Unix Commands

Is a Google Talk Contact Invisible?

noreply@blogger.com (Janu) — Wed, 24 Feb 2010 06:44:00 +0000

Is a Google Talk Contact Invisible?

Sometimes error messages can reveal more than they were supposed to. Rahul Bansal writes about a simple trick that helps you find out if one of your Google Talk contacts is offline or uses the invisible mode. The trick takes advantage of Google's off the record feature which lets you chat with your contacts without saving the conversations in Gmail.

"Chats that have been taken off the record aren't stored in your Gmail chat history, or in the Gmail chat history of your contact. You and the person you're talking to can both see when a chat is taken off the record, and you'll be notified if off the record mode is disabled. Your off the record settings will apply whenever you chat with this person, until one of you makes a change."

Let's say you want to know if your co-worker Michael is really offline. If you start a chat when he is online and select "go off the record", none of your messages will be saved in Michael's Gmail account. That means the next time Michael appears to be offline and you send a message, there are three possibilities:

1. Michael is offline or he has blocked you: Google will display the error "Michael did not receive your chat" (Gmail Chat) or "Michael may not have received your message" (Google Talk gadget). Offline messages are sent as regular messages in Gmail, but this is not possible because the conversations between you and Michael are off the record. Michael won't receive your message.

2. Michael is invisible: you won't see any error, but Michael will receive your message.

Michael is "invisible"

Michael is now offline

"Now the only tricky part is finding a user online for once to set chat off the records. This doesn't seem hard as invisible status is still limited to Gmail version of Google Talk and you may be in luck if your friend uses Google Talk desktop clients/gadgets or third party IM client to chat," It's important to note that the invisible status is available in Gmail Chat, Google Talk gadget

Hack Yahooo Messenger and GoogleTalk to Open Multiple instances

noreply@blogger.com (Janu) — Wed, 24 Feb 2010 05:48:00 +0000

HACK YAHOO MESSENGER AND GOOGLE TALK TO OPEN MULTIPLE INSTANCES

HERE’s a simple hack for yahoo messenger and google talk through which u can create multiple instances if in case u need to..

FOR YAHOO MESSENGER

Go to Start -> Run -> Type regedit -> hit enter

Go to HKEY_CURRENT_USER->> Software ->> Yahoo ->> pager ->>Test

Right click on test -> choose new Dword value .

Rename it as Plural.

Double click it -> assign a decimal value of 1.

Close registry -> Restart yahoo messenger.

NOW you can open yahoo messenger N number of times

FOR GOOGLE TALK

Create a shortcut of Google Talk messenger on your desktop or any other location.

Right click on the Google Talk messenger icon and select properties option

Modify target location text by this

“c:\program files\google\google talk\googletalk.exe” /startmenu

“c:\program files\google\google talk\googletalk.exe” /nomutex

Click OK

Now you can run multiple instances of google talk .

Happy chatting J

SSH & SCP

noreply@blogger.com (Janu) — Tue, 03 Feb 2009 09:49:00 +0000

What is SSH

SSH (Secure SHell) is a network protocol which provides a replacement for insecure remote login

and command execution facilities, such as telnet, rlogin and rsh. SSH encrypts traffic in both

directions, preventing traffic sniffing and password theft. SSH also offers several additional useful

features:

• Compression: traffic may be optionally compressed at the stream level.

• Public key authentication: optionally replacing password authentication.

• Authentication of the server: making ”man-in-the-middle” attack more difficult

• Port forwarding: arbitrary TCP sessions can be forwarded over an SSH connection.

• X11 forwarding: SSH can forward your X11 sessions too.

• File transfer: the SSH protocol family includes two file transfer protocols.

Basic SSH usage

Remote login

The basic syntax to log into a remote host is:

ssh hostname

If you want to specify a username, you may do it using an rlogin-compatible format:

ssh -l user hostname

or a slightly more simple syntax:

ssh user@hostname

If you are running your sshd on a non-stand

--------------------------------------------------------------------------

SCP

scp is the original SSH file transfer mechanism. It is modeled on BSD rcp, a protocol with a 15+

year history which has no RFC. Its syntax is very simple:

scp [user@]host:/path/to/source/file /path/to/destination/file

Will copy a remote file to a local destination. To copy a local file to a remote destination, one

uses the opposite syntax:

scp /path/to/source/file [user@]host:/path/to/destination/file

In either of these cases, the source file may be a wild-card matching multiple files. If a patch is

left off the destination file specification, the remote user’s home directory is assumed. E.g.:

scp /home/djm/*.diff hachi:

scp does not support copying between two remote destinations very well. It is possible using the

following syntax:

scp [user@]host1:/path [user@]host2:/path

For this to work, host1 must be configured for password less access to host2 (see section 4). Also

little feedback is given to the user on whether the operation succeeded.

scp can also copy files recursively:

scp -r source-path [user@]host:/destination-path

scp -r [user@]host:/source-path /destination-path

While it is useful for simple file transfer tasks, it has a number of limitations. The most annoying

of these is poor handling of file which contain characters which may be interpreted by the shell

(e.g. spaces). For example:

[djm@roku djm]$ scp "hachi:/mp3/J.S Bach/Matthaus Passion 0101.ogg" /tmp

cp: cannot stat ‘/mp3/J.S.’: No such file or directory

cp: cannot stat ‘Bach/Matthaus’: No such file or directory

cp: cannot stat ‘Passion’: No such file or directory

cp: cannot stat ‘0101.ogg’: No such file or directory

In these cases you need to double-escape the characters in question:

scp "hachi:/mp3/J.S.\ Bach/Matthaus\ Passion\ 0101.ogg" /tmp

Another problem inherent to scp is that it needs to be able to find a scp binary at the remote end.

Usually such commands are correctly installed in the remote systems $PATH, but if they are not

then transfers will fail:

[djm@roku djm]$ scp hachi:/tmp/foo /tmp

bash: scp: command not found

How to find the runlevel in linux

noreply@blogger.com (Janu) — Fri, 23 Jan 2009 12:27:00 +0000

How to find number of processors in linux

$cat /proc/cpuinfo | grep processor
processor : 0
processor : 1
It has two logical processors
$cat /proc/cpuinfo|grep physical
physical id : 0
physical id : 0
It has single physical processor

Processor: Intel dual core

Janu

IP addresses to set up fault tolerance?

noreply@blogger.com (Janu) — Thu, 15 Jan 2009 08:37:00 +0000

Why do I need so many IP addresses to set up fault tolerance?

There are three 'classes' of IP addresses that we use:

1) 'Front-end' IP addresses - think of these as what are the current IP addresses of each of the Load Balancer machines. Each machine must have a unique IP address to identify itself, so you can contact it directly.

'2) Traffic' IP addresses - these are the addresses of your load balancers that the outside world will see and know about. You need at least two of these (so the balancers can have an address each). Unlike the 'front-end' IP addresses, traffic IP addresses are not tied to one machine - they get shared around and moved. For instance, if one of the balancer machines dies, then the other balancer will take its traffic IP address. This way, visitors will always be able to reach your site.

'3) Back-end' IP addresses - the balancer machines use these IP addresses to contact the back-end servers. The balancer machines will normally have two network cards for performance. The front-end and traffic IP addresses should be on one of the network cards, and the back-end IP address will be on the other card.

The Load Balancer will control the traffic IP addresses itself. The other IP addresses should be configured properly in the operating system.

Janu

How Virtual Private Networks Work

noreply@blogger.com (Janu) — Thu, 15 Jan 2009 08:37:00 +0000

As the popularity of the Internet grew, businesses turned to it as a means of extending their own networks. First came intranets, which are password-protected sites designed for use only by company employees. Now, many companies are creating their own VPN (virtual private network) to accommodate the needs of remote employees and distant offices.

A typical VPN might have a main LAN at the corporate headquarters of a company, other LANs at remote offices or facilities and individual users connecting from out in the field.

http://computer.howstuffworks.com/vpn2.htm

Basically, a VPN is a private network that uses a public network (usually the Internet) to connect remote sites or users together. Instead of using a dedicated, real-world connection such as leased line, a VPN uses "virtual" connections routed through the Internet from the company's private network to the remote site or employee. In this article, you will gain a fundamental understanding of VPNs, and learn about basic VPN components, technologies, tunneling and security.

Domain Names

noreply@blogger.com (Janu) — Tue, 13 Jan 2009 17:55:00 +0000

Domain Names

Because most people have trouble remembering the strings of numbers that make up IP addresses, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, www.howstuffworks.com is a permanent, human-readable name. It is easier for most of us to remember www.howstuffworks.com than it is to remember 209.116.69.66.
The name www.howstuffworks.com actually has three parts:
1. The host name ("www")
2. The domain name ("howstuffworks")
3. The top-level domain name ("com")
Domain names within the ".com" domain are managed by the registrar called VeriSign. VeriSign also manages ".net" domain names. Other registrars (like RegistryPro, NeuLevel and Public Interest Registry) manage the other domains (like .pro, .biz and .org). VeriSign creates the top-level domain names and guarantees that all names within a top-level domain are unique. VeriSign also maintains contact information for each site and runs the "whois" database. The host name is created by the company hosting the domain. "www" is a very common host name, but many places now either omit it or replace it with a different host name that indicates a specific area of the site. For example, in encarta.msn.com, the domain name for Microsoft's Encarta encyclopedia, "encarta" is designated as the host name instead of www.

IP Addresses

noreply@blogger.com (Janu) — Tue, 13 Jan 2009 17:54:00 +0000

The Internet

Client Servers

IP Addresses

To keep all of these machines straight, each machine on the Internet is assigned a unique address called an IP address. IP stands for Internet protocol, and these addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this:
216.27.61.137
The four numbers in an IP address are called octets because they can have values between 0 and 255, which is 28 possibilities per octet.
Every machine on the Internet has a unique IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when the machine dials in. That IP address is unique for that session -- it may be different the next time the machine dials in. This way, an ISP only needs one IP address for each modem it supports, rather than for each customer.
If you are working on a Windows machine, you can view a lot of the Internet information for your machine, including your current IP address and hostname, with the command WINIPCFG.EXE (IPCONFIG.EXE for Windows 2000/XP). On a UNIX machine, type nslookup at the command prompt, along with a machine name, like www.howstuffworks.com -- e.g. "nslookup www.howstuffworks.com" -- to display the IP address of the machine, and you can use the command hostname to learn the name of your machine. (For more information on IP addresses, see IANA.)
As far as the Internet's machines are concerned, an IP address is all you need to talk to a server. For example, in your browser, you can type the URL http://209.116.69.66 and arrive at the machine that contains the Web server for HowStuffWorks. On some servers, the IP address alone is not sufficient, but on most large servers it is -- keep reading for details.

How Web Works

noreply@blogger.com (Janu) — Tue, 12 Feb 2008 16:42:00 +0000

Inside This Article

1.Introduction to How Web Servers Work
2.The Basic Process
3.Behind the Scenes
4.The Internet
5.Clients and Servers
6.IP Addresses
7.Domain Names
8.Name Servers
9.Ports
10.Protocols
11.Putting It All Together
12.Extras: Security
13.Extras: Dynamic Pages
14.Lots More Information
15.See all Internet articles

Basic Process

Your browser formed a connection to a Web server, requested a page and received it.

Behind the Scenes

If you want to get into a bit more detail on the process of getting a Web page onto your computer screen, here are the basic steps that occurred behind the scenes:
• The browser broke the URL into three parts:
1. The protocol ("http")
2. The server name ("www.howstuffworks.com")
3. The file name ("web-server.htm")
• The browser communicated with a name server to translate the server name "www.howstuffworks.com" into an IP Address, which it uses to connect to the server machine.
• The browser then formed a connection to the server at that IP address on port 80. (We'll discuss ports later in this article.)
• Following the HTTP protocol, the browser sent a GET request to the server, asking for the file "http://www.howstuffworks.com/web-server.htm." (Note that cookies may be sent from browser to server with the GET request -- see How Internet Cookies Work for details.)
• The server then sent the HTML text for the Web page to the browser. (Cookies may also be sent from server to browser in the header for the page.)
• The browser read the HTML tags and formatted the page onto your screen.
If you've never explored this process before, that's a lot of new vocabulary. To understand this whole process in detail, you need to learn about IP addresses, ports, protocols... The following sections will lead you through a complete explanation.

The Internet

Client Servers

IP Addresses

To keep all of these machines straight, each machine on the Internet is assigned a unique address called an IP address. IP stands for Internet protocol, and these addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this:
216.27.61.137
The four numbers in an IP address are called octets because they can have values between 0 and 255, which is 28 possibilities per octet.
Every machine on the Internet has a unique IP address. A server has a static IP address that does not change very often. A home machine that is dialing up through a modem often has an IP address that is assigned by the ISP when the machine dials in. That IP address is unique for that session -- it may be different the next time the machine dials in. This way, an ISP only needs one IP address for each modem it supports, rather than for each customer.
If you are working on a Windows machine, you can view a lot of the Internet information for your machine, including your current IP address and hostname, with the command WINIPCFG.EXE (IPCONFIG.EXE for Windows 2000/XP). On a UNIX machine, type nslookup at the command prompt, along with a machine name, like www.howstuffworks.com -- e.g. "nslookup www.howstuffworks.com" -- to display the IP address of the machine, and you can use the command hostname to learn the name of your machine. (For more information on IP addresses, see IANA.)
As far as the Internet's machines are concerned, an IP address is all you need to talk to a server. For example, in your browser, you can type the URL http://209.116.69.66 and arrive at the machine that contains the Web server for HowStuffWorks. On some servers, the IP address alone is not sufficient, but on most large servers it is -- keep reading for details.

Domain Names

Because most people have trouble remembering the strings of numbers that make up IP addresses, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, www.howstuffworks.com is a permanent, human-readable name. It is easier for most of us to remember www.howstuffworks.com than it is to remember 209.116.69.66.
The name www.howstuffworks.com actually has three parts:
1. The host name ("www")
2. The domain name ("howstuffworks")
3. The top-level domain name ("com")
Domain names within the ".com" domain are managed by the registrar called VeriSign. VeriSign also manages ".net" domain names. Other registrars (like RegistryPro, NeuLevel and Public Interest Registry) manage the other domains (like .pro, .biz and .org). VeriSign creates the top-level domain names and guarantees that all names within a top-level domain are unique. VeriSign also maintains contact information for each site and runs the "whois" database. The host name is created by the company hosting the domain. "www" is a very common host name, but many places now either omit it or replace it with a different host name that indicates a specific area of the site. For example, in encarta.msn.com, the domain name for Microsoft's Encarta encyclopedia, "encarta" is designated as the host name instead of www.

Name Servers

The whois Command
On a UNIX machine, you can use the whois command to look up information about a domain name. You can do the same thing using the whois form at VeriSign. If you type in a domain name, like "howstuffworks.com," it will return to you the registration information for that domain, including its IP address.
A set of servers called domain name servers (DNS) maps the human-readable names to the IP addresses. These servers are simple databases that map names to IP addresses, and they are distributed all over the Internet. Most individual companies, ISPs and universities maintain small name servers to map host names to IP addresses. There are also central name servers that use data supplied by VeriSign to map domain names to IP addresses.
If you type the URL "http://www.howstuffworks.com/web-server.htm" into your browser, your browser extracts the name "www.howstuffworks.com," passes it to a domain name server, and the domain name server returns the correct IP address for www.howstuffworks.com. A number of name servers may be involved to get the right IP address. For example, in the case of www.howstuffworks.com, the name server for the "com" top-level domain will know the IP address for the name server that knows host names, and a separate query to that name server, operated by the HowStuffWorks ISP, may deliver the actual IP address for the HowStuffWorks server machine.
On a UNIX machine, you can access the same service using the nslookup command. Simply type a name like "www.howstuffworks.com" into the command line, and the command will query the name servers and deliver the corresponding IP address to you.
So here it is: The Internet is made up of millions of machines, each with a unique IP address. Many of these machines are server machines, meaning that they provide services to other machines on the Internet. You have heard of many of these servers: e-mail servers, Web servers, FTP servers, Gopher servers and Telnet servers, to name a few. All of these are provided by server machines.
Ports
Any server machine makes its services available to the Internet using numbered ports, one for each service that is available on the server. For example, if a server machine is running a Web server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. Clients connect to a service at a specific IP address and on a specific port.
Each of the most well-known services is available at a well-known port number. Here are some common port numbers:
• echo 7
• daytime 13
• qotd 17 (Quote of the Day)
• ftp 21
• telnet 23
• smtp 25 (Simple Mail Transfer, meaning e-mail)
• time 37
• nameserver 53
• nicname 43 (Who Is)
• gopher 70
• finger 79
• WWW 80
If the server machine accepts connections on a port from the outside world, and if a firewall is not protecting the port, you can connect to the port from anywhere on the Internet and use the service. Note that there is nothing that forces, for example, a Web server to be on port 80. If you were to set up your own machine and load Web server software on it, you could put the Web server on port 918, or any other unused port, if you wanted to. Then, if your machine were known as xxx.yyy.com, someone on the Internet could connect to your server with the URL http://xxx.yyy.com:918. The ":918" explicitly specifies the port number, and would have to be included for someone to reach your server. When no port is specified, the browser simply assumes that the server is using the well-known port 80.

Protocols

Once a client has connected to a service on a particular port, it accesses the service using a specific protocol. The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser. Protocols are often text, and simply describe how the client and server will have their conversation.
Perhaps the simplest protocol is the daytime protocol. If you connect to port 13 on a machine that supports a daytime server, the server will send you its impression of the current date and time and then close the connection. The protocol is, "If you connect to me, I will send you the date and time and then disconnect." Most UNIX machines support this server. If you would like to try it out, you can connect to one with the Telnet application. In UNIX, the session would look like this:
%telnet web67.ntx.net 13
Trying 216.27.61.137...
Connected to web67.ntx.net.
Escape character is '^]'.
Sun Oct 25 08:34:06 1998
Connection closed by foreign host.
On a Windows machine, you can access this server by typing "telnet web67.ntx.net 13" at the MSDOS prompt.
In this example, web67.ntx.net is the server's UNIX machine, and 13 is the port number for the daytime service. The Telnet application connects to port 13 (telnet naturally connects to port 23, but you can direct it to connect to any port), then the server sends the date and time and disconnects. Most versions of Telnet allow you to specify a port number, so you can try this using whatever version of Telnet you have available on your machine.
Most protocols are more involved than daytime and are specified in Request for Comment (RFC) documents that are publicly available (see http://sunsite.auc.dk/RFC/ for a nice archive of all RFCs). Every Web server on the Internet conforms to the HTTP protocol, summarized nicely in The Original HTTP as defined in 1991. The most basic form of the protocol understood by an HTTP server involves just one command: GET. If you connect to a server that understands the HTTP protocol and tell it to "GET filename," the server will respond by sending you the contents of the named file and then disconnecting. Here's a typical session:
%telnet www.howstuffworks.com 80
Trying 216.27.61.137...
Connected to howstuffworks.com.
Escape character is '^]'.

GET http://www.howstuffworks.com/

Connection closed by foreign host.

In the original HTTP protocol, all you would have sent was the actual filename, such as "/" or "/web-server.htm." The protocol was later modified to handle the sending of the complete URL. This has allowed companies that host virtual domains, where many domains live on a single machine, to use one IP address for all of the domains they host. It turns out that hundreds of domains are hosted on 209.116.69.66 -- the HowStuffWorks IP address.

Regards,
Janu

AIX monitoring commands

noreply@blogger.com (Janu) — Tue, 12 Feb 2008 13:13:00 +0000

ps -mo THREAD -p