SSH Server (Secure Shell )

 SSH- Secure Shell is a cryptographic network protocol for secure data communication, remote command-line login, remote command execution, and other secure network services between two networked computers that connects, via a secure channel over an insecure network, a server and a client.

                                     

Package-                 openssh
Port-                        22
Daemon-                 sshd  
Script-                     /etc/init.d/sshd
Configuration file-/etc/ssh/sshd_config

# yum install openssh* -y          (Install open-ssh package)
               
# ssh 192.168.10.2                   (Access the System )
YES     (finger print)
password
login success

# cat /root/ssh/know_hosts

# ssh user1 192.168.10.2
# ssh user1 server1.exampl.com
#  ssh -X 192.168.10.2  ( for gui commond)


BLOCK FORWARDING

# vim /etc/ssh/sshd_conf

  #X11Forwarding yes                     comment(line 108)


{ AUTHENTICATION BY PORT NUMBER)


# vim /etc/ssh/sshd_conf

Port 22        remove the comment (line 13)
port 2222      (place of port 22)
:wq

# ssh -p 2222 192.168.10.2


{ TO BLOCK ROOT}

# vim /etc/ssh/sshd_conf

Denyusers root    (add this line no 12) (means only root deny others allowed)

Alloowusers root    (means only root allow and others are deny)

:wq


# vim /etc/ssh/sshd_conf

MaxAuthTries 2          (remove comment line no 44)
MaxSessions 4           (remove comment linr no 45)
:wq



{SSH WITH KEY AUTHENTICATION}


2 Types of ssh key authentication

1- RSA (RSA provides encryption, digital signatures and key distribution.)

2- DSA (DSA provides only digital signatures.)

RSA
# ssh-keygen
enter
enter
enter

Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
2c:03:d6:6c:12:a6:91:00:6d:ab:8c:94:c1:a8:c3:83 root@localhost.localdomain
The key's randomart image is:
+--[ RSA 2048]----+
|*o..o            |
|.o++ +           |
|+.+.+ +          |
|E=.. + .         |
|+o.   o S        |
|o.     o         |
|                 |
|                 |
|                 |
+-----------------+




# cd /root/ssh1
# ll
# ssh-copy-id -i 192.168.10.2  (next machine ip)
 .ssh/authorized_keys
         

# ssh 192.168.0.100      { on same system}
#  cat /root/.ssh/authoried_keys


DSA

# ssh-keygen -t dsa
enter
enter
enter

Your identification has been saved in /root/.ssh/id_dsa.
Your public key has been saved in /root/.ssh/id_dsa.pub.
The key fingerprint is:
75:ea:c6:e4:e2:f3:a4:72:58:98:f1:56:3a:3d:58:3e root@localhost.localdomain
The key's randomart image is:
+--[ DSA 1024]----+
|                 |
|                 |
|          . .    |
|      .  .oo     |
|       =SBo      |
|      o B=E      |
|       +..*o     |
|      o.o=       |
|       ooo.      |
+-----------------+


# ssh-copy-id -i /root/.ssh/id_dsa.pub 192.168.0.100
Now try logging into the machine, with "ssh '192.168.0.100'", and check in:

  .ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.




# ssh 192.168.0.100
# cat /root/.ssh/authorised_keys










(ssh session time out)

# vim /etc/ssh/sshd_config
ClientAliveInerval 300
:wq
# /etc/init.d/sshd restart


_____________________________________________________________________________________________

Click Back..                              Click Home..