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