The UNIX OS

The UNIX OS

Peter J. Vasquez Sr.CSCI 6303.01

The UNIX OS

What is UNIX? OpenBSD Installation Introduction to VI OpenBSD Configuration Introduction to ksh ksh Scripting

What is UNIX?

Design Architecture Filesystems Brief History

UNIX Design

Modular Programming software design technique that increases the extent to

which software is composed from separate parts, called modules. http://en.wikipedia.org/wiki/Modularity_(programming)

Re-Usable Code the likelihood a segment of source code can be used

again to add new functionalities with slight or no modification. http://en.wikipedia.org/wiki/Reusability

UNIX Architecture

Kernel – manages the computer's resources and controls their use by programs.

Consists of: CPU – responsible for running or executing

programs. The kernel decides which processes are allocated to the processor.

Memory – used to store instructions and data. The kernel decides what memory is available to a process, and whether nor not enough is available.

I/O – input and output devices (keyboards, mice, disk drives, etc). The kernel allocates requests to these devices from applications to perform I/O.

UNIX Architecture (cont.)

Shell - user interface to the kernel, where commands are input (whether on the command line interface or in a GUI)

Shell Examples: Bourne Shell (and variants) C Shell (and variants) Blackbox, fluxbox, fvwm, GNOME, KDE, XFCE,

CDE


System Processes (Daemons) – programs that assist the kernel with specific system tasks. Refers to background processes Handles tasks in the background that the user

cannot be bothered with Most daemons are child processes of another

running process (usually the init process, which is the initialization shell script responsible for starting up most processes after the kernel has loaded)


Parent/Child Processes Relationship of running process to other running

processes. If one process initiates a new process, it is called the parent, while the new process is known as a child

New processes are spawned through a procedure called 'fork', which creates a copy of the parent along with the needed memory space and parameters to run with a task/set of instructions

Common example is the execution of shell commands, which remain interactive while child processes can be sent to the background to run

UNIX Filesystems

UFS – UNIX File System (4.2/4.4BSD) a few block at the beginning reserved for boot

blocks a superblock containing a magic number identifying

as UFS filesystem a collection of cylinder groups, each containing the

following: backup copy of the superblock cylinder group header with statistics number of inodes number of data blocks

UNIX Filesystems (cont)

<swap> - form of virtual memory used to extend available

main memory dedicated partition, which should be at least the

size of main memory not required, but highly recommended

UNIX Brief History

A Brief Overview of OpenBSD

UNICS -> UNIX TSS -> BSD -> NetBSD -> OpenBSD Designed with Security and Simplicity as primary goals

(only 2 remote holes in the default install in the past 10 years)

Major contributions to other UNIX/Linux Operating Systems include OpenSSH : free implementation of SSH (secure shell)

which provides for encrypted remote administration of UNIX/Linux systems (85% of installed systems world-wide)

pf : or packet filter (firewall) has been used in a wide range of embedded systems (for example, the syswall security appliance)

OpenBSD Installation

Obtain CD (can be purchased at openbsd.org, or ISO download from ftp.openbsd.org)

Boot up using correct version (i386 in this example)

Set up partition sizes, choose filesystem type Set up basic system and package configuration

ftp://ftp.openbsd.org/

OpenBSD Installation (cont.)

Boot from CD


Press 'i' for install


Press <enter>


Press <enter>


Press <enter>


Type 'yes' to proceed with install


Press <enter>


Press <enter> for default disk, or specify disk


Type 'yes' to use the entire disk for OpenBSD


Press <enter>


Now, type '?' for help, then press <enter>


Now type 'p' to see current partition map


Press <enter>


Create (/) root, <swap>, /tmp and /var partitions


Create /usr and /home partitions


Type 'p' and press <enter> to see partitions


Type 'w', <enter>, 'q', <enter>, to write and exit


Now begin basic system, package configuration


Type hostname, networking info, press <enter>


Type in root password, press <enter> for CD


Type in 'all' to select all packages


Press <enter>, type 'done', and press <enter>


Packages begin unpacking/installing to disk


Type timezone 'US/Central', type 'halt' to reboot


Press <enter>, the system will now reboot

Introduction to VI

Two modes of operation Insert mode : type in a character to modify the

contents under the cursor directly Command mode : type in a “:” followed by the

command string for more advanced options We can create files, modify their contents, and

write the changes back to the disk We can search within files for common strings Useful in modification of the OS configuration

files

Introduction to VI (cont.)

Login as new user, list contents of directory


Type 'vi sample' for a new file named 'sample'


Type 'I' for insert mode, type, press <esc> ': wq'


We can open the same file to make changes


Type 'yy' and then 'p' to copy and paste the line


You can type 'dd' to delete the current line


We can search/replace a word, ':%s/new/old/g'


Now our file reads the following:


We can undo the change by typing 'u'


A lot of changes are available, for a complete reference you can type in 'vi reference' into a search browser, which will provide many results

The most common uses of vi are for the modification of system configuration files, and in shell programming (scripting)

OpenBSD Configuration

Default configuration is listed in /etc/rc.conf

OpenBSD Configuration (cont.)

/etc/rc.local for startup change (not /etc/rc.conf)


For the GUI, configuration is in /etc/xorg.conf


Login as root user Type 'man afterboot' on first boot to see list of

configurable options (new admin's guide) Run 'adduser' script to setup defaults Create User (best practice not to use root for

everything)


Login as 'root' and type the password


Press <enter> for default terminal type


Type 'man afterboot' for admin guide (overview)


Type 'adduser' and setup defaults for system


Create User


Now that we have a local user, we will exit the session as 'root' and re-login as the new user to continue configuration process

Configure networking parameters (done at installation, but can be changed after boot)

Configure GUI for X Windows


Login, type 'su', root password, press <enter>


Type 'ifconfig -a' , and vi '/etc/hostname.vic0'


The network configuration is set to DHCP


We can setup the GUI with 'X -configure'

Introduction to ksh (K Shell)

A shell is primarily used to interpret commands into instructions for the operating system

When we first log in, the command line we are presented uses the korn shell (ksh)

Behavior of ksh is defined through shell variables

The following screens will show navigation through commands is ksh to create a directory, list it's contents, and either dump the sample file to the screen, or move it into our new directory

Introduction to ksh (cont.)

Some sample shell variables


We can also issue 'cat sample' to show our file


We can list the contents of our directory, 'ls -al'


And make a new directory, 'mkdir temp'


Change directory with 'cd temp', list with 'ls -al'


Now we can move our file, 'mv ../sample .'


And show the directory contains our file, 'ls -al'


We can see the contents again with 'cat sample'

ksh Scripting

Combining the previous slides, we can begin to see how commands can be chained together

These chains of commands can be used to form shell scripts for common or routine tasks of the operating system

ksh Scripting Defined

At the beginning of this file, we need to include !#/usr/bin/ksh

File starts on first line and ends at last line or when encountering the word 'exit'

There are four types of lines the shell defining line empty lines commentary (begin with a '#') commands

ksh Scripting Defined (cont)

Script files should be change to permissions “chmod 700” (rwx – user, no permissions for group or world)

Commands start at the first word and end with the end of the line, or with a ';'

Examples: print -n “Name: “; read name; print “” grep filename | sort -u awk '{print $4}' | \

uniq -c >> /longpath/file

ksh Variables

Example ksh variables

ksh Arrays

Example ksh arrays

ksh Branching (Conditional Statements)

Example Branching

ksh Branching (Conditional Statements) plus Case Statement

Example Branching/Case Statements

ksh Looping

Example Loop Statements

ksh Looping plus continue,break

Example Loop Statements (cont)

ksh Command Line Arguments (Positional Parameters)

Example Command Line Arguments

ksh Comparisons

Example Use of Comparisons

ksh Variable Manipulation

Example variable manipulation

ksh Regular Expressions

Use * for matching any string (for example, to get all files end in .c, use *.c)

?(pattern) matches zero or one times *(pattern) matches any time the pattern +(pattern) matches one or more times @(pattern) matches one time the pattern !(pattern) matches string without the pattern

ksh Functions

Making a Function function foo { #commands } foo() { #commands }

Calling the Function foo arg1 arg2 ... (arguments $1...$n or $*)

Return exits the function immediately with value specified

after return as exit status (for example, 'return 0')

ksh Data Redirection

Done with “>” “>>” “<” “<<” Command Output to File

To write to a new file: 'command > file' To Append to an existing file: 'command >> file'

Standard Error Redirection To redirect the error output: 'command 2> file' Discard the error: 'command 2>/dev/null'

File into Command replaces standard input with file: 'command < file'

ksh Data Redirection (cont)

Combine Input and Output Redirection 'command < infile > outfile' 'command < infile > outfile 2>/dev/null'

Commands into Program 'command <<EOF

input1 input2 input3 EOF'

ksh Pipes and Co-processes

To send output of one command to another ' command1 | command2 | command3 ' for example “last | awk '{print $1}' | sort -u”

Background Processes command |& for example, ksh in background 'ksh |&'

ksh Input from User and Files

Read in a Variable print -n “Enter your favorite color: “;read var; print””

Read into a File Line for Line get each line of a file into a variable

{ while read myline; do # process $myline done } < filename

catch output last | sort | {

while read myline;do #commands done }

ksh Special Variables

$# - Number of arguments on command line $? - Exit status of last command $$ - Process id of current program $! - Process id of last background job $0 – Program name including path $1..$n – Command line arguments, one by one $* - All command line arguments in one string

ksh Sample Script

Create new file with vi, add shell to top

ksh Sample Script (cont)

Keep looping until our condition is met


Now we can ask the user for some information


If we have the right person, verify password


Add condition to limit number of guesses


If the user login is successful, run command


Now we make sure script is executable


We can run the script now with './sample'


If the name doesn't match, ask again


Now the name matches, so ask the password


Password doesn't match, so ask again


Password matches, run authorized command

Any Questions?

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The UNIX OS