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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  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.
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 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 set-
       groups() requires privilege, it is not covered by POSIX.1-2001.
NOTES
       A  process  can have up to NGROUPS_MAX supplementary group IDs in addi-
       tion to the effective group ID.  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 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.
       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.
SEE ALSO
       getgid(2), setgid(2), getgrouplist(3), initgroups(3),  capabilities(7),
       credentials(7)
COLOPHON
       This  page  is  part of release 3.53 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                             2010-11-22                      GETGROUPS(2)