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Linux Networking, Part 7: Implementing NFS - page 2

Sharing Data Between Machines

  • November 24, 2000
  • By William Wong

NFS client and server support is actually built into the Linux kernel. The NFS server application is named rpc.nfsd and the client is rpc.mountd. There is also a quota support application named rps.rquotad. These NFS deamons are normally started at boot time from the script /etc/rc.d/init.d/nfs. Most Linux implementations include this NFS support by default.

The NFS script only operates if the /etc/exports file exists and is not empty (zero length). The /etc/exportsNFS Server Support

Dynamic sharing of directories is done by rpc.nfsd using the exportfs program that changes the /etc/exports file. The following is an example using exportfs: 

exportfs clientDomainName:/a/path/name/on/the/server
exportfs -o rw  :/a/path/name/on/the/server

The first exports the directory /a/path/name/on/the/server to a specified client. In this case the domain name is clientDomainName*.foo.com. This could also be an IP address or an IP address and subnet mask. NIS group names can also be used. The directory is exported as read-only when no options specified.

The second instance of exportfs exports the same directory but allows the world to access it. The exportfs supports a number of options. In this case, the command allows read-write access.

The exportfs program is also used to remove an export. This is done using the -u option as shown below: 

exportfs -u client DomainName:/a/path/name/on/the/server

The /etc/exports file is used to define exported NFS directories when NFS is started. Each line in the file defines the directory to be exported and how the directory can be accessed. The following is a sample /etc/exports file: 

/home/guest     (ro)
/pub                 *.local.dom(rw) (ro)

The first allows any user read-only access to the /home/guest directory. The second allows read-write access to computers with a domain name of local.dom and read-only access to everyone else.