SSH is the predominant remote management tool for administering Linux systems.
Whether you are working between linux servers or from your Mac (which is basically pretty Linux) you will be using ssh to get a terminal / command line on the remote server. A few people get stuck on this if they are learning to do it for the 1st time.
Let me start by referring you to the AWS document on troubleshooting SSH connections There are some recommendation there you should probably look thought.
To gain the most information about the problem add a -v to the command to get the error in verbose mode.
Here are the common issues that other students have had:
- Key does not have the right permissions attached. If it is too loose SSH will refuse to use it for security reasons. The recommendation is chmod 400.
sudo chmod 400 /path/my-key-pair.pem
- Using the right IP address for the target. For the labs keep it simple and use the IP address not DNS names (various reasons) once you have it working experiment with the DNS names. In more complex environment you should use the DNS names, however while you are learning, keep it simple.
- Security Groups not correct to allow network access to or from the bastion host.
- Wrong type of key. PuTTy and PPK keys are only used when you are connecting from a Windows server. If you are not using Windows and PuTTy, use the .pem key and the ssh format.
ssh ec2-user@##.##.##.## -i my-key-pair.pem
sudo ssh ec2-user@##.##.##.## -i my-key-pair.pem
sudo ssh ec2-user@##.##.##.## -i /path/my-key-pair.pem
- Inadequate personal right.
When SSH asks for the passphrase it is doing so to ensure that you have the right to use that key. You can prove that you do by providing the passphrase. However for our labs that should not be necessary. If you run the ssh command with root permissions, it is assumed by the operating system that you have the necessary rights. To do this you can pre-pend sudo in front of the ssh this tells the operating system to give you root permissions for this one command.The other options is to run sudo su previously to attempting ssh. This tells the operating system to give you root permissions until you leave or cancel the command. As you watch the lectures you will see the lecturers do this sometimes at the beginning of the lab so that they have all the access needed to complete the lab.
- Sometime people try to use the wrong user account. for the basic AWS AMI the user is ec2-user . For other Linux distributions or custom AMIs the default username may be different (root, ubuntu, bob, etc) but you will not have to worry about that until you are much more proficient.
- From time to time someone accidentally types -1 instead of -i . The -1 forces the SSH session to use the old SSH v.1 version. Which is no longer supported. Take a few minutes to read of the MAN page to understand what you have accidentally called.
here is a good short video that take a broader look at SSH and will help you better understand the what the elements do and a bit more about the background.