how to install ssh serve in Ubuntu

OpenSSh is opensource ssh server in Linux.

Ubuntu SSHD Installation

Type the following two command to install both ssh client and server:
# sudo apt-get install openssh-server openssh-client

SSHD Configuration

To be frank your server is ready by default. Just test it from your home computer or from same system with the command:
# ssh localhost
OR
# ssh user@your-server-ip-address

How do I use ssh client?

Assuming that your server hostname is userver.kasun.com and username is kasun, you need to type the following command:
# ssh kasun@userver.kasun.com
To stop ssh server, enter:
# sudo /etc/init.d/ssh stop
To start sshs server, enter:
# sudo /etc/init.d/ssh start
To restart ssh server, enter:
# sudo /etc/init.d/ssh restart

ssh and telnet

In networking world lot of people use ssh and telnet but they don't have more idea
in this protocol.actually one of my friend also ask me some question related with these things.Ok now you can follow this blog and get some idea.



SSH - secure shell(normally it use port 22)

SSH is network related protocol but it work in application layer which use SSL.SSL(443) make trusted relation ship.And also SSH Basically it is secured. It is most often used by network administrators as a remote login / remote control way to manage their business server.


#######for your knowledge--- SSL is most often used for transmitting credit card, tax, banking, or personal information to a business server.##########


Telnet - port 23-Application layer


Telnet is normal way u can connect to the server and work.Telnet send the data's in Ascii format and its not a secure shell.so we must't use telnet and ftp becoz hackers
can easy to identify our data.

difference between programming and scripting language

The primary difference between a "programming language" (C, C++, VB etc.) and a "scripting language" (PHP, ASP, JSP, JavaScript, VBScript)is that code written in a programming language needs to be compiled before it is run. Once it is compiled, it can be run any number of times.

Scripting languages, on the other hand, are interpreted at run-time. This means that every time you want to run the program, a separate program needs to read the code, interpret it, and then follow the instructions in the code. Compiled code has already been interpreted into machine language, so it is will typically execute faster because the conversion into machine language has already been done.

Interpreted vs complied source code

Interpreted language -

In interpreter to process the source code every time you want to run the program.This translate the source code down to a lower level for the computer's consumption as it goes along.we call the lower level language machine code.this codes are't human readable.

compiled language -

A compiled language , on the other hand ,such as C,uses a complier to do all this processing one time only before the code is ever run.After that ,you can run the machine code directly ,without needing the compiler any more.

How to use Internet Connection Sharing in Windowxp

How to use Internet Connection Sharing

To use Internet Connection Sharing to share your Internet connection, the host computer must have one network adapter that is configured to connect to the internal network, and one network adapter or modem that is configured to connect to the Internet.

On the host computer

On the host computer, follow these steps to share the Internet connection:

1. Log on to the host computer as Administrator or as Owner.
2. Click Start, and then click Control Panel.
3. Click Network and Internet Connections.
4. Click Network Connections.
5. Right-click the connection that you use to connect to the Internet. For example, if you connect to the Internet by using a modem, right-click the connection that you want under Dial-up.
6. Click Properties.
7. Click the Advanced tab.
8. Under Internet Connection Sharing, select the Allow other network users to connect through this computer's Internet connection check box.
9. If you are sharing a dial-up Internet connection, select the Establish a dial-up connection whenever a computer on my network attempts to access the Internet check box if you want to permit your computer to automatically connect to the Internet.
10. Click OK. You receive the following message:
    When Internet Connection Sharing is enabled, your LAN adapter will be set to use IP
    address 192.168.0.1. Your computer may lose connectivity with other computers on
    your network. If these other computers have static IP addresses, it is a good idea to set them
    to obtain their IP addresses automatically. Are you sure you want to enable Internet
    Connection Sharing?
11. Click Yes.

The connection to the Internet is shared to other computers on the local area network (LAN). The network adapter that is connected to the LAN is configured with a static IP address of 192.168.0.1 and a subnet mask of 255.255.255.0

"CACHE"............
in TI world cache memory is very important area.but lot of people haven't perfect idea in this area. i think if u can get some better idea follow this blog...

Cache Memory

Cache is a component that improves performance by transparently storing data such that future requests for that data can be served faster.

It has several types

CPU Cache -

Small memories on or close to the CPU can operate faster than the much larger main memory.

DISK Cache -

While CPU caches are generally managed entirely by hardware, a variety of software manages other caches. The page cache in main memory, which Is an example of disk cache, is managed by the operating system kernel.

WEB Cache -

is the Caching of web document to reduce bandwidth usage, server load, and perceived lag. A web cache stores copies of documents passing through it ,subsequent requests may be satisfied from the cache if certain conditions are met.

Mail server

Related protocols –

POP3 - port 110

IMAP - port 143

SMTP - port 25

HTTP - port 80

Secure SMTP (SSMTP) - port 465

Secure IMAP (IMAP4-SSL) - port 585

IMAP4 over SSL (IMAPS) - port 993

Secure POP3 (SSL-POP) - port 995

ICMP – Internet control message protocol

1. Layer -transportation layer

2. TCP/IP

3. purpose of these control messages is to provide feedback about problems in the communication environment.

Some function in ICMP

• Announce network errors. - Packet unreachable

• Announce network congestion. - Due to traffic give ICMP Source Quench message

• Assist Troubleshooting. - Give support to Echo massage (ping)

• Announce Timeouts. -IP packet's TTL field drops to zero(using traceroute easy to find out)

in Ubuntu we can find ICMP relate files in /proc/sys/net/ipv4 …

SMTP – Simple Mail Transfer Protocol

1. port – 25 (TCP)

2. Application Layer

3. E-mail and other mail transfer argent use SMTP to send and receive mail message. user-level client mail applications typically only use SMTP for sending messages to a mail server for relaying. For receiving messages, client applications usually use either the POP or the IMAP or a proprietary system (such as Microsoft Exchange or Lotus Notes/Domino) to access their mail box accounts on a mail server.

POP -Post Office Protocol

1.Application Layer

2. TCP/IP(110)

3. POP and IMAP (Internet Message Access Protocol) are the two most prevalent Internet standard protocols for e-mail retrieval

POP3	IMAP
You only check e-mail from one computer. May get confused if you need to check email both in the office and at home.	You check e-mail from multiple locations. Easier to identify the unread email.
You want to remove your e-mail from the mail server.	You use Webmail.
All messages as well as their attachments will be downloaded into desktop PC during the 'check new email' process.	A whole message will be downloaded only when it is opened for display from its content.
Mailboxes can only be created on desktop PC. There is only one mailbox (INBOX) exists on the server.	Multiple mailboxes can be created on the desktop PC as well as on the server.
Filters can transfer incoming/outgoing messages only to local mailboxe	Filters can transfer incoming/outgoing messages to other mailboxes no matter where the mailboxes locate (on the server or the PC).
Outgoing email is stored only locally on the desktop PC	Outgoing email can be filtered to a mailbox on server for accessibility from other machine
Messages are deleted on the desktop PC. Comparatively, it is inconvenient to clean up your mailbox on the server.	Messages can be deleted directly on the server to make it more convenient to clean up your mailbox on the server
Messages may be reloaded onto desktop PC several times due to the corruption of system file	The occurrence of reloading messages from the server to PC is much less when compared to POP3.

Install postfix in ubuntu

first go to terminal

sudo aptitude install postfix

configuration

sudo dpkg-reconfigure postfix

Insert the following details when asked (replacing server1.example.com with your domain name if you have one):

• General type of mail configuration: Internet Site

• NONE doesn't appear to be requested in current config

• System mail name: server1.example.com

• Root and postmaster mail recipient:

• Other destinations for mail: server1.example.com, example.com, localhost.example.com, localhost

• Force synchronous updates on mail queue?: No

• Local networks: 127.0.0.0/8

• Yes doesn't appear to be requested in current config

• Mialbox size limit (bytes): 0

• Local address extension character: +

• Internet protocols to use: all

  
  

  To configure the mailbox format for Maildir:

  sudo postconf -e 'home_mailbox = Maildir/'

You may need to issue this as well:

sudo postconf -e 'mailbox_command ='

Note: This will place new mail in /home/username/Maildir so you will need to configure your Mail Delivery Agent to use the same path.

Configure Postfix to do SMTP AUTH using SASL (saslauthd):

sudo postconf -e 'smtpd_sasl_local_domain =' sudo postconf -e 'smtpd_sasl_auth_enable = yes' sudo postconf -e 'smtpd_sasl_security_options = noanonymous' sudo postconf -e 'broken_sasl_auth_clients = yes' sudo postconf -e 'smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination' sudo postconf -e 'inet_interfaces = all'

Next edit /etc/postfix/sasl/smtpd.conf and add the following lines:

pwcheck_method: saslauthd mech_list: plain login

Generate certificates to be used for TLS encryption and/or certificate Authentication:

touch smtpd.key chmod 600 smtpd.key openssl genrsa 1024 > smtpd.key openssl req -new -key smtpd.key -x509 -days 3650 -out smtpd.crt # has prompts openssl req -new -x509 -extensions v3_ca -keyout cakey.pem -out cacert.pem -days 3650 # has prompts sudo mv smtpd.key /etc/ssl/private/ sudo mv smtpd.crt /etc/ssl/certs/ sudo mv cakey.pem /etc/ssl/private/ sudo mv cacert.pem /etc/ssl/certs/

Configure Postfix to do TLS encryption for both incoming and outgoing mail:

sudo postconf -e 'smtp_tls_security_level = may' sudo postconf -e 'smtpd_tls_security_level = may' sudo postconf -e 'smtpd_tls_auth_only = no' sudo postconf -e 'smtp_tls_note_starttls_offer = yes' sudo postconf -e 'smtpd_tls_key_file = /etc/ssl/private/smtpd.key' sudo postconf -e 'smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt' sudo postconf -e 'smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem' sudo postconf -e 'smtpd_tls_loglevel = 1' sudo postconf -e 'smtpd_tls_received_header = yes' sudo postconf -e 'smtpd_tls_session_cache_timeout = 3600s' sudo postconf -e 'tls_random_source = dev:/dev/urandom' sudo postconf -e 'myhostname = server1.example.com' # remember to change this to yours

The file /etc/postfix/main.cf should now look like this:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version  smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu) biff = no  # appending .domain is the MUA's job. append_dot_mydomain = no  # Uncomment the next line to generate "delayed mail" warnings #delay_warning_time = 4h  myhostname = server1.example.com alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases myorigin = /etc/mailname mydestination = server1.example.com, example.com, localhost.example.com, localhost relayhost = mynetworks = 127.0.0.0/8 mailbox_command = procmail -a "$EXTENSION" mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all smtpd_sasl_local_domain = smtpd_sasl_auth_enable = yes smtpd_sasl_security_options = noanonymous broken_sasl_auth_clients = yes smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination smtpd_tls_auth_only = no #Use these on Postfix 2.2.x only #smtp_use_tls = yes #smtpd_use_tls = yes #For Postfix 2.3 or above use: smtp_tls_security_level = may smtpd_tls_security_level = may smtp_tls_note_starttls_offer = yes smtpd_tls_key_file = /etc/ssl/private/smtpd.key smtpd_tls_cert_file = /etc/ssl/certs/smtpd.crt smtpd_tls_CAfile = /etc/ssl/certs/cacert.pem smtpd_tls_loglevel = 1 smtpd_tls_received_header = yes smtpd_tls_session_cache_timeout = 3600s tls_random_source = dev:/dev/urandom

Restart the postfix daemon like this:

sudo /etc/init.d/postfix restart