'groupmanage' is /usr/local/bin/groupmanage - NOT setuid root
-rwxr-xr-x   1 root     root /usr/local/bin/groupmanage
'groupmanage.conf' is /etc/groupmanage.conf - edit to taste
-rw-rw-r--   1 root     root /etc/groupmanage.conf
'services' is (typically) /etc/userv/services.d/groupmanage
-rw-rw-r--   1 root     root /etc/userv/services.d/groupmanage
Edit /etc/userv/system.default to add a line

include-lookup service /etc/userv/services.d

Depends on /etc/environment setting up a sensible PATH; /etc/grouplist
existing (suggest inserting the comment 
# Syntax:
# group:description:manager:maint-users:home
) There must be no blank lines in /etc/grouplist.

Error messages of the form 
userv: failure: read error in data: Interrupted system call
appear to be normal (!)

Groupmanage is copyright (C)1995-8 Ian Jackson
<ijackson@chiark.greenend.org.uk>

and is distributed under the terms of the GNU General Public License;
however, since Ian does not yet consider it ready for general release,
please be selective when sending him reports of bugs.