Week Thirteen Agenda

2. Week Thirteen Agenda • Link of the week • Announcements • Review week twelve lab assignment • Week eleven expected outcomes • Next lab assignment • Break-out problems • Upcoming deadlines • Open Source Presentation Will Lee • Lab assistance • Quiz

3. Link of the week Purchase CGI scripts http://www.cgiscript.net "How to Create Your Own Home Page" Home Page http://www.intergalact.com/hp/part3/part3.html CGI Programming FAQ by Nick Kews http://www.webthing.com/tutorials/cgifaq.html Introduction to CGI Scripts http://linux.die.net/man/3/cgi 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 provide a more dynamic avenue for information servers to pursue rather than as a HTML file server.

4. 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.

5. Week Thirteen Agenda • Link of the week • Announcements • Review week twelve lab assignment • Week eleven expected outcomes • Next lab assignment • Break-out problems • Upcoming deadlines • Lab assistance

6. Review Week Twelve Lab Assignment PROCESS STATE CODES D uninterruptible sleep (usually IO) R runable (on run queue) S sleeping T traced or stopped Z a defunct ("zombie") process For BSD formats and when the “STAT" keyword is used, additional letters may be displayed: W has no resident pages < high-priority process N low-priority task L has pages locked into memory (for real-time and custom IO) Use the ps –aux | less command to display the above mentioned codes listed under the STAT column heading.

7. Review Week Twelve Lab Assignment Inode Attributes An inode holds all the information about a named file. Exception: Name and actual data. Type of information: User owner Group Permissions Access times for a file stored in its inode Size of the data it holds Number of hard links Disk addresses to data blocks

8. Review Week Twelve Lab Assignment Non-Inherited Process Attributes File locks Resource utilization of a child process areset to zero Pending signals

9. Review Week Twelve Lab Assignment What is the function of the cron daemon? To initiate all timed events. The cron daemon is started at boot time and remains active while the system is operating in multi-user mode. cron wakes up every minute, exams all stored crontab records, checking to see which command is ready to execute in the current minute. crontab record format: <minute> <hour> <day> <month> <day of week> Command line * * * * * Command line crontab Restrictions You can execute crontab if your name appears in /usr/lib/cron/cron.allow. If the cron.allow files doesn’t exist, you can use crontab if your name isn’t listed in the /usr/lib/cron/cron.deny file. If only cron.deny exists, and is empty, all users can use crontab. If neither file exists, only root user can use crontab.

10. Review Week Twelve Lab Assignment 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 service 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. FYI -dos2unix is a function that converts DOS/MAC plain text files into Unix format. What is the “lost+found” area on a Unix-like system? It is the lost file directory. Usually, there is one directory on every disk partition. Disk errors or incorrect system shutdowns cause files to become lost.

11. Review Week Twelve Lab Assignment Security on UNIX systems Basic Unix-like system security is the accessmodes for files and directories. Default file and directory permission settings are set by the umask variable value. The initial recommended umask setting of 077 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 ready for use.

12. Review Week Twelve Lab Assignment Security on UNIX systems Directory protection is vital for file security. Administrators and users create “publicly writeable” directories which provide the most opportunities for compromising UNIX security system. Administrators tend to make these”open” for users to move around and access public files and utilities. 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. Although passwords offer an additional level of security, they lend themselves to computer system compromising. Lack of awareness and responsibility contributes largely to this form of computer insecurity. In summation, the corporate policy must be implemented to the explicitly. Network security is important so limit access to powerful commands like uucp, uux, uucico, and uuxqt commands. LANs were designed to transfer files between computers quickly, and security for them should be as consideration today as any other software.

13. Review Week Twelve Lab Assignment Kernel functions in two types of modes: Autonomous is where allocation of memory and CPU are performed without being explicitly requested by user processes. Responsive is where resource allocation and process creation and management are initiated from processes. These requests are system calls to the operating system. Examples are as follows: fork read exec write kill close open exit What is copy-on-write (COW)? It is an optimization strategy mainly used in virtual memory operating systems. Multiple users can be given a pointer to the same resource. When a process creates a copy of itself, the pages in memory that might be modified by either the parent or child process are marked copy-on-write. When one process modifies the memory, the kernel intercepts the operation and copies the memory so that changes in one process’s memory are transparent to the other. COW is intended to use memory sparsely because usage of physical memory utilization increases as data is stored.

14. Review Week Twelve Lab Assignment 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.

15. Review Week Twelve Lab Assignment File Systems UNIX/Linux file system is contained under the root directory denoted by a forward slash “/”. Users don’t have to worry about the physical locations of files. The file system is transparent to the user. 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.

16. Review Week Twelve Lab Assignment One-Way Encryption (Message Digest 5) 1. MD5 encrypted password (option secret 0) 2. MD5 encryption text string (option secret 5) The optional 0 keyword enables MD5 encryption on a clear text password; the 5 keyword enters an MD5 encryption string and saves it as the user MD5-encrypted secret. MD5 encryption is a strong encryption method which is not retrievable; thus, you cannot use MD5 encryption with protocols that require clear text passwords, such as CHAP MD5 encryption is one way hash encryption algorithm and cannot be decrypted (except by brute force). MD5 encryption can be compromised using brute force on 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 reasonablysafe.

17. Review Week Twelve Lab Assignment 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

18. Review Week Twelve Lab Assignment Types of information found in a super-block Device identifier, inode pointers, block size, file system type and pointer 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. Ext3FS The ext3 filesystem now installed as the default file system in most Linux distributions. Essentially ext2 with journaling, ext3 retains the stability and robustness of ext2 while adding the much needed journal for high- availability .

19. Review Week Twelve Lab Assignment fsck fsck is a utility that analyses and repairs file system inconsistencies. The file system is checked by providing the name of the block or character special device or by giving the name of its mount point if a matching entry exists in /etc/fstab. fsck File SystemInconsistency checks include: Blocks claimed by more than one inode or the free list. Blocks claimed by an inode or the free list outside therange of the file system. Incorrect link counts. Incorrect directory sizes. Bad inode format. Blocks not accounted for anywhere. Directory checks, file pointing to unallocated inode, inode number out of range, and absence of `.' and `. .' as the first two entries in each directory. Super Block checks: more blocks for inodes than there are in the file system. Bad free block list format. Total freeblock and/or freeinode count incorrect.

20. Review Week Twelve Lab Assignment Notes about fsck: - The fsck command does not make corrections to a mounted file system. - The fsck command can be run on a mounted file system for reasons other than repairs. However, inaccurate error messages may be returned when the file system is mounted.

21. Review Week Twelve Lab Assignment

22. Review Week Thirteen Lab Assignment 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

23. Review Week Twelve Lab Assignment

24. Review Week Twelve Lab Assignment

25. Review Week Twelve Lab Assignment 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 on the 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 the 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.

26. Review Week Twelve Lab Assignment 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.

27. 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.

28. Next Lab Assignment 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.

29. Next Lab Assignment 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.

30. Next lab assignment The Apache HTTP server must be instructed to locate the CGI scripts. Two more pieces of information are needed. 1) A program in that directory to be used as a CGI script. 2) 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.

31. Next lab assignment URL that points to the CGI script. http://cs.franklin.edu/~dandrear/itec400/CGI/sysInfo.cgi Apache Web Server A user can test from a Web browser on the same machine using the host name “localhost.” http://localhost will try to find a Web server on the same machine as the Web browser. Demonstrate: Script /CGI/sysInfo.cgi

32. Break-out problems UNIXcommands: fg bg uname –n df ln -s UNIX function: umask What are the file permissions if the umask 027? What are the directory permissions if the umask 027? What are the base directory permissions? What are the base file permissions? What is the function of the file manager? What is an Apache Web Server? What would be considered an advantage of using copy-on-write? List five top level domains?

33. Upcoming Deadlines • Public Domain/Open Source Paper, 13-1 is due 12/2/08 and 12/9/08. • Programming Assignment 3, 14-1 is due 12/16/08. • Final Exam, 15-1 will be administered 12/16/08. • Final Exam Outline is posted under the Bulletin Board. This outline will be considered a “living document” and information will be added to it until one week prior to the exam.

34. Lab assistance • Questions • Comments • Concerns • I will be available after this Franklin Live session to discuss any problems and/or concerns regarding lab assignments.