Download Week_13

Week Thirteen Agenda
•Link of the week
•Use of the Virtual Machine
•Review the next lab assignment
•Expected outcomes
•Next lab assignment
•Upcoming deadlines
•Questions and answers
Link of the week
Purchase CGI scripts
http://www.cgiscript.net
CGI Programming FAQ by Nick Kews
http://www.webthing.com/tutorials/cgifaq.html
Introduction to CGI Scripts
http://snowwhite.it.brighton.ac.uk/~mas/mas/courses/html/html.html
Define: CGI (Common Gateway Interface) script
A standard for interfacing with external applications and
information servers. The information servers can be
HTTP or Web servers. The CGI scripts provides a more
dynamic avenue for information servers to pursue rather
than as a HTML file server.
Link of the week
Common
In the sense that there are many programming
languages that scripts can be written in and interact with
different types of systems. The user isn’t limited to just
one way.
Gateway
CGI strengths lie in not only what it can do itself, but with
it’s potential access it offers to other systems
(databases/graphic generators).
Interface
CGI provides a well-defined way to call up its features.
The interface between the CGI script and the web server
is fixed.
Review DNS
What is a domain name?
It is a name that refers to a numeric notation (similar to an alias).
A name that identifies one or more IP addresses.
What is the function of a Domain Name Service (DNS)?
It is a system that resolves names to an IP address(es) of clients. Domain
name system is a hierarchical system where the top level domain serving
sub domain clients with names and IP addresses. A DNS is similar to a
“phone book”.
The most popular DNS software is generally BIND.
dos2unix is a function that converts DOS/MAC plain text files into Unix
format.
What is the “lost+found” area considered on a Unix/Linux system?
It is the lost file directory. Usually, there is one on every disk partition.
Disk errors or incorrect system shutdowns cause files to become lost.
Review Network Services
Network Services
A variety of services available across a network
NFS
Remote login
Utilize a Web browser
All network services rely on the ability to convert a host or domain name to
an IP address.
DNS are complex. The number of host names and IP addresses in the
Internet is very large.
DNS Local contains actual translations for the machines in its local
network
DNS Global contains more information about translations.
A single translation could involve several DNS before resolving the IP
address.
Review Security
Security on UNIX systems
Basic Unix-like operating system security is the access
modes for files and directories. Default file and directory
permission settings are set by the umask variable value.
The recommended umask 077 setting would enable all
permissions for the directory owner, disabling all
permissions for the group, and others.
Base directory values = 777
Base file values = 666
Access permissions cannot be granted one way for one
user and another way for a different user.
The chmod command should be used to make the final
permissions settings once the information is intended for
use.
Review Week Twelve Lab Assignment
Directory Calculation
umask 077
777
077
700
111 111 111
000 111 111
111 000 000 (1’s complement)
111 000 000
700 (rwx------)
Review Week Twelve Lab Assignment
File Calculation
umask 077
666
077
700
110 110 110
000 111 111
111 000 000 (1’s complement)
110 000 000
600 (rw-------)
Review Security
Security on UNIX systems
PATH environment variable should be organized with so that system paths
are searched first rather than the users current directory. The users current
directory should be searched last.
Unix utilizes a combination of one-way and DES password
encryption.
MD5 passwords all begin with “$1$” denoting that encryption form.
Network security is important so limit access to powerful commands
like uucp, uux, uucico, and uuxqt commands.
Because LANs have been designed to transfer files between
computers quickly, and security should be more of a consideration
today.
Review Filesystems/passwords
File Systems
UNIX/Linux file system is contained under the root directory denoted by a slash “/”.
Users don’t have to worry about the physical locations of files.
The system administrator must be familiar with mounting and un-mounting storage space
(/mnt).
A file system cannot be utilized unless it has been mounted.
One-Way Encryption
Encryption that produces cipher text from which the original data cannot be reproduced.
MD5 is a method to create a hash or message digest, it will create a unique MD5sum for
every different message or file.
You cannot reverse it so you have to brute force it. Rainbow tables use a mathematic
algorithm so its easier and faster than a common brute force.
And yes, there are tables which can crack your MD5, I just don’t know how big they are.
Usually if you have a password which is bigger than 15 characters, it takes to much time to
create a table for it, and you need a lot of disk space.
So if your password is bigger than 15 characters you are reasonably safe.
Review Super Block
Super Block Attributes
Contains information about each mounted file system.
The super-block is the first block of each ext2FS/ext3FS partition. It contains
important data about the file system, such as its size, free space, etc. (it is similar to the
method used by FAT partitions). A partition with a damaged super-block cannot be mounted.
Fortunately, ext2FS/ext3FS keeps several super-block backup copies scattered over the
partition.
Most of the information stored in the super-block is considered static. Static
information can be critical in recovering data.
Types of information found in a super-block
Device identifier, inode pointers, block size, file system type and pointer.
Inode contains information about a file. The name and the inode number are stored in the
directory.
Data block are used to store the data in the file. There is a limited amount of space in an inode for
pointers.
Number of mounted file systems
The Linux 2.0 kernel keeps a static array of such structures to store up to 64 mounted file
systems. A file system must be mounted before it is usable.
Review Directory Tree
Review Directory Definitions
Directory Structure
Unix arranges files and directories in an inverted tree topology.
/proc directory contains a hierarchy of special files which represent the current state
of the kernel.
/bin directory contains shells (bash and csh), vi editor, and commands.
/etc directory contains system related configuration files.
/mnt directory is intended to be used as the temporary mount points for mounting
storage devices.
drwxr-xr-x
6 root
root
1024 Dec 29 2005 mnt
/opt directory is where new or untested software is stored.
/dev directory is where device files are located that access hardware.
/ directory contains several main directories.
/root directory is reserved for the super-user.
drwxr-x--- 4 root root
1024 Nov 16 22:35 root
Review Filesystem Structure
ext3 File System
Super Block
File Manager
Linux Virtual File System
Kernel
Review Filesystems
Linux virtual File System
The purpose of a VFS is to allow client applications to access
different types of file systems in a uniform way.
Manages kernel file abstractions in one format for all file systems.
Receives system call requests from user level
(e.g. write, open, stat, link).
Interacts with a specific file system based mount point
traversal
Receives requests from other parts of the kernel, mostly from memory
management.
File Manager
Is a program that provides a user interface to work with file system.
They are very useful for speeding up interaction with files. The most
common operations on files are create, open, edit, print, rename,
move, and copy.
Review LDAP
Define LDAP (Lightweight Directory Access Protocol ):
A set of protocols for accessing information directories. LDAP is
considered the simplified version of the X-500 standard. Unlike the
X-500 standard, LDAP supports TCP/IP for Internet access.
LDAP Characteristics:
• Relatively Static Data -- The data is rarely modified. How often do you
change your telephone number?
• Extremely Fast Read Operations - The directory is tuned for high read
performance because the data in the directory is frequently read but rarely
written or updated.
• Distributed - The data is located on a number of systems on the network for
redundancy, performance, and scalability.
• Hierarchical -This ensures there is an authoritative source of the data in the
directory system.
Week Thirteen Expected Outcomes
Upon successful completion of this module, the
student will be able to:
•
•
•
Describe the structure and use of Web
servers.
Create and run CGI scripts.
Evaluate a current Web technology project.
Apache/CGI
Apache Web Server
Apache Web server is free and distributed as source files by the Apache
Software Foundation.
Apache is generally recognized as the world's most popular Web server
(HTTP server). Originally designed for Unix servers, the Apache Web
server has been ported to Windows and other network operating systems.
The name "Apache" derives from the word "patchy" that the Apache
developers used to describe early versions of their software.
Describe the structure and use of Web servers.
Early Web sites consisted of HTML pages that could only provide data that
was written into the HTML page itself. This was sufficient for that time
frame.
Currently, Web sites provide dynamic data into an HTML page with the
use of CGI scripts.
CGI stands for Common Gateway Interface. It is a mechanism for a Web
server to be able to interact with an external program. These external
programs are CGI scripts.
Apache/CGI
Describe the structure and use of Web servers.
CGI scripts can be written in any programming languages. Perl is the
common choice because of its feature richness.
The web is composed of clients and servers. CGI is used on the server
to provide additional services and functionality to the client.
http://search.cpan.org/~jhi/perl-5.8.0/lib/CGI.pm
http://stein.cshl.org/~lstein/talks/marjorie/
Apache/CGI
The Apache HTTP server must be instructed to locate the CGI scripts.
Two more pieces of information are needed.
A program in that directory to be used as a CGI script.
A link in an HTML page to your CGI scrip
The CGI script itself simply produces output to stdout. The HTTP server captures that output and
sends it to the Web browser. The format of the output must be in a form that the Web browser
can understand (HTML).
The CGI script creates the HTML page every time it is run.
The data provided to the HTML page can change with each execution of the script.
Link to CGI script example: http://cs.franklin.edu/~varneyg/cgi-bin/myScript.cgi
Logic script: http://cs.franklin.edu/~varneyg/itec400/LogicScripts/lab_14-1.txt
Can test from a Web browser on the same machine by using the host name “localhost.”
http://localhost will try to find a Web server on the same machine as the Web browser.
CGI Logic Script
xxx CGI ":standard";
$uptime = `xxxxxx`;
$servertime = `xxxx`;
print header,
xxxxx_html("sysInfo"),
h1({-align=>xxxxx},"System Information"),
p,
start_form,
radio_group(-name => 'system',
-values => ['Up time','Server time'],
-default => 'Up time'),
p,
submit,
end_form,
hr;
$system=xxxxx("system");
if($system xx "Server time")
{
print $servertime;
}
else
{
print $uptime;
}
print hr;
xxx_html;
Upcoming deadlines
• Programming Assignment 2, 12-1 is due April 1. The second option
can be written in any programming language that will display the
requested information. (First option is questions about filesystems)
• Archives Exercise, 12-2 is due April 1.
• Public Domain/Open Source Paper, 13-1 is due April 8
(presented during the Franklin live session on April 2).
Don’t forget to submit your paper to turnitin.com
• Programming Assignment 3, 14-1 is due April 14.
• Final Exam, 15-1 will be administered April 9-14
• Final Exam Outline is posted at
http://cs.franklin.edu/~varneyg/itec400/StudyGuides/Final_Exam_Ou
tline.doc
Questions and Answers
• Questions
• Comments
• Concerns
• I will be available after this Franklin Live
session to discuss any problems and/or
concerns regarding lab assignments.