getutxent man page on CentOS

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GETUTENT(3)		       Library functions		   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);

       void utmpname(const char *file);

DESCRIPTION
       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.

       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(), getutline() and pututline() return a pointer  to
       a  struct  utmp	on  success, and NULL on failure.  This struct utmp is
       allocated in static storage,  and  may  be  overwritten	by  subsequent
       calls.

REENTRANT VERSIONS
       These  above  functions	are not thread-safe. Glibc adds reentrant ver‐
       sions

       #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 parameter 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.

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() and ttyname().

       #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(0)+strlen("/dev/"));
	 /* only correct for ptys named /dev/tty[pqr][0-9a-z] */
	 strcpy(entry.ut_id,ttyname(0)+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();
	 return 0;
       }

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);

       The  utmpx  structure  is  a superset of the utmp structure, with addi‐
       tional fields, and larger versions of the existing fields.  The	corre‐
       sponding files are often /var/*/utmpx and /var/*/wtmpx.

       Linux  glibc on the other hand does not use utmpx since its utmp struc‐
       ture is already large enough. The functions getutxent etc. are  aliases
       for getutent etc.

SEE ALSO
       utmp(5)

				  1996-07-25			   GETUTENT(3)
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