ESXi 3.5 does ship with the ability to run SSH, but this is disabled by default (and is not supported).
At the console of the ESXi host, press ALT-F1 to access the console window.
Enter unsupported in the console and then press Enter. You will not see the text ou type in.
If you typed in unsupported correctly, you will see the Tech Support Mode warning and a password prompt. Enter the password for the root login.
You should then see the prompt of ~ #. Edit the file inetd.conf (enter the command vi /etc/inetd.conf).
Find the line that begins with #ssh and remove the #. Then save the file. If you’re new to using vi, then move the cursor down to #ssh line and then press the Insert key. Move the cursor over one space and then hit backspace to delete the #. Then press ESC and type in :wq to save the file and exit vi. If you make a mistake, you can press the ESC key and then type it :q! to quit vi without saving the file.
Once you’ve closed the vi editor, run the command /sbin/services.sh restart to restart the management services. You’ll now be able to connect to the ESXi host with a SSH client.