Linux with Operating System Concepts

dependencies
, that is, require addi-
tional files. In the case that those dependencies are not already installed, the installer will 
find the appropriate package(s) to install and ask you if the additional package(s) should 
also be installed. If you do not install the dependent packages, your installation will fail. 
FIGURE 13.2 
Installing dependencies found through the Add/Remove Software GUI.

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Figure 13.2 shows the dependencies required to complete the installation for GIMP (the 
GNU Image Manipulation Program). In this figure, we see that eight additional packages 
need to be installed. Fortunately, installation is not any more challenging than selecting 
the Install button. The only downside to installing these additional packages is the time 
and disk space that they will take up. We will return to the Add/Remove Software GUI in 
Section 13.7 as we can use it to remove software packages.
13.3.2 Ubuntu Software Center
Ubuntu has taken a different approach to software installation, through the Software 
Center as shown in Figure 13.3. From this GUI, you can explore installed software 
or all software titles that are currently available. All software includes titles provided 
by Ubuntu, those provided by “canonical partners,” proprietary software and soft-
ware provided by independent programmers. You can view software based on type: 
Accessories, Books & Magazines, Developer Tools, Education, Fonts, Games, Graphics, 
Internet, Office, Science & Engineering, Sound & Video, System, Themes & Tweaks, and 
Universal Access. Within these categories, software may be divided into subcategories. 
For instance, Science & Engineering is divided into categories like Astronomy, Biology, 
Chemistry, Computer Science & Robotics, and Mathematics. Developer Tools is subdi-
vided into categories like Debugging, Graphical Interface Design, IDEs, Java, Lisp, Perl, 
and Web Development.
Once you have selected a software title, you are asked to authenticate. Recall in Ubuntu, 
you are not provided the root password. However, the initial user is made an administrator. 
FIGURE 13.3 
Ubuntu Software Center.

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Linux with Operating System Concepts
So this user is able, through sudo, to perform software installation. This user should be the 
one who authenticates. When done, installation takes place and the new software title is 
installed. Installation will most likely take place under /usr.
13.4 INSTALLATION FROM PACKAGE MANAGER
A package manager is a program used by users or system administrators to install, update, 
upgrade, or remove software. In Red Hat Linux, the primary forms of package manag-
ers are 
rpm
and 
yum
. Rpm stands for Red Hat Package Manager and yum stands for 
Yellowdog Updater Modifier. Rpm is the more primitive approach requiring more effort by 
the user/administrator. Yum on the other hand calls upon rpm to accomplish its tasks. As 
such, yum is a much simpler way to install software. In Debian Linux, the primary package 
manager is 
apt
(Advanced Packaging Tool). Rpm, yum, and apt are now available in other 
Linux distributions, so it is useful to learn all three tools.
In general, a package manager, or a package management system, provides several dif-
ferent useful functions for both installation and maintenance of software. The package 
manager can be used to verify the correctness of the contents of a package. Correctness 
means that the files themselves have proper checksum values (for error detection) and 
proper signatures. A digital signature is not required for software installation. But when 
one is provided with a software package, you can use this to ensure that the software is 
legitimate. The package manager operates as an archival tool in that it can unpack and 
uncompress the files in the package. Since the packages typically consist of executable 
files, library files, and supporting files (e.g., documentation and data files), there is no need 
to compile the files. However, the files must be placed correctly. The package manager 
performs installation by testing files and moving them to their destination directories. 
Testing of files involves checking dependencies. For instance, if one file requires a particu-
lar library file to function, then that library file must be available in your Linux system or 
the dependency is not met.
Libraries consist primarily of .so files. The so extension stands for “shared object” where 
shared means that the item is to be shared among multiple programs and object means that 
it is an object (already compiled) file.
The .so files play a similar role in Linux as the .dll files (dynamic linked library) in 
Windows. However, in Linux, so files are versioned, meaning that they are stored based 
on the version number of the Linux system or software that will use them. Thus, the same 
named library may exist under slightly different names. In Windows, a newer version of 
the same dll file will replace an older version so that software requiring the given library is 
forced to use the most recent version. This may or may not complicate matters in running 
the older software. This leads to a situation that many Windows programmers have dubbed 
“DLL Hell.”
The majority of Linux library files are found under either /lib or /lib64. These directories 
are divided into subdirectories for classes of library files. For instance, you might find secu-
rity library files under 
/lib/security
and/or 
/lib64/security
while most library 
files are found directly under /lib64. Most of these files have the name 
lib