1GETUTENT(3) Linux Programmer's Manual GETUTENT(3)
2
6 getutent, getutid, getutline, pututline, setutent, endutent, utmpname -
7 access utmp file entries
8
10 #include <utmp.h>
11 struct utmp *getutent(void);
13 struct utmp *getutid(const struct utmp *ut);
14 struct utmp *getutline(const struct utmp *ut);
15 struct utmp *pututline(const struct utmp *ut);
17 void setutent(void);
19 void endutent(void);
20 int utmpname(const char *file);
22
24 New applications should use the POSIX.1-specified "utmpx" versions of
25 these functions; see CONFORMING TO.
26 utmpname() sets the name of the utmp-format file for the other utmp
28 functions to access. If utmpname() is not used to set the filename be‐
29 fore the other functions are used, they assume _PATH_UTMP, as defined
30 in <paths.h>.
31 setutent() rewinds the file pointer to the beginning of the utmp file.
33 It is generally a good idea to call it before any of the other func‐
34 tions.
35 endutent() closes the utmp file. It should be called when the user
37 code is done accessing the file with the other functions.
38 getutent() reads a line from the current file position in the utmp
40 file. It returns a pointer to a structure containing the fields of the
41 line. The definition of this structure is shown in utmp(5).
42 getutid() searches forward from the current file position in the utmp
44 file based upon ut. If ut->ut_type is one of RUN_LVL, BOOT_TIME,
45 NEW_TIME, or OLD_TIME, getutid() will find the first entry whose
46 ut_type field matches ut->ut_type. If ut->ut_type is one of
47 INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, getutid()
48 will find the first entry whose ut_id field matches ut->ut_id.
49 getutline() searches forward from the current file position in the utmp
51 file. It scans entries whose ut_type is USER_PROCESS or LOGIN_PROCESS
52 and returns the first one whose ut_line field matches ut->ut_line.
53 pututline() writes the utmp structure ut into the utmp file. It uses
55 getutid() to search for the proper place in the file to insert the new
56 entry. If it cannot find an appropriate slot for ut, pututline() will
57 append the new entry to the end of the file.
58
60 getutent(), getutid(), and getutline() return a pointer to a struct
61 utmp on success, and NULL on failure (which includes the "record not
62 found" case). This struct utmp is allocated in static storage, and may
63 be overwritten by subsequent calls.
64 On success pututline() returns ut; on failure, it returns NULL.
66 utmpname() returns 0 if the new name was successfully stored, or -1 on
68 failure.
69 In the event of an error, these functions errno set to indicate the
71 cause.
72
74 ENOMEM Out of memory.
75 ESRCH Record not found.
77 setutent(), pututline(), and the getut*() functions can also fail for
79 the reasons described in open(2).
80
82 /var/run/utmp
83 database of currently logged-in users
84 /var/log/wtmp
86 database of past user logins
87
89 For an explanation of the terms used in this section, see at‐
90 tributes(7).
91 ┌────────────┬───────────────┬──────────────────────────────┐
93 │Interface │ Attribute │ Value │
94 ├────────────┼───────────────┼──────────────────────────────┤
95 │getutent() │ Thread safety │ MT-Unsafe init race:utent │
96 │ │ │ race:utentbuf sig:ALRM timer │
97 ├────────────┼───────────────┼──────────────────────────────┤
98 │getutid(), │ Thread safety │ MT-Unsafe init race:utent │
99 │getutline() │ │ sig:ALRM timer │
100 ├────────────┼───────────────┼──────────────────────────────┤
101 │pututline() │ Thread safety │ MT-Unsafe race:utent │
102 │ │ │ sig:ALRM timer │
103 ├────────────┼───────────────┼──────────────────────────────┤
104 │setutent(), │ Thread safety │ MT-Unsafe race:utent │
105 │endutent(), │ │ │
106 │utmpname() │ │ │
107 └────────────┴───────────────┴──────────────────────────────┘
108 In the above table, utent in race:utent signifies that if any of the
109 functions setutent(), getutent(), getutid(), getutline(), pututline(),
110 utmpname(), or endutent() are used in parallel in different threads of
111 a program, then data races could occur.
112
114 XPG2, SVr4.
115 In XPG2 and SVID 2 the function pututline() is documented to return
117 void, and that is what it does on many systems (AIX, HP-UX). HP-UX in‐
118 troduces a new function _pututline() with the prototype given above for
119 pututline().
120 All these functions are obsolete now on non-Linux systems.
122 POSIX.1-2001 and POSIX.1-2008, following SUSv1, does not have any of
123 these functions, but instead uses
124 #include <utmpx.h>
126 struct utmpx *getutxent(void);
128 struct utmpx *getutxid(const struct utmpx *);
129 struct utmpx *getutxline(const struct utmpx *);
130 struct utmpx *pututxline(const struct utmpx *);
131 void setutxent(void);
132 void endutxent(void);
133 These functions are provided by glibc, and perform the same task as
135 their equivalents without the "x", but use struct utmpx, defined on
136 Linux to be the same as struct utmp. For completeness, glibc also pro‐
137 vides utmpxname(), although this function is not specified by POSIX.1.
138 On some other systems, the utmpx structure is a superset of the utmp
140 structure, with additional fields, and larger versions of the existing
141 fields, and parallel files are maintained, often /var/*/utmpx and
142 /var/*/wtmpx.
143 Linux glibc on the other hand does not use a parallel utmpx file since
145 its utmp structure is already large enough. The "x" functions listed
146 above are just aliases for their counterparts without the "x" (e.g.,
147 getutxent() is an alias for getutent()).
148
150 Glibc notes
151 The above functions are not thread-safe. Glibc adds reentrant versions
152 #include <utmp.h>
154 int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
156 int getutid_r(struct utmp *ut,
157 struct utmp *ubuf, struct utmp **ubufp);
158 int getutline_r(struct utmp *ut,
159 struct utmp *ubuf, struct utmp **ubufp);
160 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
162 getutent_r(), getutid_r(), getutline_r():
164 _GNU_SOURCE
165 || /* since glibc 2.19: */ _DEFAULT_SOURCE
166 || /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
167 These functions are GNU extensions, analogs of the functions of the
169 same name without the _r suffix. The ubuf argument gives these func‐
170 tions a place to store their result. On success, they return 0, and a
171 pointer to the result is written in *ubufp. On error, these functions
172 return -1. There are no utmpx equivalents of the above functions.
173 (POSIX.1 does not specify such functions.)
174
176 The following example adds and removes a utmp record, assuming it is
177 run from within a pseudo terminal. For usage in a real application,
178 you should check the return values of getpwuid(3) and ttyname(3).
179 #include <string.h>
181 #include <stdlib.h>
182 #include <pwd.h>
183 #include <unistd.h>
184 #include <utmp.h>
185 #include <time.h>
186 int
188 main(int argc, char *argv[])
189 {
190 struct utmp entry;
191 system("echo before adding entry:;who");
193 entry.ut_type = USER_PROCESS;
195 entry.ut_pid = getpid();
196 strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
197 /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
198 strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
199 time(&entry.ut_time);
200 strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
201 memset(entry.ut_host, 0, UT_HOSTSIZE);
202 entry.ut_addr = 0;
203 setutent();
204 pututline(&entry);
205 system("echo after adding entry:;who");
207 entry.ut_type = DEAD_PROCESS;
209 memset(entry.ut_line, 0, UT_LINESIZE);
210 entry.ut_time = 0;
211 memset(entry.ut_user, 0, UT_NAMESIZE);
212 setutent();
213 pututline(&entry);
214 system("echo after removing entry:;who");
216 endutent();
218 exit(EXIT_SUCCESS);
219 }
220
222 getutmp(3), utmp(5)
223
225 This page is part of release 5.10 of the Linux man-pages project. A
226 description of the project, information about reporting bugs, and the
227 latest version of this page, can be found at
228 https://www.kernel.org/doc/man-pages/.
229 2020-06-09 GETUTENT(3)