hpux man page for ngroups_max

ngroups_max(5)							File Formats Manual						    ngroups_max(5)

NAME
       ngroups_max - maximum number of supplementary group IDs per process

VALUES
   Default
   Allowed values
DESCRIPTION
       A process may have up to ngroups_max supplementary group IDs in addition to the effective group ID.

   Who is Expected to Change This Tunable?
       Anyone who needs users to be able to belong to more than the default 20 groups.

   Restrictions on Changing
       Processes that exist when this limit is changed (as well as future descendants of such processes) may not observe the new limit.  New login
       sessions will observe the new limit immediately.

   When Should the Value of This Tunable Be Raised?
       This tunable should be raised if any users need to belong to more groups than currently permitted.

   What Are the Side Effects of Raising the Value?
       If no users are associated with more groups than permitted by the old value, then there are no side-effects of raising this value.

       Any user who is associated with more groups than permitted by the old value will observe on their next login that more of those groups  now
       appear in their supplementary group IDs list.

       The more groups a user belongs to, the more kernel storage that user's processes will require to store the list of groups and the longer it
       will take both kernel and user-space code to search that list.  If users belonging to a large number of groups run a large number  of  pro-
       cesses, overall system performance may degrade proportionally.

       Users who have more than 20 supplementary group IDs may observe problems with older applications.  See the section below for details.

   When Should the Value of This Tunable Be Lowered?
       This tunable may be lowered if no users require so many supplementary group IDs.

   What Are the Side Effects of Lowering the Value?
       Users  who  are	associated with more groups than permitted by the new limit will observe on their next login that some of those groups are
       missing from their set of supplementary group IDs.  Any file accesses or other operations which depended on  these  groups  may	no  longer
       work.

       Lowering  this  tunable	will  not  cause any groups to be removed from the set of supplementary group IDs associated with any current pro-
       cesses.	Nor will it prevent future descendants of those processes from inheriting the full set of supplementary group IDs from their  par-
       ents.  A call to setgroups(2) with a subset of the current supplementary group IDs will always succeed.

   What Other Tunable Values Should Be Changed at the Same Time?
       None.

WARNINGS
       Users who are associated with more than 20 groups may observe problems with older applications when ngroups_max is set greater than 20.

       Older  applications  that  call	getgroups(2)  generally  use the constant NGROUPS_MAX (defined in to size the storage for group IDs.  get-
       groups(2) will return an error if the caller did not provide enough storage for all the supplementary group IDs that the caller belongs to.
       These applications may fail or operate as though the user belongs only to the group identified by the effective group ID.

       Compatibility with older applications can be achieved by several means:

       o  Don't associate users with more than 20 groups if they must run older applications.

       o  An individual user may require more than 20 groups, but have some applications which fail with more than 20 groups.

	  One workaround is to start those applications with a wrapper program which truncates the list of supplementary group IDs to the first 20
	  groups and then invokes the application.

	  An example of such a wrapper program follows:

	      #include <limits.h>
	      #include <stdio.h>
	      #include <stdlib.h>
	      #include <unistd.h>

	      main (int argc, char **argv)

	      {

		      gid_t   *list;
		      int     ngroups;
		      int     ret;

		      ngroups = getgroups(0, NULL);

		      if (ngroups > NGROUPS_MAX) {
			      list = (gid_t *)malloc(ngroups * sizeof(gid_t));

			      ngroups = getgroups(ngroups, list);

			      ret = setgroups(NGROUPS_MAX, list);

			      if (ret == -1) {
				      perror("setgroups");
				      exit(-1);
			      }
		      }

		      execvp(argv[1], &argv[1]);

		      perror("execvp");
		      exit(-1);
	      }

       All HP-UX kernel tunable parameters are release specific.  This parameter may be removed or have its meaning changed in future releases	of
       HP-UX.

       Installation  of  optional  kernel  software, from HP or other vendors, may cause changes to tunable parameter values.  After installation,
       some tunable parameters may no longer be at the default or recommended values.  For information about the effects of installation  on  tun-
       able  values,  consult  the documentation for the kernel software being installed.  For information about optional kernel software that was
       factory installed on your system, see at

AUTHOR
       was developed by HP.

SEE ALSO
       getconf(1), groupadd(1M), groupmod(1M), useradd(1M), usermod(1M), getaccess(2),	getgroups(2),  setgroups(2),  sysconf(2),  group(4),  lim-
       its(5), glossary(9).

							     Tunable Kernel Parameters						    ngroups_max(5)