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1 '\" t
2 .\" Copyright 1995 Mark D. Roth (roth@uiuc.edu)
3 .\"
4 .\" SPDX-License-Identifier: GPL-2.0-or-later
5 .\"
6 .\" References consulted:
7 .\" Linux libc source code
8 .\" Solaris manpages
9 .\"
10 .\" Modified Thu Jul 25 14:43:46 MET DST 1996 by Michael Haardt
11 .\" <michael@cantor.informatik.rwth-aachen.de>
12 .\"
13 .TH getutent 3 (date) "Linux man-pages (unreleased)"
14 .SH NAME
15 getutent, getutid, getutline, pututline, setutent, endutent,
16 utmpname \- access utmp file entries
17 .SH LIBRARY
18 Standard C library
19 .RI ( libc ", " \-lc )
20 .SH SYNOPSIS
21 .nf
22 .B #include <utmp.h>
23 .P
24 .B struct utmp *getutent(void);
25 .BI "struct utmp *getutid(const struct utmp *" ut );
26 .BI "struct utmp *getutline(const struct utmp *" ut );
27 .P
28 .BI "struct utmp *pututline(const struct utmp *" ut );
29 .P
30 .B void setutent(void);
31 .B void endutent(void);
32 .P
33 .BI "int utmpname(const char *" file );
34 .fi
35 .SH DESCRIPTION
36 New applications should use the POSIX.1-specified "utmpx" versions of
37 these functions; see STANDARDS.
38 .P
39 .BR utmpname ()
40 sets the name of the utmp-format file for the other utmp
41 functions to access.
42 If
43 .BR utmpname ()
44 is not used to set the filename
45 before the other functions are used, they assume \fB_PATH_UTMP\fP, as
46 defined in \fI<paths.h>\fP.
47 .P
48 .BR setutent ()
49 rewinds the file pointer to the beginning of the utmp file.
50 It is generally a good idea to call it before any of the other
51 functions.
52 .P
53 .BR endutent ()
54 closes the utmp file.
55 It should be called when the user
56 code is done accessing the file with the other functions.
57 .P
58 .BR getutent ()
59 reads a line from the current file position in the utmp file.
60 It returns a pointer to a structure containing the fields of
61 the line.
62 The definition of this structure is shown in
63 .BR utmp (5).
64 .P
65 .BR getutid ()
66 searches forward from the current file position in the utmp
67 file based upon \fIut\fP.
68 If \fIut\->ut_type\fP is one of \fBRUN_LVL\fP,
69 \fBBOOT_TIME\fP, \fBNEW_TIME\fP, or \fBOLD_TIME\fP,
70 .BR getutid ()
71 will
72 find the first entry whose \fIut_type\fP field matches \fIut\->ut_type\fP.
73 If \fIut\->ut_type\fP is one of \fBINIT_PROCESS\fP, \fBLOGIN_PROCESS\fP,
74 \fBUSER_PROCESS\fP, or \fBDEAD_PROCESS\fP,
75 .BR getutid ()
76 will find the
77 first entry whose
78 .I ut_id
79 field matches \fIut\->ut_id\fP.
80 .P
81 .BR getutline ()
82 searches forward from the current file position in the utmp file.
83 It scans entries whose
84 .I ut_type
85 is \fBUSER_PROCESS\fP
86 or \fBLOGIN_PROCESS\fP and returns the first one whose
87 .I ut_line
88 field
89 matches \fIut\->ut_line\fP.
90 .P
91 .BR pututline ()
92 writes the
93 .I utmp
94 structure \fIut\fP into the utmp file.
95 It uses
96 .BR getutid ()
97 to search for the proper place in the file to insert
98 the new entry.
99 If it cannot find an appropriate slot for \fIut\fP,
100 .BR pututline ()
101 will append the new entry to the end of the file.
102 .SH RETURN VALUE
103 .BR getutent (),
104 .BR getutid (),
105 and
106 .BR getutline ()
107 return a pointer to a \fIstruct utmp\fP on success,
108 and NULL on failure (which includes the "record not found" case).
109 This \fIstruct utmp\fP is allocated in static storage, and may be
110 overwritten by subsequent calls.
111 .P
112 On success
113 .BR pututline ()
114 returns
115 .IR ut ;
116 on failure, it returns NULL.
117 .P
118 .BR utmpname ()
119 returns 0 if the new name was successfully stored, or \-1 on failure.
120 .P
121 On failure, these functions
122 .I errno
123 set to indicate the error.
124 .SH ERRORS
125 .TP
126 .B ENOMEM
127 Out of memory.
128 .TP
129 .B ESRCH
130 Record not found.
131 .P
132 .BR setutent (),
133 .BR pututline (),
134 and the
135 .BR getut* ()
136 functions can also fail for the reasons described in
137 .BR open (2).
138 .SH FILES
139 .TP
140 .I /var/run/utmp
141 database of currently logged-in users
142 .TP
143 .I /var/log/wtmp
144 database of past user logins
145 .SH ATTRIBUTES
146 For an explanation of the terms used in this section, see
147 .BR attributes (7).
148 .TS
149 allbox;
150 lb lb lbx
151 l l l.
152 Interface Attribute Value
153 T{
154 .na
155 .nh
156 .BR getutent ()
157 T} Thread safety T{
158 .na
159 .nh
160 MT-Unsafe init race:utent
161 race:utentbuf sig:ALRM timer
162 T}
163 T{
164 .na
165 .nh
166 .BR getutid (),
167 .BR getutline ()
168 T} Thread safety T{
169 .na
170 .nh
171 MT-Unsafe init race:utent
172 sig:ALRM timer
173 T}
174 T{
175 .na
176 .nh
177 .BR pututline ()
178 T} Thread safety T{
179 .na
180 .nh
181 MT-Unsafe race:utent
182 sig:ALRM timer
183 T}
184 T{
185 .na
186 .nh
187 .BR setutent (),
188 .BR endutent (),
189 .BR utmpname ()
190 T} Thread safety MT-Unsafe race:utent
191 .TE
192 .P
193 In the above table,
194 .I utent
195 in
196 .I race:utent
197 signifies that if any of the functions
198 .BR setutent (),
199 .BR getutent (),
200 .BR getutid (),
201 .BR getutline (),
202 .BR pututline (),
203 .BR utmpname (),
204 or
205 .BR endutent ()
206 are used in parallel in different threads of a program,
207 then data races could occur.
208 .SH STANDARDS
209 None.
210 .SH HISTORY
211 XPG2, SVr4.
212 .P
213 In XPG2 and SVID 2 the function
214 .BR pututline ()
215 is documented to return void, and that is what it does on many systems
216 (AIX, HP-UX).
217 HP-UX introduces a new function
218 .BR _pututline ()
219 with the prototype given above for
220 .BR pututline ().
221 .P
222 All these functions are obsolete now on non-Linux systems.
223 POSIX.1-2001 and POSIX.1-2008, following SUSv1,
224 does not have any of these functions, but instead uses
225 .P
226 .RS 4
227 .EX
228 .B #include <utmpx.h>
229 .P
230 .B struct utmpx *getutxent(void);
231 .B struct utmpx *getutxid(const struct utmpx *);
232 .B struct utmpx *getutxline(const struct utmpx *);
233 .B struct utmpx *pututxline(const struct utmpx *);
234 .B void setutxent(void);
235 .B void endutxent(void);
236 .EE
237 .RE
238 .P
239 These functions are provided by glibc,
240 and perform the same task as their equivalents without the "x", but use
241 .IR "struct utmpx" ,
242 defined on Linux to be the same as
243 .IR "struct utmp" .
244 For completeness, glibc also provides
245 .BR utmpxname (),
246 although this function is not specified by POSIX.1.
247 .P
248 On some other systems,
249 the \fIutmpx\fP structure is a superset of the \fIutmp\fP structure,
250 with additional fields, and larger versions of the existing fields,
251 and parallel files are maintained, often
252 .I /var/*/utmpx
253 and
254 .IR /var/*/wtmpx .
255 .P
256 Linux glibc on the other hand does not use a parallel \fIutmpx\fP file
257 since its \fIutmp\fP structure is already large enough.
258 The "x" functions listed above are just aliases for
259 their counterparts without the "x" (e.g.,
260 .BR getutxent ()
261 is an alias for
262 .BR getutent ()).
263 .SH NOTES
264 .SS glibc notes
265 The above functions are not thread-safe.
266 glibc adds reentrant versions
267 .P
268 .nf
269 .B #include <utmp.h>
270 .P
271 .BI "int getutent_r(struct utmp *" ubuf ", struct utmp **" ubufp );
272 .BI "int getutid_r(struct utmp *" ut ,
273 .BI " struct utmp *" ubuf ", struct utmp **" ubufp );
274 .BI "int getutline_r(struct utmp *" ut ,
275 .BI " struct utmp *" ubuf ", struct utmp **" ubufp );
276 .fi
277 .P
278 Feature Test Macro Requirements for glibc (see
279 .BR feature_test_macros (7)):
280 .P
281 .BR getutent_r (),
282 .BR getutid_r (),
283 .BR getutline_r ():
284 .nf
285 _GNU_SOURCE
286 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
287 || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
288 .fi
289 .P
290 These functions are GNU extensions, analogs of the functions of the
291 same name without the _r suffix.
292 The
293 .I ubuf
294 argument gives these functions a place to store their result.
295 On success, they return 0, and a pointer to the result is written in
296 .IR *ubufp .
297 On error, these functions return \-1.
298 There are no utmpx equivalents of the above functions.
299 (POSIX.1 does not specify such functions.)
300 .SH EXAMPLES
301 The following example adds and removes a utmp record, assuming it is run
302 from within a pseudo terminal.
303 For usage in a real application, you
304 should check the return values of
305 .BR getpwuid (3)
306 and
307 .BR ttyname (3).
308 .P
309 .\" SRC BEGIN (getutent.c)
310 .EX
311 #include <pwd.h>
312 #include <stdlib.h>
313 #include <string.h>
314 #include <time.h>
315 #include <unistd.h>
316 #include <utmp.h>
317 \&
318 int
319 main(void)
320 {
321 struct utmp entry;
322 \&
323 system("echo before adding entry:;who");
324 \&
325 entry.ut_type = USER_PROCESS;
326 entry.ut_pid = getpid();
327 strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
328 /* only correct for ptys named /dev/tty[pqr][0\-9a\-z] */
329 strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
330 entry.ut_time = time(NULL);
331 strcpy(entry.ut_user, getpwuid(getuid())\->pw_name);
332 memset(entry.ut_host, 0, UT_HOSTSIZE);
333 entry.ut_addr = 0;
334 setutent();
335 pututline(&entry);
336 \&
337 system("echo after adding entry:;who");
338 \&
339 entry.ut_type = DEAD_PROCESS;
340 memset(entry.ut_line, 0, UT_LINESIZE);
341 entry.ut_time = 0;
342 memset(entry.ut_user, 0, UT_NAMESIZE);
343 setutent();
344 pututline(&entry);
345 \&
346 system("echo after removing entry:;who");
347 \&
348 endutent();
349 exit(EXIT_SUCCESS);
350 }
351 .EE
352 .\" SRC END
353 .SH SEE ALSO
354 .BR getutmp (3),
355 .BR utmp (5)