This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       The getgrnam_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.

       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                                      GETGRNAM(3POSIX)

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

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

       Applications  wishing  to check for error situations should set errno to 0 before calling getgrnam().  If
       getgrnam() returns a null pointer and errno is set to non-zero, an error occurred.

       The getgrnam_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 name.  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 is returned at the location pointed to by result on error or if
       the requested entry is not found.

       The getgrnam() and getgrnam_r() functions may fail if:

       EIO    An I/O error has occurred.

       EINTR  A signal was caught during getgrnam().

       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 getgrnam_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.

       Thefollowingsectionsareinformative.

       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 getgrnam_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 = getgrnam_r("somegroup", &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);

       None.

       getgrnam, getgrnam_r — search group database for a name

       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.

       None.

       The getgrnam() function shall return a pointer to a structgroup with the structure  defined  in  <grp.h>
       with  a matching entry if one is found. The getgrnam() function shall return a null pointer if either the
       requested entry was not found, or an error occurred. 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
       getgrent(), getgrgid(), or getgrnam().  The returned pointer, and pointers within  the  structure,  might
       also be invalidated if the calling thread is terminated.

       The  getgrnam_r()  function  shall  return zero on success or if the requested entry was not found and no
       error has occurred. If any error has occurred, an error number shall be returned to indicate the error.

endgrent(), getgrgid(), sysconf()

       The Base Definitions volume of POSIX.1‐2017, <grp.h>, <sys_types.h>

       #include <grp.h>

       struct group *getgrnam(const char *name);
       int getgrnam_r(const char *name, struct group *grp, char *buffer,
           size_t bufsize, struct group **result);