| 1 | \define{versionidgs} \versionid $Id$ |
| 2 | |
| 3 | \C{gs} Getting started with PuTTY |
| 4 | |
| 5 | This chapter gives a quick guide to the simplest types of |
| 6 | interactive login session using PuTTY. |
| 7 | |
| 8 | \H{gs-insecure} \ii{Starting a session} |
| 9 | |
| 10 | When you start PuTTY, you will see a \i{dialog box}. This dialog box |
| 11 | allows you to control everything PuTTY can do. See \k{config} for |
| 12 | details of all the things you can control. |
| 13 | |
| 14 | You don't usually need to change most of the configuration options. |
| 15 | To start the simplest kind of session, all you need to do is to |
| 16 | enter a few basic parameters. |
| 17 | |
| 18 | In the \q{Host Name} box, enter the Internet \i{host name} of the server |
| 19 | you want to connect to. You should have been told this by the |
| 20 | provider of your login account. |
| 21 | |
| 22 | Now select a login \i{protocol} to use, from the \q{Connection type} |
| 23 | buttons. For a login session, you should select \i{Telnet}, |
| 24 | \i{Rlogin} or \i{SSH}. See \k{which-one} for a description of the |
| 25 | differences between the three protocols, and advice on which one to |
| 26 | use. The fourth protocol, \I{raw protocol}\e{Raw}, is not used for |
| 27 | interactive login sessions; you would usually use this for debugging |
| 28 | other Internet services (see \k{using-rawprot}). The fifth option, |
| 29 | \e{Serial}, is used for connecting to a local serial line, and works |
| 30 | somewhat differently: see \k{using-serial} for more information on |
| 31 | this. |
| 32 | |
| 33 | When you change the selected protocol, the number in the \q{Port} |
| 34 | box will change. This is normal: it happens because the various |
| 35 | login services are usually provided on different network ports by |
| 36 | the server machine. Most servers will use the standard port numbers, |
| 37 | so you will not need to change the port setting. If your server |
| 38 | provides login services on a non-standard port, your system |
| 39 | administrator should have told you which one. (For example, many |
| 40 | \i{MUDs} run Telnet service on a port other than 23.) |
| 41 | |
| 42 | Once you have filled in the \q{Host Name}, \q{Protocol}, and |
| 43 | possibly \q{Port} settings, you are ready to connect. Press the |
| 44 | \q{Open} button at the bottom of the dialog box, and PuTTY will |
| 45 | begin trying to connect you to the server. |
| 46 | |
| 47 | \H{gs-hostkey} \ii{Verifying the host key} (SSH only) |
| 48 | |
| 49 | If you are not using the \i{SSH} protocol, you can skip this |
| 50 | section. |
| 51 | |
| 52 | If you are using SSH to connect to a server for the first time, you |
| 53 | will probably see a message looking something like this: |
| 54 | |
| 55 | \c The server's host key is not cached in the registry. You |
| 56 | \c have no guarantee that the server is the computer you |
| 57 | \c think it is. |
| 58 | \c The server's rsa2 key fingerprint is: |
| 59 | \c ssh-rsa 1024 7b:e5:6f:a7:f4:f9:81:62:5c:e3:1f:bf:8b:57:6c:5a |
| 60 | \c If you trust this host, hit Yes to add the key to |
| 61 | \c PuTTY's cache and carry on connecting. |
| 62 | \c If you want to carry on connecting just once, without |
| 63 | \c adding the key to the cache, hit No. |
| 64 | \c If you do not trust this host, hit Cancel to abandon the |
| 65 | \c connection. |
| 66 | |
| 67 | This is a feature of the SSH protocol. It is designed to protect you |
| 68 | against a network attack known as \i\e{spoofing}: secretly |
| 69 | redirecting your connection to a different computer, so that you |
| 70 | send your password to the wrong machine. Using this technique, an |
| 71 | attacker would be able to learn the password that guards your login |
| 72 | account, and could then log in as if they were you and use the |
| 73 | account for their own purposes. |
| 74 | |
| 75 | To prevent this attack, each server has a unique identifying code, |
| 76 | called a \e{host key}. These keys are created in a way that prevents |
| 77 | one server from forging another server's key. So if you connect to a |
| 78 | server and it sends you a different host key from the one you were |
| 79 | expecting, PuTTY can warn you that the server may have been switched |
| 80 | and that a spoofing attack might be in progress. |
| 81 | |
| 82 | PuTTY records the host key for each server you connect to, in the |
| 83 | Windows \i{Registry}. Every time you connect to a server, it checks |
| 84 | that the host key presented by the server is the same host key as it |
| 85 | was the last time you connected. If it is not, you will see a |
| 86 | warning, and you will have the chance to abandon your connection |
| 87 | before you type any private information (such as a password) into |
| 88 | it. |
| 89 | |
| 90 | However, when you connect to a server you have not connected to |
| 91 | before, PuTTY has no way of telling whether the host key is the |
| 92 | right one or not. So it gives the warning shown above, and asks you |
| 93 | whether you want to \I{trusting host keys}trust this host key or |
| 94 | not. |
| 95 | |
| 96 | Whether or not to trust the host key is your choice. If you are |
| 97 | connecting within a company network, you might feel that all the |
| 98 | network users are on the same side and spoofing attacks are |
| 99 | unlikely, so you might choose to trust the key without checking it. |
| 100 | If you are connecting across a hostile network (such as the |
| 101 | Internet), you should check with your system administrator, perhaps |
| 102 | by telephone or in person. (Some modern servers have more than one |
| 103 | host key. If the system administrator sends you more than one |
| 104 | \I{host key fingerprint}fingerprint, you should make sure the one |
| 105 | PuTTY shows you is on the list, but it doesn't matter which one it is.) |
| 106 | |
| 107 | \# FIXME: this is all very fine but of course in practice the world |
| 108 | doesn't work that way. Ask the team if they have any good ideas for |
| 109 | changes to this section! |
| 110 | |
| 111 | \H{gs-login} \ii{Logging in} |
| 112 | |
| 113 | After you have connected, and perhaps verified the server's host |
| 114 | key, you will be asked to log in, probably using a \i{username} and |
| 115 | a \i{password}. Your system administrator should have provided you |
| 116 | with these. Enter the username and the password, and the server |
| 117 | should grant you access and begin your session. If you have |
| 118 | \I{mistyping a password}mistyped your password, most servers will |
| 119 | give you several chances to get it right. |
| 120 | |
| 121 | If you are using SSH, be careful not to type your username wrongly, |
| 122 | because you will not have a chance to correct it after you press |
| 123 | Return; many SSH servers do not permit you to make two login attempts |
| 124 | using \i{different usernames}. If you type your username wrongly, you |
| 125 | must close PuTTY and start again. |
| 126 | |
| 127 | If your password is refused but you are sure you have typed it |
| 128 | correctly, check that Caps Lock is not enabled. Many login servers, |
| 129 | particularly Unix computers, treat upper case and lower case as |
| 130 | different when checking your password; so if Caps Lock is on, your |
| 131 | password will probably be refused. |
| 132 | |
| 133 | \H{gs-session} After logging in |
| 134 | |
| 135 | After you log in to the server, what happens next is up to the |
| 136 | server! Most servers will print some sort of login message and then |
| 137 | present a \i{prompt}, at which you can type |
| 138 | \I{commands on the server}commands which the |
| 139 | server will carry out. Some servers will offer you on-line help; |
| 140 | others might not. If you are in doubt about what to do next, consult |
| 141 | your system administrator. |
| 142 | |
| 143 | \H{gs-logout} \ii{Logging out} |
| 144 | |
| 145 | When you have finished your session, you should log out by typing |
| 146 | the server's own logout command. This might vary between servers; if |
| 147 | in doubt, try \c{logout} or \c{exit}, or consult a manual or your |
| 148 | system administrator. When the server processes your logout command, |
| 149 | the PuTTY window should close itself automatically. |
| 150 | |
| 151 | You \e{can} close a PuTTY session using the \i{Close button} in the |
| 152 | window border, but this might confuse the server - a bit like |
| 153 | hanging up a telephone unexpectedly in the middle of a conversation. |
| 154 | We recommend you do not do this unless the server has stopped |
| 155 | responding to you and you cannot close the window any other way. |