getgrnam

GETGRNAM(3P)                POSIX Programmer's Manual               GETGRNAM(3P)



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
       getgrnam, getgrnam_r — search group database for a name

SYNOPSIS
       #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);

DESCRIPTION
       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.

RETURN VALUE
       The getgrnam() function shall return a pointer to a struct group 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.

ERRORS
       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.

       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 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);

APPLICATION USAGE
       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.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       endgrent(), getgrgid(), sysconf()

       The Base Definitions volume of POSIX.1‐2017, <grp.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                          GETGRNAM(3P)