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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
       is returned.  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.

SEE ALSO

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

COLOPHON

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