Transcript Week_Twelve_12_UNIX_ppt - Computing Sciences

Week Twelve Agenda
•Announcements
The final exam will be True/False, Multiple
Choice, and Essay.
Presentation dates for Section number V2WW
are December 5 and 12.
Presentation dates for Section number V1FF
are December 8 and 15.
Make your reservation now!
•Link of the week
•Review week eleven lab assignment
•Week eleven expected outcomes
•Next lab assignment
•Break-out problems
•Upcoming deadlines
Link of the week
• Domain name registration Web site
https://www.pairnic.com/services.html?gclid=COXiuLv6mI0
CFSCTWAod81M57A
• 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
Top 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 week
http://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 week
UNIX-like file system is hierarchical. It is
interpreted from left to right. The top-level
domain name appears at the left end.
/var/mail/dandrear
The URL (Uniform Resource Locator) is also
hierarchical. Its top-level domain name
appears at the end, but is read from right to
left.
alpha.einstein.edu
beta.ca.mail2web.com
Link of the week
Review week eleven lab assignment
Kernel Initialization
Kernel initialization generates output on the console. You can
examine the output from the initialization by viewing
/var/log/dmesg, which logs all kernel messages during this
procedure.
User Initialization
The /etc/inittab format has not changed:
id:runlevels:action:process
The init process accesses the /etc/inittab file for system
configuration settings.
1:2345:respawn:/sbin/mingetty tty 1
Review week eleven lab assignment
User Initialization
/etc/profile file
Basic setup for all users
$HOME/.profile User preferred environmental set up
$HOME/.bash_profile
Use the ls –a command to display the .profile or .bash_profile
file under your $HOME directory.
Review week eleven lab assignment
Pre-Red Hat 6.0 Release:
# initdefault run level is 3
id:3:initdefault:
# System initialization.
si::sysinit:/etc/rc.d/rc.sysinit
# Create a login terminal
1:2345:respawn:/sbin/mingetty tty 1
# Trap CTRL-ALT-DELETE
ca::ctrlaltdel:/sbin/shutdown -t3 -r now
# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon
Review week eleven lab assignment
Pre-Red Hat 6.0 Release:
# When our UPS tells us power has failed, assume we
have a few minutes
# of power left. Schedule a shutdown for 2 minutes from
now.
# This does, of course, assume you have powerd installed
and your
# UPS connected and working correctly.
pf::powerfail:/sbin/shutdown -f -h +2 "Power Failure;
System Shutting Down“
# If power was restored before the shutdown kicked in,
cancel it.
pr:12345:powerokwait:/sbin/shutdown -c "Power
Restored; Shutdown Cancelled“
# Run xdm in runlevel 5
x:5:respawn:/etc/X11/prefdm -nodaemon
Review week eleven lab assignment
Red Hat 6.0 Release:
Runlevels are a concept from UNIX System V used by the init
daemon or other system initialization system to define modes of
system operation.
Eight runlevels are permitted, the first seven are numbered 0-6 and
the eighth is named S or s (both are permitted).
System initialization is started by /etc/init/rcS.conf
The rcS.conf file contains no information about previous run levels.
The stop run level is set to “S”. In the event that the system stops, the
default is single user. The /etc/rc.d/rc.sysinit script is executed.
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and
/etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
Review week eleven lab assignment
Red Hat 6.0 Release:
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
# 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)
#
id:3:initdefault:
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.
Review week eleven lab assignment
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 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 –aux
ps –x
ls –a
ps -aux | grep crond
nice
(view zombie processes)
(view status of all processes)
(view only active processes)
(view “.” processes)
(view crond executing)
(modified scheduling priority)
(-20 to 19 range)
(displays umask numeric values)
(displays umask symbolic values)
umask
umask –S
fg (Continues a stopped job by running it in the foreground, some
shells are not able to run this command ).
bg (Continues a stopped job in the background)
Review week eleven lab assignment
UNIX-like commands:
cat /etc/shells
echo $SHELL
chsh –s /bin/ksh
printenv
df
(Display available shells on system).
(Display current shell being utilized).
(Change to a different shell) .
(command to display environment
variables).
(report file system disk space)
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
(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.
Review week eleven lab assignment
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 assignment
Non-Inherited Parent 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.
Review week eleven lab assignment
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
Review week eleven lab assignment
Crontab Utilization:
Typical directory configuration
/etc/cron.d/hourly
/etc/cron.d/daily
/etc/cron.d/weekly
/etc/cron.d/monthly
Review week eleven lab assignment
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>&1
The /dev/null device is a special file that disregards all data written
to it.
Review week eleven lab assignment
crontab format:
* * * * * command to be executed
crontab values:
Field
Value
minute
00-59
hour
00-23 (military time)
day
1-31
month
1-12
weekday
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”
Review week eleven lab assignment
Demonstrate: Display crontab entries and /var/mail/dandrear file
and 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 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
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.
Review week eleven lab assignment
Samba
The /etc/samba/smb.conf file controls
most aspects of how Samba
works and is divided into two
sections. Each section begins with
a line that starts with an open
bracket ([), includes some text, and ends
with a closed bracket (]).
Review week eleven lab assignment
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[globals] Defines global parameters
[printers] Defines printers
[home]
Defines shares in the homes directory
Comments in the smb.conf can start with either a
pound (#) or (;).
# A private directory, usable only by Bob.
; [bobsdir]
; comment = Bob’s Service
; path = /usr/somewhere/in/space
; writeable = yes
; printable = no
; public = no
Review week eleven lab assignment
Linux 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.
Review week eleven 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.
Review week eleven lab assignment
Linux 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 for the other system files to be
accessed.
Review week eleven 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.
Review week eleven lab assignment
Network Services
A variety of services available across a network
NFS:
Developed by Sun Micro Systems
Runs on UNIX, DOS, Windows, VMS, and Linux
Files on the remote computer appear as if they are present
on the
local system.
Server configuration - /etc/exports file is the main NFS
configuration file and it consists of two columns:
Column #1 - lists the directories the network or DNS domains the
can get access to the directories.
Column #2 – lists NFS options in brackets.
#/etc/exports/data
/files
*(ro,sync)
/home
192.168.1.0/24 (rw,sync)
/data/test
*.my-site.com (rw,sync)
/data/database
192.168.1.203/32 (rw,sync)
Review week eleven lab assignment
Network Services
A variety of services available across a network
NFS:
Use the chkconfig command to configure the required
NFS daemons to start at boot.
Use exportfs –a command when no directories have been
exported to NFS.
Use exports –r command when adding a shared directory
to export only the new entries.
Use the showmount –a command to list all currently
exported directories.
In the /etc/fstab file, add a similar entry:
#/etc/fstab
192.168.1.100:/data/files /mnt/nfs nfs soft,nfssvers=2 o 2
Review week eleven lab assignment
Network Services
A variety of services available across a network
Remote login:
rlogin (remote login) is a UNIX command that allows an
authorized user to login to other UNIX machines (hosts)
on a network and to interact as if the user were physically
at the host computer. Once logged in to the host, the user
can do anything that the host has given permission for,
such as read, edit, or delete files.
SSH is a protocol that allows computers to communicate
with each other over encrypted connections. An SSH
client is used to log in to a remote machine (running an
SSH server) and allows the execution of commands on
that machine.
Review week eleven lab assignment
Orphan Process:
dandrear 7160 7158 0 17:12 pts/4 00:00:00 -ksh
dandrear
7189 7160 0 17:13 pts/4 00:00:00
/bin/ksh ./pid_ppid.sh dandrear
dandrear 7190 7189 0 17:13 pts/4 00:00:00 ps -ef
dandrear 7191 7189 0 17:13 pts/4 00:00:00 grep dandrear
dandrear 7192 7189 0 17:13 pts/4 00:00:00 sort
dandrear 7001 7113 0 8:13 pts/3 23:00:00 cp
root
7158 938 0 17:12 ?
00:00:00 sshd:
dandrear@pts/4
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 copyon-write.
Next lab assignment
Network Services
A variety of services available across a network
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
File System
1. 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.
File System
Next Lab Assignment
Next Lab Assignment
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.
Data Block
Data 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 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)
Next lab assignment
lost+found directory
The fsck utility 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
umask
PATH variable
password authentication
UNIX to UNIX commands
One-way function
Break-out problems
1. 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 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
10. Compare a block device to a character device
Upcoming deadlines
Section number V2WW:
Lab Assignment 11-1, Knoppix File System Exercise
is due November 27, 2011
Lab Assignments 12-1 and 12-2, Programming
Assignment 2 and Archive Exercise due December 1,
2011
Section number V1FF:
Lab Assignment 11-1, Knoppix File System Exercise
is due November 24, 2011
Lab Assignments 12-1 and 12-2, Programming
Assignment 2 and Archive Exercise due December 4,
2011.
Lab assistance
• Questions
• Comments
• Concerns
• I will be available after this Franklin Live
session to discuss any problems and/or
concerns regarding lab assignments.