Click the Secure Shell (SSH) Access link from the Hosting panel of the 1&1 Control panel.
Click Secure Shell (SSH) Access
Take note of your Host Name, User Name and Password. If you do not know the current password, set a new password at this time.
Click anywhere on the Desktop of your Mac. At the Top, you should see the Finder menu. Select Go -> Applications.
Select applications image
Find the Utilities folder and double-click it or click the arrow next to the folder to expand it.
Select utilities image
Find the Terminal utility and double-click it to open.
Select terminal image
When the Terminal window opens type the command ssh email@example.com and press ENTER. You will need to replace u12345678 with your User Name and replace 1and1help.com with your Host Name from the 1&1 Control Panel.
Type ssh command image
If this is your first time connecting, you will be informed that the secure fingerprint is unknown. Typeyes and press ENTER at the Are you sure you want to continue connecting (yes,no)? prompt.
Yes to continue image
You will then be informed the fingerprint has been permanently stored and you will then be prompted for a password. Please type out the password (as you type, the characters typed will not display on the screen; this is normal) and press ENTER.
Enter password image
You should then see a disclaimer message and be presented with a command prompt.
Login success image
You have now successfully logged in!
For additional information, you may want to reference: