Transcript Week_Twelve_12 - Computing Sciences

Week Twelve Agenda
•Announcements
Proctor faxes final exam before mailing
Grade submission is December 23
•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=COXiuLv6mI0C
FSCTWAod81M57A
• 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?
Link of the week
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Top Level Domain (TLD)
gov – Government
edu – Educational
org – Organizations (nonprofit)
mil – Military
com – Commercial business
net – Network organizations
ca – Canada
th - Thailand
Review week eleven lab assignment
User 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 environment
Use the ls –a command to display the .profile file under your
$HOME directory.
Use the printenv or env commands to display environment
variables.
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.
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 assignment
$HOME/.profile
The $HOME/.profile file in your home directory is a collection of shell
commands that are executed whenever you login. The $HOME/.profile file
is used to set environment variables and shell options.
PATH – executable search path
- adding a directory either pre or post within PATH
variable
- set PATH for single user or all users umask – defaults:
umask 077
Alias - alias search=grep
TERM=vt100
Option – set –o vi
export SHELL TERM EDITOR VISUAL MAIL PRINTER USER PS1
• Command to display available shells on system cat /etc/shells
• Command to display current shell being utilized echo $SHELL
• Command to change to a different shell
chsh –s /bin/ksh
Review week eleven lab assignment
Linux runlevels:
0 - halt (Do NOT set initdefault to this)
1 - Single user mode
2 - Multiuser, without NFS (The same as 3, if you do not have
networking)
3 - Full multiuser mode
4 - unused
5 - X11
6 - 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 actions
respawn – 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 actions
powerwait – 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.
Review week eleven lab assignment
UNIX-like commands:
ps –s
ps –x
ls –a
ps -aux | grep crond
nice
(view zombie processes)
(view only active processes)
(view “.” processes)
(view crond executing)
(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
assignment
Unix/Linux Processes
Linux 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.
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.
Background processes run 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.
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.
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.
Review week eleven lab assignment
Non-Inherited Process Attributes
File locks
Resource utilization of a child process are set to zero
Pending signals
inode is a data structure on the traditional UNIX file system.
Each file has an inode and is identified by an inode number
(often referred to as an "i-number" or "inode") in the file
system where it resides.
On many file system types the number of inodes available is
fixed when the filesystem is created, giving a maximum
number of files the file system can hold. Typically when a file
system is created about 1% of it is devoted to inodes.
Review week eleven lab assignment
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 for input
• sending regular reports
• sends 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 cron execute on a Unix-like system?
Review week eleven lab assignment
• Demonstrate: Display crontab entries and /var/mail/dandrear file
• Who can use the crontab commands (create, list, edit or remove)?
• Each line of CRONTAB has the following structure:
<Minute> <Hour> <Day> <Month> <Day of Week> <Command line>
There are a total of 6 fields in the crontab file
# This is a comment.
* * * * * c:\tools\CheckForNewFiles.exe
• What does the “*” character represent in the first five fields of a crontab
record?
• A single integer that matches that exact value.
• A comma separated list of integers, like 1,2,3 to match one of the listed
values.
Review week eleven lab assignment
crontab format:
* * * * * command to be executed
crontab values:
Field
minute
hour
day
month
weekday
Value
00-59
00-23 (military time)
1-31
1-12
0-6 (0=Sunday)
Example records:
30 5 11 12 * “Welcome to Franklin University”
30 * * * * “Unix Administration”
Review week eleven lab assignment
crontab 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.
Review week eleven lab assignment
Lab exercise:
Create a crontab entry
The command part of the entry should
perform a simple shell function
Monitor your mail file using the tail command
Week ten, eleven, and twelve expected
outcomes
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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.
Use:
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 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.
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).
• Security on UNIX systems
Files, directories, PATH variable, password
authenication, uucp commands
One-way function
Super 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.
Next lab assignment
Directory tree
/
jones
dandrear
date
dev
tmp
bin
usr
wc
ksh
tty03
.profile
bin
foo
null
Next Lab Assignment
ext3 File System
Super Block
File Manager
Linux Virtual File System
Kernel
Next lab assignment
UNIX 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)
Break-out problems
1. How often do the following 2 commands execute?
# This is a comment.
1.1 * * * * * c:\tools\CheckForNewFiles.exe
# This is a comment.
1.2 0 * * * * c:\tests\backup.bat
2. Define: File System Super block
3. Define: Domain Name Server
4. Define: Domain name
4. Define: RFC
6. What application is BIND associated
7. What is the “lost+found” area considered on a Unix-like
system?
8. Linux Virtual File System
9. One-Way Encryption or One-Way Function
Upcoming deadlines
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Knoppix File System Exercise, 11-1 is due 11/30/08.
Programming Assignment 2, 12-1 is due 12/7/08.
Archives Assignment, 12-2 is due 12/7/08
Public Domain/Open Source Lab Assignment 13-1.
In-class presentations will be 12/8 and 12/15.
• Programming Assignment 3, 14-1 is due 12/20.
• Final Exam, 15-1 will be administered 12/15 - 20/08.
• Final Exam Outline is posted on the Bulletin Board.
This outline will be considered a “living” document. I
will add additional information to it up to one week
prior to the exam. All 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.