Week Twelve Agenda

Week Twelve Agenda• Announcements

Proctor fax final answer sheets before mailing final exam to the Student Learning Center.Grade submission is before 12:00 p.m.,

December 24.• Link of the week• Review week eleven lab assignment• Week eleven expected outcomes• Next lab assignment• Break-out problems• Upcoming deadlines• Lab assistance

Link of the week• Domain name registration Web site

https://www.pairnic.com/services.html?gclid=COXiuLv6mI0CFSCTWAod81M57A

• Determine if a domain is currently in use.http://www.pair.com/

• What is a domain name?

• What is the function of the Domain Name System?

• BIND (Berkley Internet Name Domain)

• What is meant by top level domain?



http://www.pair.com/

Link of the weekTop Level Domain (TLD)

• gov – Government• edu – Educational• org – Other organizations ( often nonprofit)• mil – Military• com – Commercial business• net – Network organizations• ca – Canada• th – Thailand

Link of the weekhttp://www.iana.org/cctld/cctld.htm

Iana - Internet Assigned Numbers Authority

Observe the Root Zone Database at the above Web site. It represents the list of top-level domains.

Each country has an ISO (International Organization for Standardization) country code designated as its domain name.

Link of the weekUnlike the file system hierarchy, the top-level

domain name appear last (reading from left to right).

The URL is hierarchy

alpha.einstein.edu

beta.ca.mail2web.com

Link of the week

Review week eleven lab assignmentUser Initialization

The /etc/inittab runlevel field format:id:runlevels:action:process

/etc/inittab file 1:2345:respawn:/sbin/mingetty tty 1

/etc/profile file Basic setup for all users

$HOME/.profile User preferred environmental set up

Use the ls –a command to display the .profile file under your $HOME directory.

Review week eleven lab assignment

Metadata

Metadata is data about data. It may describe a single piece of data or multiple content items and hierarchical levels.

Metadata can be the name of a US corporation, or a registered trademark.

Metadata is structured information that describes and allows us to find, manage, control and understand other information.


Metadata

There are many different types of metadata.

Business Intelligence metadata

General IT metadata

IT metadata management products

File system metadata

Image metadata

Review week eleven lab assignmentLinux runlevels:

0 - halt (Do NOT set initdefault to this)1 - Single user mode2 - Multiuser, without NFS (The same as 3, if you do not have networking)3 - Full multiuser mode4 - unused5 - X116 - reboot (Do NOT set initdefault to this)

The runlevel may contain multiple characters for different runlevels.

1:23:respawn:/sbin/mingetty tty1 2:23:respawn:/sbin/mingetty tty2

3:23:respawn:/sbin/mingetty tty3 4:23:respawn:/sbin/mingetty tty4

Review week eleven lab assignment/etc/inittab actionsrespawn – The process will be restarted whenever it

terminates.wait – The process will be started once when the

specific runlevel is entered.once – The process will be executed once when the

specific runlevel is entered.boot – The process will be executed during system

initialization.initdefault – This entry specifies the runlevel which

should be entered after system boot.sysinit – The process will be executed during system

boot. It will be executed before any boot or bootwait entries.

Review week eleven lab assignment/etc/inittab actionspowerwait – The process will be executed when the

power goes down.powerokwait – This process will be executed as soon as

init process is informed that the power has been restored.

powerfailnow – This process will be executed when the init process is informed that the battery of the external UPS power is failing.

ctraltdel – The process is executed when the init process receives the SIGINT signal. This means that someone on the system console has pressed the Ctrl-Alt-Del key combination.


UNIX-like commands:

ps –s (view zombie processes)

ps –aux (view status of all processes)

ps –x (view only active processes)

ls –a (view “.” processes)

ps -aux | grep crond (view crond executing)

nice (execute with modified scheduling priority)

umask (displays umask numeric values)

umask –S (displays umask symbolic values)

fg (Resume jobspec in the foreground, and make it the

current job)

bg (Resume the suspended job jobspec in the background, as if it had been started with &)

Review week eleven lab assignmentUNIX-like commands:

cat /etc/shells (Display available shells on system). echo $SHELL (Display current shell being utilized). chsh –s /bin/ksh (Change to a different shell) . printenv or env (commands to display environment

variables).


Unix/Linux ProcessesLinux defines a unit of work as a task or

process.UNIXdefines a unit of work as a process.

Each process is identified by a unique PID (Process ID).

Each user is identified by a unique UID (User ID).

Each process is started from a previous process using the fork and exec command.

The init process is created by the kernel using a non-traditional procedure called hand-crafted or spontaneous.


Unix/Linux Processes

A background processes runs with a relatively low priority, require little or no input, and generate a minimum of output. Background process is unlike with a foreground process, the shell does not have to wait for a background process to end before it can run more processes. Background jobs are run at a lower priority to the foreground jobs.

A foreground process is one that can show the user an interface, through which the user can interact with the program. The user must wait for one foreground process to complete before running another one.

Review week eleven lab assignmentNon-Inherited Process Attributes

File locks (semaphores)

Child resource utilization is set to zero

Pending signals (kill –l signals)

Daemon processes offer services like web pages serving, email transferring, time synchronization, and similar. They usually consume little CPU and memory, and run quietly without user interaction. They mainly communicate with other computer programs, or with other computers via network.


Crontab Utilization:cron is the periodic event scheduler of your system. The following examples

give you an idea of its usefulness and necessity.• regular daily backups• periodic mail checking • polling a device(s) for input • sending regular reports• sending user email every time a cron function is performed

cron file locations/etc/crontab/etc/cron.deny /etc/cron.allow

Typical directory configuration/etc/cron.d/hourly /etc/cron.d/daily /etc/cron.d/weekly /etc/cron.d/monthly


How frequent does crond execute on Unix-like systems?

Disable email

To prevent email messages from being sent to your mail account, create a record that contains the following syntax:

* * * * * echo [email protected] > .trash_bin

To cancel the email redirection, enter the following:

rm trash_bin

If the output is not needed, the following syntax can be included:

* * * * * echo “Hello Administrator” > /dev/null 2>&1The /dev/null device is a special file that disregards all data written to it.

mailto:[email protected]

Review week eleven lab assignmentcrontab format:

* * * * * command to be executedcrontab values:

Field Valueminute 00-59hour 00-23 (military time)day 1-31month 1-12weekday 0-6 (0=Sunday)

Example records:There are a total of 6 fields in the crontab file

30 5 11 12 * echo “Welcome to Franklin University”

30 * * * * echo “Unix Administration”


Demonstrate: Display crontab entries and /var/mail/dandrear fileand introduce the tail –f command.

Who can use the crontab commands (create, list, edit or remove)?

What does the “*” character represent in the first five fields of a crontab record? Match all values

A single integer will match that exact time value.

A comma separated list of integers can invoke multiple matches like 1,2,3.

Example: 5,10,45 * * * * echo “Unix Administration”

Review week eleven lab assignmentcrontab restrictions

If your name appears in the cron.allow file. If that files doesn’t exist, you can use crontab.

If your name does not appear in the cron.deny file. If cron.deny exists and is empty, all users can use crontab. If neither file exists, only the root user can use crontab.

crontab command without options

Read standard input

Exit using “Control C” so that the existing crontab is unmodified.

Exit using “Control D” will cause the current users’ crontab to be replaced with no information.


crontab commands

crontab -e Edit crontab file

crontab –l Display your crontab file

crontab –r Remove your crontab file

crontab –v Display last time crontab was edited.

Week ten, eleven, and twelve expected outcomes

Upon successful completion of this module, the student will be able to:

Manipulate user accounts. Describe how cron is used to invoke repetitive processes. Manipulate process structure including:

a. fork and exec, b. Initialization process, c. Background/foreground, d. PS tool.

Explain basic UNIX security issues. Describe disk and file system structure. Use backup and restore archival operations on a system. Establish network services. Investigate the structure of the LDAP directory using LDAP commands.

Next lab assignment• Copy-on-Write

It is an optimization strategy for multiple users can give the same pointer for a resource. The primary advantage is that if a caller never

makes any modifications, no private copy is needed.

This strategy is used in virtual memory operating systems pages in memory that might be modified by either the process or its copy are marked copy- on-write.

Next lab assignmentNetwork Services

A variety of services available across a networkNFSRemote 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.

Next Lab Assignment• 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).

• NIS+ (Network Information Service) is a directory service.

Next Lab Assignment

What is the functionality of Network File System (NFS)

• It is a remote file system designed by Sun Microsystems, available on computers from most UNIX system vendors.

• It allows the server to share selected local directory hierarchies with client systems on a heterogeneous network. Files on the remote computer (fileserver) appear as if they are present on the local system. The physical location of a file is irrelevant to an NFS user.

Next Lab AssignmentFile System1. It is an organization of data and metadata on a storage device. 2. It is the methods and data structure that an operating system

uses to keep track of files on a disk or partition; that is the way the files are organized on the disk.

3. Think of a file system as a protocol. File systems give meaning to the data on a particular storage device.

What is a block device?It is a device in which the data that moves to and from occurs in

blocks (like a disk sector) and supports attributes such as buffering and random access behavior. Block devices include hard drives, CD-ROMs, and RAM disks.

What is a character device?It is a device that does not have a physical addressable media.

Character devices include serial ports and tape devices, where data is streamed character by character.

Next Lab AssignmentFile System

Next Lab AssignmentSuper Block

Contains information about each mounted file system.The actual data structure in Linux is called struct

vfsmount.Information held is mount flags, mount time, device name, pointer to super block and device block size.The Linux 2.0 kernel keeps a static array of such

structures to store up to 64 mounted file systems. Data BlockData blocks are used to store the data for a file. There is space

only for a few data block numbers in the inode, however if more are needed, more space for pointers to the data blocks is allocated dynamically. These dynamically allocated blocks are indirect blocks. The name indicates that in order to find the data block, one has to find its number in the indirect block first.

Next Lab AssignmentInodeAn inode contains all the information about a file except its name

and actual data.The name is stored in the directory, together with the number of inode. The data is stored in a data structure.

Next lab assignment

usr bin tmp dev

tty03nulldate wc ksh

dandrearjones

.profile bin

foo

Directory tree

/

Next Lab Assignment

Super Block File Manager

ext3 File System

Linux Virtual File SystemKernel

Next lab assignmentUNIX base root file system tree structure

/bin (commands)/dev (devices)/etc (system configuration/executables)/sbin (boot commands)/usr/sbin (administrative commands)/home (users home directories)/lib (shared libraries)/mnt (temporary mount directory)/opt (optional software)/proc (processes)/stand (boot-related files)/var (spooling)

Next lab assignmentlost+found directory

fsck is generally able to repair most system damage and the frequency with which you will find anything at all in your lost+found directories has slowed significantly

If you have a system crash and the Linux file system checker (fsck) recovers corrupt files they are placed here.

Next lab assignment

Unix-like System Security• Security on UNIX-like systems has focused on

the following areas:

Files and directories PATH variablepassword authenication UNIX to UNIX commandsOne-way function

Next lab assignmentLinux Security

SELinux developed by the U.S. National Security Agency (NSA), implements Mandatory Access Control (MAC) in the Linux kernel. MAC enforces security policies that limit what a user or program can do. It defines a security policy that controls some or all objects, such as files, devices, sockets, and ports, and some subjects like processes. Utilizing SELinux, you can grant a process only those permissions it needs to be functional.

Next lab assignment

Linux Security

TCP Wrapper is part of the client/server model, and can be used with any daemon that is linked against libwrap.a, and relies on the /etc/hosts.allow and /etc/hosts.deny files as the basis of a simple access control language. This access control language defines rules that selectively allow clients to access server daemons on a local system based on the client’s address and the daemon the client tries to access.

Next lab assignmentLinux Security

chroot jail

On early UNIX systems, the root directory was a fixed point in the file system. Chroot jail allows users on UNIX-like system to define the root directory on a process bases. The chroot jail utility allows you to run a process with a root directory other than /.

By creating an artificial root directory, frequently called (chroot) jail, you can make it harder tfor the other system files to be accessed.

Break-out problems1. How often do the following two commands execute? # 1.1. This is a comment.

* * * * * c:\tools\CheckForNewFiles.exe # 1.2. This is a comment. * * 3 * * c:\tests\backup.bat 2. Define: File System Super block3. Define: Domain Name Server4. Define: Domain name4. Define: RFC6. What application is BIND associated 7. What is the “lost+found” area considered on a Unix-like

system?8. Linux Virtual File System9. One-Way Encryption or One-Way Function10. Compare a block device to a character device

Upcoming deadlines• Account/LDAP Script, 10-1 is due November 22, 2009.

Process, 10-2 is due November 22, 2009.• Knoppix File System Exercise, 11-1 is due November 29,

2009.• Programming Assignment 2, 12-1 is due December 6, 2009.

Archives Exercise, 12-2 is due December 6, 2009.• Presentations for Public Domain/Open Source Lab

Assignment 13-1 will be November 30 and December 7, 2009.• Programming Assignment 3, 14-1 is due December 19, 2009.• Final Exam, 15-1 will be administered December 14 - 19,

2009.• Final Exam Outline will be posted on the Bulletin Board

November 29, two weeks prior to the final exam date. This outline will be considered a “living” document. I will add additional information to it up to one week prior to the exam. The additional information posted after the initial posting will be highlighted/indicated.

Lab assistance

• Questions• Comments• Concerns

• I will be available after this Franklin Live session to discuss any problems and/or concerns regarding lab assignments.

Documents

Week Twelve Agenda