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NAME

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

SYNOPSIS

       #include <utmp.h>

       struct utmp *getutent(void);
       struct utmp *getutid(struct utmp *ut);
       struct utmp *getutline(struct utmp *ut);

       struct utmp *pututline(struct utmp *ut);

       void setutent(void);
       void endutent(void);

       int utmpname(const char *file);

DESCRIPTION

       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
       functions.

       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
       INIT_PROCESS,  LOGIN_PROCESS,  USER_PROCESS, or DEAD_PROCESS, getutid()
       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.

RETURN VALUE

       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
       failure.

ERRORS

       ENOMEM Out of memory.

       ESRCH  Record not found.

       setutent(),  pututent(),  and the getut* () functions can also fail for
       the reasons described in open(2).

FILES

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

CONFORMING TO

       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, Linux
       libc5).   HP-UX  introduces  a  new  function  _pututline()  with   the
       prototype given above for pututline() (also found in Linux libc5).

       All   these   functions   are   obsolete   now  on  non-Linux  systems.
       POSIX.1-2001, 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
       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
       /var/*/wtmpx.

       Linux glibc on the other hand does not use a parallel utmpx file  since
       its  utmp structure is already large enough.  The functions getutxent()
       etc. are aliases for getutent() etc.

NOTES

   Glibc Notes
       The above functions are not thread-safe.  Glibc adds reentrant versions

       #define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE */
       #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.)

EXAMPLE

       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"));
           time(&entry.ut_time);
           strcpy(entry.ut_user, getpwuid(getuid())->pw_name);
           memset(entry.ut_host, 0, UT_HOSTSIZE);
           entry.ut_addr = 0;
           setutent();
           pututline(&entry);

           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);
           setutent();
           pututline(&entry);

           system("echo after removing entry:;who");

           endutent();
           exit(EXIT_SUCCESS);
       }

SEE ALSO

       getutmp(3), utmp(5), feature_test_macros(7)

COLOPHON

       This  page  is  part of release 3.27 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

                                  2008-06-29                       GETUTENT(3)