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Arcom Embedded Linux Technical Manual Secure Shell (SSH)

Using SSH commands

The ssh command

The ssh command enables you to remotely login to a machine. For example to login to

the machine ael.example.net, you would enter the following command:

$ ssh ael.example.net

The first time you login to a machine, a message similar to the following (but with a

different fingerprint) is displayed:

The authenticity of host 'ael.example.net (10.2.4.14)' can't be

established.

RSA key fingerprint is

e0:79:67:58:78:e4:bc:0a:6a:e2:f8:62:f8:62:f8:ea:fa:bc

Are you sure you want to continue connecting (yes/no)?

This gives you the opportunity to verify that the machine you are logging into is the

machine you are expecting by confirming that the host’s cryptographic key is correct.

Verify that the fingerprint is correct before typing yes to continue logging in.

You can obtain the host fingerprint of a system by asking the administrator or by logging

in at the console and running the command:

$ ssh-keygen –l –f /etc/sshd/ssh_host_key.pub

There are likely to be several ssh_host_*key.pub files. Examine them all.

Once you verify the fingerprint of a system, it is written to ~/.ssh/known_hosts, so you

are not asked this question again. If the remote host’s fingerprint changes for any

reason, ssh displays an error message. If, on investigation, you determine that the

change is legitimate, you can edit ~/.ssh/known_hosts to remove the incorrect

fingerprint. For example, the remote operating system may be reinstalled, causing the

SSH server’s host key to change.

After you have accepted the remote system’s fingerprint, you are asked to authenticate

yourself. You normally do this by entering your password. However, there are

alternative authentication methods, such as public key authentication. See Public key

authentication methods

, page 27.

The ssh command logs in to the remote machine using the current user name from

your local host. To login as a different user, for example as the user ‘arcom’, you may

use one of these two command forms:

$ ssh –l arcom ael.example.net

Many of the commands in the SSH suite accept both these forms for specifying

a login user. The examples in this manual use the user@host form.

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