SSH | SCP

r  ssh authentication
 
·         Password Based Authentication
·         Key Based Authentication
    o    Key Pair Value [Public Key + Private Key]

r  ssh server
 
·         Package: openssh-server
·         Config File: /etc/ssh/sshd_config [For server]
            /etc/ssh/ssh_config [For client]
·         Port: 22/tcp
·         Service Name: sshd
·         By Default: All users allowed

r  ssh client
 
·         Server IP
·         Username
    o   PermitRootLogin yes
    o   AllowUsers shohan root
    o   DenyUser Alex
·         Password
·         Port

r  ssh server configuration
               
·         PermitRootLogin
·         Port
·         Listen
·         Key Based Authentication
    o   ssh-keygen
    o   ssh-copy-id

r  From SSH client:
 
·         ssh ip
·         ssh user@ip
·         ssh -l root 192.168.56.72
·         ssh -p <port> user@ip

r  Deny root login via ssh
 
·         PermitRootLogin no

r  SSH procedure
 
·         For server
 
[root@B ~]# rpm -qa openssh
[root@B ~]# yum install openssh-server
[root@B ~]# systemctl start sshd
[root@B ~]# systemctl enable sshd
 
·         For client [Clinet will provide ssh command]
 
[root@B ~]# rpm -q openssh-clients
openssh-clients-8.7p1-38.el9_4.4.x86_64
 
1.Generate keypair using ssh-key-gen
2.Copy public key to server (path depends on sshd_config file)
3.Login to ssh server using private key
 
step01:
 
[root@ServerA ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
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:
SHA256:JHSgwdyPgWCAZTNdrYed2Bbs97ZC+1nPZmEfnmyAE6w root@a
The key's randomart image is:
+---[RSA 2048]----+
|ooB=.+++.        |
|.o o=+o.+        |
|    . .@.o.      |
|      =oO .o     |
|       oS...o    |
|         E.oo. + |
|         . o..* =|
|          o .o B+|
|           oo .oo|
+----[SHA256]-----+
 
step02:
 
[root@ ServerA ~]# cd .ssh/
[root@ ServerA .ssh]# ll
id_rsa
id_rsa.pub
step03:
 
[root@ServerA .ssh]# ssh-copy-id root@192.168.56.72
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now, it is to install the new keys
root@192.168.56.72's password:
 
Number of key(s) added: 1
 
Now try logging into the machine, with:   "ssh 'root@192.168.56.72'"
and check to make sure that only the key(s) you wanted were added.

r  SCP
 
[root@SysAdmin]# scp -P 44 -r /tmp/abc.txt root@192.168.56.72:/opt/