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(struct utmp *ut);
14 struct utmp *getutline(struct utmp *ut);
15 struct utmp *pututline(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
29 before 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 database of currently logged-in users
83 /var/log/wtmp database of past user logins
84
86 XPG2, SVr4.
87 In XPG2 and SVID 2 the function pututline() is documented to return
89 void, and that is what it does on many systems (AIX, HP-UX, Linux
90 libc5). HP-UX introduces a new function _pututline() with the proto‐
91 type given above for pututline() (also found in Linux libc5).
92 All these functions are obsolete now on non-Linux systems.
94 POSIX.1-2001, following SUSv1, does not have any of these functions,
95 but instead uses
96 #include <utmpx.h>
98 struct utmpx *getutxent(void);
100 struct utmpx *getutxid(const struct utmpx *);
101 struct utmpx *getutxline(const struct utmpx *);
102 struct utmpx *pututxline(const struct utmpx *);
103 void setutxent(void);
104 void endutxent(void);
105 These functions are provided by glibc, and perform the same task as
107 their equivalents without the "x", but use struct utmpx, defined on
108 Linux to be the same as struct utmp. For completeness, glibc also pro‐
109 vides utmpxname(), although this function is not specified by POSIX.1.
110 On some other systems, the utmpx structure is a superset of the utmp
112 structure, with additional fields, and larger versions of the existing
113 fields, and parallel files are maintained, often /var/*/utmpx and
114 /var/*/wtmpx.
115 Linux glibc on the other hand does not use a parallel utmpx file since
117 its utmp structure is already large enough. The "x" functions listed
118 above are just aliases for their counterparts without the "x" (e.g.,
119 getutxent() is an alias for getutent()).
120
122 Glibc notes
123 The above functions are not thread-safe. Glibc adds reentrant versions
124 #define _GNU_SOURCE /* or _SVID_SOURCE or _BSD_SOURCE;
126 see feature_test_macros(7) */
127 #include <utmp.h>
128 int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
130 int getutid_r(struct utmp *ut,
132 struct utmp *ubuf, struct utmp **ubufp);
133 int getutline_r(struct utmp *ut,
135 struct utmp *ubuf, struct utmp **ubufp);
136 These functions are GNU extensions, analogs of the functions of the
138 same name without the _r suffix. The ubuf argument gives these func‐
139 tions a place to store their result. On success they return 0, and a
140 pointer to the result is written in *ubufp. On error these functions
141 return -1. There are no utmpx equivalents of the above functions.
142 (POSIX.1 does not specify such functions.)
143
145 The following example adds and removes a utmp record, assuming it is
146 run from within a pseudo terminal. For usage in a real application,
147 you should check the return values of getpwuid(3) and ttyname(3).
148 #include <string.h>
150 #include <stdlib.h>
151 #include <pwd.h>
152 #include <unistd.h>
153 #include <utmp.h>
154 int
156 main(int argc, char *argv[])
157 {
158 struct utmp entry;
159 system("echo before adding entry:;who");
161 entry.ut_type = USER_PROCESS;
163 entry.ut_pid = getpid();
164 strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
165 /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
166 strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
167 time(&entry.ut_time);
168 strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
169 memset(entry.ut_host, 0, UT_HOSTSIZE);
170 entry.ut_addr = 0;
171 setutent();
172 pututline(&entry);
173 system("echo after adding entry:;who");
175 entry.ut_type = DEAD_PROCESS;
177 memset(entry.ut_line, 0, UT_LINESIZE);
178 entry.ut_time = 0;
179 memset(entry.ut_user, 0, UT_NAMESIZE);
180 setutent();
181 pututline(&entry);
182 system("echo after removing entry:;who");
184 endutent();
186 exit(EXIT_SUCCESS);
187 }
188
190 getutmp(3), utmp(5)
191
193 This page is part of release 3.53 of the Linux man-pages project. A
194 description of the project, and information about reporting bugs, can
195 be found at http://www.kernel.org/doc/man-pages/.
196 2013-04-19 GETUTENT(3)