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

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  getutx-
       ent() 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 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.)

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)