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 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  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 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 3.54 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/.