We all know that one can configure SSH to login automatically by adding the client's public key to the server's ~/.ssh/authorized_keys file. But what if you need to run commands on 200 machines and don't want to login to every single machine to add the key? Search no more, this tutorial has the answer!

1. Installing sshpass

sshpass is a tool for non-interactivly performing password authentication with SSH's so called "interactive keyboard password authentication".

Here's a standard SSH connect command:


First you have to answer "yes" to accept the host key and then to enter the password.

With sshpass, you are able to specify the password on the command line and skip this step. Here's how to install it:


sshpass is now ready to be used!

2. Using sshpass

The sshpass' syntax is:


So instead of doing:


You can simply do:


You will be automatically logged in, without any password prompt:


3. Automatically accepting host keys

The last problem is this prompt:


When you're using sshpass to connect on a single machine that you use often, it's not a big deal because you will get the prompt once and never again after. But if you want to connect to 200 machines, you definitely don't want to type "yes" 200 times.

To fix this issue, simply add this line in /etc/ssh/ssh_config on the CLIENT machine:


With this setting enabled, SSH will automatically accept the host keys and will not prompt you about it.

4. Automating the process

This section will show you how to easily automate the process of running commands on any number of machines you want.

First you will need a file containing the hostname, username and password for each of the servers you want to run commands on, in a CSV format. For example:

ssh_magic.csv:

Then you will create this bash script:

ssh_magic.sh:

Simply place ssh_magic.csv and ssh_magic.sh together and run the script.

Conclusion

You now know how to run commands on any number of SSH machines, without any prompt! Make sure you check the other ways to pass the password to sshpass - they offer more secure ways than directly on the command line with the -p option.

If you get an error message about SIGWINCH undeclared, add this to your main.c:

Thanks Michel...