SSH Host Key Changed
I am using FileZilla to access my Linode server from my Mac. However, when I first login it gives an error stating that the server's host key is unknown. But when I click ok it connects and then I am able to upload/download files without any issue.
I did not put any port number in the Port field. It is empty. Is this the reason for my issue? If so, what should I do? Or should I check "Always trust this host…." option.
This message may actually be normal if this is either the first time you've ever connected to your Linode or if you've made a major configuration change to your server (e.g. reinstalling the OS) since the last time you connected. If either of these scenarios fits your situation, then you can safely check off the "Always trust this host" option.
Essentially, what that message is saying is that the fingerprint for your Linode is either unrecognized entirely (new server) or has changed from what it expects for that IP address/DNS entry (major config change). The main scenario under which you should need to do anything is if you changed your server's config, in which case you will need to remove the old entry from your known_hosts file. On a Mac or Linux machine, this file is typically located in your user folder, under a hidden directory called '.ssh/'. For example, you could reference the file as '~/.ssh/known_hosts'. You technically can clear this file entirely, but if you connect to other servers from that machine then you will receive this prompt the next time you connect to each of them as well, since their entries have been removed.
All of this being said, the reason that this error is generated is so that if someone ever sets up what is called a "Man in the Middle" attack - in which a third system is setup in between your system and the server you are attempting to connect to - you will be alerted to it's presence. In most cases, however you should only need to consider this third possibility if the two scenarios outlined above do not apply to you.
Linode Support Team