getutent(3)

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
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SYNOPSIS

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

24       New applications should use the POSIX.1-specified "utmpx"  versions  of
25       these functions; see CONFORMING TO.
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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
29       before the other functions are used, they assume _PATH_UTMP, as defined
30       in <paths.h>.
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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.
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36       endutent() closes the utmp file.  It should be  called  when  the  user
37       code is done accessing the file with the other functions.
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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).
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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.
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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.
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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.
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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.
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ERRORS

71       ENOMEM Out of memory.
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73       ESRCH  Record not found.
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75       setutent(),  pututent(),  and the getut* () functions can also fail for
76       the reasons described in open(2).
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FILES

79       /var/run/utmp  database of currently logged-in users
80       /var/log/wtmp  database of past user logins
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CONFORMING TO

83       XPG2, SVr4.
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85       In XPG2 and SVID 2 the function pututline()  is  documented  to  return
86       void,  and  that  is  what  it  does on many systems (AIX, HP-UX, Linux
87       libc5).  HP-UX introduces a new function _pututline() with  the  proto‐
88       type given above for pututline() (also found in Linux libc5).
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90       All   these   functions   are   obsolete   now  on  non-Linux  systems.
91       POSIX.1-2001, following SUSv1, does not have any  of  these  functions,
92       but instead uses
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94       #include <utmpx.h>
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96       struct utmpx *getutxent(void);
97       struct utmpx *getutxid(const struct utmpx *);
98       struct utmpx *getutxline(const struct utmpx *);
99       struct utmpx *pututxline(const struct utmpx *);
100       void setutxent(void);
101       void endutxent(void);
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103       These  functions  are  provided  by glibc, and perform the same task as
104       their equivalents without the "x", but use  struct  utmpx,  defined  on
105       Linux to be the same as struct utmp.  For completeness, glibc also pro‐
106       vides utmpxname(), although this function is not specified by POSIX.1.
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108       On some other systems, the utmpx structure is a superset  of  the  utmp
109       structure,  with additional fields, and larger versions of the existing
110       fields, and parallel  files  are  maintained,  often  /var/*/utmpx  and
111       /var/*/wtmpx.
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113       Linux  glibc on the other hand does not use a parallel utmpx file since
114       its utmp structure is already large enough.  The functions  getutxent()
115       etc. are aliases for getutent() etc.
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NOTES

118   Glibc Notes
119       The above functions are not thread-safe.  Glibc adds reentrant versions
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121       #define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE */
122       #include <utmp.h>
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124       int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
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126       int getutid_r(struct utmp *ut,
127                     struct utmp *ubuf, struct utmp **ubufp);
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129       int getutline_r(struct utmp *ut,
130                       struct utmp *ubuf, struct utmp **ubufp);
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132       These  functions  are  GNU  extensions, analogs of the functions of the
133       same name without the _r suffix.  The ubuf argument gives  these  func‐
134       tions  a  place to store their result.  On success they return 0, and a
135       pointer to the result is written in *ubufp.  On error  these  functions
136       return  -1.   There  are  no  utmpx equivalents of the above functions.
137       (POSIX.1 does not specify such functions.)
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EXAMPLE

140       The following example adds and removes a utmp record,  assuming  it  is
141       run  from  within  a pseudo terminal.  For usage in a real application,
142       you should check the return values of getpwuid(3) and ttyname(3).
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144       #include <string.h>
145       #include <stdlib.h>
146       #include <pwd.h>
147       #include <unistd.h>
148       #include <utmp.h>
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150       int
151       main(int argc, char *argv[])
152       {
153           struct utmp entry;
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155           system("echo before adding entry:;who");
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157           entry.ut_type = USER_PROCESS;
158           entry.ut_pid = getpid();
159           strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
160           /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
161           strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
162           time(&entry.ut_time);
163           strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
164           memset(entry.ut_host, 0, UT_HOSTSIZE);
165           entry.ut_addr = 0;
166           setutent();
167           pututline(&entry);
168
169           system("echo after adding entry:;who");
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171           entry.ut_type = DEAD_PROCESS;
172           memset(entry.ut_line, 0, UT_LINESIZE);
173           entry.ut_time = 0;
174           memset(entry.ut_user, 0, UT_NAMESIZE);
175           setutent();
176           pututline(&entry);
177
178           system("echo after removing entry:;who");
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180           endutent();
181           exit(EXIT_SUCCESS);
182       }
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COLOPHON

188       This page is part of release 3.25 of the Linux  man-pages  project.   A
189       description  of  the project, and information about reporting bugs, can
190       be found at http://www.kernel.org/doc/man-pages/.
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194                                  2008-06-29                       GETUTENT(3)