Saturday, February 5, 2011

How to configure linux ssh server step by step guide Example and Implementation

Telnet and FTP are well-known protocol but they send data in plain text format, which can be captured by someone using another system on the same network, including the Internet.
On the other hand, all data transferred using OpenSSH tools is encrypted, making it inherently more secure. The OpenSSH suite of tools includes ssh for securely logging in to a remote system and executing remote commands, scp for encrypting files while transferring them to a remote system, and sftp for secure FTP transfers.
OpenSSH uses a server-client relationship. The system being connected to is referred to as the server. The system requesting the connection is referred to as the client. A system can be both an SSH server and a client. OpenSSH also has the added benefits of X11 forwarding and port forwarding.
X11 forwarding, if enabled on both the server and client, allows users to display a graphical application from the system they are logged in to on the system they are logged in from.
Port forwarding allows a connection request to be sent to one server but be forwarded to another server that actually accepts the request.
In this article we will discusses how to use OpenSSH, both from the server-side and the client-side.

Configuring the ssh Server

The openssh-server RPM package is required to configure a Red Hat Enterprise Linux system as an OpenSSH server. If it is not already installed, install it with rpm commands as described in our pervious article. After it is installed, start the service as root with the command service sshd start . The system is now an SSH server and can accept connections. To configure the server to automatically start the service at boot time, execute the command chkconfig sshd on as root. To stop the server, execute the command service sshd stop. To verify that the server is running, use the command service sshd status.

Configure ssh server

In this example we will configure a ssh server and will invoke connection from client side.
For this example we are using two systems one linux server one linux clients . To complete these per quest of ssh server Follow this link
  • A linux server with ip address 192.168.0.254 and hostname Server
  • A linux client with ip address 192.168.0.1 and hostname Client1
  • Updated /etc/hosts file on both linux system
  • Running portmap and xinetd services
  • Firewall should be off on server
We have configured all these steps in our pervious article.
We suggest you to review that article before start configuration of ssh server. Once you have completed the necessary steps follow this guide.
Three rpm are required to configure ssh server. openssh-server, portmap, xinetd check them if not found then install
rpm
Now check sshd, portmap, xinetd service in system service it should be on

#setup
Select System service from list
[*]portmap
[*]xinetd
[*]sshd
Now restart xinetd and portmap and sshd service
service restart
ssh restart
To keep on these services after reboot on then via chkconfig command
chkconfig
After reboot verify their status. It must be in running condition
service status
Create a normal user named vinita
useradd

On Linux client

ping from ssh server and run ssh command and give root password
root login
By default ssh command will enable root session. If you want to login from normal user then specify his name with -l options.
user login
With ssh you can run any command on server without login (user password require)
ssh command
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