getutline man page on ElementaryOS

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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 func‐
       tions.

       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.

       In  the	event  of  an error, these functions errno set to indicate the
       cause.

ERRORS
       ENOMEM Out of memory.

       ESRCH  Record not found.

       setutent(), pututline(), 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 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
       /var/*/wtmpx.

       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()).

NOTES
   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	 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)

COLOPHON
       This page is part of release 3.54 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/.

				  2013-04-19			   GETUTENT(3)
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