blob: 6996cc74ab8e5e37353e1ee0dcacf2dfb40e2294 (
plain)
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
|
<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN">
<HTML
><HEAD
><TITLE
>What login does</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet"><LINK
REL="HOME"
TITLE="The Linux System Administrators' Guide"
HREF="book1.html"><LINK
REL="UP"
TITLE="Logging In And Out"
HREF="c1905.html"><LINK
REL="PREVIOUS"
TITLE="Logins via the network"
HREF="x1944.html"><LINK
REL="NEXT"
TITLE="X and xdm"
HREF="x1988.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="x1944.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 8. Logging In And Out</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x1988.html"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN1956"
>What <B
CLASS="COMMAND"
>login</B
> does</A
></H1
><P
>The <B
CLASS="COMMAND"
>login</B
> program takes care of
authenticating the user (making sure that the username and
password match), and of setting up an initial environment for
the user by setting permissions for the serial line and starting
the shell. </P
><P
> Part of the initial setup is outputting the contents of
the file <TT
CLASS="FILENAME"
>/etc/motd</TT
> (short for message of the
day) and checking for electronic mail. These can be disabled
by creating a file called <TT
CLASS="FILENAME"
>.hushlogin</TT
> in
the user's home directory. </P
><P
> If the file <TT
CLASS="FILENAME"
>/etc/nologin</TT
>
exists, logins are disabled. That file is typically
created by <B
CLASS="COMMAND"
>shutdown</B
> and relatives.
<B
CLASS="COMMAND"
>login</B
> checks for this file, and will
refuse to accept a login if it exists. If it does exist,
<B
CLASS="COMMAND"
>login</B
> outputs its contents to the terminal
before it quits. </P
><P
> <B
CLASS="COMMAND"
>login</B
> logs all failed login attempts in
a system log file (via <B
CLASS="COMMAND"
>syslog</B
>). It also logs
all logins by root. Both of these can be useful when tracking
down intruders. </P
><P
> Currently logged in people are listed in
<TT
CLASS="FILENAME"
>/var/run/utmp</TT
>. This file is valid only
until the system is next rebooted or shut down; it is cleared
when the system is booted. It lists each user and the terminal
(or network connection) he is using, along with some other useful
information. The <B
CLASS="COMMAND"
>who</B
>, <B
CLASS="COMMAND"
>w</B
>,
and other similar commands look in <TT
CLASS="FILENAME"
>utmp</TT
>
to see who are logged in. </P
><P
> All successful logins are recorded into
<TT
CLASS="FILENAME"
>/var/log/wtmp</TT
>. This file will grow without
limit, so it must be cleaned regularly, for example by having
a weekly <B
CLASS="COMMAND"
>cron</B
> job to clear it.
<A
NAME="AEN1980"
HREF="#FTN.AEN1980"
>[1]</A
>
The <B
CLASS="COMMAND"
>last</B
> command browses
<TT
CLASS="FILENAME"
>wtmp</TT
>. </P
><P
> Both <TT
CLASS="FILENAME"
>utmp</TT
> and
<TT
CLASS="FILENAME"
>wtmp</TT
> are in a binary format (see the
<TT
CLASS="FILENAME"
>utmp</TT
> manual page); it is unfortunately not
convenient to examine them without special programs. </P
></DIV
><H3
>Notes</H3
><TABLE
BORDER="0"
CLASS="FOOTNOTES"
WIDTH="100%"
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="5%"
><A
NAME="FTN.AEN1980"
HREF="x1956.html#AEN1980"
>[1]</A
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
WIDTH="95%"
><P
>Good Linux distributions do this out
of the box.</P
></TD
></TR
></TABLE
><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="x1944.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="x1988.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Logins via the network</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c1905.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>X and xdm</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
|
