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           #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);


           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  INIT_PRO-
           CESS, 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.


           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


           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 proto-
           type 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 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
           #define _GNU_SOURCE    /* or _SVID_SOURCE or _BSD_SOURCE;
           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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