Running Synaptic

Synaptic is the graphical interface for selecting packages for installation. To open it, choose the System Administration Synaptic Package Manager menu (see Figure 4-1). The Synaptic Package Manager displays the available sections on the left, and the available packages on the right. At any time, you can select a package for installation or deselect an already installed package. If you select a package that has dependencies, then all dependencies are automatically selected (or deselected). The bottom status line of the window displays a summary of the selections.

Figure 4-1: The Synaptic Package Manager

When you are ready to make the system changes, select the Apply button. Although there are a few confirmation and status screens, the installations usually require no manual efforts.

Searching with Synaptic

The most powerful part of Synaptic is its search capabilities. You can search for packages by name, description, version, dependencies, and more. Searches are listed as a category on the left side, with search results showing the packages on the right.

To switch back to the repository list, click the Sections button. You can always return to your search history by clicking on the lower Search button.

Synaptic Gaps

As powerful as Synaptic is, it has a couple of usability issues. First, there isn't a Stop button available when you do a search. If you have a slow computer (or slow network connection) and you search for a common term, such as the word the, you should be prepared to wait until the search completes.

A second limitation concerns the search button itself: there are two of them. One is at the top and the other is at the bottom. The top Search button allows you to conduct a new search. The bottom Search button shows you the search history and previous search results.

Finally, the search history is limited to the current session. When you close Synaptic, you will lose your search history.

Changing Repositories

The default Ubuntu installation only has the officially supported dapper, dapper-updates, and dapper-security distributions enabled. You may want to also enable the universe and multiverse repositories. You can do this while in Synaptic through the Settings Repositories menu. A list of standard distributions is provided-you can simply check the appropriate entries to enable them.

Besides enabling distributions, you can select specific repositories from the distributions using the Add button (see Figure 4-2). After modifying the repositories, you will need to click Reload to rescan the list of packages.

Figure 4-2: Adding to the repository list

Warning 

Synaptic does little to prevent you from adding invalid repository-component combinations, or from adding the same distribution twice. Bad choices may result in error messages later, but you will get no warning when you make the selection.

Installing from a CD-ROM or Directory

Besides installing over the network, Synaptic supports installations from a CD-ROM drive or fixed directory. This can come in really handy when working without a network connection or in a close network environment such as a mission critical server room. Installing from a CD-ROM is very easy-simply put the CD-ROM in the drive. Ubuntu will recognize the disk as being a repository and will prompt you to add it to the repository list. At this point, the CD-ROM will act like any other repository.

Note 

If the CD-ROM is not automatically recognized, you can use Settings Repositories to get to the Add Cdrom button.

In closed environments, it is usually more convenient to install from a shared or local directory. You can configure this using Settings Repositories. Rather than selecting a pre-set value, click on the Add button and then select Custom to add your own repository. For example, the following enables package installation from a downloaded ISO file:

1. Download one of the Ubuntu installation CD-ROMs. Let's call it ubuntu.iso.

2. Mount the disk image.

    sudo mkdir -p /mnt/iso sudo mount -o loop ubuntu.iso /mnt/iso 

3. Using the custom add button under Synaptic (Settings Repositories Add Custom), add the following repository:

    deb file:/mnt/iso dapper main restricted 

Note 

When using Synaptic to add repositories, each repository will appear at the end of /etc/apt/ source.list file. However, when searching for a package, the repositories are scanned from the top of the file to the bottom. If you want your new repository to be used first, you will need to edit /etc/apt/sources.list and change the order of the repositories.

Synaptic will look for the dapper distribution's main repository in the /mnt/iso/dists/ dapper/main and /mnt/iso/pool/dapper/main directories. The dists directory contains the indexes for packages, whereas the pool directory contains the actual packages.

Turning Off Repositories

Using a repository from a CD-ROM or local directory can improve install speeds since you are not dependent on the network. Local repositories also give you the ability to customize the software your system can access.

However, as useful as it is to use a CD-ROM or local directory as a repository, you may want to disable them after you do an installation. Without turning them off, Synaptic will complain that the repository is no longer accessible after you remove the CD-ROM or disable the directory.

To turn off repositories, select System Repositories. You can clear the CD-ROMs and custom directories to turn them off. If you do not think you will need them again, you can also click on the Remove button.

Managing Updates

The default Synaptic installation periodically checks for new revisions. If there are updates or patches for packages that you already have installed, then Synaptic can flag these or automatically install them. When new updates are available, you will see a star icon on the top panel. Hovering the mouse over this icon will show you the number of pending updates (see Figure 4-3), and clicking on the icon will allow you to apply updates.

Figure 4-3: The indicator showing that updates are available

You can change the update settings by using Software Preferences applet. Either select it from the System Administration Software Properties menu, or by right-clicking the update indicator. The Internet Updates tab shows the settings. You can tell Ubuntu to periodically check for updates (or never check), download updates (but not install), or automatically install security updates.

Some updates require a special confirmation before installing. These include kernel updates and critical libraries. Upgrading these usually requires a reboot and could break some applications. As a result, these packages require additional confirmation and are not automatically installed.

By default, Dapper checks for updates daily and automatically installs all security updates. For critical systems and controlled environments, you may want to completely disable automatic updates. This enables you to apply updates during a scheduled period rather than when updates they are available. In contrast, regular home users should keep the defaults: check for updates daily and automatic installation of security updates. If you are on a slow network connection, you may want to change the check for update frequency, but it should be at least every two weeks.

Warning 

Completely disabling updates is usually a bad decision. While many updates apply security patches, others address stability issues. The only time you may want to disable auto-updates is when you have some other plan for maintaining the system.