1GETUTENT(3)                Linux Programmer's Manual               GETUTENT(3)
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NAME

6       getutent, getutid, getutline, pututline, setutent, endutent, utmpname -
7       access utmp file entries
8

SYNOPSIS

10       #include <utmp.h>
11
12       struct utmp *getutent(void);
13       struct utmp *getutid(const struct utmp *ut);
14       struct utmp *getutline(const struct utmp *ut);
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16       struct utmp *pututline(const struct utmp *ut);
17
18       void setutent(void);
19       void endutent(void);
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21       int utmpname(const char *file);
22

DESCRIPTION

24       New applications should use the POSIX.1-specified "utmpx"  versions  of
25       these functions; see CONFORMING TO.
26
27       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
32       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
36       endutent() closes the utmp file.  It should be  called  when  the  user
37       code is done accessing the file with the other functions.
38
39       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
43       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
50       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
54       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

RETURN VALUE

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.
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65       On success pututline() returns ut; on failure, it returns NULL.
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67       utmpname() returns 0 if the new name was successfully stored, or -1  on
68       failure.
69
70       In  the  event  of  an error, these functions errno set to indicate the
71       cause.
72

ERRORS

74       ENOMEM Out of memory.
75
76       ESRCH  Record not found.
77
78       setutent(), pututline(), and the getut*() functions can also  fail  for
79       the reasons described in open(2).
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FILES

82       /var/run/utmp
83              database of currently logged-in users
84
85       /var/log/wtmp
86              database of past user logins
87

ATTRIBUTES

89       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
90       tributes(7).
91
92       ┌────────────┬───────────────┬──────────────────────────────┐
93Interface   Attribute     Value                        
94       ├────────────┼───────────────┼──────────────────────────────┤
95getutent()  │ Thread safety │ MT-Unsafe init race:utent    │
96       │            │               │ race:utentbuf sig:ALRM timer │
97       ├────────────┼───────────────┼──────────────────────────────┤
98getutid(),  │ Thread safety │ MT-Unsafe init race:utent    │
99getutline() │               │ sig:ALRM timer               │
100       ├────────────┼───────────────┼──────────────────────────────┤
101pututline() │ Thread safety │ MT-Unsafe race:utent         │
102       │            │               │ sig:ALRM timer               │
103       ├────────────┼───────────────┼──────────────────────────────┤
104setutent(), │ Thread safety │ MT-Unsafe race:utent         │
105endutent(), │               │                              │
106utmpname()  │               │                              │
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

CONFORMING TO

114       XPG2, SVr4.
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116       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
121       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
125           #include <utmpx.h>
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127           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
134       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
139       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
144       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

NOTES

150   Glibc notes
151       The above functions are not thread-safe.  Glibc adds reentrant versions
152
153       #include <utmp.h>
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155       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
161       Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
162
163       getutent_r(), getutid_r(), getutline_r():
164           _GNU_SOURCE
165           || /* since glibc 2.19: */ _DEFAULT_SOURCE
166           || /* glibc <= 2.19: */    _SVID_SOURCE || _BSD_SOURCE
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168       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

EXAMPLES

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
180       #include <string.h>
181       #include <stdlib.h>
182       #include <pwd.h>
183       #include <unistd.h>
184       #include <utmp.h>
185       #include <time.h>
186
187       int
188       main(int argc, char *argv[])
189       {
190           struct utmp entry;
191
192           system("echo before adding entry:;who");
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194           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
206           system("echo after adding entry:;who");
207
208           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
215           system("echo after removing entry:;who");
216
217           endutent();
218           exit(EXIT_SUCCESS);
219       }
220

SEE ALSO

222       getutmp(3), utmp(5)
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COLOPHON

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/.
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232                                  2020-06-09                       GETUTENT(3)
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