The GNOME Desktop

The GNOME desktop provides all the capabilities of GUI-based operating systems. You can drag-and-drop files, applications, and directories to the desktop, and then drag and drop them back to GNOME-compliant applications. If the desktop stops functioning, you can restart it by starting the GNOME file manager (Nautilus). The desktop is actually a back-end process in the GNOME file manager, but you needn’t have the file manager open to use the desktop.


Drag-and-Drop Files to the Desktop
Any icon for an item that you drag-and-drop from a file manager window to the desktop also appears on the desktop. However, the default drag-and-drop operation is a move operation. If you select a file in your file manager window and drag it to the desktop, you are actually moving the file from its current directory to the GNOME desktop directory, which is located in your home directory and holds all items on the desktop. For GNOME, the desktop directory is DESKTOP. In the case of dragging directory folders to the desktop, the entire directory and its subdirectories will be moved to the GNOME desktop directory. To remove an icon from the desktop, you drag-and-drop it in the trash.

As an alternative to using the desktop, you can drag-and-drop any program, file, or directory to the top panel and use the icons from the panel instead.

You can also copy a file to your desktop by pressing the CTRL key and then clicking and dragging it from a file manager window to your desktop. You will see a small arrow in the upper-right corner of the copied icon change to a + symbol, indicating that you are creating a copy instead of moving the original.

You can also create a link on the desktop to any file. This is useful if you want to keep a single version in a specified directory and be able to access it from the desktop. You can also use links for customized programs that you may not want to appear on a menu or panel. You can create a link in two ways: While holding down the CTRL and SHIFT keys (CTRL-SHIFT), drag the file to where you want the link created. A copy of the icon appears with a small arrow in the right corner indicating it is a link. You can click this link to start the program, open the file, or open the directory, depending on the type of file to which you linked.

Alternatively, first click and drag the file out of the window, and after moving the file but before releasing the mouse button, press the ALT key. This will display a pop-up menu with selections for Cut, Copy, and Link. Select the Link option to create a link. GNOME’s drag-and-drop file operation works on virtual desktops provided by the GNOME Workspace Switcher. The GNOME Workspace Switcher on the bottom panel creates icons for each virtual desktop in the panel, along with task buttons for any applications open on them.

Be careful when removing icons from the desktop. If you have moved the file to the desktop, its original file resides in the DESKTOP folder, and if you remove it you are erasing the original. If you have copied or linked the original, you can simply delete the link or the copy; the original will still exist in its original folder. When you drag applications from the menu or panel to the desktop, you are creating a copy of the application launcher button in the DESKTOP directory. These you can safely remove.

Although the GNOME desktop supports drag-and-drop operations, these normally work only for applications that are GNOME-compliant. You can drag any items from a GNOMEcompliant application to your desktop, and vice versa.

Source of Information : McGraw Hill Ubuntu The Complete Reference

GNOME Help

The GNOME Help browser (Yelp) provides a browser-like interface for displaying the GNOME user’s manual, man pages, and info documents. To access help, choose System | Help And Support. You’ll see a toolbar that enables you to move through the list of previously viewed documents. You can even bookmark specific items. A browser interface lets you to use links to connect to different documents. On the main page, expandable links for several GNOME desktop topics are displayed on left side, with entries for the GNOME User Manual and Administration Guide on the right. At the bottom of the left side listing are links you can click to access the man and info pages. Use the Search box to locate help documents. Special URL-like protocols are supported for the different types of documents: ghelp for GNOME help; man for man pages; and info for the info documents: so, for example, man:fstab would display the man page for the fstab file.

The GNOME Help browser provides a detailed manual on every aspect of your GNOME interface. The left-hand links display GNOME categories for different application categories such as the System tools and GNOME applets. The GNOME Applets entry provides detailed descriptions of all available GNOME applets. Applications categories such as Internet, Programming, System Tools, and Sound and Video will provide help documents for applications developed as part of the GNOME project, such as the Evolution mail client, the Totem movie player, the Disk Usage Analyzer, and the GNOME System Monitor. Click the Desktop entry at the top of the left-hand list to display links for GNOME User and Administration manuals.

Source of Information : McGraw Hill Ubuntu The Complete Reference

Ubuntu Update Manager

Ubuntu will automatically tell you when updates are available for the operating system and other software. Years ago, GNU/Linux users had to use the terminal to enter commands when they wanted to update their operating system. Tasks like these prompted casual computer users to use operating systems that were easier to update. As the popularity of GNU/Linux began to make its way onto the desktops of less-advanced computer users, graphical interfaces began popping up that would allow users to easily update their system software.

As a Debian-based operating system, Ubuntu uses Update Manager as a graphical interface. Alert will pop up on the desktop screen whenever there are updates that the operating system feels you need to attend to.

While Ubuntu will notify you of important updates, at times you may want to manually check to see if there is anything available to be updated. Should you feel the need to start the Update Manager yourself, simply click System Administration Update Manager. This will start Ubuntu searching the software repositories for updates. This is good practice should your automatic update fail or report errors when trying to update any of the software packages.

Running the Update Manager can take some time, especially if you have 391 updates available. So you may want to set the Update Manager to run when you won’t likely be using the computer. To do this, you need to use the terminal to edit what is called the crontab file. A crontab file is a text file that contains a list of commands that run at specific times set in the crontab file. These files run in the background at their specified time. If you set commands to run through the crontab file, it is always good to make sure they are running by checking the log files. More of this will be covered later in the book. Remember, editing the crontab file to run the Update Manager is strictly an optional task. If you feel intimidated by editing commands through the terminal at this point, skip the rest of this section and move on to the next. Don’t worry if you opt for this. Plenty of GNU/Linux users never touch the crontab files, and their systems work just fine! So if you are ready to dive into the crontab editor, let’s roll up our sleeves and start to get dirty.

The first step you need to take is to open the Terminal window. This can be done by going to Applications Accessories Terminal.

In the Terminal window, you should see something similar to the jeff@jeffdesktop:~$. Jeff is the user who is currently logged in, and jeff-desktop is the name of the computer itself. After the $ is where we will begin to enter the basic commands to bring up the crontab editor. Go ahead and type the following into your terminal:

sudo gedit /root/.crontab

The name of the sudo command is short for “super user do.” This allows you, a user on the computer, to run programs and commands with the security privileges of the computer’s super user. If you leave this piece of the command out, you will not be able to save any editing you do. gedit simply means edit. The /root/.crontab is the file you will be editing.

After you enter this command in the terminal, press ENTER. You should now be asked for your password. Use the same one you have set up for your account. When you enter this password, nothing will show up as you type. This is typical of a GNU/Linux system dating back to its Unix days. This is a security feature that prevents people from looking over your shoulder to see how many characters your password has. These “shoulder surfers” could make an educated guess at your password with this knowledge. Again, after you enter your password, press ENTER. After waiting a couple of seconds, you should see the crontab editor open up. Click the editor’s window to make sure you have a cursor and type the following:

00 00 * * * /usr/bin/apt-get update && /usr/bin/apt-get upgrade -y

Let’s analyze this before we save our changes. The command starts with a series of zeros. These tell the crontab file at what time to run the command. Thus, 00 00 would mean 12:00 A.M. If you wanted to set the time to run this file at 4:30 P.M., the command should read 16 30. The three asterisks following the time give us the ability to control the date, month, and/or day of the week. The date can contain a value from 1 to 31, the month can range from 1 to 12, and the day of the week can be set between 0 and 6, with 0 being a Sunday. The asterisk means run every day.

The rest of the command tells the operating system what to do and where to do it. The file location is /usr/bin, and apt-get is the actual program that runs to update and upgrade your software. Update Manager is the graphical user interface for the update/upgrade portion of the apt-get program. The -y means answer yes to any questions that may be asked during the process.

If you wish to leave your command to run at 12:00 A.M., then you can leave your file alone at this point and select File Save. If you wish to set a different time, or even to adjust the date, go ahead and adjust this and then save your file. Once this file has been saved, you can close your crontab editor and your terminal, and then take pride that you once again have journeyed into the depths of GNU/Linux and lived to tell about it! But be careful, when you work more and more in the terminal, you really begin to feel how much control you have over your operating system. After a while, you may find yourself ignoring the graphical interfaces in Ubuntu and beginning to make the terminal your tool of choice!

By now, you have probably noticed update, which can be associated with patches, fixes, and added features to various software packages, and upgrade. An upgrade is when you move from one version of an operating system or other software to the latest distribution release, or when patches to the software are applied. The Ubuntu Update Manager’s graphical interface will handle this for you as well. Whether you are responding to a notice from Ubuntu that updates are available, or you have manually started the Update Manager, if an upgrade for the operating system is available, you will see a box pop up.

It is important to remember that this image was taken from a computer running the 7.04 Feisty Fawn and upgrading to the 7.10 release of Gutsy Gibbon. When you are upgrading your Ubuntu distribution, the release numbers will most likely be different to reflect the newest versions of the software.

Source of Information : McGraw Hill Osborne Media How to Do Everything Ubuntu

Changing Ubuntu Login Screen

The login screen is one of the first things you see when you start up the Ubuntu operating system. Since the login screen is sort of like a first impression, it should reflect the individual user. Like everything else in a GNU/Linux operating system, this can be configured to do so.

Unlike the desktop wallpaper or the themes, the login screen allows for much more configuration. While you can still change the look of the login screen, you have many other options as well. Each of the six tabs allows the user to determine how the computer will react at the login screen. These tabs—General, Local, Remote, Accessibility, Security, and Users—can be accessed by selecting System from the top panel and then going to Administration | Login Window.

To understand how to configure the login screen to your tastes, it is important to understand what can be changed under each one of the six tabs.


General
The General tab contains some simple changes that you can make to your login screen and some that you should not try to edit until you have much more experience with Ubuntu.

The first change you can make is if you would like asterisks or circles to replace the characters at the login screen. Changes can be made by checking the check box, or by removing the check by clicking it again. The only other item you should adjust at this time is Use 24 Hour Clock. The default is Auto, but you can choose Yes or No as well. The three options of Disable Multiple Logins For A Single User, Default Session, and GtkRC File should not be altered at this time. These are for more advanced users and can create problems for you when you are using Ubuntu.


Local
This tab offers the most choices for you because you can alter the actual login screen here. You can choose the theme, the background color, and you can even create a custom welcome message here. This is also where you can add new login screens to use. Don’t worry about this tab; you can feel free to make any changes you want here because they all have to do with the aesthetics of the login rather than its behaviors.


Remote
This option dictates what remote users see at their login screen. You only have three choices under the Style menu. By default, the remote login is disabled; however, you can set it to be the same as the Local login or as a plain login screen. Unless you are planning to set up remote logins later, this tab is not overly important at this time.


Accessibility
The Accessibility tab provides you with choices regarding what users see, hear, and can do at login. The option to Enable Accessible Login should be left unchecked. The Themes section allows users greater control over their greeter screen. The Sounds section gives you the most configuration options, allowing you to choose what sounds users hear at successful and failed login attempts.


Security
The security section helps you protect your computer from unauthorized login attempts, idle logins, and permissions for heightened security. While a great deal of security is a good thing when it comes to computers, a great deal of common sense is often far better. You may be inclined to set all of the security settings to their strictest levels, but keep in mind that security experts warn that the higher a computer’s (or network’s) security levels are elevated, the less user friendly the computer (or network) becomes.

In the Security tab, you should only worry about two sections as a novice Ubuntu user. The first is the Enable Automatic Login option. By default, this first option is left unchecked. Checking it allows you to select a user that your Ubuntu computer will automatically log in as. If you are trying to protect your computer, leave this option unchecked, forcing users to provide a username and password at the login screen. Instances where someone would enable the automatic login may be to allow small children or guests to use the computer.

The only other tab you should worry about now is the one below the Enable Automatic Login, which is Enable Timed Login. Again, this is unchecked by default. Choosing this option by checking the box would automatically log in a specified user after a certain amount of time. For instance, a coffee shop running Ubuntu can set all of the computers to log in to the Guest account if no one else logs in after 30 seconds. This gives an employee, or a member, the opportunity to log in with his or her account before the Guest login automatically takes place. The time set before the timed login is determined in this tab as well. Obviously, too short a time period does not allow users the opportunity to log in, and too long a wait can be annoying to the automatic login user.


Users
The Users tab serves two functions; it allows you to exclude or to include users in the lists that appear in the Security tab. By default, all users are included in these lists. The second thing that the Users tab can do is set the default face image for users who have not selected one. Face images are icons that appear next to the user’s name at the login screen. If you wish to use face images, the default login screen needs to be changed. This can be done by going back to the Local tab and selecting a login screen that includes lists such as Human List.

Source of Information : McGraw Hill Osborne Media How to Do Everything Ubuntu 

GNOME Components

From a user’s point of view, the GNOME interface has four components: the desktop, the panels, the main menus, and the file manager. You can display two panels—one used for menus, application icons, and running applets at the top of the screen, and another at the bottom of the screen used primarily for managing your windows and desktop spaces. In its standard default configuration for Ubuntu, the GNOME desktop will display nothing. If you have any removable media, such as CD/DVD discs or attached partitions, icons for those will be displayed.

In addition to menus and items already mentioned, the top panel has icons for the Mozilla Firefox Web browser (globe with fox) and the Evolution mail tool (envelope). At the far right are the time and date icons. An update button will appear if updates are available. You can use the update button to update your system automatically. The bottom panel holds icons for minimized windows as well as running applets and the trash can. These include a Workspace Switcher (the colored squares) at the right. An icon on the left lets you minimize all your open windows. When you open a window, a corresponding button for it will be displayed in the lower panel, which you can use to minimize and restore the window size. Click the trash can icon on the far right side of the bottom panel to empty deleted files stored there.

Your home directory, as well as any partitions, removable media, and remote file systems, can be accessed from entries on the Places menu on the top panel. If you want an icon for an item displayed on your desktop, right-click the item in the Places menu and choose Add To Desktop. To add the computer icon to the desktop, you would open the Places menu, right-click Computer, and select Add This Launcher To The Desktop. You can do the same for Network, which will show just your remote directories and devices. The home directory icon cannot be added to the desktop.

To start a program, you can select its entry from the Applications menu. You can also click its application icon in the panel (if one appears) or drag-and-drop a data file to its icon. To add an icon for an application to the desktop, right-click its name in the Applications menu and choose Add This Launcher To The Desktop.

Source of Information : McGraw Hill Ubuntu The Complete Reference

GNOME 2.22 Features

Check www.gnome.org for a detailed description of GNOME features and enhancements, with screen shots and references. GNOME releases new versions on a frequent schedule. Several versions since the 2.0 release have added many new capabilities. GNOME now has efficiencies in load time and memory use, making for a faster response time. Desktop search is integrated into the file chooser dialog. For laptops, power management has been improved along with battery monitoring. For developers, a new version of the GTK+ toolkit provides better documentation and improved development tools. With GNOME 2.22, the GNOME Virtual File System (GVFS) provides direct file manager support for virtual file systems, letting you access Samba shares and FTP sites directly.


GNOME Resources
gnome.org Official - GNOME Web site
developer.gnome.org - GNOME developer Web site
art.gnome.org - Desktop themes and background art
gnomefiles.org - GNOME software applications, applets, and tools
live.gnome.org/GnomeOffice - GNOME office applications
library.gnome.org - GNOME documentation Web site for Users, Administrators, and Developers

GNOME Desktop Features
Following are new desktop features:
• File Roller can now work on archives on networked systems. You can also copy and paste or drag-and-drop files between archives.

• For right-to-left languages, window, menu, and workspace components are now mirrored, also positioned right-to-left.

• The GNOME documentation site at http://library.gnome.org organizes documentation into Users, Administrators, and Developers sections.

• An easy-to-use file permissions dialog allows changing permissions for all files in a folder.

• Basic window compositing is provided using drop shadows, live previews, and transparency effects. Support is included for 3-D effects for windows in the Appearance Visual Effects tab (wobble, shrink, and explode).

• Home directories now have data-specific folders set up including Pictures, Documents, Videos, and Music. GNOME applications may use these as defaults.

• With the GNOME Volume Manager, a computer window is now included, listing your file system devices, including CD-ROMs as well as network file system devices.

• GNOME automatically mounts removable devices at the /media directory.


GNOME Applications
The following applications are included:
• The Cheese application manages Web cam photos. For image collections, enhanced browsing is available.

• The GNOME video player, Totem, supports Web access, digital video broadcast (DVB), and DVD. It also provides YouTube and MythTV support.

• Tomboy note taker can now synchronize your notes from different computers. Connecting to a central server, all your notes from different systems can be integrated and synchronized, providing a single set of notes for all your systems.

• The International Clock applet is now used for the time applet on the top panel. It lets you see the time and weather at any location on the planet.

• GNOME sound and video applications can now prompt the user to search for any needed codecs. The mechanism for finding and installing the codec is handled separately by the codec wizard.

• The Disk Usage Analyzer (Accessories Disk Usage Analyzer) details disk and partition usage, as well as usage by directory, with totals for your entire file systems with space availability.

• GEdit has been reworked to adhere to the Multiple Documentation Interface specs. It now has a new syntax highlighting system for script languages such as PHP, Ruby, and HTML.

• The Vinagre remote desktop viewer lets you access desktops remotely.


GNOME Administration Features
Administration features include the following:
• Appearance administrative preferences integrates Theme, Background, Fonts, Interface, and Visual Effects into five tabs in the Appearance Preferences window.

• Seahorse integrates GPG encryption, decryption, and signing of files and text
(Applications Accessories Passwords And Encryption Keys. For Seahorse
configuration, choose System Preferences Keyrings And Encryption).

• Integrates PolicyKit controls for GNOME administration tools such as network-admin and users-admin.

• User Profile Editor (Sabayon) allows administrators to create and manage user profiles on either a current or a remote system. Profiles can contain personal information as well as application preferences, including OpenOffice.

• Integrated power management is controlled with Power Management Preferences.

• The Preferred Applications control panel now has an Accessibility tab with visual and mobility options.

• The GNOME Control Center for basic preferences is integrated into Ubuntu as menus items in the System Preferences menu. You can also start up the GNOME Control Center directly by entering gnome-control-center in a terminal window.

• Mouse accessibility options supporting different kinds of clicks is now integrated with the Mouse Preferences tool.

• The menu editor, Alacarte, lets you customize your menus easily.

• The disk usage analyzer, Baobab, lets you quickly see how much disk space is used.

• For developers, the Anjuta Integrated Development Environment (IDE) provides integrated access to debuggers, Glade UI editor, and Valgrind analysis.


GNOME File Manager Features
Nautilus is the official file manager for the GNOME desktop. You can find out more about Nautilus from the Nautilus user’s manual that is part of the GNOME User’s Guide at www.gnome.org. The Nautilus file manager, as part of GNOME, also has several new features added:

• Nautilus File manager now includes a disk usage chart when displaying properties for file systems. Images are displayed with their appropriate orientation using Exchangeable Image File (EXIF) camera information.

• Nautilus is now more integrated into other applications such as File Roller for archives, the image viewer for pictures, and the GNOME media player for audio and video. You can now preview sound and video files within a Nautilus window.

• Nautilus uses GNOME Virtual File System (GVFS) for remote file systems, which replaces GnomeVFS. GVFS uses the GO object-based abstraction layer for I/O (GIO). With GVFS, Nautilus can support FUSE user-based file system access. Applications no longer have to be written for GVFS access. Any application can access a GVFS-mounted file system.

• With GVFS, Nautilus now manages automounts for remote file systems. Access is stateful, requiring the user input a password only once, before granting continual access.
• Nautilus can burn files and ISO images to DVD/CD writers.

• Context-sensitive menus let you perform appropriate actions, such as extracting archive files. An Open With option lets you choose from a selection of appropriate applications. Multiple applications can now be registered for use with a file.

• The file manager can display network shares on local networks, using DNS-based service discovery. The file manager also supports access to password-protected FTP sites.

• The file manager can display audio tracks on music CDs with the cdda:// protocol and access connected digital cameras with the gphoto2:// protocol.

Source of Information : McGraw Hill Ubuntu The Complete Reference

Checking Software Package Digital Signatures

One very effective use for digital signatures is to verify that a software package has not been tampered with. A software package could be intercepted in transmission and some of its system-level files changed or substituted. Software packages from your distribution, as well as those by reputable GNU and Linux projects, are digitally signed. The signature provides modification digest information with which to check the integrity of the package. The digital signature may be included with the package file or posted as a separate file. To import a key that APT can use to check a software package, you use the apt-key command. APT will automatically check for digital signatures. To check the digital signature of a software package file that is not part of the APT repository system, you use the gpg command with the --verify option. These would include packages such as those made available as compressed archives, .tar.gz, whereas APT can check all DEB packages itself.


Importing Software Public Keys with apt-key
First, however, you will need to make sure that you have the signer’s public key. The digital signature was encrypted with the software distributor’s private key; that distributor is the signer. Once you have that signer’s public key, you can check any data you receive from them. In the case of third-party software repositories, you have to install their public key. Once the key is installed, you do not have to install it again.

Ubuntu includes and installs its public keys with its distribution. For any packages on the Ubuntu repositories, the needed public keys are already installed and checked by APT automatically. For other sites, such as Wine (the Linux Windows emulator), you may need to download the public key from its site and install it (http://winehq.org). You may also have to add repository support to access its Ubuntu compatible software. The Wine public key is available from the winhq.org site, with the public key for Ubuntu located at http://wine.budgetdedicated.com/apt/387EE263.gpg. You could download the public key and then install it on your system with the apt-key command. The following downloads the Wine public key:

wget -q http://wine.budgetdedicated.com/apt/387EE263.gpg

Once the public key is downloaded, you can then use the apt-key command to install it for use by APT in software verification. Ubuntu uses the apt-key command to maintain public keys for software packages. Use the command with the add option to add the key:

sudo apt-key add 387EE263.gpg

To access the software repository, you would also have to install its APT configuration file in the /etc/apt/sources.list.d directory. For Wine, this is named winehq.ist. Check the Wine site for download instructions.


Checking Software Compressed Archives
Many software packages in the form of compressed archives, .tar.gz or tar.bz2, will provide signatures in separate files that end with the .sig extension. To check these, use the gpg command with the --verify option. For example, the most recent Sendmail package is distributed in the form of a compressed archive, .tar.gz. Its digital signature is provided in a separate .sig file. First you download and install the public key for Sendmail software obtained from the Sendmail Web site (the key may have the year as part of its name). Sendmail has combined all its keys into one armored text file, PGPKEYS. You can download and then import the key file with gpg.

gpg --import PGPKEYS

You can also use the gpg command with the --search-key and –keyserver options to import the key. Keys matching the search term will be displayed in a numbered list. You will be prompted to enter the number of the key you want. The 2007 Sendmail key that results from the following example would be 7. This is the key used for 2007 released software.

$ gpg --keyserver pgp.mit.edu --search-keys Sendmail

Instead of using gpg you could use the Encryptions and Password Keys application to find and import the key (choose Applications Accessories Encryption and Password Keys).

To check a software archive, tar.gz file, you also need to download its digital signature files. For the compressed archive (.tar.gz) you can use the .sig file ending in .gz.sig, and for the uncompressed archive use .tar.sig. Then, with the gpg command and the --verify option, use the digital signature in the .sig file to check the authenticity and integrity of the software compressed archive:

$ gpg --verify sendmail.8.14.2.tar.gz.sig sendmail.8.14.2.tar.gz
gpg: Signature made Wed 31 Oct 2007 08:23:07 PM PDT using RSA key ID 7093B841
gpg: Good signature from "Sendmail Signing Key/2007 "$

You can also specify just the signature file, and gpg will automatically search for and select a file of the same name, but without the .sig or .asc extension:

# gpg --verify sendmail.8.14.2.tar.gz.sig

In the future, when you download any software from the Sendmail site that uses this key, you simply have to perform the --verify operation. Bear in mind, though, that different software packages from the same site may use different keys. You will have to make sure that you have imported and signed the appropriate key for the software you are checking.

Source of Information : McGraw Hill Ubuntu The Complete Reference