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


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


     #include <utmp.h>
     struct utmp *getutent(void);
     struct utmp *getutid(const struct utmp *ut);
     struct utmp *getutline(const struct utmp *ut);
     struct utmp *pututline(const struct utmp *ut);
     void setutent(void);
     void endutent(void);
     int utmpname(const char *file);


     New applications should use the POSIX.1-specified "utmpx"  versions  of
     these functions; see CONFORMING TO.
     utmpname()  sets  the  name  of the utmp-format file for the other utmp
     functions to access.  If utmpname() is not used  to  set  the  filename
     before the other functions are used, they assume _PATH_UTMP, as defined
     in <paths.h>.
     setutent() rewinds the file pointer to the beginning of the utmp  file.
     It  is  generally  a good idea to call it before any of the other func-
     endutent() closes the utmp file.  It should be  called  when  the  user
     code is done accessing the file with the other functions.
     getutent()  reads  a  line  from  the current file position in the utmp
     file.  It returns a pointer to a structure containing the fields of the
     line.  The definition of this structure is shown in utmp(5).
     getutid()  searches  forward from the current file position in the utmp
     file based upon ut.  If  ut->ut_type  is  one  of  RUN_LVL,  BOOT_TIME,
     NEW_TIME,  or  OLD_TIME,  getutid()  will  find  the  first entry whose
     ut_type  field  matches  ut->ut_type.   If  ut->ut_type   is   one   of
     will find the first entry whose ut_id field matches ut->ut_id.
     getutline() searches forward from the current file position in the utmp
     file.   It scans entries whose ut_type is USER_PROCESS or LOGIN_PROCESS
     and returns the first one whose ut_line field matches ut->ut_line.
     pututline() writes the utmp structure ut into the utmp file.   It  uses
     getutid()  to search for the proper place in the file to insert the new
     entry.  If it cannot find an appropriate slot for ut, pututline()  will
     append the new entry to the end of the file.


     getutent(),  getutid(),  and  getutline()  return a pointer to a struct
     utmp on success, and NULL on failure (which includes  the  "record  not
     found" case).  This struct utmp is allocated in static storage, and may
     be overwritten by subsequent calls.
     On success pututline() returns ut; on failure, it returns NULL.
     utmpname() returns 0 if the new name was successfully stored, or -1  on
     In  the  event  of  an error, these functions errno set to indicate the


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


            database of currently logged-in users
            database of past user logins


     For   an   explanation   of   the  terms  used  in  this  section,  see
     |Interface   | Attribute     | Value                        |
     |getutent()  | Thread safety | MT-Unsafe init race:utent    |
     |            |               | race:utentbuf sig:ALRM timer |
     |getutid(),  | Thread safety | MT-Unsafe init race:utent    |
     |getutline() |               | sig:ALRM timer               |
     |pututline() | Thread safety | MT-Unsafe race:utent         |
     |            |               | sig:ALRM timer               |
     |setutent(), | Thread safety | MT-Unsafe race:utent         |
     |endutent(), |               |                              |
     |utmpname()  |               |                              |
     In  the  above  table, utent in race:utent signifies that if any of the
     functions setutent(), getutent(), getutid(), getutline(),  pututline(),
     utmpname(),  or endutent() are used in parallel in different threads of
     a program, then data races could occur.


     XPG2, SVr4.
     In XPG2 and SVID 2 the function pututline()  is  documented  to  return
     void,  and  that  is  what it does on many systems (AIX, HP-UX).  HP-UX
     introduces a new function _pututline() with the prototype  given  above
     for pututline().
     All   these   functions   are   obsolete   now  on  non-Linux  systems.
     POSIX.1-2001 and POSIX.1-2008, following SUSv1, does not  have  any  of
     these functions, but instead uses
         #include <utmpx.h>
     struct  utmpx  *getutxent(void);  struct  utmpx  *getutxid(const struct
     utmpx *); struct utmpx *getutxline(const struct utmpx *); struct  utmpx
     *pututxline(const  struct  utmpx *); void setutxent(void); void endutx-
     These functions are provided by glibc, and perform  the  same  task  as
     their  equivalents  without  the  "x", but use struct utmpx, defined on
     Linux to be the same as struct utmp.  For completeness, glibc also pro-
     vides  utmpxname(), although this function is not specified by POSIX.1.
     On some other systems, the utmpx structure is a superset  of  the  utmp
     structure,  with additional fields, and larger versions of the existing
     fields, and parallel  files  are  maintained,  often  /var/*/utmpx  and
     Linux  glibc on the other hand does not use a parallel utmpx file since
     its utmp structure is already large enough.  The "x"  functions  listed
     above  are  just  aliases for their counterparts without the "x" (e.g.,
     getutxent() is an alias for getutent()).


 Glibc notes
     The above functions are not thread-safe.  Glibc adds reentrant versions
         #include <utmp.h>
     int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
     int  getutid_r(struct utmp *ut,               struct utmp *ubuf, struct
     utmp **ubufp);
     int getutline_r(struct utmp *ut,                   struct  utmp  *ubuf,
     struct utmp **ubufp);
     Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     getutent_r(), getutid_r(), getutline_r():
         || /* since glibc 2.19: */ _DEFAULT_SOURCE
         || /* glibc <= 2.19: */    _SVID_SOURCE || _BSD_SOURCE
     These functions are GNU extensions, analogs of  the  functions  of  the
     same  name  without the _r suffix.  The ubuf argument gives these func-
     tions a place to store their result.  On success, they return 0, and  a
     pointer  to the result is written in *ubufp.  On error, these functions
     return -1.  There are no utmpx  equivalents  of  the  above  functions.
     (POSIX.1 does not specify such functions.)


     The  following  example  adds and removes a utmp record, assuming it is
     run from within a pseudo terminal.  For usage in  a  real  application,
     you should check the return values of getpwuid(3) and ttyname(3).
     #include  <string.h>  #include  <stdlib.h>  #include  <pwd.h>  #include
     <unistd.h> #include <utmp.h>
     int main(int argc, char *argv[]) {
         struct utmp entry;
         system("echo before adding entry:;who");
         entry.ut_type = USER_PROCESS;
         entry.ut_pid = getpid();
         strcpy(entry.ut_line, ttyname(STDIN_FILENO) + strlen("/dev/"));
         /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
         strcpy(entry.ut_id, ttyname(STDIN_FILENO) + strlen("/dev/tty"));
         strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
         memset(entry.ut_host, 0, UT_HOSTSIZE);
         entry.ut_addr = 0;
         system("echo after adding entry:;who");
         entry.ut_type = DEAD_PROCESS;
         memset(entry.ut_line, 0, UT_LINESIZE);
         entry.ut_time = 0;
         memset(entry.ut_user, 0, UT_NAMESIZE);
         system("echo after removing entry:;who");
         exit(EXIT_SUCCESS); }


     getutmp(3), utmp(5)


     This page is part of release 4.16 of the Linux  man-pages  project.   A
     description  of  the project, information about reporting bugs, and the
     latest    version    of    this    page,    can     be     found     at
                                2017-09-15                       GETUTENT(3)
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