a symbolic link in /var/statmon/sm to the unqualified host name using the IP address of the client. The new link will look like:

# ls -l /var/statmon/sm
lrwxrwxrwx   1 root          11 Apr 29 16:32 ipv4.192.9.200.1 -> myhost
--w-------   1 root          11 Apr 29 16:32 myhost

In this example, the client host name is myhost and the clients' IP address is 192.9.200.1. If another host with the name myhost were mounting a file system, there would be two symbolic links to the host name.