Transcript UNIX Operating System - Computing Sciences

Agenda
Administrative Issues
Link of the Week
This Week’s Expected Outcomes
Points of interest
Moving around in UNIX
Break-Out Problems
Upcoming Deadlines
Hands-on Information
Lab Assistance, Questions, and Answers
Announcements
Announcements
No script logic for Lab Assignments 12-1 and 122.
Final exam review recording will be available on
April 5, 2015.
Link of the week

Domain name registration Web site
https://www.pairnic.com/services.html?gclid=COXiuLv6mI0CF
SCTWAod81M57A

Determine if a domain is currently in use.
http://www.pair.com/
Online success starts with a great domain.

What is a domain name?
A domain name (for instance, "example.com") is an
identification string that defines a realm of administrative
autonomy, authority, or control on the Internet. Domain names
are formed by the rules and procedures of the Domain Name
System (DNS). Any name registered in the DNS is a domain
name.
Link of the week
What is the function of the Domain Name
System?
The DNS translates Internet domain name
and host names to IP addresses. DNS
automatically converts the names we type in our
Web browser address bar to the IP addresses of
Web servers hosting those sites.
Link of the week
What is the function of the Domain Name System?
The Domain Name System (DNS) is a hierarchical
distributed naming system for computers, services, or any
resource connected to the Internet or a private network. It
associates various information with domain names
assigned to each of the participating entities. Most
prominently, it translates easily memorized domain
names to the numerical IP addresses needed for the
purpose of locating computer services and devices
worldwide. By providing a worldwide, distributed
keyword-based redirection service, the Domain Name
System is an essential component of the functionality of
the Internet.
Link of the week
BIND (Berkley Internet Name Domain)
BIND is the most widely used DNS software
on the Internet. On Unix-like operating systems
it is the de facto standard.
Originally written by four graduate students
at the Computer Systems Research Group at the
University of California, Berkeley (UCB), the
name originates as an acronym from Berkeley
Internet Name Domain, reflecting the
application's use within UCB.
Link of the week
What is meant by top level domain?
A top-level domain (TLD) is one of the
domains at the highest level in the
hierarchical Domain Name System of the
Internet. The top-level domain names are
installed in the root zone of the name
space. For all domains in lower levels, it is
the last part of the domain name, that is,
the last label of a fully qualified domain
name (FQDN).
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
Link of the week
Who owns the Internet root?
The authoritative name servers that
serve the DNS root zone, commonly
known as the “root servers”, are a network
of hundreds of servers in many countries
around the world. They are configured in
the DNS root zone as 13 named
authorities, as named on the next slide.
Link of the week
Who owns the Internet root?
VeriSign, Inc.
University of Southern California (ISI)
Cogent Communications
Internet Systems Consortium, Inc
University of Maryland
NASA (Ames Research Center)
US Department of Defence (NIC)
US Army (Research Lab)
Netnod
VeriSign, Inc.
RIPE NCC
ICANN
WIDE Project
Link of the week
Who owns the Internet root?
https://maps.google.com/maps/ms?ie=UTF8&hl=e
n&msa=0&msid=103993808347197645891.00043
a30b2657ea61ea33&ll=11.424429,26.178063&spn
=142.883537,288.632813&z=2&om=1&dg=featur
e
Link of the week
Who is ICANN?
Today, the Internet Corporation for
Assigned Names and Numbers (ICANN) is
one of several managers of the top-level
development and architecture for Internet
domain name space. It authorizes domain
name registrars, through which domain
names may be registered and reassigned.
Link of the week
Top level domain name
The right-most label conveys the top-level domain;
for example, the domain name www.example.com
belongs to the top-level domain com.
The hierarchy of domains descends from the right
to the left label in the name; each label to the left
specifies a subdivision, or subdomain of the domain to
the right. For example: the label example specifies a node
example.com as a subdomain of the com domain, and
www is a label to create www.example.com, a subdomain
of example.com.
Link of the week
IANA - Internet Assigned Numbers Authority
The top-level domains (TLDs) such as com,
net and org are the highest level of domain
names of the Internet. Top-level domains form
the DNS root zone of the hierarchical Domain
Name System. Every domain name ends with a
top-level domain label.
Each country has an IOS (International
Organization for Standardization) country code
designated as its domain name.
Link of the week
Hostname
A hostname is a domain name that has
at least one associated IP address. For
example, the domain names
www.example.com and example.com are
also hostnames, whereas the com is not a
domain. However, other top-level domains,
particularly country code top-level domains,
may indeed have an IP address, and if so,
they are also hostnames.
Link of the week
Hostname
Hostnames impose restrictions on the
characters allowed in the corresponding
domain name. A valid hostname is also a
valid domain name, but a valid domain name
may not necessarily be valid as a hostname.
Link of the week
UNIX-like file systems
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
This Week’s Expected Outcomes
Upon successful completion of this
module, thers should be a better understanding of :
User initialization
Crontab
File System and disks
Action words in /etc/inittab file
UNIX Operating System
User Initialization
/etc/profile file is the basic setup for all users.
The /etc/profile contains the environmental
variables and commands used by most shell
users.
User preferred environmental set up
$HOME/.profile
$HOME/.bash_profile
If the /etc/profile and .profile files are not
present during the initialization, a prompt is still
displayed.
Use the ls –a command to display the
.profile or .bash_profile file under your
$HOME directory.
UNIX Operating System
Metadata
Metadata is data about data. It may
describe a single piece of data or multiple
content items and hierarchical levels.
Example: Legacy card catalogs in a library.
Metadata can be the name of a US
corporation, or a registered trademark.
UNIX Operating System
Metadata
Metadata is structured information
that describes and allows us to find,
manage, control and understand other
information. Structured metadata
represents the specifications of this
information. In this case, a better
definition of this design concept would
be "data about the containers of data".
UNIX Operating System
Metadata
There are many different types of
metadata.
Business Intelligence metadata
General IT metadata
IT metadata management products
File system metadata
Image metadata
UNIX Operating System
/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.
UNIX Operating System
/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.
UNIX Operating System
UNIX-like commands
ps –s
(view zombie processes)
ps –e –o pid,ppid,stat
(display all processes /
listed fields)
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 (UNIX)
(modified scheduling
priority)
(-20 to 19 range)
If a user wanted to compress a large file, but not slow
down other processes, they might run the following:
nice -n 19 tar cvzf archive.tgz largefile
UNIX Operating System
UNIX-like commands
umask (displays umask numeric values)
umask –S (displays umask symbolic values)
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)
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 (command to display environment
variables).
df (report file system disk space)
UNIX Operating System
Unix/Linux Processes
Linux defines a unit of work as a task or
process.
UNIX defines 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 group of users is uniquely identified by
a GID (Group 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 Operating System
Non-Inherited Parent Process Attributes
File locks (semaphores)
Child resource utilization is set to zero
Pending signals (kill –l signal name)
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.
UNIX Operating System
Linux Kernel Modules
Hardware in Linux is handled by kernel drivers,
many come from kernel modules. These are standard
driver files, which are stored in the /lib/modules
directory. Typically, Linux loads the needed modules
at boot time.
UNIX Operating System
Loading Kernel Modules
Unix-like systems allow loading kernel modules
with two programs: insmod and modprobe.
The insmod program loads a module into the
kernel. The process requires that you have
already loaded modules on which you’re
loading relies. The modprobe program
automatically loads any dependent modules.
UNIX Operating System
Loading Kernel Modules
Examples:
lnsmod /lib/modules/3.7.33/kernel/block/floppy.ko
(extension is required)
When executing the lnsmod program, if it fails
during the download of floppy.ko, chances are some
dependencies are needed. You can manually
download the dependent modules or execute the
modprobe program.
modprobe floppy
(extension not required)
The –n or –dry-run option causes modprobe to
perform checks and all other operations except the
actual download.
UNIX Operating System
Modules loaded on system using insmod command
Module
Size
Used by
af_packet
27392
2
8139too
30592
0
snd_cs46xx
96872
3
snd_pcm_oss 55808
1
snd_mixer_oss 21760
2
iptable_filter
7424
1
ip6_tables
19728
1
UNIX
Operating
System
Crontab Utilization
Cron is the periodic event scheduler of your
system. cron enables users to schedule jobs
(commands or shell scripts) to run periodically at
certain times or dates. It is commonly used to
automate system maintenance or administration,
though its general-purpose nature means that it can be
used for other purposes, such as connecting to the
Internet and downloading email. 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
UNIX Operating System
Crontab Utilization
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
UNIX
Operating
System
How frequent does crond execute on Unix-like systems?
Crond executes every minute
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.
UNIX Operating System
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.
UNIX Operating System
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 starts with an open
bracket ([), includes text, and ends with a
closed bracket (]).
UNIX Operating System
[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
UNIX Operating System
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
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.
UNIX Operating System
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.
UNIX Operating System
Network Services
Server configuration - /etc/exports file is
the main NFS configuration file and it consists of
two columns:
Column #1 - lists the directories of the network
or DNS domains that 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)
UNIX Operating System
Network Services
A variety of services available across a network
NFS:
Use the Linux chkconfig command to configure
the required NFS daemons to start at boot.
chkconfig provides a simple command-line tool
for maintaining the /etc/rc[0-6].d directory hierarchy
by relieving system administrators of the task of
directly manipulating the numerous symbolic links in
those directories.
UNIX Operating System
Network Services
A variety of services available across a network
NFS:
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
UNIX Operating System
Network Services
Remote (rlogin) 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.
UNIX Operating System
Is there an orphan process?
root
1 0 0 2011 ?
03:20:28 /sbin/init
dandrear 13087 13085 0 22:26 pts/3 00:00:00 grep init
root 11856 9595 0 21:13 ?
00:00:00 sshd: dandrear [priv]
root 11406 9595 0 20:58 ?
00:00:00 sshd: dandrear [priv]
root 10542 9595 0 20:18 ?
00:00:00 sshd: dandrear [priv]
dandrear 13090 13085 0 22:26 pts/3 00:00:00 sort -r
dandrear 13089 13085 0 22:26 pts/3 00:00:00 grep dandrear
dandrear 13088 13085 0 22:26 pts/3 00:00:00 ps -ef
dandrear 13085 11427 0 22:26 pts/3 00:00:00 /bin/ksh ./pid_ppid.sh
dandrear
dandrear 13074 1 0 22:26 pts/4 00:00:00 client_ser
dandrear 11859 11858 0 21:13 pts/4 00:00:00 -ksh
dandrear 11858 11856 0 21:13 ?
00:00:00 sshd: dandrear@pts/4
dandrear 11427 11426 0 20:59 pts/3 00:00:00 -ksh
dandrear 11426 11406 0 20:59 ?
00:00:00 sshd: dandrear@pts/3
dandrear 10548 10547 0 20:18 pts/2 00:00:00 -ksh
dandrear 10547 10542 0 20:18 ?
00:00:00 sshd: dandrear@pts/2
UNIX Operating System
X-11
X-11 is the name of the window manager
used for most UNIX and Linux operating
systems. A window manager is software that
interfaces the video, keyboard and mouse drivers
together to allow the user to communicate with
the computer via a GUI.
X-11 is unique in the sense that it runs over a
network connection, specifically over IP. This
enables a remote user to use his or her local XWindows environment to interact directly with
the other computer’s window manager as if they
were sitting on that machine.
UNIX Operating System
X-11
X-11 uses a client-server model, where the
window manager is the server, and the user is
using various clients. Applications that can be
run in the graphical user interface are often
written to use the X-11 software libraries to
enable them to be used remotely. This is one of
the strengths and power of the Unix system.
X-11 enables a remote system to treat your
local computer, it’s screen, keyboard and
mouse as just another set of terminal interface
devices that use an X-11 driver to
communicate with the X-Windows manager.
UNIX Operating System
Disk and File System Structure
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.
UNIX Operating System
Disk and File System Structure
It is an organization of data and metadata on a
storage device.
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.
Think of a file system as a protocol. File systems
give meaning to the data on a particular storage device.
UNIX Operating System
UNIX Operating System
Directory tree
/
jones
dandrear
date
dev
tmp
bin
usr
wc
ksh
tty03
.profile
bin
foo
null
UNIX Operating System
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)
UNIX Operating System
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.
UNIX Operating System
Unix-like System Security
Security on UNIX-like systems has
focused on the following areas:
Files and directories umask
PATH variable
SELinux
iptables
TCP Wrapper
chroot jail
password authentication
UNIX to UNIX commands
One-way function
UNIX Operating System
Disks versus File Systems
Application(s) interface with file systems
and not disks.
Why?
Because disks have shortcomings and are
not responsible for data recovery. File systems
must return the stored data to a consistent
state after an unplanned system crash.
UNIX Operating System
File System
Data recovery
Data loss
Fsync system call
The fsync() function requests that all data for
the open file descriptor named by fildes is to
be transferred to the storage device associated
with the file described by fildes. The nature of
the transfer is implementation-defined. The
fsync() function shall not return until the
system has completed that action or until an
error is detected.
UNIX Operating System
File System
Track caching
Shortcoming of track caching – the file
system expects the data to be stable store. A
system crash with data in the cache will not
deliver the user application integrity that was
promised.
Ways to circumvent this shortcoming – use
non-volatile memory and provide microcode
restart after power failures.
UNIX Operating System
The problem with using non-volatile memory
and microcode to restart is the cost. This solution
is the disk controller, but is rarely an option.
Newer Disks
Provide tag queuing – each request passed to
the disk driver is assigned a unique number. Most
disk controllers can accept at least 16 pending
requests. In combination, the fsync() and tag
queuing are combined.
Tag queuing was first implemented in SCSI disks.
Enabling both reliability and speed. ATA disks
lacked tag queuing. Later ATA adopted a tag
queuing but called it Tag Command Queuing
(TCQ).
UNIX Operating System
Serial ATA has a new definition called Native
Command Queuing (NCQ) that has a bit set in the write
command that tells the drive if it should report
completion when media has been written or when
cache has been hit. If the driver correctly sets this bit,
then the disk will display the correct behavior.
Disk Sector Size
From 1950s to 2010 the disk sector size was 512. In
2010, the sector size was increased to 4,096.
Problems associated with this retrofit
Error rate per bit has risen, requiring the use of
ever longer correction codes. The error code must have
enough redundancy for each sector to handle a high
correction rate even though most sectors will not
require it.
UNIX Operating System
Is the increase density worth the extra
overhead?
Sectors are 8 times larger, which
eliminates 88% of the sector start and stop
headers. You want to reduce the number of
non-data bits on the disk. In effect, using 4,096
byte sectors doubles the amount of user data
that can be stored on a given disk.
Legacy File Systems
The 4,096-byte sectors have to emulate the
old 512-byte sector disks. This mode causes
the disk to be at least 50% slower.
UNIX Operating System
How to avoid the slowdown
Files smaller than or equal to 512-bytes are
accumulated (buffered) into a 4,096-byte
block.
Conclusion
Your file system must know the type of disk
technology to which they are running to ensure
reliable data retrieval and performance.
Use flash-memory technology!
UNIX Operating System
Points of interest
A USB can be a bit challenging for operating
systems designed as a hot-pluggable device. The
Linux kernel was not originally designed to
handle this type of technology. The kernel relies
on external utilities to help manage matters. Two
tools are used to help manage USB devices:
usbmgr and hotplug.
Moving Around in UNIX
lsmod – is a program to show the status of
modules in the Linux kernel.
insmod – is a simple program to insert a
module into the Linux Kernel
modprobe – is a program to add and
remove modules from the Linux Kernel
lsusb - list USB devices
Moving Around in UNIX
chkconfig - has five distinct functions:
adding new services for management,
removing services from management,
listing the current startup information for
services, changing the startup information
for services, and checking the startup state
of a particular service.
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. What application is BIND associated
4. What is the “lost+found” area considered on a Unixlike system?
5. Linux Virtual File System
6. One-Way Encryption or One-Way Function
Hands on information
Lab Assignment 11-1,Knoppix File
System due March 29, 2015.
Lab Assignment 12-1, 12-2
Programming Assignment 2 /Archives
due April 5, 2015
Lab Assignment 13-1Open Source
presentation due April 7 and 14, 2015
Lab Assignment 14-1 CGI Script April
18, 2015.
After class assistance
 Questions
 Comments
 Concerns
I
am available after this Franklin Live
session to discuss any problems and/or
concerns regarding the lab assignments
Lab Assistance available by phone
and/or email