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NetworkingC Shell Programming

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Network Services

Having your systems available over a network is required for most businesses today

Providing those services is the task of the System Administrator

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Network Services

How do your users connect to your systems tera term telnet rlogin rcp ftp

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Type of Networks

broadcast each system examines the address of every

message and picks up its own i.e. Ethernet can be CSMA/CD or CSMA/CA

token ring only one system transmits at a time i.e. FDDI

point-to-point only two endpoints most connections to WANs are point-to-point

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Internetworking

Gateways devices that switch packets between different

physical networks deciding which gateway to use is called

routing

Routers a device that filters traffic based on IP address

Bridges a device that filters traffic based on ethernet

address

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Network Protocols

TCP/IP Transmission Control Protocol/Internet

Protocol Not based on OSI model, has a 4 layer model

UDP - User Datagram Protocol Alternate layer above IP, less robust than TCP NFS is based on UDP

XNS (Xerox Network Software)DECnet (DEC Network)Can coexist on the same network or even

the same computer...

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Unix Network Services

Seven layer model - OSI Reference Model Application Presentation Session Transport Network Data Link Physical

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Communicating on the Network

use the hostname command to find the identity of your local system#hostname -saries

uname -a will show hostname, domain name and version of operating system#uname -aSunOS poincare 5.6 Generic_105181-11 sun4u sparc

SUNW,Ultra-1

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Communicating on the Network

finger used to learn about remote users finger @aries

shows info about all users logged onto host aries

finger dbittrol@airesshows info about the user dbittrol on host

aries only works if the site is running the

appropriate software (the finger daemon)

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Communicating on the Network

mail and mailx most commonly available email software create, send and receive email front end to sendmail daemon you need to know address considered by some to be difficult to use

...actually these programs are just very basic...and command line oriented

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Host Addresses

most common is IP addresses four octets separated by periods 192.192.192.2 Will talk about more in Sys Admin classes

Network Information Center (NIC) hands out blocks of addresses to organizations each organization assigns individual addresses

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Host Addresses

Typically.... 131.251.252.253 131.251 represents campus/company 252 represents subnetwork 253 represents individual equipment Example is a Class B Address

range for each octet is 0 to 255symbolic names can be associated

with each IP address

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Host Addresses

127.0.0.1 is reserved for localhost name hook for network software when no

network is actually available.more efficient name services include...

DNS (Domain Name Service) NIS (Network Information Service) NIS+

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Host Addresses

oldest (and simplest) name service is /etc/hosts file127.0.0.1 localhost192.168.3.8 aries loghost192.168.3.12 linux01192.168.3.251 matthew

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Network Utilities

rlogin and telnet provide ability to connect to a remote host

over the network and start a login session there.

you must have an account on the remote system to gain access

rlogin assumes your user name at loginif your rhost allows, no password needed

telnet asks for user name at login telnet also works with non-UNIX systems

and has more configuration options

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Network Utilities

Tera Term (Pro) is a free software terminal emulator (communication program) for MS-Windows. It supports VT100 emulation, telnet connection, serial port connection, and so on.

Reflection connectivity software establishes and maintains communications between your computer and a host computer .  This software allows your computer to operate like a Digital VT terminal.

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Trusted Hosts

Some commands only work if the remote system trusts your local computer like rcp and rsh trusted systems are listed in /etc/hosts.equiv

Often not allowed due to security

can also use .rhosts in your home directorybeware - using .rhosts allows another user to log in

as you on a remote system, without knowing your password!!!

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Transferring Files

rcp (remote copy) works like cp (but only for Trusted Hosts) copy between systems without logging in examples

rcp memo.921 bravo:memo.921• copies from home directory on current system to

home directory on bravorcp memo.921 watson@bravo:memos

• if memos exists as directory then memo.921 is copied into it - if not memo.921 is copied to file memos

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Transferring Files

ftp (file transfer protocol) an interactive program use commands like:

binary, ascii, promptput, get, mput, mgetcd, lshelp, quit

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Commands

rsh (remote shell) run a command on a remote system without

logging in (see Trusted Hosts)will prompt for your password if the local host is not

trustedlocal host gets standard out from remote hostspecial characters on command line are interpreted by the

local hostrsh bravo ls -Fla - list home dir on remote hostrsh bravo - start shell on remote host

traceroute - you provide IP or full name and the route from your machine to the system named is shown

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Testing Network Connection

ping - sends a test packet to a remote system which then sends back a reply

# /usr/sbin/ping matthewmatthew is alive# /usr/sbin/ping -s matthewPING matthew: 56 data bytes64 bytes from matthew (192.168.3.251): icmp_seq=0. time=1. ms64 bytes from matthew (192.168.3.251): icmp_seq=1. time=0. ms64 bytes from matthew (192.168.3.251): icmp_seq=2. time=0. ms64 bytes from matthew (192.168.3.251): icmp_seq=3. time=0. ms----matthew PING Statistics----4 packets transmitted, 4 packets received, 0% packet lossround-trip (ms) min/avg/max = 0/0/1- end with <ctrl>-c

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Domain Name Service (DNS)

a distributed servicename servers around the world

cooperate to keep the database up to date

no one system has a complete copy organized hierarchically local name server knows local hosts and how to contact other name servers

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DNS

Seven original top level domains countries outside U.S. use ISO country

codeau for Australia, ja for Japan

inside U.S. the other six are:• .com commercial enterprises• .edu educational institutions• .gov nonmilitary government agencies• .mil military government agencies• .net networking organizations• .org other (often nonprofit) organizations

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DNS

New TLDs started coming online late 2001 .biz .info .name .museum .coop .aero .pro

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DNS

some examples the same host name can be used by two

completely different systems!okeefe.berkeley.edu

• host okeefe at University of California

okeefe.mma.org• host okeefe at Museum of Modern Art

NOTE: DNS is not case-sensitive

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DNS

most common interface is BIND software Berkeley Internet Name Domain translates host name <=> ip address follows client/server model client looks to name server to resolve host

ip addressesnslookup - interface to any DNS server

DNS Server resolving, name and ip

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Network Information Service (NIS)

developed by Sun Microsystems to help simplify network administration

formerly called Yellow Pages (yp) hence, commands like....

ypcat - display NIS database tableypmatch - search NIS database tableetc... etc...

used in addition to /etc system config fileswhich now only contain minimum info

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Network File System (NFS)

work locally with files that are stored on a remote system’s disks

remote file system appears to be localremote system acts as serverlocal system acts as clientusers mount dirs from other systems

on their systems to use. Can “automount”

df command (display filesystems)

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example output of df

aries% df/ (/dev/dsk/c0d0s0 ): 106980 blocks 85665 files/usr (/dev/dsk/c0d0s6 ): 17590 blocks 30931 files/proc (/proc ): 0 blocks 958 files/dev/fd (fd ): 0 blocks 0 files/export (/dev/dsk/c0d0s3 ): 1415974 blocks 498944 files/usr/openwin (/dev/dsk/c0d0s4 ): 59752 blocks 68067 files/tmp (swap ): 114808 blocks 11689 files/cdrom/devpro_v5n1_intel(/vol/dev/dsk/c1d0/devpro_v5n1_intel): -1 blocks -1 files

aries% df -kFilesystem kbytes used avail capacity Mounted on/dev/dsk/c0d0s0 159919 106429 37500 74% //dev/dsk/c0d0s6 91039 82244 0 100% /usr/proc 0 0 0 0% /procfd 0 0 0 0% /dev/fd/dev/dsk/c0d0s3 1013807 305820 606607 34% /export/dev/dsk/c0d0s4 137631 107755 16116 87% /usr/openwinswap 57416 12 57404 1% /tmp/vol/dev/dsk/c1d0/devpro_v5n1_intel 234370 -1 0 100% /cdrom/devpro_v5n1_intel

From Aries(Solaris)

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AFS File System

created at Carnegie Mellon University - hence name “Andrew File System”

commercially available from Transarcprovides ability for few sys admins to

administer hundreds of systemsprovides virtual file system,

transparent to users, looks like one big tree

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AFS File System (cont)

provides enhanced security on top of Unix rwlidka

read, write, lookup, insert, delete, lock, admin

On every directory (not file level) Permissions granted to users or groups of

users Overlays Unix owner permissions

Unix group and other permissions are ignored

User obtains a data structure called a “token” to authenticate themselves

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DFS File System

Distributed File System - follow on to AFS

Added more layers of permissions Mask for files created in a dir Another mask for dirs created in a dir Very hard to manage permissions

New versions of AFS are now being made available

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C Shell

The Bourne shell and the C shell are not compatible syntactically Both interactive commands and shell

scripts differThe aim was to allow users to easily

substitute custom programs for existing UNIX commands

Made the syntax for shell scripts similar to that of the C programming language

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C Shell

When you are using the C shell your prompt should either be $ or % $ standard shell % C shell

C shell has special files you can use to customize your working environment .login #For things that you want active during current

login .cshrc#Defines special characteristics local to a shell .logout #What happens when you log off the

system

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Built-in Commands

history set history = 20 history will list out last # of commands

(but not history command) !! repeats last command !4 repeats 4th command

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Built-in Commands

alias is an abbreviation for a frequently used command alias h history would set up h alias dir ls –l if you liked your old DOS

commands like dir

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Built-in Commands

Some that are built into the C-shell are:

bg cd setecho exec stopexit fg suspendglob jobs umaskkill notify unalias

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C-Shell

Filename completion (must be turned on) set filec (this turns it on, you must be in

csh) cat myrpt [press ESC key not Enter] Will look for a match for myrpt, it will display

the remainder of the file name (if it’s unique) so you can press enter to run the command. If the match isn’t found then it will do nothing. Sometimes you need to type in more of the file name to get a unique match

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C-Shell

~ represents your home directory du ~ > disk_info&

Pattern matching (BSD only) =~ match !~ does not match

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.login

stty - set terminal command will show your current terminal settings

to change your settings type in:

stty erase ^h

stty kill ^x

stty intr DEL

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.login

env is established from hereUse setenv to declare

setenv TERM vt100.login should include anything you

want executed once

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.cshrc

Is invoked each time you start up a new C shell

Used to establish variables and parameters that are local to a specific shell

It is not required that there is a .cshrc file

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.logout

Runs when you end your sessionYou can use it to clean up

directories, track your sessions etc.This is a file you can create (not

required by the system)

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C Shell

To do the equivalent of a read command you would do the following: set variablename =$<

To display a string of data to the screen use the echo command such as: echo “Hello World!”

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C Shell - If Constructs

You’ll find that script syntax differs from what you used in the bash, bourne or ksh environments

If statements do not end in fi, etc.

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C Shell - If Constructs

1. if (expression) command2. if (expression) then

command(s) endif

3. if (expression) then command(s)

else command(s)

endif

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C Shell - If Constructs

4. if (expression) then command(s)

else if (expression) then command(s)

else command(s) endif

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C Shell - goto

Has the formgoto wordword:for examplegoto errerr:

exit 1

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C Shell -Foreach

Allows script to process a set number of items placed in a listforeach person ( ann bruce tim sam deb)

echo “Dear $person.\You are cordially invited to a

Welcome luncheon for our new employee, Jane Doe” | mail $personend

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C Shell – While Loop

While loop handles situations where the number of iterations is not know in advance. This loop terminates when the controlling expression becomes false.

while (expression)command(s)

end

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C Shell - Switch

Used when a variable can take a wide variety of values

Can replace a long sequence of if-then-else statements

Used similar to C++

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C Shell - Switch

switch (string)case pattern1:

command(s)breaksw

case pattern2:command(s)breaksw

default:command(s)breaksw

endsw

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C Shell - Interrupts

break causes execution to resume after the end statement of the innermost loop

continue makes the shell skip the rest of the commands within the innermost loop and resume execution just before the end statement

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C-Shell

The source command causes the current C Shell to execute a shell script given as its argument. The source command expects a C Shell script so no leading pound sign is required in the script.

The current shell executes source so the commands such as set will affect the current shell (I.e; % set history = 100)

After you make changes to the .cshrc or .login file, you can use source to execute it from within the login shell in order to put the changes into effect. i.e.; % source .cshrc

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find

You’ve used which and whereis to find paths

But these only search a few pathsUse find

find / -name vi -print