07 September, 2010

Remote login using SSH and copying files from remote machines


copy files remotely over internt

SSH stands for “secure shell” and its a program and protocol also. Through SSH you can  use the applications that are available in a remote computer on internet even if you don't have it in local machine. Only requirement is a working internet connection and an account in the remote machine.  The OpenSSH program suite, developed by the OpenBSD project, offers a free SSH facility with everything necessary to use encrypted connections on different operating systems: 
  :: commandline tools for working on remote machines
  :: to execute programs remotely 
  :: to tunnel Internet services via SSH 
  :: tools for secure file copying

   OpenSSH is a must-have application in any recent Linux distribution. Most systems offer separate packages for the client and the server. Server program is necessary if you want to access your Linux computer via SSH from another machine. 

Applications . . .
- You can login to your office computer remotely from
   home and do all the office work @ home
- Using ssh tunnelling you can communicate over the
   restrictions imposed by proxies and firewalls 
Functions of SSH

ssh       :The command-line client establishes   
             encrypted connections to remote machines 
             and will run commands on these machines if
             needed.

scp      :To copy files (non-interactively) locally to or 
             from remote computers, you can use scp
             (“secure copy”).

sftp      :The ftp client (“secure ftp”) supports
             interactive copying. Like other command line
             ftp clients, the tool offers many other options
             such as copying, changing and listing 
             directories, modifying permissions, deleting
             directories and files, and more...

sshd     :The SSH server is implemented as a daemon
             and listens on port 22 by default. SSH clients 
             establish connections to the sshd.

Installation & Configuration

Take the terminal and type in following commands to install SSH

$ sudo apt-get install openssh-server openssh-client
 
Inorder to test ssh please type in the following command...

$ ssh localhost 
 
To stop ssh server, type in

$ sudo /etc/init.d/ssh stop

To start sshs server, type in

$ sudo /etc/init.d/ssh start

To restart ssh server, type in

 # sudo /etc/init.d/ssh restart


Remote login using SSH

You can remotely login to another machine on the internet by using the following command,

$ ssh  -X  username@100.100.100.3

Replace the username and ip (100.100.100.3) with the one corresponding to you. X option enables the Xserver.

                On executing the above command, the terminal prompt changes to user@remotemachine:~$  you can execute any command as if you are logged in at the remotemachine. Any application from that remote machines can be run by executing the command

examples :
user@remotemachine:~$ firefox
          for starting firefox on a remote machine
user@remotemachine:~$ nautilus
          for starting the file manager on remote  
           machine 
user@remotemachine:~$gnome-session
          to start the gnome session so that you get the   
          desktop with all the features, then you can 
          perform everything in graphical user 
          environment  


Copying files from remote system

                The ssh command alone allows remote login only, but you can copy a file in a remote system to your local machine using the 'scp' command.

1. You are already logged in at user@local$

2. Login to the remote machine  using the ssh  
    command. Then the terminal prompt will change to 
    user@remote

3. Type in the scp command as follows

$ scp  filename user@ip_local:destination

               filename      :: the file to be copied which is 
                                      in remote machine
               ip_local        :: ip adress of your machine
               destination  :: destination folder where the 
                                     copied files are to be saved
       Then the terminal will prompt for your accounts password...


Thats all for now with ssh and scp. You can refer the man page of ssh and scp to see more details in case of using them under a proxy server and also for advanced features...






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