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 On failure, these functions errno set to indicate the error.
71
73 ENOMEM Out of memory.
74 ESRCH Record not found.
76 setutent(), pututline(), and the getut*() functions can also fail for
78 the reasons described in open(2).
79
81 /var/run/utmp
82 database of currently logged-in users
83 /var/log/wtmp
85 database of past user logins
86
88 For an explanation of the terms used in this section, see at‐
89 tributes(7).
90 ┌────────────┬───────────────┬─────────────────────────────────────────┐
92 │Interface │ Attribute │ Value │
93 ├────────────┼───────────────┼─────────────────────────────────────────┤
94 │getutent() │ Thread safety │ MT-Unsafe init race:utent race:utentbuf │
95 │ │ │ sig:ALRM timer │
96 ├────────────┼───────────────┼─────────────────────────────────────────┤
97 │getutid(), │ Thread safety │ MT-Unsafe init race:utent sig:ALRM │
98 │getutline() │ │ timer │
99 ├────────────┼───────────────┼─────────────────────────────────────────┤
100 │pututline() │ Thread safety │ MT-Unsafe race:utent sig:ALRM timer │
101 ├────────────┼───────────────┼─────────────────────────────────────────┤
102 │setutent(), │ Thread safety │ MT-Unsafe race:utent │
103 │endutent(), │ │ │
104 │utmpname() │ │ │
105 └────────────┴───────────────┴─────────────────────────────────────────┘
106 In the above table, utent in race:utent signifies that if any of the
107 functions setutent(), getutent(), getutid(), getutline(), pututline(),
108 utmpname(), or endutent() are used in parallel in different threads of
109 a program, then data races could occur.
110
112 XPG2, SVr4.
113 In XPG2 and SVID 2 the function pututline() is documented to return
115 void, and that is what it does on many systems (AIX, HP-UX). HP-UX in‐
116 troduces a new function _pututline() with the prototype given above for
117 pututline().
118 All these functions are obsolete now on non-Linux systems.
120 POSIX.1-2001 and POSIX.1-2008, following SUSv1, does not have any of
121 these functions, but instead uses
122 #include <utmpx.h>
124 struct utmpx *getutxent(void);
126 struct utmpx *getutxid(const struct utmpx *);
127 struct utmpx *getutxline(const struct utmpx *);
128 struct utmpx *pututxline(const struct utmpx *);
129 void setutxent(void);
130 void endutxent(void);
131 These functions are provided by glibc, and perform the same task as
133 their equivalents without the "x", but use struct utmpx, defined on
134 Linux to be the same as struct utmp. For completeness, glibc also pro‐
135 vides utmpxname(), although this function is not specified by POSIX.1.
136 On some other systems, the utmpx structure is a superset of the utmp
138 structure, with additional fields, and larger versions of the existing
139 fields, and parallel files are maintained, often /var/*/utmpx and
140 /var/*/wtmpx.
141 Linux glibc on the other hand does not use a parallel utmpx file since
143 its utmp structure is already large enough. The "x" functions listed
144 above are just aliases for their counterparts without the "x" (e.g.,
145 getutxent() is an alias for getutent()).
146
148 Glibc notes
149 The above functions are not thread-safe. Glibc adds reentrant versions
150 #include <utmp.h>
152 int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
154 int getutid_r(struct utmp *ut,
155 struct utmp *ubuf, struct utmp **ubufp);
156 int getutline_r(struct utmp *ut,
157 struct utmp *ubuf, struct utmp **ubufp);
158 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
160 getutent_r(), getutid_r(), getutline_r():
162 _GNU_SOURCE
163 || /* Since glibc 2.19: */ _DEFAULT_SOURCE
164 || /* Glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
165 These functions are GNU extensions, analogs of the functions of the
167 same name without the _r suffix. The ubuf argument gives these func‐
168 tions a place to store their result. On success, they return 0, and a
169 pointer to the result is written in *ubufp. On error, these functions
170 return -1. There are no utmpx equivalents of the above functions.
171 (POSIX.1 does not specify such functions.)
172
174 The following example adds and removes a utmp record, assuming it is
175 run from within a pseudo terminal. For usage in a real application,
176 you should check the return values of getpwuid(3) and ttyname(3).
177 #include <string.h>
179 #include <stdlib.h>
180 #include <pwd.h>
181 #include <unistd.h>
182 #include <utmp.h>
183 #include <time.h>
184 int
186 main(int argc, char *argv[])
187 {
188 struct utmp entry;
189 system("echo before adding entry:;who");
191 entry.ut_type = USER_PROCESS;
193 entry.ut_pid = getpid();
194 strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
195 /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
196 strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
197 time(&entry.ut_time);
198 strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
199 memset(entry.ut_host, 0, UT_HOSTSIZE);
200 entry.ut_addr = 0;
201 setutent();
202 pututline(&entry);
203 system("echo after adding entry:;who");
205 entry.ut_type = DEAD_PROCESS;
207 memset(entry.ut_line, 0, UT_LINESIZE);
208 entry.ut_time = 0;
209 memset(entry.ut_user, 0, UT_NAMESIZE);
210 setutent();
211 pututline(&entry);
212 system("echo after removing entry:;who");
214 endutent();
216 exit(EXIT_SUCCESS);
217 }
218
220 getutmp(3), utmp(5)
221
223 This page is part of release 5.12 of the Linux man-pages project. A
224 description of the project, information about reporting bugs, and the
225 latest version of this page, can be found at
226 https://www.kernel.org/doc/man-pages/.
227 2021-03-22 GETUTENT(3)