Summary

SSH (Secure SHell) is a program to let you login securely to another computer on the Internet in order to use typed commands. It encrypts your username, password, and your session commands and output. For some applications this is much faster and simpler than using a Web interface. You must have a valid, authorised username and password for the remote machine.

Telnet is an earlier, insecure form of a similar service. SSH is now used instead of Telnet because Telnet transmits all data unencrypted, which is a security risk.

Most computers that you can log into this way use the Unix operating system or one of its derivatives (Linux and recent Apple Mac systems are all Unix-based). You will need to know what commands to type if you want to use such systems. There is a brief summary of some of the common commands in unixtips.

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§4. Telnet

Section by section

2. SSH

Traditional terminal programs have no graphical interface of their own. You can use them in a window inside a graphical user interface like Microsoft Windows, the X Window System, or Mac OS X, but there are no menus or icons.

There are some useful graphical versions of the SSH program for windowing systems which add extra functions like letting you store frequently-used addresses, usernames, and passwords. In these cases, it is generally A Bad Idea to store the passwords, as anyone who can use your computer would then also be able to log in to your remote sites.

SSH comes with all Unix-based systems by default (Linux, Apple Mac, Sun, HP, IBM, etc). To connect, open a terminal window and type ssh username@hostname (substituting the login username and hostname of your account where shown, eg ssh ontology@www.ucc.ie).
Windows users should download and install Simon Tatham's puTTY program from his web site at http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html, which provides an SSH window. Download or run the program called putty.exe.

You enter the hostname in the box provided, make sure it is set to use port 22 and SSH, and click on Open .

Figure 1. Setting up the connection in puTTY for Windows

2.1. Logging in

The very first time you connect to the server with SSH from a computer where you haven't done this before, it may ask if you wish to accept the public security key (this may be displayed in a separate pop-up window): answer by clicking OK or by typing yes and pressing Enter.

Terminal Commands

_=X

The authenticity of host 'www.ucc.ie (143.239.1.112)' can't be established.
RSA key fingerprint is fc:10:cc:1e:54:53:f3:03:46:58:6c:0f:32:e3:5f:79.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'www.ucc.ie' (RSA) to the list of known hosts.

login as: ontology
ontology@www.ucc.ie's password:

SSH will then ask for your password: type in your password and press Enter. Once you are logged in, it's just a normal terminal.

The password will not be displayed, not even as a row of dots. Make sure you type it correctly!

On subsequent occasions you will just be asked for your username and password.

2.2. Changing your password

Passwords expire every 90 days on UCC servers. If you cannot log in, it's probably because your password has expired. To have your password reset, email the webmaster.

If you log in a few days after expiry, most systems will immediately ask you to set a new password. Make one up and type it in when asked (it asks you to repeat it, for safety). Remember that passwords do not display anything at all while being typed.
To change your password at any other time, type the command passwd . The system will ask first for your existing password. Then make up a new password and type it in when asked (it asks you to repeat it, for safety). Remember that passwords do not display anything at all while being typed.
Terminal Commands

_=X
```
$ passwd
Changing password for user ontology.
Changing password for ontology
(current) UNIX password:         
Enter new UNIX password:          
Retype new UNIX password:          
passwd: password changed
$
```
On systems where passwords are stored in Microsoft Active Directory, it will ask for your Kerberos 5 password instead. Changing your password here will also change your Microsoft Windows logon and email password (they are all the same thing).

3. Using the command terminal

Commands may differ according to what kind of machine you are logged into. There is a summary of some common Unix commands in unixtips.

3.1. Typing commands

The very first time you access a machine, your SSH program will ask you to confirm that you really do mean that machine. Assuming you got the address right, answer yes

The remote system will then ask you to login, and may then display a welcome message and any security announcements of its own. When the system displays a $ sign, it's ready for you to type a command.

Terminal Commands

_=X

The authenticity of host 'www.ucc.ie (143.239.1.112)' can't be established.
RSA key fingerprint is fc:10:cc:1e:54:53:f3:03:46:58:6c:0f:32:e3:5f:79.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'www.ucc.ie' (RSA) to the list of known hosts.

login as: ontology
ontology@www.ucc.ie's password:        

This is www.ucc.ie (nina), the main UCC web server.
Access to this system is for registered website owners ONLY.
Continued use implies acceptance of the Acceptable Use Policy
(see http://www.ucc.ie/aup/). Unauthorised use is prohibited.
$

Don't forget you must press the Enter key after every command you type: until you do so, the system doesn't know you've typed anything!

To know what commands to type, refer back to the documentation that told you to use SSH. Some elementary Unix commands are listed in unixtips.

One of the most common reasons for web site owners to log in is to change password.

3.2. Logging out

You must log out when you have finished, otherwise the next user will be able to use your account. Type exit at the $ sign when you have finished. If you fail to do this, you are leaving your account open to the next person to use your computer.

How to use SSH

Logging into remote services using SSH