#include <sys/types.h>
       #include <unistd.h>

       int getgroups(int size, gid_t list[]);

       #include <grp.h>

       int setgroups(size_t size, const gid_t *list);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setgroups(): _BSD_SOURCE

       getgroups()  returns the supplementary group IDs of the calling process
       in list.  The argument size should be set  to  the  maximum  number  of
       items  that  can  be  stored  in the buffer pointed to by list.  If the
       calling process is a member of more  than  size  supplementary  groups,
       then  an  error results.  It is unspecified whether the effective group
       ID of the calling process is included in the returned list.  (Thus,  an
       application should also call getegid(2) and add or remove the resulting

       If size is zero, list is not modified, but the total number of  supple-
       mentary  group IDs for the process is returned.  This allows the caller
       to determine the size of a dynamically allocated list to be used  in  a
       further call to getgroups().

       setgroups()  sets  the supplementary group IDs for the calling process.
       Appropriate privileges (Linux: the CAP_SETGID capability) are required.
       The  size  argument  specifies the number of supplementary group IDs in
       the buffer pointed to by list.

       On success, getgroups() returns the number of supplementary group  IDs.
       On error, -1 is returned, and errno is set appropriately.

       On success, setgroups() returns 0.  On error, -1 is returned, and errno
       is set appropriately.

       EFAULT list has an invalid address.

       getgroups() can additionally fail with the following error:

       EINVAL size is less than the number of supplementary group IDs, but  is
              not zero.

       setgroups() can additionally fail with the following errors:

       EINVAL size  is  greater than NGROUPS_MAX (32 before Linux 2.6.4; 65536
              since Linux 2.6.4).

       inherited from the parent process, and preserved across an execve(2).

       The  maximum  number  of  supplementary  group  IDs  can be found using

           long ngroups_max;
           ngroups_max = sysconf(_SC_NGROUPS_MAX);

       The maximum return value of getgroups() cannot be larger than one  more
       than this value.

       The  original Linux getgroups() system call supported only 16-bit group
       IDs.  Subsequently, Linux 2.4 added  getgroups32(),  supporting  32-bit
       IDs.   The  glibc getgroups() wrapper function transparently deals with
       the variation across kernel versions.

       getgid(2), setgid(2), getgrouplist(3), initgroups(3),  capabilities(7),

       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux                             2010-11-22                      GETGROUPS(2)
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