Linux with Operating System Concepts

SLS/Slackware
: This branch was first produced by a German company which led to 
SuSE Linux. Although there are dozens of spin-offs of SLS/Slackware, it is far less 
popular than either Debian or Red Hat.
• 
Miscellany
: There are dozens of dialects that either led nowhere or have few successors.
Linux and Unix operating systems are partially or completely POSIX conforming. 
POSIX is the portable operating system interface, a set of standards that operating system 
developers might attempt to target when they implement their systems. POSIX defines 
an application programming interface (API) so that programmers know what functions, 
data structures, and variables they should define or utilize to implement the code they are 
developing for the operating system.
In the development of Linux, the POSIX API has been used to generate a standard called 
the Linux Standard Base (LSB). Anyone implementing a dialect of Linux who wishes to 
include this standard knows what is expected by reading the LSB. The LSB, among other 
things, defines the top-level directory structure of Linux and the location of significant Linux 
files such as libraries, executables, and configuration files, a base set of Linux commands and 
utilities to be implemented, and implementations for such programs as gcc, the C compiler. 
Thus, underlying most dialects of Linux, you will find commonalities. In this way, learning 
one version of Linux is made easier once you have learned any other version of Linux.
1.7 TYPES OF USERS
The Linux operating system provides for two classes of users that we might term normal 
users and superusers. The term superuser is commonly used in many operating systems 
although in Linux, we call such a user 
root
. The root user (or users) has access to all system 
commands and so can access all system resources through those commands. Normal users 
have greatly restricted access in that they can execute public programs, access public files 
and access their own file space. We can add a third category of user account to this list: 
software accounts. We look at the types of users in detail in Chapter 9 when we introduce 
user account creation.

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Linux with Operating System Concepts
The role of root is to properly administer the computer system. In this section, we will 
discuss the types of duties of a system administrator. Operating systems divide accessibil-
ity into two or more categories, the ordinary user and the administrator (sometimes called 
privileged mode). Some operating systems have intermediate categories between the two 
extremes where a user is given more privileges but not full administrator privileges. We 
will see in Chapter 9 that we can do this in Linux through the sudo command.
The reason for the division between normal user and administrator modes is to ensure 
that normal users can not impact other users. Consider a home computer shared by a fam-
ily. If all users had administrator privileges, then they could view and manipulate each 
other’s files. If a parent had important financial data, one of the children could delete or 
alter the data without adequate protection. In a work environment, keeping data secure 
becomes even more important. Different users would have access to different types of data 
(financial, personnel, management, research), based on their identified role within the 
organization. Performing administrator duties (creating accounts, scheduling backups, 
installing software, etc.), if performed by the wrong person, can cause disastrous results 
if the person does not do things correctly. Imagine that when installing new software, the 
person unknowingly wipes out the boot sector of the disk. Upon reboot, the computer no 
longer functions correctly.
And so we have a unique account in all operating systems that is capable of full system 
access. It is through this account that all (or most) administrative functions will be per-
formed. What does a system administrator do? The role of the administrator will vary based 
on the number of users of the computer system(s), the complexity of the computer system(s), 
the types of software made available, and more significantly, the size of the organization.
A small organization with just a few employees might employ a single system adminis-
trator who is also in charge of network administration, computer security, and user train-
ing. In a large organization, there may be several system administrators, several network 
administrators, a few people specifically in charge of all aspects of security, and another 
group in charge of training.
The following list is common to many system administrators:
• Install the operating system
• Update the operating system when needed
• Configure the operating system to fit the needs of the users in the organization
• Secure the operating system
• Configure and maintain network communication
• Install, configure, and maintain application software
• Create and manage user accounts and ensure the use of strong passwords
• Install and troubleshoot hardware connected to computers directly or through a 
network

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Introduction to Linux
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• Manage the file system including partitioning the disk drives and performing 
backups
• Schedule operations as needed such as backing up file systems, mounting and 
unmounting file systems, updating the operating system and other application soft-
ware, examining log files for troubleshooting and suspicious activity
• Define (for your organization’s management) computer usage policies and disaster 
recovery plans
• Create documentation and training materials for users
• Make recommendations for system upgrades to management
System administrators may not be responsible for all of the above duties. Other forms of 
administration (e.g., network administration, webserver administration, database admin-
istration, DNS administration, and computer security specialist) may take on some of the 
duties or have overlapping duties with the system administrator(s). For instance, a network 
administrator would be in charge of installing, configuring, and securing the network but 
the system administrator may also be involved by configuring each individual workstation 
to the network. A webserver administrator would be in charge of configuring, maintain-
ing, and troubleshooting the webserver but the system administrator may be in charge of 
installing it and setting up a special account for the webserver administrator so that he/she 
can access some system files.
For the first half of this book (through Chapter 7), we will concentrate on Linux from the 
normal user’s perspective, introducing computer concepts that should be known of all users 
and the Linux commands that support the normal user. Starting in Chapter 8, we will focus 
on Linux from the system administrator’s perspective. From that point forward, we will 
focus on more advanced concepts and the Linux commands that usually require root access.
1.8 WHAT IS A COMPUTER?
We should probably more formally discuss a computer before we wrap up this introduc-
tory chapter. A computer is generally taken to be an electronic device that performs the 
IPOS (input-process-output-storage) cycle. It should be noted that computers do not have 
to be electronic (the earliest computing devices were mechanical in nature, using rotating 
gears or other movable parts). However, by making the computer electronic, it is capable of 
performing at truly amazing speeds because of how fast electrical current can flow through 
digital circuitry.
1.8.1 The IPOS Cycle
The IPOS cycle represents the four basic tasks of any computer: input, processing, output, 
and storage. Input is obtaining data from the outside world and delivering it to one or more 
components in the computer. Output is taking information stored in the computer and 
delivering it to the outside world, usually for humans to view. You might think of input as 
the raw data for a process and output as the results of the process.

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Linux with Operating System Concepts
Processing is the execution of one or more computer programs on the data. Processes 
can vary greatly in size, complexity, and function. Processes will often perform mathemat-
ical operations, string operations, computer graphics, storage operations, and/or operating 
system activities.
Storage is applied today to both data and program code. Storage usually refers to sec-
ondary storage, that is, the permanent placement of information on a device like a disk, 
but it can also refer to temporary storage in some form of memory such as main memory 
(RAM) or short-term storage such as registers and cache.
Figure 1.17 illustrates the IPOS cycle. Although a computer will do all four of these, it 
is not necessarily the case that all four of them are done in this sequence. For instance, a 
program may require some input followed by processing followed by additional input fol-
lowed by more processing. Also, results from a process can either be output or stored in a 
file, thus omitting either output or storage.
1.8.2 Computer Hardware
All computers have one or more processors. The processor, or central processing unit 
(CPU), is the device which controls the components within the computer. It performs an 
operation called the