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 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 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  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.

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

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

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 set  of  supple-
       mentary group IDs is inherited from the parent process, and preserved across an execve(2).

       The maximum number of supplementary group IDs can be found 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.

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

COLOPHON
       This  page  is  part of release 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-06-03                                               GETGROUPS(2)