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GETPWUID(3P)		   POSIX Programmer's Manual		  GETPWUID(3P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       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 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 occurred.

       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 contain an entry from the user database
       with a matching uid.  Storage referenced by the structure is  allocated
       from  the  memory  provided with the buffer parameter, which is bufsize
       bytes in size. A call to sysconf(_SC_GETPW_R_SIZE_MAX)  returns	either
       −1 without changing errno or an initial value suggested for the size of
       this buffer.  A null pointer shall be returned at the location  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 application shall not modify the  structure	to  which  the	return
       value  points,  nor any storage areas pointed to by pointers within the
       structure. The returned pointer, and  pointers  within  the  structure,
       might  be  invalidated  or  the structure or the storage areas might be
       overwritten by a subsequent call to getpwent(),	getpwnam(),  or	 getp‐

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

       These functions may fail if:

       EIO    An I/O error has occurred.

       EINTR  A signal was caught during getpwuid().

       EMFILE All file descriptors available  to  the  process	are  currently

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

       The getpwuid_r() function may fail if:

       ERANGE Insufficient storage was supplied via buffer and bufsize to con‐
	      tain  the	 data  to be referenced by the resulting passwd struc‐

       The following sections are informative.

       Note that sysconf(_SC_GETPW_R_SIZE_MAX) may return −1 if	 there	is  no
       hard  limit  on	the  size of the buffer needed to store all the groups
       returned. This example shows how an application can allocate  a	buffer
       of sufficient size to work with getpwuid_r().

	   long int initlen = sysconf(_SC_GETPW_R_SIZE_MAX);
	   size_t len;
	   if (initlen == −1)
	       /* Default initial length. */
	       len = 1024;
	       len = (size_t) initlen;
	   struct passwd result;
	   struct passwd *resultp;
	   char *buffer = malloc(len);
	   if (buffer == NULL)
	       ...handle error...
	   int e;
	   while ((e = getpwuid_r(42, &result, buffer, len, &resultp)) == ERANGE)
	       size_t newlen = 2 * len;
	       if (newlen < len)
		   ...handle error...
	       len = newlen;
	       char *newbuffer = realloc(buffer, len);
	       if (newbuffer == NULL)
		   ...handle error...
	       buffer = newbuffer;
	   if (e != 0)
	       ...handle error...
	   free (buffer);

   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: get‐
       pwuid(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.

       Portable applications should take into account that it is usual for  an
       implementation  to return −1 from sysconf() indicating that there is no
       maximum for _SC_GETPW_R_SIZE_MAX.



       getpwnam(), geteuid(), getuid(), getlogin(), sysconf()

       The Base Definitions volume of POSIX.1‐2008, <pwd.h>, <sys_types.h>

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 original Standard can be  obtained	online
       at .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013			  GETPWUID(3P)

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