Chapter 17. Network File System (NFS)

249

100005

3

tcp

1106

mountd

100003

2

udp

2049

nfs

100003

3

udp

2049

nfs

100021

1

udp

1028

nlockmgr

100021

3

udp

1028

nlockmgr

100021

4

udp

1028

nlockmgr

The

 p

option probes the portmapper on the specified host or defaults to localhost if no specific host

is listed. Other options are available from the

rpcinfo

man page.

From the output above, various NFS services can be seen running. If one of the NFS services does

not start up correctly,

portmap

will be unable to map RPC requests from clients for that service to

the correct port. In many cases, restarting NFS as root (

/sbin/service nfs restart

) will cause

those service to correctly register with

portmap

and begin working.

17.2. NFS Server Configuration Files

Configuring a system to share files and directories using NFS is straightforward. Every file system

being exported to remote users via NFS, as well as the access rights relating to those file systems, is

located in the

/etc/exports

file. This file is read by the

exportfs

command to give

rpc.mountd

and

rpc.nfsd

the information necessary to allow the remote mounting of a file system by an autho 

rized host.

The

exportfs

command allows you to selectively export or unexport directories without restarting

the various NFS services. When

exportfs

is passed the proper options, the file systems to be ex 

ported are written to

/var/lib/nfs/xtab

. Since

rpc.mountd

refers to the

xtab

file when deciding

access privileges to a file system, changes to the list of exported file systems take effect immediately.

Various options are available when using

exportfs

:

   r

  Causes all directories listed in

/etc/exports

to be exported by constructing a new export

list in

/etc/lib/nfs/xtab

. This option effectively refreshes the export list with any changes that

have been made to

/etc/exports

.

   a

  Causes all directories to be exported or unexported, depending on the other options passed

to

exportfs

.

   o options

  Allows the user to specify directories to be exported that are not listed in

/etc/exports

. These additional file system shares must be written in the same way they are

specified in

/etc/exports

. This option is used to test an exported file system before adding it

permanently to the list of file systems to be exported.

   i

  Tells

exportfs

to ignore

/etc/exports

; only options given from the command line are

used to define exported file systems.

   u

  Unexports directories from being mounted by remote users. The command

exportfs  ua

effectively suspends NFS file sharing while keeping the various NFS daemons up. To allow NFS

sharing to continue, type

exportfs  r

.

   v

  Verbose operation, where the file systems being exported or unexported are displayed in

greater detail when the

exportfs

command is executed.

If no options are passed to the

exportfs

command, it displays a list of currently exported file systems.

Changes to

/etc/exports

can also be read by reloading the NFS service with the

service nfs

reload

command. This keeps the NFS daemons running while re exporting the

/etc/exports

file.