Linux – How to make sure that ssh is ready to go while booting

linuxssh

We have an automation tool which tries to log in through ssh and send commands, which works fine when server is running. On the other hand while server is booting up, our tool check if the ssh port (22) is open, and if it is open it tries to connect to server and send commands.

However, when the server is in bootup sequence and our automation tool checks if the port 22 open, it tries to connect to server using ssh client but server rejects or ssh client returns error "ssh port is not open".

We have tried to investigate this issue with telnet and saw that, while in the bootup sequence, sshd starts and opens the port 22 and start listening but it is somehow closes again the port and opens it up again in a while. And that is the exact same time our automation tool tries to login.

My question is; how can we make sure that ssh port is succesfully open and ready to take commands ?

Thank you for your time to answer,
Best regards

Best Answer

First it seems that the automation tool is not verifying the exit status of ssh. I would try to fix the problem there.

One solution is to try to fill a bug for the team that created the tool.

Another solution would be to wrap the ssh command in a script that would do this transparently. E.g. create a script in /opt/myproject/ssh_wraper.sh

Here you can have something like:

SSH_EXIT_STATUS=255
while [[ $SSH_EXIT_STATUS -eq 255 ]];do
    ssh ....
    SSH_EXIT_STATUS=$?
done
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