getgrgid(3p) — Linux manual page


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

PROLOG         top

       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         top

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

SYNOPSIS         top

       #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         top

       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         top

       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

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

ERRORS         top

       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

       ENFILE The maximum allowable number of files is currently open in the

       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

       The following sections are informative.

EXAMPLES         top

       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;
               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);
               printf(" %-8d", statbuf.st_gid);


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

       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         top




SEE ALSO         top

       endgrent(3p), getgrnam(3p), sysconf(3p)

       The Base Definitions volume of POSIX.1‐2008, grp.h(0p),

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                        GETGRGID(3P)

Pages that refer to this page: grp.h(0p)find(1p)endgrent(3p)getgrnam(3p)getgrnam_r(3p)