GETGROUPS(2)                        Linux Programmer's Manual                        GETGROUPS(2)



NAME
       getgroups, setgroups - get/set list of supplementary group IDs

SYNOPSIS
       #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

DESCRIPTION
       getgroups() returns the supplementary group IDs of the calling process in list.  The argu‐
       ment 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 value.)

       If size is zero, list is not modified, but the total number of supplementary 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  privi‐
       leges  (Linux:  the  CAP_SETGID capability) are required.  The size argument specifies the
       number of supplementary group IDs in the buffer pointed to by list.

RETURN VALUE
       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 appropri‐
       ately.

ERRORS
       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).

       ENOMEM Out of memory.

       EPERM  The calling process has insufficient privilege.

CONFORMING TO
       SVr4, 4.3BSD.  The getgroups() function is in POSIX.1-2001.   Since  setgroups()  requires
       privilege, it is not covered by POSIX.1-2001.

NOTES
       A  process can have up to NGROUPS_MAX supplementary group IDs in addition to the effective
       group ID.  The constant NGROUPS_MAX is defined in <limits.h>.  The  set  of  supplementary
       group IDs is inherited from the parent process, and preserved across an execve(2).

       The maximum number of supplementary group IDs can be found at run time using sysconf(3):

           long ngroups_max;
           ngroups_max = sysconf(_SC_NGROUPS_MAX);

       The  maximum  return  value of getgroups() cannot be larger than one more than this value.
       Since Linux 2.6.4, the maximum number of supplementary group IDs is also exposed  via  the
       Linux-specific read-only file, /proc/sys/kernel/ngroups_max.

       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 func‐
       tion transparently deals with the variation across kernel versions.

SEE ALSO
       getgid(2),  setgid(2),  getgrouplist(3),  group_member(3), initgroups(3), capabilities(7),
       credentials(7)

COLOPHON
       This page is part of release 3.74 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at http://www.kernel.org/doc/man-pages/.



Linux                                       2014-08-19                               GETGROUPS(2)