File Sharing

Chapter 9: File Sharing

The ability to share information by sharing files is the fundamental service of a departmental

network. Linux is a perfect system for this service because it provides a wide range of different

file−sharing mechanisms that integrate Microsoft Windows clients, Unix clients, and other clients

that are not compatible with either of these into a single, cohesive network.

Compared with proprietary servers that see the world in only one way, Linux servers provide

increased flexibility for designing the right network. Linux does this by providing three distinct types

of file sharing:

Mainframe technique

through the Linux filesystem. This model works with any client system that can

emulate a terminal.

Allows clients to log in to the server and share files directly

Unix network technique

Network File System (NFS). NFS is the most popular file−sharing software on Unix

networks.

Allows clients to share files across the network with the

Microsoft network technique

(SMB) protocol to share files across the network. SMB is the NetBIOS protocol used

by Microsoft LanManager and Windows NT/2000 systems to provide file−sharing

services to Microsoft Windows clients.

This chapter examines all three file−sharing techniques, beginning with the mainframe model that

uses the basic capabilities of the Linux filesystem.

Allows clients to use the Server Message Block

Linux Filesystem

telnet and ssh permit users to log in to the server and work together there on shared files. Using

tools such as FTP and scp, files developed elsewhere can be placed on the server when users want

to permit shared access to those files. As shown in Chapter 3, "Login Services," all that is required

for this type of access is a user account for each user and the necessary daemons to provide the

services. After a user successfully logs in to a Linux server, file sharing is controlled through the file

permissions that exist in the Linux filesystem.

Linux File Permissions

When the user's account is created, every Linux user is assigned a user ID (UID) and a group ID

(GID), which are used to identify the user for file access. Every file is also given a UID and GID. By

default, these are the UID and GID of the person who creates it, though that can be changed.

Permissions are granted based on matching the UIDs and GIDs of the file and the user as follows:

Owner permissions

the file. In addition to being called owner permissions, they are also called

permissionsThe permissions granted to the user who has the same UID asuser.