Translations by EsatYuce

Computer networks are often comprised of diverse systems, and while operating a network made up entirely of Ubuntu desktop and server computers would certainly be fun, some network environments must consist of both Ubuntu and <trademark class="registered">Microsoft</trademark><trademark class="registered">Windows</trademark> systems working together in harmony. This section of the <phrase>Ubuntu</phrase> Server Guide introduces principles and tools used in configuring your Ubuntu Server for sharing network resources with Windows computers.

Successfully networking your Ubuntu system with Windows clients involves providing and integrating with services common to Windows environments. Such services assist the sharing of data and information about the computers and users involved in the network, and may be classified under three major categories of functionality:

<emphasis role="bold">Directory Services</emphasis>. Sharing vital information about the computers and users of the network with such technologies as the Lightweight Directory Access Protocol (LDAP) and Microsoft <trademark class="registered">Active Directory</trademark>.

<emphasis role="bold">Authentication and Access</emphasis>. Establishing the identity of a computer or user of the network and determining the information the computer or user is authorized to access using such principles and technologies as file permissions, group policies, and the Kerberos authentication service.

Groups define a collection of computers or users which have a common level of access to particular network resources and offer a level of granularity in controlling access to such resources. For example, if a group <emphasis role="italic">qa</emphasis> is defined and contains the users <emphasis role="italic">freda</emphasis>, <emphasis role="italic">danika</emphasis>, and <emphasis role="italic">rob</emphasis> and a second group <emphasis role="italic">support</emphasis> is defined and consists of users <emphasis role="italic">danika</emphasis>, <emphasis role="italic">jeremy</emphasis>, and <emphasis role="italic">vincent</emphasis> then certain network resources configured to allow access by the <emphasis role="italic">qa</emphasis> group will subsequently enable access by freda, danika, and rob, but not jeremy or vincent. Since the user <emphasis role="italic">danika</emphasis> belongs to both the <emphasis role="italic">qa</emphasis> and <emphasis role="italic">support</emphasis> groups, she will be able to access resources configured for access by both groups, whereas all other users will have only access to resources explicitly allowing the group they are part of.

Several tools are available for interacting with Ubuntu's package management system, from simple command-line utilities which may be easily automated by system administrators, to a simple graphical interface which is easy to use by those new to Ubuntu.

Ubuntu's package management system is derived from the same system used by the Debian GNU/Linux distribution. The package files contain all of the necessary files, meta-data, and instructions to implement a particular functionality or software application on your Ubuntu computer.

Debian package files typically have the extension '.deb', and typically exist in <emphasis role="italics">repositories</emphasis> which are collections of packages found on various media, such as CD-ROM discs, or online. Packages are normally of the pre-compiled binary format; thus installation is quick and requires no compiling of software.

The <application>apt-get</application> command is a powerful command-line tool used to work with Ubuntu's <emphasis>Advanced Packaging Tool</emphasis> (APT) performing such functions as installation of new software packages, upgrade of existing software packages, updating of the package list index, and even upgrading the entire Ubuntu system.

Being a simple command-line tool, <application>apt-get</application> has numerous advantages over other package management tools available in Ubuntu for server administrators. Some of these advantages include ease of use over simple terminal connections (SSH) and the ability to be used in system administration scripts, which can in turn be automated by the <application>cron</application> scheduling utility.

<emphasis role="bold">Install a Package</emphasis>: Installation of packages using the <application>apt-get</application> tool is quite simple. For example, to install the network scanner <emphasis role="italics">nmap</emphasis>, type the following: <screen> <command>sudo apt-get install nmap</command> </screen>

<emphasis role="bold">Remove a Package</emphasis>: Removal of a package or packages is also a straightforward and simple process. To remove the nmap package installed in the previous example, type the following: <screen> <command>sudo apt-get remove nmap</command> </screen>

<emphasis role="bold">Multiple Packages</emphasis>: You may specify multiple packages to be installed or removed, separated by spaces.

<emphasis role="bold">Update the Package Index</emphasis>: The APT package index is essentially a database of available packages from the repositories defined in the <filename>/etc/apt/sources.list</filename> file. To update the local package index with the latest changes made in repositories, type the following: <screen> <command>sudo apt-get update</command> </screen>

Actions of the <application>apt-get</application> command, such as installation and removal of packages, are logged in the /var/log/dpkg.log log file.

Some examples of popular uses for the <application>apt-get</application> utility: <placeholder-1/>

For further information about the use of <application>APT</application>, read the comprehensive <ulink url="http://www.debian.org/doc/user-manuals#apt-howto">Debian APT User Manual</ulink> or type: <screen>apt-get help</screen>

<application>Aptitude</application> is a menu-driven, text-based front-end to the <emphasis>Advanced Packaging Tool</emphasis> (APT) system. Many of the common package management functions, such as installation, removal, and upgrade, are performed in <application>Aptitude</application> with single-key commands, which are typically lowercase letters.

When <application>Aptitude</application> starts, you will see a menu bar at the top of the screen and two panes below the menu bar. The top pane contains package categories, such as <emphasis role="italics">New Packages</emphasis> and <emphasis role="italics">Not Installed Packages</emphasis>. The bottom pane contains information related to the packages and package categories.

<emphasis role="bold">Install Packages</emphasis>: To install a package, locate the package via the Not Installed Packages package category, for example, by using the keyboard arrow keys and the <keycap>ENTER</keycap> key, and highlight the package you wish to install. After highlighting the package you wish to install, press the <keycap>+</keycap> key, and the package entry should turn <emphasis role="italics">green</emphasis>, indicating it has been marked for installation. Now press <keycap>g</keycap> to be presented with a summary of package actions. Press <keycap>g</keycap> again, and you will be prompted to become root to complete the installation. Press <keycap>ENTER</keycap> which will result in a Password: prompt. Enter your user password to become root. Finally, press <keycap>g</keycap> once more and you'll be prompted to download the package. Press <keycap>ENTER</keycap> on the <emphasis role="italics">Continue</emphasis> prompt, and downloading and installation of the package will commence.

<emphasis role="bold">Remove Packages</emphasis>: To remove a package, locate the package via the Installed Packages package category, for example, by using the keyboard arrow keys and the <keycap>ENTER</keycap> key, and highlight the package you wish to remove. After highlighting the package you wish to install, press the <keycap>-</keycap> key, and the package entry should turn <emphasis role="italics">pink</emphasis>, indicating it has been marked for removal. Now press <keycap>g</keycap> to be presented with a summary of package actions. Press <keycap>g</keycap> again, and you will be prompted to become root to complete the installation. Press <keycap>ENTER</keycap> which will result in a Password: prompt. Enter your user password to become root. Finally, press <keycap>g</keycap> once more, and you'll be prompted to download the package. Press <keycap>ENTER</keycap> on the <emphasis role="italics">Continue</emphasis> prompt, and removal of the package will commence.

<emphasis role="bold">c</emphasis>: Package not installed, but package configuration remains on system

<emphasis role="bold">p</emphasis>: Purged from system

<emphasis role="bold">v</emphasis>: Virtual package

<emphasis role="bold">B</emphasis>: Broken package

<emphasis role="bold">u</emphasis>: Unpacked files, but package not yet configured

The first column of information displayed in the package list in the top pane, when actually viewing packages lists the current state of the package, and uses the following key to describe the state of the package: <placeholder-1/>

To exit Aptitude, simply press the <keycap>q</keycap> key and confirm you wish to exit. Many other functions are available from the Aptitude menu by pressing the <keycap>F10</keycap> key.

Configuration of the <emphasis>Advanced Packaging Tool</emphasis> (APT) system repositories is stored in the /etc/apt/sources.list configuration file. An example of this file is referenced here, along with information on adding or removing repository references from the file.

<ulink url="../sample/sources.list">Here</ulink> is a simple example of a typical <filename>/etc/apt/sources.list</filename> file.

You may edit the file to enable repositories or disable them. For example, to disable the requirement of inserting the Ubuntu CD-ROM whenever package operations occur, simply comment out the appropriate line for the CD-ROM, which appears at the top of the file:

Extra Repositories

Be advised that neither the <emphasis>Universe</emphasis> or <emphasis>Multiverse</emphasis> repositories contain officially supported packages. In particular, there may not be security updates for these packages.

Many other package sources are available, sometimes even offering only one package, as in the case of package sources provided by the developer of a single application. You should always be very careful and cautious when using non-standard package sources, however. Research the source and packages carefully before performing any installation, as some package sources and their packages could render your system unstable or non-functional in some respects.

References

Networking

Network Configuration

Ubuntu ships with a number of graphical utilities to configure your network devices. This document is geared toward server administrators and will focus on managing your network on the command line.

Ethernet

Many more configurations are possible, including dialup PPP interfaces, IPv6 networking, VPN devices, etc. Refer to <application>man 5 interfaces</application> for more information and supported options. Remember that <filename>/etc/network/interfaces</filename> is used by the <application>ifup</application>/<application>ifdown</application> scripts as a higher level configuration scheme than may be used in some other Linux distributions, and that the traditional, lower level utilities such as <application>ifconfig</application>, <application>route</application>, and <application>dhclient</application> are still available to you for ad hoc configurations.

Managing DNS Entries

search com nameserver 204.11.126.131 nameserver 64.125.134.133 nameserver 64.125.134.132 nameserver 208.185.179.218

Managing Hosts

If your network contains computers whose IP addresses are not listed in DNS, it is recommended that you add them to the <filename>/etc/hosts</filename> file.

The Transmission Control Protocol and Internet Protocol (TCP/IP) is a standard set of protocols developed in the late 1970s by the Defense Advanced Research Projects Agency (DARPA) as a means of communication between different types of computers and computer networks. TCP/IP is the driving force of the Internet, and thus it is the most popular set of network protocols on Earth.

TCP/IP Introduction

The TCP/IP protocol configuration consists of several elements which must be set by editing the appropriate configuration files, or deploying solutions such as the Dynamic Host Configuration Protocol (DHCP) server which in turn, can be configured to provide the proper TCP/IP configuration settings to network clients automatically. These configuration values must be set correctly in order to facilitate the proper network operation of your Ubuntu system.

<emphasis role="bold">IP address</emphasis> The IP address is a unique identifying string expressed as four decimal numbers ranging from zero (0) to two-hundred and fifty-five (255), separated by periods, with each of the four numbers representing eight (8) bits of the address for a total length of thirty-two (32) bits for the whole address. This format is called <emphasis>dotted quad notation</emphasis>.

<emphasis role="bold">Netmask</emphasis> The Subnet Mask (or simply, <emphasis>netmask</emphasis>) is a local bit mask, or set of flags which separate the portions of an IP address significant to the network from the bits significant to the <emphasis>subnetwork</emphasis>. For example, in a Class C network, the standard netmask is 255.255.255.0 which masks the first three bytes of the IP address and allows the last byte of the IP address to remain available for specifying hosts on the subnetwork.

<emphasis role="bold">Gateway Address</emphasis> A Gateway Address is the IP address through which a particular network, or host on a network, may be reached. If one network host wishes to communicate with another network host, and that host is not located on the same network, then a <emphasis>gateway</emphasis> must be used. In many cases, the Gateway Address will be that of a router on the same network, which will in turn pass traffic on to other networks or hosts, such as Internet hosts. The value of the Gateway Address setting must be correct, or your system will not be able to reach any hosts beyond those on the same network.