1getutent(3) Library Functions Manual getutent(3)
2
6 getutent, getutid, getutline, pututline, setutent, endutent, utmpname -
7 access utmp file entries
8
10 Standard C library (libc, -lc)
11
13 #include <utmp.h>
14 struct utmp *getutent(void);
16 struct utmp *getutid(const struct utmp *ut);
17 struct utmp *getutline(const struct utmp *ut);
18 struct utmp *pututline(const struct utmp *ut);
20 void setutent(void);
22 void endutent(void);
23 int utmpname(const char *file);
25
27 New applications should use the POSIX.1-specified "utmpx" versions of
28 these functions; see STANDARDS.
29 utmpname() sets the name of the utmp-format file for the other utmp
31 functions to access. If utmpname() is not used to set the filename be‐
32 fore the other functions are used, they assume _PATH_UTMP, as defined
33 in <paths.h>.
34 setutent() rewinds the file pointer to the beginning of the utmp file.
36 It is generally a good idea to call it before any of the other func‐
37 tions.
38 endutent() closes the utmp file. It should be called when the user
40 code is done accessing the file with the other functions.
41 getutent() reads a line from the current file position in the utmp
43 file. It returns a pointer to a structure containing the fields of the
44 line. The definition of this structure is shown in utmp(5).
45 getutid() searches forward from the current file position in the utmp
47 file based upon ut. If ut->ut_type is one of RUN_LVL, BOOT_TIME,
48 NEW_TIME, or OLD_TIME, getutid() will find the first entry whose
49 ut_type field matches ut->ut_type. If ut->ut_type is one of
50 INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, getutid()
51 will find the first entry whose ut_id field matches ut->ut_id.
52 getutline() searches forward from the current file position in the utmp
54 file. It scans entries whose ut_type is USER_PROCESS or LOGIN_PROCESS
55 and returns the first one whose ut_line field matches ut->ut_line.
56 pututline() writes the utmp structure ut into the utmp file. It uses
58 getutid() to search for the proper place in the file to insert the new
59 entry. If it cannot find an appropriate slot for ut, pututline() will
60 append the new entry to the end of the file.
61
63 getutent(), getutid(), and getutline() return a pointer to a struct
64 utmp on success, and NULL on failure (which includes the "record not
65 found" case). This struct utmp is allocated in static storage, and may
66 be overwritten by subsequent calls.
67 On success pututline() returns ut; on failure, it returns NULL.
69 utmpname() returns 0 if the new name was successfully stored, or -1 on
71 failure.
72 On failure, these functions errno set to indicate the error.
74
76 ENOMEM Out of memory.
77 ESRCH Record not found.
79 setutent(), pututline(), and the getut*() functions can also fail for
81 the reasons described in open(2).
82
84 /var/run/utmp
85 database of currently logged-in users
86 /var/log/wtmp
88 database of past user logins
89
91 For an explanation of the terms used in this section, see at‐
92 tributes(7).
93 ┌────────────┬───────────────┬─────────────────────────────────────────┐
95 │Interface │ Attribute │ Value │
96 ├────────────┼───────────────┼─────────────────────────────────────────┤
97 │getutent() │ Thread safety │ MT-Unsafe init race:utent race:utentbuf │
98 │ │ │ sig:ALRM timer │
99 ├────────────┼───────────────┼─────────────────────────────────────────┤
100 │getutid(), │ Thread safety │ MT-Unsafe init race:utent sig:ALRM │
101 │getutline() │ │ timer │
102 ├────────────┼───────────────┼─────────────────────────────────────────┤
103 │pututline() │ Thread safety │ MT-Unsafe race:utent sig:ALRM timer │
104 ├────────────┼───────────────┼─────────────────────────────────────────┤
105 │setutent(), │ Thread safety │ MT-Unsafe race:utent │
106 │endutent(), │ │ │
107 │utmpname() │ │ │
108 └────────────┴───────────────┴─────────────────────────────────────────┘
109 In the above table, utent in race:utent signifies that if any of the
110 functions setutent(), getutent(), getutid(), getutline(), pututline(),
111 utmpname(), or endutent() are used in parallel in different threads of
112 a program, then data races could occur.
113
115 None.
116
118 XPG2, SVr4.
119 In XPG2 and SVID 2 the function pututline() is documented to return
121 void, and that is what it does on many systems (AIX, HP-UX). HP-UX
122 introduces a new function _pututline() with the prototype given above
123 for pututline().
124 All these functions are obsolete now on non-Linux systems.
126 POSIX.1-2001 and POSIX.1-2008, following SUSv1, does not have any of
127 these functions, but instead uses
128 #include <utmpx.h>
130 struct utmpx *getutxent(void);
132 struct utmpx *getutxid(const struct utmpx *);
133 struct utmpx *getutxline(const struct utmpx *);
134 struct utmpx *pututxline(const struct utmpx *);
135 void setutxent(void);
136 void endutxent(void);
137 These functions are provided by glibc, and perform the same task as
139 their equivalents without the "x", but use struct utmpx, defined on
140 Linux to be the same as struct utmp. For completeness, glibc also pro‐
141 vides utmpxname(), although this function is not specified by POSIX.1.
142 On some other systems, the utmpx structure is a superset of the utmp
144 structure, with additional fields, and larger versions of the existing
145 fields, and parallel files are maintained, often /var/*/utmpx and
146 /var/*/wtmpx.
147 Linux glibc on the other hand does not use a parallel utmpx file since
149 its utmp structure is already large enough. The "x" functions listed
150 above are just aliases for their counterparts without the "x" (e.g.,
151 getutxent() is an alias for getutent()).
152
154 glibc notes
155 The above functions are not thread-safe. glibc adds reentrant versions
156 #include <utmp.h>
158 int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
160 int getutid_r(struct utmp *ut,
161 struct utmp *ubuf, struct utmp **ubufp);
162 int getutline_r(struct utmp *ut,
163 struct utmp *ubuf, struct utmp **ubufp);
164 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
166 getutent_r(), getutid_r(), getutline_r():
168 _GNU_SOURCE
169 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
170 || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
171 These functions are GNU extensions, analogs of the functions of the
173 same name without the _r suffix. The ubuf argument gives these func‐
174 tions a place to store their result. On success, they return 0, and a
175 pointer to the result is written in *ubufp. On error, these functions
176 return -1. There are no utmpx equivalents of the above functions.
177 (POSIX.1 does not specify such functions.)
178
180 The following example adds and removes a utmp record, assuming it is
181 run from within a pseudo terminal. For usage in a real application,
182 you should check the return values of getpwuid(3) and ttyname(3).
183 #include <pwd.h>
185 #include <stdlib.h>
186 #include <string.h>
187 #include <time.h>
188 #include <unistd.h>
189 #include <utmp.h>
190 int
192 main(void)
193 {
194 struct utmp entry;
195 system("echo before adding entry:;who");
197 entry.ut_type = USER_PROCESS;
199 entry.ut_pid = getpid();
200 strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
201 /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
202 strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
203 time(&entry.ut_time);
204 strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
205 memset(entry.ut_host, 0, UT_HOSTSIZE);
206 entry.ut_addr = 0;
207 setutent();
208 pututline(&entry);
209 system("echo after adding entry:;who");
211 entry.ut_type = DEAD_PROCESS;
213 memset(entry.ut_line, 0, UT_LINESIZE);
214 entry.ut_time = 0;
215 memset(entry.ut_user, 0, UT_NAMESIZE);
216 setutent();
217 pututline(&entry);
218 system("echo after removing entry:;who");
220 endutent();
222 exit(EXIT_SUCCESS);
223 }
224
226 getutmp(3), utmp(5)
227Linux man-pages 6.05 2023-07-20 getutent(3)