SSH KEY GEN

1. Create ssh key at localhost
   

ssh-keygen -t rsa -b 4096 -C user@remotehost.com

Then they will ask to enter default .ssh path

Enter file in which to save the key (/home/yourusername/.ssh/id_rsa):

We can key in any passphrase to make extra security but just press enter with empty key it will automate gen-key for you

Enter passphrase (empty for no passphrase):

Now the public and private key will be kept in

ls -al
/home/yourusername/.ssh/id_rsa /home/yourusername/.ssh/id_rsa.pub

2. In your local host copy public key (id_rsa.pub) to remote host

ssh-copy-id remote_username@server_ip_address

or with manual ssh with

cat ~/.ssh/id_rsa.pub | ssh remote_username@server_ip_address "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

3. Now you can ssh with out prompt for password

Tunnel ssh

Ref ​ref

Remote to local

At localhost user create tunnel to remote host with following

ssh -R 8022:localhost:22 remoteUser@remotehost.com

Then, at remote host, user can ssh -p 8022 localUser@127.0.0.1 to localhost

If we want to bind to specific interface (NICs), we use

ssh -R 128.199.96.250:8022:localhost:22 krit@128.199.96.250

and at 128.199.96.250 server on /etc/ssh/sshd_config file add this line

GatewayPorts clientspecified

Then user can access ssh -p 8022 128.199.96.250 will forward to client on this tunnel

Local to Remote

At localhost user create tunnel to remote host with following

[krit@mini ~]$ ssh -L 2000:localhost:22 remoteUser@remotehost.com

Then, at localhost, user can ssh -p 2000 krit@127.0.0.1 at localhost it will tunnel to remote host

ssh rsync

rsync from local to remote server via ssh we need to install apt install sshpass

[omd@local Test]$ sshpass -p "password" /usr/bin/rsync -a ~/var/log/Rsync/out.txt krit@172.17.0.1:Tmp/Test

ssh tunnel

At remote server that we would like to ssh in used following config with ssh_public key place at local server.

root@dwdm:/etc/systemd/system# more sshtunnel.service 
[Unit]
Description=SSH Tunnel
After=network.target

[Service]
Restart=always
RestartSec=20
User=root
ExecStart=/usr/bin/ssh -NT -o ServerAliveInterval=60 -o ExitOnForwardFailure=yes -R 32022:localhost:22 vodka@18x.1xx.217.xx

[Install]
WantedBy=multi-user.target

Then run

root@dwdm:/etc/systemd/system# systemctl daemon-reload
root@dwdm:/etc/systemd/system# systemctl enable sshtunnel
root@dwdm:/etc/systemd/system# systemctl start sshtunnel
root@dwdm:/etc/systemd/system# systemctl status sshtunnel
● sshtunnel.service - SSH Tunnel
   Loaded: loaded (/etc/systemd/system/sshtunnel.service; enabled; vendor preset: enabled)
   Active: active (running)