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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
     allbox; lb lb lbw28 l l  l.   Interface Attribute Value  T{  getutent()
     T}   Thread safety    T{ MT-Unsafe init race:utent
     race:utentbuf sig:ALRM timer T} T{ getutid(),
     getutline() T}   Thread safety  T{ MT-Unsafe init race:utent
     sig:ALRM  timer  T}  T{  pututline()  T}   Thread  safety  T{ MT-Unsafe
     sig:ALRM timer T} T{ setutent(),
     utmpname() T}   Thread safety  MT-Unsafe race:utent
     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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