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 differ (consult the correspond-
       ing 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 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 allo-
       cated  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(), getpwnam(), 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 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);
	      else
		  printf(" %-8d", statbuf.st_uid);

APPLICATION USAGE

       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 associ-
       ated 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, Standard for Information Technol-
       ogy -- 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 original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							      GETPWUID(3P)