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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

       getgrgid, getgrgid_r — get group database entry for a group ID

SYNOPSIS

       #include <grp.h>

       struct group *getgrgid(gid_t gid);
       int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
           size_t bufsize, struct group **result);

DESCRIPTION

       The getgrgid() function shall search the group database for an entry with a matching gid.

       The getgrgid() function need not be thread-safe.

       The  getgrgid_r()  function shall update the group structure pointed to by grp and store a
       pointer to that structure at the location pointed  to  by  result.   The  structure  shall
       contain  an  entry from the group database with a matching gid.  Storage referenced by the
       group structure is allocated from the memory provided with the buffer parameter, which  is
       bufsize  bytes  in size. A call to sysconf(_SC_GETGR_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

       Upon successful completion, getgrgid() shall return a pointer to a struct group  with  the
       structure  defined  in  <grp.h>  with  a  matching  entry  if one is found. The getgrgid()
       function shall return a null pointer if either the requested entry was not  found,  or  an
       error occurred. 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 getgrent(), getgrgid(), or getgrnam().

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

ERRORS

       The getgrgid() and getgrgid_r() functions may fail if:

       EIO    An I/O error has occurred.

       EINTR  A signal was caught during getgrgid().

       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 getgrgid_r() function may fail if:

       ERANGE Insufficient  storage was supplied via buffer and bufsize to contain the data to be
              referenced by the resulting group structure.

       The following sections are informative.

EXAMPLES

       Note that sysconf(_SC_GETGR_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 getgrid_r().

           long int initlen = sysconf(_SC_GETGR_R_SIZE_MAX);
           size_t len;
           if (initlen == −1)
               /* Default initial length. */
               len = 1024;
           else
               len = (size_t) initlen;
           struct group result;
           struct group *resultp;
           char *buffer = malloc(len);
           if (buffer == NULL)
               ...handle error...
           int e;
           while ((e = getgrgid_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);

   Finding an Entry in the Group Database
       The following example uses getgrgid() to search the group database for a group ID that was
       previously  stored  in a stat structure, then prints out the group name if it is found. If
       the group is not found, the program prints the numeric value of the group for the entry.

           #include <sys/types.h>
           #include <grp.h>
           #include <stdio.h>
           ...
           struct stat statbuf;
           struct group *grp;
           ...
           if ((grp = getgrgid(statbuf.st_gid)) != NULL)
               printf(" %-8.8s", grp->gr_name);
           else
               printf(" %-8d", statbuf.st_gid);
           ...

APPLICATION USAGE

       Applications wishing to check for error situations should set errno to  0  before  calling
       getgrgid().  If errno is set on return, an error occurred.

       The getgrgid_r() function is thread-safe and shall return 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_GETGR_R_SIZE_MAX.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       endgrent(), getgrnam(), sysconf()

       The Base Definitions volume of POSIX.1‐2008, <grp.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 .