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



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

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. If the requested entry was not found, errno shall not
       be changed. 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().  The returned pointer, and pointers within the structure,
       might also be invalidated if the calling thread is terminated.

       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.1-2017, <pwd.h>, <sys_types.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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 .



IEEE/The Open Group                  2017                          GETPWUID(3)
