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



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

NAME
       getpwuid, getpwuid_r - search user database for a user ID

SYNOPSIS
       #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);


DESCRIPTION
       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 reentrant is not required
       to be thread-safe.

       Applications wishing to check for error situations should set errno to 0 before calling  getpwuid().  If  getp-
       wuid() 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. 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 location pointed to by
       result on error or if the requested entry is not found.

RETURN VALUE
       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(),  getpw-
       nam(), or getpwuid().

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

ERRORS
       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.

EXAMPLES
   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 struc-
       ture 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);
              else
                  printf(" %-8d", statbuf.st_uid);

APPLICATION USAGE
       Three names associated with the current process can be determined: getpwuid( geteuid()) returns the name  asso-
       ciated 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.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

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

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, the original IEEE and The Open Group Standard is the referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                         GETPWUID(3P)