1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
|
<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN">
<HTML
><HEAD
><TITLE
>Logging In And Out</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet"><LINK
REL="HOME"
TITLE="The Linux System Administrators' Guide"
HREF="book1.html"><LINK
REL="PREVIOUS"
TITLE="Booting in single user mode"
HREF="x1880.html"><LINK
REL="NEXT"
TITLE="Logins via the network"
HREF="x1944.html"></HEAD
><BODY
BGCOLOR="#FFFFFF"
TEXT="#000000"
><DIV
CLASS="NAVHEADER"
><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>The Linux System Administrators' Guide</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x1880.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
></TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x1944.html"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="CHAPTER"
><H1
><A
NAME="LOG-IN-AND-OUT"
>Chapter 8. Logging In And Out</A
></H1
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="c1905.html#AEN1911"
>Logins via terminals</A
></DT
><DT
><A
HREF="x1944.html"
>Logins via the network</A
></DT
><DT
><A
HREF="x1956.html"
>What <B
CLASS="COMMAND"
>login</B
> does</A
></DT
><DT
><A
HREF="x1988.html"
>X and xdm</A
></DT
><DT
><A
HREF="x1991.html"
>Access control</A
></DT
><DT
><A
HREF="x2008.html"
>Shell startup</A
></DT
></DL
></DIV
><BLOCKQUOTE
><P
>“I don't care to belong to a club
that accepts people like me as a member.”
(Groucho Marx)</P
></BLOCKQUOTE
><P
> This section describes what happens when a user logs
in or out. The various interactions of background processes,
log files, configuration files, and so on are described in
some detail.
</P
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN1911"
>Logins via terminals</A
></H1
><P
><A
HREF="c1905.html#TERMINAL-LOGINS"
>Figure 8-1</A
> shows how logins happen via
terminals. First, <B
CLASS="COMMAND"
>init</B
> makes sure there is
a <B
CLASS="COMMAND"
>getty</B
> program for the terminal connection
(or console). <B
CLASS="COMMAND"
>getty</B
> listens at the terminal
and waits for the user to notify that he is ready to login in
(this usually means that the user must type something). When it
notices a user, <B
CLASS="COMMAND"
>getty</B
> outputs a welcome message
(stored in <TT
CLASS="FILENAME"
>/etc/issue</TT
>), and prompts for
the username, and finally runs the <B
CLASS="COMMAND"
>login</B
>
program. <B
CLASS="COMMAND"
>login</B
> gets the username as a
parameter, and prompts the user for the password. If these
match, <B
CLASS="COMMAND"
>login</B
> starts the shell configured
for the user; else it just exits and terminates the process
(perhaps after giving the user another chance at entering the
username and password). <B
CLASS="COMMAND"
>init</B
> notices that
the process terminated, and starts a new <B
CLASS="COMMAND"
>getty</B
>
for the terminal.
</P
><DIV
CLASS="FIGURE"
><P
><B
><A
NAME="TERMINAL-LOGINS"
>Figure 8-1. Logins via terminals: the interaction of <B
CLASS="COMMAND"
>init</B
>, <B
CLASS="COMMAND"
>getty</B
>, <B
CLASS="COMMAND"
>login</B
>, and the shell.</A
></B
></P
><P
><IMG
SRC="logins-via-terminals.gif"></P
></DIV
><P
> Note that the only new process is the
one created by <B
CLASS="COMMAND"
>init</B
> (using the
<TT
CLASS="FUNCTION"
>fork</TT
> system call); <B
CLASS="COMMAND"
>getty</B
>
and <B
CLASS="COMMAND"
>login</B
> only replace the program running in
the process (using the <TT
CLASS="FUNCTION"
>exec</TT
> system call).
</P
><P
> A separate program, for noticing the user, is needed
for serial lines, since it can be (and traditionally was)
complicated to notice when a terminal becomes active.
<B
CLASS="COMMAND"
>getty</B
> also adapts to the speed and other
settings of the connection, which is important especially for
dial-in connections, where these parameters may change from call
to call. </P
><P
> There are several versions of <B
CLASS="COMMAND"
>getty</B
>
and <B
CLASS="COMMAND"
>init</B
> in use, all with their good and
bad points. It is a good idea to learn about the versions on
your system, and also about the other versions (you could use the
Linux Software Map to search them). If you don't have dial-in's,
you probably don't have to worry about <B
CLASS="COMMAND"
>getty</B
>,
but <B
CLASS="COMMAND"
>init</B
> is still important. </P
></DIV
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x1880.html"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x1944.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Booting in single user mode</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
> </TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>Logins via the network</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
|
