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Linux 2.6 - man page for getpwuid_r (linux section 3posix)

GETPWUID(P)			    POSIX Programmer's Manual			      GETPWUID(P)

       getpwuid, getpwuid_r - search user database for a user ID

       #include <pwd.h>

       struct passwd *getpwuid(uid_t uid);

       int getpwuid_r(uid_t uid, struct passwd *pwd, char *buffer,
	      size_t bufsize, struct passwd **result);

       The getpwuid() function shall search the user database for an entry with a matching uid.

       The getpwuid() function need not be reentrant. A function that is not required to be reen-
       trant is not required to be thread-safe.

       Applications wishing to check for error situations should set errno to  0  before  calling
       getpwuid().  If	getpwuid()  returns a null pointer and errno is set to non-zero, an error

       The getpwuid_r() function shall update the passwd structure pointed to by pwd and store	a
       pointer	to  that structure at the location pointed to by result. The structure shall con-
       tain an entry from the user database with a matching uid. Storage referenced by the struc-
       ture  is  allocated  from  the memory provided with the buffer parameter, which is bufsize
       bytes in size. The maximum size	needed	for  this  buffer  can	be  determined	with  the
       {_SC_GETPW_R_SIZE_MAX}  sysconf() parameter. A NULL pointer shall be returned at the loca-
       tion pointed to by result on error or if the requested entry is not found.

       The getpwuid() function shall return a pointer to a struct passwd with  the  structure  as
       defined in <pwd.h> with a matching entry if found. A null pointer shall be returned if the
       requested entry is not found, or an error occurs. On error, errno shall be set to indicate
       the error.

       The  return  value may point to a static area which is overwritten by a subsequent call to
       getpwent(), getpwnam(), or getpwuid().

       If successful, the getpwuid_r() function shall return zero;  otherwise,	an  error  number
       shall be returned to indicate the error.

       The getpwuid() and getpwuid_r() functions may fail if:

       EIO    An I/O error has occurred.

       EINTR  A signal was caught during getpwuid().

       EMFILE {OPEN_MAX} file descriptors are currently open in the calling process.

       ENFILE The maximum allowable number of files is currently open in the system.

       The getpwuid_r() function may fail if:

       ERANGE Insufficient  storage was supplied via buffer and bufsize to contain the data to be
	      referenced by the resulting passwd structure.

       The following sections are informative.

   Getting an Entry for the Root User
       The following example gets the user database entry for the user with user ID 0 (root).

	      #include <sys/types.h>
	      #include <pwd.h>
	      uid_t id = 0;
	      struct passwd *pwd;

	      pwd = getpwuid(id);

   Finding the Name for the Effective User ID
       The following example defines pws as a pointer to a structure of  type  passwd,	which  is
       used  to  store the structure pointer returned by the call to the getpwuid() function. The
       geteuid() function shall return the effective user ID of the calling process; this is used
       as  the search criteria for the getpwuid() function. The call to getpwuid() shall return a
       pointer to the structure containing that user ID value.

	      #include <unistd.h>
	      #include <sys/types.h>
	      #include <pwd.h>
	      struct passwd *pws;
	      pws = getpwuid(geteuid());

   Finding an Entry in the User Database
       The following example uses getpwuid() to search the user database for a user ID	that  was
       previously  stored  in a stat structure, then prints out the user name if it is found.  If
       the user is not found, the program prints the numeric value of the user ID for the entry.

	      #include <sys/types.h>
	      #include <pwd.h>
	      #include <stdio.h>
	      struct stat statbuf;
	      struct passwd *pwd;
	      if ((pwd = getpwuid(statbuf.st_uid)) != NULL)
		  printf(" %-8.8s", pwd->pw_name);
		  printf(" %-8d", statbuf.st_uid);

       Three names associated with the current process can be  determined:  getpwuid(  geteuid())
       returns	the name associated with the effective user ID of the process; getlogin() returns
       the name associated with the current login activity; and getpwuid( getuid())  returns  the
       name associated with the real user ID of the process.

       The  getpwuid_r()  function  is	thread-safe  and returns values in a user-supplied buffer
       instead of possibly using a static data area that may be overwritten by each call.



       getpwnam() ,  geteuid()	,  getuid()  ,	getlogin()  ,  the  Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <limits.h>, <pwd.h>, <sys/types.h>

       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				      GETPWUID(P)

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