| The operating system is a set of
programs that manages all computer operations. It also provides a link
between the user and system resources, converting requests that come
from the mouse and/or keyboard into computer operations. Most
operating systems, including UNIX, have three main components: the
Kernel, the Shell and the File System. The Kernel manages the
operation of the computer. The Shell provides for interaction between
the user and the computer, and the File System provides a way to
organize and manage the information on the computer's hard disk(s).
Much of the following information applies to all varieties of UNIX,
although some of the information is Solaris specific.
The OS Kernel 
The kernel is the core operating system with the necessary basic
capabilities to run the computer. The kernel is the closest to the CPU
and hardware. It is an executable file that gets
loaded when the computer starts or boots. The name of the file that
gets loaded is called /kernel/genunix.
Once the kernel has loaded, it performs the following functions:
- Manages devices, memory, and
processes.
- Controls the functions (transmission
of information) between the system programs (utilities) and the
system hardware.
- Manages functions such as: Swap
space, Daemons, and File Systems.
Swap space - A reserved part
of the hard disk for the kernel to use during processing. Portions
of running programs can be "swapped out" to the hard disk
and then brought back in later if needed. This swap space is
actually on the hard disk, but it looks like additional memory or RAM
and is sometimes called virtual memory.
Daemons - Programs or
processes that perform a particular task or monitor disks and
program execution. Daemons are special processes that begin after the OS
loads. Daemons then wait for something to do in support of the OS. They can be
started or stopped as necessary. An example is the printer daemon,
lpsched (line printer scheduler). It starts when the system starts
up and then waits in the background until someone needs to print
something. Daemons in the UNIX world are similar to Services with
Windows NT/2000 or NetWare Loadable Modules (NLMs) with Novell
NetWare.
File Systems - A hierarchy of
directories, subdirectories and files that organize and manage the
information on hard disks. File systems can be either local or
remote. Local file systems are located on the hard disk of your
workstation. Remote file systems are located on another computer,
which is usually a server.
The Shell 
A shell is an interface between the user and the kernel. It acts as an
interpreter or translator. In other words, the shell accepts commands
issued by you, interprets these commands, and executes the appropriate
programs. Shells can be command-line driven or graphical. Three
command line shells are available in the Solaris UNIX environment. It
is possible to initiate or switch between these shells when working on
the computer. You can use the ps
(process status) command to see which shell you are using.
- Bourne shell ($) - The Bourne
shell was the original shell program for UNIX. It is the
default shell for the Solaris computing environment. Stephen
Bourne developed the Bourne shell for the AT&T System V.2 UNIX
environment. This shell does not have aliasing or history
capabilities. It is mostly used by system administrators. The
Bourne shell prompt is a dollar sign ($) which is similar to a DOS
C:\> prompt.
- Korn shell ($) - The Korn
shell is a superset of the Bourne shell and was developed by
Stephen Korn at Bell Labs. It has many of the Bourne shell
features plus added features such as aliasing and history. This is
the most widely used shell and is the industry standard for system
users. The Korn shell prompt is also a dollar sign ($). Note:
Examples given in this course are based primarily on the Korn
shell.
- C shell (%) - A shell based
on the C programming language. Like the Korn shell, it has
additional features such as aliasing and history. The C shell was
developed by Sun's Bill Joy and is still widely used today. The C
shell prompt is a percent sign (%).
The File System
The file system provides a way to separate and keep track of the
information on a hard disk. The Solaris operating environment file
structure is a hierarchy of directories, subdirectories, and files
that are grouped together for a specific purpose. The file system is
integrated with the Kernel to provide an organizational structure for
your software and data. The file structure subdivides hard disks to
make them more manageable and enables us to locate files. Hard disks
can be divided into file systems, directories, subdirectories, and
files. The file system organizes your data similar to the way a file
cabinet stores information. The file system is like the file cabinet,
directories are like drawers, subdirectories are like folders and
files are like the pages in a folder. 
A directory hierarchy looks like an
inverted tree with the root at the top. The following is the hierarchy
of the UNIX file system: 
- File System - A group of
directories that can be thought of as a separate tree structure. A
hard disk can be divided into multiple separate file systems which
are similar to logical partitions in the Windows/DOS world (like
drive C: or D: ) or volumes as with Novell NetWare. The file
systems can be made available (mounted) or unavailable (unmounted)
at the administrator's discretion. Each file system has its own
directory structure and can either be local (on your computer) or
remote (on another computer).
- Directory - A location for
other files and subdirectories. The Solaris File System, or
directory structure, enables you to create files and directories
accessed through a hierarchy of directories. A directory is like a
file drawer in a file cabinet. The highest directory in the
directory structure of a file system is the root directory, which
is designated as a single forward slash (/).
- Subdirectory - Any directory
below another directory. For example, some of the subdirectories
under the root (/) directory are /usr, /etc, and /kernel.
- Files - Files are contained
in directories and subdirectories. They are the lowest level of
the file system. There are usually thousands of files on hard disk
and there are several different types:
- Directories - Directories
are considered a type of file under the UNIX file system.
- Plain ASCII - (American
Standard Code for Information Interchange). These files are
pure text files with no special formatting characters in them.
- Applications Files -
These files are created by an application such as a Word
Processor, Spreadsheet or Database program.
- Executable Programs -
These are UNIX utility commands and application programs.
Common Solaris Directories 
The top most directory in a file system is called the root directory.
It is the starting point of the file system hierarchy. The root
directory (/) is required for the operating system to function and
contains critical system files (such as the kernel). The following is
a list of some of the more important directories and their
purpose. The slash in front of the following directories indicates
they are actually subdirectories off the root directory.
- /usr directory - Contains
executable commands, system administration utilities, and library
routines.
- /opt (optional) directory -
Contains Sun's unbundled software applications and third party
applications.
- /etc (etcetera) directory -
Contains system administration files such as the passwd file.
- /export/home directory -
Contains the user home directories. Depending on how the system
has been set up by the administrator, the home directories may
instead be found in /home.
- /dev (devices) directory -
Contains files which are pointers to device names. All devices in
UNIX have standard file names.
- /kernel directory - Contains
the basic operating system files such as the main UNIX kernel
genunix.
- /var (variable) directory -
Contains print spooling and mail system error messages.
|