ssh script returns 255 error

Question

In my code I have the following to run a remote script.

ssh root@host.domain.com \"sh /home/user/backup_mysql.sh\"

For some reason it keeps

Answer 1

As @wes-floyd and @zpon wrote, add these parameters to SSH to bypass "Are you sure you want to continue connecting (yes/no)?"

-o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no

Answer 2

This is usually happens when the remote is down/unavailable; or the remote machine doesn't have ssh installed; or a firewall doesn't allow a connection to be established to the remote host.

ssh returns 255 when an error occurred or 255 is returned by the remote script:

 EXIT STATUS

     ssh exits with the exit status of the remote command or
     with 255 if an error occurred.

Usually you would an error message something similar to:

ssh: connect to host host.domain.com port 22: No route to host

Or

ssh: connect to host HOSTNAME port 22: Connection refused

Check-list:

• What happens if you run the ssh command directly from the command line?

• Are you able to ping that machine?

• Does the remote has ssh installed?

• If installed, then is the ssh service running?