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Chapter 9 . Running Debian GNU/Linux 313 This sets the owner and group of /usr/bin/wall to root and root and disables all permissions on the file. You can find more information about file permissions in the Understanding File Permissions section of Chapter 2. Unlike dpkg-divert, dpkg-statoverride does not keep track of the original file permissions. As a result, removing an override does not restore the old permissions. After removing the override, you need to either set the permissions manually or reinstall the package that contained the file: # dpkg-statoverride –remove /usr/bin/wall # apt-get –reinstall install bsdutils Reading Package Lists… Done Building Dependency Tree… Done 0 upgraded, 0 newly installed, 1 reinstalled, 0 to remove and 0 not upgraded. Need to get 0B/62.5kB of archives. After unpacking 0B of additional disk space will be used. Do you want to continue? [Y/n]Y (Reading database … 16542 files and directories currently installed.) Preparing to replace bsdutils 1:2.12-10 (using …/bsdutils_1%3a2.12-10_i386.deb) … Unpacking replacement bsdutils … Setting up bsdutils (2.12-10) … Managing Package Configuration with debconf All packages that include support for configuration management through debconf are configured as they are being installed. If you want to change a configuration option later, you can do so using the dpkg-reconfigure utility. For instance, you can change the configuration options for ssh using the following command: # dpkg-reconfigure ssh Every configuration parameter is assigned a priority by the package maintainer. This allows debconf to select the default values for settings below a specific priority. By default, you will only be prompted to answer questions of medium, high, or critical priority; low-priority questions are answered automatically. You can change this by reconfiguring the debconf package: # dpkg-reconfigure debconf Advanced users who are maintaining multiple systems may want to create a database of configuration settings that can be distributed to every computer (or to sets of computers) to reduce the number of repeated steps. This process is documented in the debconf and debconf.conf man pages. Note Note
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312 Part III . Choosing and Installing a Linux Distribution The system administrator can designate which program is referenced in the alternatives database, through the use of the update-alternatives command: # update-alternatives –config editor These are alternatives that provide editor . Selection Alternative ———————————————– 1 /bin/ed *+ 2 /bin/nano 3 /usr/bin/nvi Press enter to keep the default[*], or type selection number:2 You can also use the –all command with update-alternatives to configure every entry in the alternatives database, one at a time. You can find more details in the update-alternatives man page. By default, all alternatives are in automatic mode, meaning that the system automatically selects a suitable program from the available candidates. Installing a new candidate program generally results in the automatic updating of the appropriate alternatives. Manually configuring an alternative disables automatic mode, preventing the system from changing these settings without prior knowledge of the system administrator. The Debian package management tools also provide a mechanism for renaming specific files in a package and for overriding the ownership and permission settings on files. Unlike when these changes are made manually using mv, chmod, or chown, changes made through the Debian tools remain in place across package upgrades and re-installations. For example, if you wanted to replace /usr/bin/users without modifying the coreutils package, you could divert it to /usr/bin/users.distrib: # dpkg-divert –local –rename –add /usr/bin/users Adding `local diversion of /usr/bin/users to /usr/bin/users.distrib Removing the diversion returns the original filename: # dpkg-divert –remove /usr/bin/users Removing `local diversion of /usr/bin/users to /usr/bin/users.distrib Stat overrides are useful when you want to disable access to a program, or when you want to make it set-UID. For instance, to disable access to the wall program: # dpkg-statoverride –update –add root root 0000 /usr/bin/wall Note
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Chapter 9 . Running Debian GNU/Linux 311 $ dpkg –info lsof_4.71-1_i386.deb new debian package, version 2.0. size 319058 bytes: control archive= 1534 bytes. 557 bytes, 16 lines control 2246 bytes, 32 lines md5sums Package: lsof Version: 4.71-1 … $ dpkg –contents lsof_4.71-1_i386.deb drwxr-xr-x root/root 0 2004-04-03 07:34:41 ./ drwxr-xr-x root/root 0 2004-04-03 07:34:36 ./usr/ drwxr-xr-x root/root 0 2004-04-03 07:34:39 ./usr/bin/ … Installing Package Sets (Tasks) with Tasksel Some package sets are too large to be managed practically through meta packages, so tasks have been created as an alternative. Tasks are installed and removed using the tasksel utility. When run without any arguments, tasksel presents a menu from which you can select tasks to install or remove. Do not install any tasks if you plan to use this system in conjunction with the server examples in Chapters 23 and 24. Additional options are available from the command line: . To see a list of known tasks, run tasksel –list-tasks. . To list the packages that are installed by a task, run tasksel –taskpackages . When a task is removed, all programs associated with that task, whether installed manually or as part of that task, are removed! To install the desktop task, which includes GNOME, KDE, and XFCE environments, run the following: # tasksel install desktop Alternatives, Diversions, and Stat Overrides In cases where there is more than one installed program that provides a specific function, package maintainers have the option of utilizing Debian s alternatives system. The alternatives system manages which program is executed when you run a specific command. For instance, the ed, nano, and nvi packages each provide a text editor. An alternative maintained in the system guarantees that a text editor is accessible through the generic editor command, regardless of which combination of these packages is installed. Caution Caution
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310 Part III . Choosing and Installing a Linux Distribution Querying the Package Database You will often need to obtain more information about packages that are already installed on your system. Because these operations do not modify the package database, they can be done as a non-root user. To list all packages known to dpkg, use the -l or –list commands: $ dpkg –list You can restrict the list by specifying a glob pattern: $ dpkg –list *lsof* The quotes are used to prevent the shell from replacing the wildcard with a list of matching files in the current directory. For more information about wildcards, see the glob man page. To view detailed information about a specific package, use the -s or –status command: $ dpkg –status lsof Package: lsof Status: install ok installed Priority: standard Section: utils … The origin package for a file can be determined using the -S or –search command: $ dpkg –search /bin/ls coreutils: /bin/ls The list of files in an installed package can be viewed using the -L or –listfiles command: $ dpkg –listfiles lsof /. /usr /usr/sbin /usr/bin /usr/bin/lsof … Examining a Package File Package files can be examined prior to installation using the –info (-I) and –contents (-c) command: Note
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Chapter 9 . Running Debian GNU/Linux 309 In this example, several other packages depend on the python2.3 package and would also need to be removed. To proceed with removing python2.3 and all packages that depend on it, run the command again without the -s flag. Upgrading Your System As new versions of packages become available, you can instruct APT to download and install them, automatically replacing the older versions. This is as simple as updating your package list, followed by a simple command: # apt-get upgrade When upgrading to a newer distribution, use dist-upgrade instead of upgrade. This will change the rules that APT uses when deciding which actions to take, making it expect major changes in dependencies and handle them appropriately. Package Management Using dpkg As mentioned earlier, the dpkg utility is the primary package management tool in Debian. Most other package management tools within the system, including APT, use dpkg to perform the midlevel work, and dpkg in turn uses dpkg-deb and dpkg-query to handle a number of the low-level functions. Far too many dpkg commands exist to list in this section, but the most common ones are explained in the following sections. In most cases, there are both short and long commands to perform the same function. Use whichever is easier for you to remember. Installing and Removing Packages Packages can be installed with dpkg using the -i or –install flags and the path to the .deb file containing the package. The path must be accessible as a file system path (HTTP, FTP, and other methods are not supported), and more than one package can be specified: # dpkg –install /home/wayne/lsof_4.71-1_i386.deb Package removal through dpkg is also straightforward and is done with the -r or –remove commands. When configuration files are to be removed, the -P or — purge command can be used instead. Both commands can also be used to specify multiple packages to remove: # dpkg –remove lsof or… # dpkg –purge lsof Note
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308 Part III . Choosing and Installing a Linux Distribution Architecture: i386 Version: 0.96 Depends: python (>=2.1), libc6 (>= 2.2.4-4) Filename: pool/main/p/pytris/pytris_0.96_i386.deb Size: 16304 MD5sum: 70eb8ad6f5a8a901a95eb37f7336fc57 Description: two-player networked console tetris clone two-player networked console based tetris clone, written in python, similar to xtet42. To view information about a specific package that is already installed on your system, use dpkg, as discussed later in this chapter. Once you know the name of the package you want to install, use the install method to download it and any packages on which it depends. For example, the ssh package is very useful for remotely accessing systems and is probably one of the first programs that you will want to install: # apt-get install ssh On this command, APT retrieves and installs the ssh package. If they are required, a list of additional packages is displayed by APT. If you choose to continue, APT will download and install those packages along with the package you requested. When installing packages that support automatic configuration through debconf, you re prompted to answer the appropriate configuration questions. While the Debian package developers have gone to great lengths to ensure that the default options for these questions will work in most situations, it s best to read the questions thoroughly to be sure that the defaults work for you. Removing Packages APT can also be used to remove packages from your system. Unlike dpkg, which removes only the package you tell it to remove, apt-get also removes any packages that depend on the package you are removing. This is best used in conjunction with the -s option to simulate what would happen if the removal were actually performed: # apt-get -s remove python2.3 Reading Package Lists… Done Building Dependency Tree… Done The following packages will be REMOVED: bittornado python python2.3 python2.3-dev 0 upgraded, 0 newly installed, 4 to remove and 0 not upgraded. Remv pytris (0.96 Debian:testing) Remv python (2.3.4-1 Debian:testing) Remv python2.3-dev (2.3.4-5 Debian:testing) Remv python2.3 (2.3.4-5 Debian:testing) Note Note
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Chapter 9 . Running Debian GNU/Linux 307 Run man sources.list on any Debian system for more information. If you aren t going to have your Debian CD available all the time, you may want to remove the cdrom: entry from the file. Use a text editor to edit the file: # editor /etc/apt/sources.list Then update the package database as described in the following section. Astute readers may notice that the pager and editor commands used in this section are not standard UNIX commands. Both are pointers to programs and are managed using Debian s alternatives system, which is discussed later in this chapter. Updating the APT Package Database Because the lists of packages available in the Debian package repositories may change from time to time, you need to instruct APT to download these lists and update its database from time to time. To perform this process, run the following command: # apt-get update You generally want to run this command before installing new packages so that you do not download an older version. Run it before checking for upgrades as well. Finding and Installing Packages When looking for new packages to install, you may not always know what package you want. The package database maintained by APT includes package descriptions and other fields that can be searched using the apt-cache utility: # apt-cache search tetris bsdgames — a collection of classic textual unix games pytris — two-player networked console tetris clone stax — collection of puzzle games similar to Tetris Attack. Specifying multiple keywords in a search prevents it from listing packages that do not contain all of the keywords you specify. This enables you to do very specific searches such as word processor. You can also use this utility to find out more information about a specific package in the repositories: # apt-cache show bsdgames Package: pytris Priority: optional Section: games Installed-Size: 101 Maintainer: Radovan Garabik Tip Note Note
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306 Part III . Choosing and Installing a Linux Distribution If your wireless network is using encryption, you will need to specify a wireless_key parameter. You can find a complete list of wireless options in the iwconfig man page. PPP Connections: Dial-up and Others Dial-up connections can be managed using the pppconfig utility. Simply run pppconfig, and you are provided with a menu from which you can create, modify, and delete dial-up connection parameters. You specify connections by name when dialing, so be sure to give it a name that is easy to type. Dial a connection using the pon command, replacing peer with the name you assigned to your connection: # pon peer You can disconnect using the poff command and can view logs (for diagnosing problems or determining status) using the plog command. Some DSL and cable modem providers require that you use PPPoE (PPP over Ethernet) to connect to their systems. PPPoE connections are managed using the pppoeconf program. Package Management Using APT For most users, APT will be the primary tool for installing, removing, and upgrading packages. This section shows how to use the apt-get and apt-cache utilities. Managing the List of Package Repositories The configuration file /etc/apt/sources.list contains a list of Debian package repositories that APT will use. Like most configuration files on a Linux system, this file is a plain-text file that can be viewed using any text editor or pager. To view its contents, run the following: # pager /etc/apt/sources.list deb cdrom:[Debian GNU/Linux _Sarge_ NetInst]/ stable main deb http://ftp.us.debian.org/debian/ stable main deb-src http://ftp.us.debian.org/debian/ stable main deb http://security.debian.org/ stable/updates main Your output will differ from this example s, of course, but the kind of information remains the same. The first part of each line indicates whether the repository is to be used for binary packages (indicated by the deb prefix) or source packages (deb-src). The rest of the line defines the method (in this case, cdrom or http), the location, the distribution (stable), and the sections (main). If you want to use software from the contrib and non-free sections, you can use a text editor to add them after main. Note
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Chapter 9 . Running Debian GNU/Linux 305 Configuring Network Connections Debian includes a set of tools for managing most types of network interfaces, including Ethernet, PPP, wireless, and even ATM. You may find that you need to add or change network settings after the system has been installed. IP Networks: Ethernet and Wireless On Debian systems, standard network connections are configured in the /etc/ network/interfaces file. If you have a network card configured to obtain an IP address automatically, this file will look like this: # This file describes the network interfaces available on # your system and how to activate them. For more information, # see interfaces(5). # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet dhcp Do not modify the loopback entry unless you are absolutely certain that you know what you are doing. In some cases, such as when the system will be acting as a server, you want to configure your network interface with a fixed IP address. To do so, edit /etc/network/ interfaces and replace the iface eth0 inet dhcp line. Use the following block as a template, replacing the parameters with the correct settings for your network: iface eth0 inet static address 192.168.1.220 netmask 255.255.255.0 gateway 192.168.1.1 You can obtain IP network settings from your ISP or network administrator. Wireless interfaces can also be configured using the interfaces file, but require that the wireless-tools package be installed. Use dpkg or apt-get to install the wirelesstools package. Then, add the necessary parameters to the entry for your wireless network interface. This example shows the settings for a wireless network with an access point (managed mode) set to the ESSID Home, and operating on channel 11: iface eth0 inet dhcp wireless_essid Home wireless_mode Managed wireless_channel 11 Note Caution
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304 Part III . Choosing and Installing a Linux Distribution 11. Assuming that you did not select any tasks, the only package needing configuration is the Exim mail transfer agent. When the Configuring Exim screen appears, you choose from a list of default configurations; here are the two most likely options: internet site; mail is sent and received directly using SMTP This option configures your server to accept incoming mail and to deliver outgoing mail directly to the servers for the recipient domain. This configuration is useful if you are running a simple mail server or if you are using mutt or pine to check your mail locally. local delivery only; not on a network Select this option if you do not need locally generated messages to be sent to a central mail host for processing. Your system will not be configured with the capability to send messages, but this configuration still enables you to check your mail using programs such as Mozilla, Evolution, and Sylpheed that include support for sending messages using the SMTP protocol. This is also the option you want if you will soon be setting up this system to act as a mail server based on the instructions in Chapter 24. Enter the mail name for this system (the default is generally what you want), and choose the user to whom you want system messages to go. In most cases, you want to select the user account that was added earlier. You now have a fully functional Debian GNU/Linux system. The server does not yet have any extra packages installed but is ready to be used for the LAMP and mail server examples in this book (which you can find in Chapters 23 and 24, respectively). There s no graphical interface installed yet, which means that all interaction will be through the command line. Take some time, as needed, to browse through Chapter 2 and familiarize yourself with the command line before continuing with the next section. You can install a complete desktop for Debian using the desktop task. See the section on tasksel later in the chapter for more information. Managing Your Debian System Some of the basic tasks that you may encounter while running Debian GNU/Linux include package installation, configuration, and removal, as well as handling some special situations that you may come across. All these steps require that you be logged in as the superuser (root). If you have just finished installing the system, you can log in as root from the login prompt. Note
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