Script to check passwordless connectivity between servers - shell

Question

I have the following script. My requirement is if I give the username and IP address the script should check whether the host server has passwordless connectivity with the given server.
script.sh
#!/bin/sh
echo "Enter username"
read user
echo "Enter IP address"
read ip
echo "Enter condition"
read conditon
if [ $condition == "test" ]
then
ssh -o 'PreferredAuthentications=publickey' $user#$ip "echo"
fi
The above script checks for passwordless connectivity and exits. I want the script to return "success" if the connection is there or "No connection" if there is no passwordless connection between the hosts.
Thanks.

Answer 1

You can give an extra option to ssh that sets it in BatchMode
BatchMode
If set to yes, passphrase/password querying will be disabled. This option is useful in scripts and other batch jobs where no user is present to supply the password. The argument must be yes or no (the default).
source: man sshconfig
The following line will return the requested error code
ssh -oBatchMode=yes user#server echo > /dev/null 2>&1
This will return 0 if it can log in and will return a non-zero value (255) if it fails to login.
So you could do something like:
ssh -oBathMode=yes "${user}#${server}" echo > /dev/null 2>&1 && echo "Success" || echo "No Connection"
Or you could even let the server answer Success as
ssh -oBathMode=yes "${user}#${server}" echo Success 2>/dev/null || echo "No Connection"

Answer 2

Prerequisites
Access to command line/terminal window
User with sudo or root privileges
A local server & a remote server
SSH access to a remote server via command line/terminal window
Before You Start
Check for existing SSH Keys, using the below command
ls -al ~/.ssh/id_*.pub
If the output tells you there are no such files, move on to the next step, which shows you how to generate SSH keys.
Step 1: Generate SSH Key Pair
ssh-keygen -t rsa -b 4096 -C "your_email#domain.com"
Next, type in the path where you want to store the keys or hit
Enter to accept the default path.
It also asks you to set a passphrase, this is to ensure more secure connection. Note that, the Passphrase may be interrupted when you set up automated processes. Else, one can just press Enter to skip this step.
The output shows you the identification & about where is your public key stored along with the key fingerprints.
Verify your newly created SSH key pair, using the below command.
ls -al ~/.ssh/id_*.pub
Step 2: Uploading the Public Key to Remote Server
There are 2 options, that one can adopt:
Using ssh-copy-id Command
Using cat Command
Using ssh-copy-id command
ssh-copy-ide [remote_username]#[server_ip_address]
Using cat Command
ssh [remote_username]#[server_ip_address] mkdir -p .ssh
Type in the password for remote server, and then cat to view the contents of the stored Public Key
cat .ssh/id_rsa.pub | ssh [remote_username]#[server_ip_address] 'cat >> .ssh/authorized_keys'
Step 3: Log in to Server Without Password
Final step is to check whether the setup works fine or not.
ssh [remote_username]#[server_ip_address]
Troubleshooting, if found any errors
If you are still prompted for a password after going through all the steps, start by editing file permissions on the remote server.
Set permissions 700 for the .ssh directory.
Set permissions 640 for the .ssh/authorized_keys directory.
Edit file permissions using this command:
ssh [remote_username]#[server_ip_address] "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"
References:
(https://stackoverflow.com/a/52744882/18154805)