29 Sharing File Systems with NFS #

The /etc/exports file contains a list of entries. Each entry indicates a directory that is shared and how it is shared. A typical entry in /etc/exports consists of:

/SHARED/DIRECTORY   HOST(OPTION_LIST)

For example:

/export/data   192.168.1.2(rw,sync)

Here the IP address 192.168.1.2 is used to identify the allowed client. You can also use the name of the host, a wild card indicating a set of hosts (*.abc.com, *, etc.), or netgroups (@my-hosts).

For a detailed explanation of all options and their meaning, refer to the man page of exports (man exports).

In case you have modified /etc/exports while the NFS server was running, you need to restart it for the changes to become active: sudo systemctl restart nfsserver.

The /etc/sysconfig/nfs file contains a few parameters that determine NFSv4 server daemon behavior. It is important to set the parameter NFS4_SUPPORT to yes (default). NFS4_SUPPORT determines whether the NFS server supports NFSv4 exports and clients.

In case you have modified /etc/sysconfig/nfs while the NFS server was running, you need to restart it for the changes to become active: sudo systemctl restart nfsserver.

Tip: Mount Options

On SUSE Linux Enterprise Server 11, the --bind mount in /etc/exports was mandatory. It is still supported, but now deprecated. Configuring directories for export with NFSv4 is now the same as with NFSv3.

Note: NFSv2

If NFS clients still depend on NFSv2, enable it on the server in /etc/sysconfig/nfs by setting:

NFSD_OPTIONS="-V2"
MOUNTD_OPTIONS="-V2"

After restarting the service, check whether version 2 is available with the command:

tux > cat /proc/fs/nfsd/versions
+2 +3 +4 +4.1 -4.2

Starting with SLE 12 SP1, the idmapd daemon is only required if Kerberos authentication is used, or if clients cannot work with numeric user names. Linux clients can work with numeric user names since Linux kernel 2.6.39. The idmapd daemon does the name-to-ID mapping for NFSv4 requests to the server and replies to the client.

If required, idmapd needs to run on the NFSv4 server. Name-to-ID mapping on the client will be done by nfsidmap provided by the package nfs-client.

Make sure that there is a uniform way in which user names and IDs (UIDs) are assigned to users across machines that might probably be sharing file systems using NFS. This can be achieved by using NIS, LDAP, or any uniform domain authentication mechanism in your domain.

The parameter Domain must be set the same for both, client and server in the /etc/idmapd.conf file. If you are not sure, leave the domain as localdomain in the server and client files. A sample configuration file looks like the following:

[General]
Verbosity = 0
Pipefs-Directory = /var/lib/nfs/rpc_pipefs
Domain = localdomain

[Mapping]
Nobody-User = nobody
Nobody-Group = nobody

To start the idmapd daemon, run systemctl start nfs-idmapd. In case you have modified /etc/idmapd.conf while the daemon was running, you need to restart it for the changes to become active: systemctl start nfs-idmapd.

For more information, see the man pages of idmapd and idmapd.conf (man idmapd and man idmapd.conf).

The opton defines the count of TCP conncetions that the clients makes to the NFS server. You can specif any number from 1 to 16, where 1 is the default value if the mount option has not been specified.

The nconnect setting is applied only during the first mount process to the particular NFS server. If the same client executes the mount command to the same NFS server, all already established connections will be shared—no new connection will be established. To change the nconnect setting, you have to unmount all clients connections to the particular NFS server. Then you can define a new value of the nconnect option.

You can find the current nconnect value in effect in output of the mount command or in the file /proc/mounts. If there is no value of the mount option, then the option has not been used during mounting and the default value 1 is in use.

The option applies to NFS v2, v3, and all v4.x variants,

Note: Different number of connections than defined by nconnect

As you can close and open connections after the first mount, the actual count of connections necessarily does not have to be the same as the value of nconnect.

the option causes that a client uses to mount its own isolated TCP connection. The client will not share the TCP connection with any other mount done before or after.

The option applies to NFS v2 and v3.

The option is a number that identifies mounts sharing the same TCP connection. If two or more mounts to a particular NFS server have a different value of sharetransport, these mounts will use different connections. If you don't specify the option value for mounts to a particular NFS server, all the mounts will shate one TCP connection.

The option applies to NFS v4.x.