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PROLOG

       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.

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 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.

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  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 getpwuid().

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

ERRORS

       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 open.

       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

       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;
           else
               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);
           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 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.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

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

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

COPYRIGHT

       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 Electrical 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 http://www.unix.org/online.html .

       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.kernel.org/doc/man-pages/reporting_bugs.html .