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       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

       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).


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


       For   an   explanation   of   the  terms  used  in  this  section,  see

       │InterfaceAttributeValue                        │
       │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(3),    getutent(3),   getutid(3),   getutline(3),
       pututline(3), utmpname(3), or  endutent(3)  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 endutxent(void);

       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
       provides  utmpxname(),  although  this  function  is  not  specified by

       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

       #define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE;
                                 see feature_test_macros(7) */
       #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);

       These functions are GNU extensions, analogs of  the  functions  of  the
       same  name  without  the  _r  suffix.   The  ubuf  argument gives these
       functions 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>

       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");



       getutmp(3), utmp(5)


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                                  2015-08-08                       GETUTENT(3)