Network File System

1
Network File System

• CIS 238

2
NFS (Network File System)

• The most commercially successful and widely
  available
• remote file system protocol
• Designed and implemented by Sun Microsystems
• (Walash et al, 1985 Sandberg et al, 1985)
• Reasons for success
• The NFS protocol is public domain
• Sun sells that implementation to all people for
  less than the cost of implementing it themselves
• Evolved from version 2 to version 3 (which is the
  common implementation today).

3
NFS Overview

• Views a set of interconnected workstations as a
  set of independent machines with independent file
  systems
• The goal is to allow some degree of sharing among
  these file systems (on explicit request)
• Sharing is based on client server relationships
• A machine may be both client and server
• The protocol is stateless
• Designed to support UNIX file system semantics
• The protocol design is transport independent

4
NFS Services

• The NFS server package includes three facilities,
  included in the portmap and nfs-utils packages.
• portmap It maps calls made from other machines
  to the correct RPC service (not required with
  NFSv4).
• nfs It translates remote file sharing requests
  into requests on the local file system.
• rpc.mountd This service is responsible for
  mounting

5
NFS Configuration Files

• /etc/exports Its a main configuration file of
  NFS, all exported files and directories are
  defined in this file at the NFS Server end.
• /etc/fstab To mount a NFS directory on your
  system across the reboots, we need to make an
  entry in /etc/fstab.
• /etc/sysconfig/nfs - or /etc/nfsconfig
  Configuration file of NFS to control on which
  port rpc and other services are listening and the
  NFS version used .

6
Server Installation Setup

• yum install nfs-utils nfs-utils-lib
• yum install portmap (NFSv2 or NFSv3) -OR-
• yum install rpcbind( NFSv4)
• /etc/init.d/portmap start -OR-
  /etc/init.d/rpcbind start
• /etc/init.d/nfs start
• chkconfig --level 35 portmap (rpcbond) on
• chkconfig --level 35 nfs on
• /etc/exports
• /nfsshare 172.27.0.0(rw,sync,no_root_squash)
• exportfs -a Exports all shares listed in
  /etc/exports, or given name
• exportfs -v Displays a list of shares files and
  options on a server
• exportfs -u Unexports all shares listed in
  /etc/exports, or given name
• exportfs -r Refresh the servers list after
  modifying /etc/exports

7
NFS Options

• ro With the help of this option we can provide
  read only access to the shared files i.e client
  will only be able to read.
• rw This option allows the client server to both
  read and write access within the shared
  directory.
• sync Sync confirms requests to the shared
  directory only once the changes have been
  committed.
• no_subtree_check This option prevents the
  subtree checking. When a shared directory is the
  subdirectory of a larger file system, nfs
  performs scans of every directory above it, in
  order to verify its permissions and details.
  Disabling the subtree check may increase the
  reliability of NFS, but reduce security.
• no_root_squash This phrase allows root to
  connect to the designated directory.

8
NFS Client

• showmount -e ltNFS Servergt
• showmount d
• mount -t nfs ltNFS Servergt/nfsshare
  /mnt/nfsshare
• /etc/fstab
• - ltNFS Servergt/nfsshare /mnt nfs defaults 0 0
• See text or man page for mount options
• df -h

9
RPC(BIND)

• Transport both TCP and UDP
• Data types atomic types and non-recursive
  structures
• Pointers are not supported
• Complex memory objects (e.g., linked lists) are
  not supported
• NFS is built on top of RPC

10
The mount protocol

• Is used to establish the initial logical
  connection between a server and a client
• Each machine has a server process (daemon)
  (outside the kernel) performing the protocol
  functions
• The server has a list of exported directories
  (/etc/exports)
• The portmap service is used to find the location
  (port number) of the server mount service

11
The mount protocol

• Clients mount process send message to the
  servers portmap (or RPCBIND) daemon requesting
  port number of the servers mountd daemon
• Servers portmap (or RPCBIND) daemon returns the
  requested info
• Clients mountd send the servers mountd a
  request with the path of the flie system it wants
  to mount
• Servers mountd request a file handle from the
  kernel
• - If the request is successful the handle is
  returned to the client
• - If not error is returned
• The clients mountd perform the mount() system
  call using the received file handle