UNIX Operating System

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Transcript UNIX Operating System

ITEC400 Week Five
Robert D’Andrea
Administrative Issues
Link of the Week
Review Week Two Information
This Week’s Expected Outcomes
Moving around in UNIX
Break-Out Problems
Upcoming Deadlines
Hands-on Information
Lab Assistance, Questions, and Answers
Administrative Announcements
The midterm and the final exam are both
electronic. Please verify that your testing facility can
administer this type of test.
The Student Learning Center has been requested
to send midterm exams to your proctors. They will
email me within a couple days that the request has been
completed. I will email each of you that your proctors
should receive the SLC packets.
Link of the week
Data Disaster
Ontrack Data Recovery
Data recovery
Knoll Ontrack is one of the worlds largest data
recovery services. They have performed more than
500K data recoveries since 1985.
Link of the week
Data Disaster Rescuers
• CompuRecovery found on the Internet for desktop
hard drive recovery.
• Datarecovery.com 7/24 found on the Internet.
Provides RAID, hard drive, and laptop data
recovery solutions.
Norman Ken Ouchi at IBM was awarded the
patent in 1978 for the recovery of data stored in failed
memory unit. Later developed into RAID 10.
Link of the week
Data Disaster
1. Big versus small company operations
2. Backup services off site location and media. Test
data occasionally
3. Trouble shooting
Link of the week
Ironkey USB Flash Drive
Data Disaster Helpful Hints
- Use dedicated circuits for your connection
- Keep your computer cool and in a dry place
- Use a UPS (Uninterrupted Power Supply)
- Don’t assume that your data is permanently
destroyed even if the situation looks bad
- Secure your work area and devices
Course expected outcome
Learning Outcomes (Week five)
 Review test condition
 Write Perl scripts, including variables, control flow,
and regular expression syntax
Course expected outcome
Test Condition
if test ! -S "$1"
echo $1 does not exist or is empty.
If the file specified by the first positional
parameter to the shell procedure, $1, does not exist or is
of size 0, the test command displays the message. If $1
exists and has a size greater than 0, the test command
displays nothing.
Course expected outcome
Test Condition
test 100 -gt 99 && echo "Yes, that's true." || echo
"No, that's false.“
This command will print the text "Yes, that's true."
because 100 is greater than 99.
text 100 -lt 99 && echo "Yes." || echo "No."
This command will print the text "No." because 100 is
not less than 99.
Course expected outcome
Test Condition
[ "awesome" = "awesome" ]; echo $?
This command will print "0" because the expression is
true; the two strings are identical.
[ 5 -eq 6 ]; echo $?
This command will print "1" because the expression is
false; 5 does not equal 6.
UNIX Operating System
Process and Multitasking
The UNIX kernel can keep track of many
processes at one time, and dividing it’s time to
other system tasks. Each process submitted to
the kernel is assigned a unique process ID
(PID). In every version of UNIX, the PID range
is 0 through 32,000 and is restrained to 5 digits.
UNIX Operating System
Single Tasking Operating System
A single-tasking operating systems only performs
one task at a time. The user of a single-task system can
switch from one window to another window, executing
a different application, but only one task is ever active
at a time. When a user switches from one window to
another window, the switched task that is left, is
suspended, until the user switches back to it. Suspended
tasks are not allocated system resources, but remain as
it was when it was suspended. When a suspended tasks
resumes execution, it starts where it left off, as if
nothing ever occurred.
UNIX Operating System
Multitasking Operating System
In multitasking, only one CPU is involved,
but the operating system switches from one
program to another so quickly that it gives the
appearance of executing all programs at the
same time.
UNIX Operating System
Multitasking Operating System
There are two basic types of
multitasking: preemptive and cooperative. In
preemptive multitasking, the operating system
parcels out CPU time slices to each program.
The UNIX operating system is preemptive.
UNIX Operating System
Multitasking Operating System
In cooperative multitasking, each program
can control the CPU for as long as it needs it. If
a program is not using the CPU, however, it can
allow another program to use it
temporarily. OS/2, Windows 95, and Windows
UNIX Operating System
Multitasking versus Concurrent Processing
A conventional processor can only execute
a single task at a time - but by rapidly switching
between tasks a multitasking operating system
can make it appear as if each task is executing
concurrently or at the same time.
UNIX Operating System
Multitasking Processing
Single-core systems are by nature multitasking, whereas multicore systems
can provide true multithreading. So what is the difference between multitasking and
multithreading? To examine multitasking, consider a single-core system that has four
applications running, each of which spawns its own thread or process.
UNIX Operating System
Multitasking Processing
UNIX Operating System
Multitasking Processing
Because the system has a single core, the operating system becomes
the gatekeeper and assigns these four processes periodically to the core for
execution as shown in the previous slide. If each process takes 25 units of
time to execute, then the total execution time for all the four tasks is 100 units
UNIX Operating System
Multithreading Processing
Multithreading is the ability of a program or an operating system
process to manage its use by more than one user at a time and to even manage
multiple requests by the same user without having to have multiple copies of
the programming running in the computer.
UNIX Operating System
Multithreading Process
Multithreading extends the idea of multitasking into
applications, so you can subdivide specific operations within a
single application into individual threads. Each of the threads
can run in parallel. The OS divides processing time not only
among different applications, but also among each thread within
an application.
UNIX Operating System
Killing Processes
At times a process must be terminated prior to its
normal intended completion. The UNIX shell provides
a utility named, kill to end the execution of a process.
Prior to issuing the kill command to terminate a
process, the processes PID must be determined by
using the ps –ef command. The kill command is also
used to send a preparatory signal(s) to an executing
process prior to receiving a termination signal. A
process can only be terminated by the owner of the
process or by root. The syntax format for the kill
command is as follows:
kill [-options] process-ID
UNIX Operating System
Parent and Child Processes
Each UNIX process has two unique
numbers associated with them. One is the
Process ID (PID) and the second one is the
Parent Process ID (PPID). All user processes in
the system have a PPID, including the init
process, which will be addressed in the course
boot-up procedure.
UNIX Operating System
Orphan and Zombie Processes
Normally, when a child process is terminated, the
parent process receives a SIGCHLD (code 17) signal
from the kernel. After the parent receives the
SIGCHLD signal, the parent can perform any last
minute task or restart a new child process prior to the
termination of its child. However, if the parent is
terminated prior to its child process, the child process is
left without a parent. This situation results in the child
process becoming an orphan and the init process
becomes its new parent process. The orphan process
will then be assigned a PPID of 1.The term used to best
describe the init processes action is re-parenting.
UNIX Operating System
Zombie Process
When a process is terminated or terminates
on its own, but only partially exits the system,
its presence can be displayed on the system as
being in a Z state. This is a zombie, or defunct
process on the system. A zombie is a process
that completed execution, and is dead (walking
dead). It does not consume system resources. It
retains an entry in the process table. A good
process display command is ps –aux.
UNIX Operating System
Daemon Process
A daemon process is often a system related
background process. Normally, a daemon process
comes into being during boot-up and terminates when
the system is rebooted or shutdown.
A daemon process is not attached to a terminal
like a foreground process. Verification of this attribute
can be observed by performing the ps –ef command,
and observing the “tty” field, all daemon processes
display a “?” in this field.
UNIX Operating System
Daemon Process
Daemon processes execute in the
background and their existence is under the
radar screen. Users don’t know they exist unless
they look for them on the system. Daemons
execute waiting for data to be passed to them
from some application, such as, a database,
network, or printer daemon waiting for a print
command. Daemon processes normal are known
as service providers.
UNIX Operating System
Umask Calculation
umask setting = 027
Complement of umask = 750
File default permission setting = 666
Directory default permission setting = 777
The resultant permissions are calculated via bitwise
AND of the unary complement of the argument (using
bitwise NOT) and the permissions specified by the
UNIX Operating System
Regular Expressions
Definition: Regular expression provides a concise and
flexible means for "matching" (specifying and
recognizing) strings of text, such as particular
characters, words, or patterns of characters.
Abbreviations for "regular expression" include
"regex" and "regexp". The concept of regular
expressions was first popularized by utilities
provided by UNIX distributions, in particular the
editor “ed” and the command/filter grep.
Example: if ( /UNIX V5/ ) {
print “UNIX V5 found on system. \n”;
UNIX Operating System
Regular Expressions
Substitution operator: s/original value/new value/
Character class: Matches a single character that is
contained within the brackets [ a-zA-Z0-9_ ]
Special or meta characters are used to denote actions
or delimit groups:
+ means “one or more of whatever was before
the + symbol”
. Matches any single character (i.e., x.z)
^ Matches the starting position within the string
$ Matches the ending position of the string or
the position just before a string-ending
UNIX Operating System
Regular Expressions
^[A-Z0-9._%+-][email protected][A-Z0-9.-]+\.[A-Z]{2,4}$
UNIX Operating System
What is ELF?
Executable and Linking Format (ELF) is a
common standard file format for executables,
object code, shared libraries, and core dumps.
ELF is flexible and extensible by design, and it
is not bound to any particular processor or architecture.
This has allowed it to be adopted by many different
operating systems on many different platforms.
UNIX Operating System
Perl Syntax
End of statement delimiter
Comma for line continuation
New line (non-printable character)
The "diamond operator", <> is
used when a program is expecting
input, but isn't concerned how it
UNIX Operating System
Perl Syntax
Singular variables prefix (single
value, number or string)
Prefix for plural variable (array)
Prefix for plural variable (hash)
Default variable
It Is the "it" variable. It's often the default
parm that built-in functions use, or return
Contains the name of the program
being run.
UNIX Operating System
Perl Syntax
while ( … )
Action statements
What is a continuous loop?
while ( 2 ) {
Action statements
UNIX Operating System
Perl Syntax
The Perl language does not support case or switch
statements. The closest way to achieve case evaluations is as
if ( $condition_one ) {
action_one ();
elsif ( $condition_two ) {
action_two ();
elsif {
action_n ();
UNIX Operating System
Three Types of for Loops
my @array;
# Old style C for loops
for (my $i = 0; $i < 10; $i++) {
$array[$i] = $i;
# Iterating loops
for my $i (@array) {
print "$i\n";
UNIX Operating System
Three Types of for Loops (continued)
# Loops
print "$_\n" for @array;
UNIX Operating System
Perl Syntax
foreach $total (12,9,3,7)
# Sum each value in the list.
$sum += $total;
UNIX Operating System
Perl Syntax
foreach (-32,10,1,2,0,-1) {
# Valid numbers are considered to be greater than zero
# The default variable is utilized,
if ( $_ > 0 )
# Print each valid number on a single output line.
print "$_\n";
UNIX Operating System
Open Statement
The open function can be used to create file
handles for different purposes (input, output, and
piping), you need to be able to specify which
behavior you want.
When you open a data file in Perl, all you have to
do is specify (a) a file handle and (b) the name of the
file you want to read from.
open (CHECKBOOK, "checkbook.txt");
UNIX Operating System
Open Functions
open(file_handler, “file_name”)
open(file_handler, “<file_name”)
open (file_handler, “>file_name”)
open (file_handler, “>>file_name”)
See page 21 in your Perl text.
UNIX Operating System
Filehandle is utilized for both input and output
files. Most file names are cryptic and are meaningless
to programmers. The purpose of a filehandle is to
help the programmer remember a simple file name
throughout a program.
A filehandle is a name given for a file, device,
socket, or pipe.
Filehandle command line format:
open(filehandle, file name, permissions,
Example: open($FH,$file_name);
UNIX Operating System
If you want to read text from a file line-by-line,
then use the following syntax:
my @lines = <FILE>;
The <FILE> operator - where FILE is a
previously opened filehandle - returns all the unread
lines of the text file in list context or a single line in
scalar context. Hence, if you had a particularly large
file and you wanted to conserve memory you could
process it line by line:
while (<FILE>) {
print $_;
UNIX Operating System
What is List Processing?
@math_array = (6 - 4, 4 * 4, 8 / 2, 9 - 8);
while ( … )
UNIX Operating System
What is List Processing?
@math_array = (6 - 4, 4 * 4, 8 / 2, 9 - 8);
while ( … )
UNIX Operating System
What is a “for” Loop?
for (counter = 0; counter < 10; counter++)
Perl's for loop, or for statement, is used to loop
through a designated block of code until a specific
condition is met.
Three expressions are contained in a for loop:
1. Set initial state of the loop variable
2. Condition test the loop variable
3. Modify the state of the loop variable
UNIX Operating System
foreach Statement Format
foreach VAR (List)
UNIX Operating System
foreach Statement Format
@myNames = ('Larry', 'Curly', 'Moe');
foreach (@myNames)
print $_;
UNIX Operating System
Perl Program Statement
#!/usr/bin/perl –w
UNIX Operating System
Print Continuation Statement
print "error: incorrect number of arguments",
"usage: intlist a b (where a < b)",
UNIX Operating System
Points of Interest
Online Documentation
Websites that have Perl documentation. The two
biggest ones are:
http://search.cpan.org/ for modules
UNIX Operating System
Perl script:
./diamond_oper.pl <file name>
`./perl_it.pl and perl_loop.pl
./linenum.pl and ./intlist.pl
UNIX Operating System
Moving Around in UNIX
cal –y (display a calendar for the year)
cal –j 2015 (display Julian dates)
cal –m 2015 (display Monday first day)
cal –s 2015 (display Sunday first day)
cal 9 2015 (display September 2015 month
UNIX Operating System
Moving Around in UNIX
top Command
The top command is a useful tool for displaying
processes sorted by various criteria.
It is an interactive tool that updates frequently
and displays data about physical and virtual devices,
CPU usage, and load averages.
UNIX Operating System
Moving Around in UNIX
Finger command
The finger command displays information about users on
a specific host.
Local host finger
Obtain specific information on a user on a local machine:
finger dandrear
View all the logged in users on a remote machine:
finger @microsoft.com
Get information about a specific user on a remote machine
finger [email protected]
Break-out problems
Define a Perl hash table
Define ELF
Define a Perl array
What convenience does a Perl filehandle provide?
What is the functionality of a regular expression?
Are continuous loops useful?
Define an object file
Perl default variable
Perl “it” variable
Explain the s/pattern/new version/ command
Lab Assignment 4-1, Simple Perl Scripting, due May
29, 2016.
Lab Assignment 5-1, Makefile Exercise, due June 12,
Lab Assignment 6-1, Programming Assignment 1,
due February 28, 2016.
Read Chapters 3 and 4 in Essential System
Administration text.
Read Module Five listed under the course Web site.
Everyone should have received a Perl Quick
After class assistance
After each Franklin Live session, I will remain on the
session to provide assistance unless otherwise
Lab Assistance available by phone
and/or email