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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 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.

SEE ALSO
       getgid(2),  setgid(2),  getgrouplist(3),  initgroups(3),  capabilities(7),  creden-
       tials(7)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of
       the project, and information about reporting bugs, can be found at  http://www.ker-
       nel.org/doc/man-pages/.



Linux                             2008-06-03                      GETGROUPS(2)

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