1GETUTENT(3) Linux Programmer's Manual GETUTENT(3)
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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
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
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
90 attributes(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.
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114 XPG2, SVr4.
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