Il Protocollo NFS Il protocollo NFS (Network File System) fornisce un sistema di recupero dati semplice ed efficiente, indipendente da: protocollo di trasporto utilizzato (opera sia su TCP che UDP), sistema operativo, file system. La versione 4 del protocollo si presuppone i seguenti scopi: Accesso affidabile e efficiente alla rete Sicurezza con sistema di negoziazione implementato Buona interoperabilità fra vari sistemi operativi Compatibilità all’indietro

L’NFS utilizza due ulteriori protocolli XDR: External Data Representation (RFC 1831) RPC: Remote Procedures Call (RFC 1832) L’XDR serve a effettuare la traduzione dei dati se l’ordinamento dei byte è opposto (Big-Endian, Little-Endian) Le RPCs sono le richieste che si effettuano verso il server. NFS v2: 16 RPCs NFS v3: 22 RPCs NFS v4: 36 RPCs

Alcune delle RPCs più comuni: ACCESS: controlla i diritti di accesso. CLOSE: chiude un file. COMMIT: rende effettive le modifiche e svuota la cache CREATE: crea un file. GETATTR: recupera gli attributi di un file LOOKUP: cerca un file OPEN: apre un file READ: legge da un file REMOVE: cancella un file SETATTR: imposta gli attributi di un file WRITE: scrive su un file

Il tipo di connessione viene negoziato da client e server ed è impostato di default a UDP se entrambi i lati lo supportano ed avviene sulla porta 2049. La dimensione massima dei pacchetti trasferiti (che viene negoziata anch’essa dalle due parti) è di 64K (il limite sia di TCP sia di UDP) ed avviene con offset a 64bit. I file possono essere di qualunque dimensione NFS è stateless.

$ man nfs NFS(5) Linux Programmer's Manual NFS(5) NAME nfs - nfs fstab format and options SYNOPSIS /etc/fstab DESCRIPTION The fstab file contains information about which filesystems to mount where and with what options. For NFS mounts, it contains the server name and exported server directory to mount from, the local directory that is the mount point, and the NFS specific options that control the way the filesystem is mounted. Here is an example from an /etc/fstab file from an NFS mount. server:/usr/local/pub /pub nfs rsize=8192,wsize=8192,timeo=14,intr Options rsize=n The number of bytes NFS uses when reading files from an NFS server. The default value is dependent on the kernel, currently 1024 bytes. (However, throughput is improved greatly by asking for rsize=8192.) wsize=n The number of bytes NFS uses when writing files to an NFS server. The default value is asking for wsize=8192.) ... tcp Mount the NFS filesystem using the TCP protocol instead of the default UDP protocol. Many NFS severs only support UDP. udp Mount the NFS filesystem using the UDP protocol. This is the default. All of the non-value options have corresponding nooption forms. For example, nointr means don't allow file operations to be interrupted. FILES SEE ALSO fstab(5), mount(8), umount(8), exports(5)

df - report filesystem disk space usage $ df $ man exports EXPORTS(5) EXPORTS(5) NAME exports - NFS file systems being exported (for Kernel based NFS) SYNOPSIS /etc/exports DESCRIPTION The file /etc/exports serves as the access control list for file systems which may be exported to NFS clients. It is used by exportfs(8) to give information to mountd(8) and to the kernel based NFS file server daemon nfsd(8). The file format is similar to the SunOS exports file, except that several additional options are permitted. Each line contains an export point and a list of machine or netgroup names allowed to mount the file system at that point. An optional parenthesized list of export parameters may follow each machine name. Blank lines are ignored, and a # introduces a comment to the end of the line. Entries may be continued across new? lines using a backslash. ... df - report filesystem disk space usage $ df Filesystem 1k-blocks Used Available Use% Mounted on /dev/hdc2 37958532 3034976 32995356 9% / /dev/hda3 1903614 1688182 117034 94% /old none 256676 0 256676 0% /dev/shm host:/home/ivenet/pub 1209576 1032976 115152 90% /home/userhome/pub $

Network Working Group Sun Microsystems, Inc. Request for Comments: 1094 March 1989 NFS: Network File System Protocol Specification STATUS OF THIS MEMO This RFC describes a protocol that Sun Microsystems, Inc., and others are using. A new version of the protocol is under development, but others may benefit from the descriptions of the current protocol, and discussion of some of the design issues. Distribution of this memo is unlimited. 1. INTRODUCTION The Sun Network Filesystem (NFS) protocol provides transparent remote access to shared files across networks. The NFS protocol is designed to be portable across different machines, operating systems, network architectures, and transport protocols. This portability is achieved through the use of Remote Procedure Call (RPC) primitives built on top of an eXternal Data Representation (XDR). Implementations already exist for a variety of machines, from personal computers to supercomputers. The supporting mount protocol allows the server to hand out remote access privileges to a restricted set of clients. It performs the operating system-specific functions that allow, for example, to attach remote directory trees to some local file system.

Network Working Group B. Callaghan Request for Comments: 1813 B. Pawlowski Category: Informational P. Staubach Sun Microsystems, Inc. June 1995 NFS Version 3 Protocol Specification Status of this Memo This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited. IESG Note Internet Engineering Steering Group comment: please note that the IETF is not involved in creating or maintaining this specification. This is the significance of the specification not being on the standards track. Abstract This paper describes the NFS version 3 protocol. This paper is provided so that people can write compatible implementations. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Scope of the NFS version 3 protocol . . . . . . . . . . 4 1.2 Useful terms . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Remote Procedure Call . . . . . . . . . . . . . . . . . 5 1.4 External Data Representation . . . . . . . . . . . . . . 5 1.5 Authentication and Permission Checking . . . . . . . . . 7

NFS version 4 Working Group S. Shepler INTERNET-DRAFT Sun Microsystems, Inc. Obsoletes: 3010 C. Beame Document: draft-ietf-nfsv4-rfc3010bis-05.txt Hummingbird Ltd. B. Callaghan Sun Microsystems, Inc. M. Eisler Network Appliance, Inc. ... November 2002 NFS version 4 Protocol Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." Abstract This document replaces [RFC3010] as the definition of the NFS version 4 protocol. Expires: May 2003 [Page 1]