You try to run a command like one of these on your non-root (private) install:
create user 'root' with password 'rootpass'
create user 'informix' with password 'ifmxpass'
but an error is returned:
-26108 You cannot grant root or informix user privilege to the user.
The GRANT ACCESS command listed either one of the user names root or informix,
or the user numbers corresponding to those names. You cannot grant a mapped
user the privileges of a surrogate user equivalent to either user root or
Resolving the problem
The purpose of a non-root (private) install is to remove the need for users root and informix to be involved in the installation and administration of Informix. The non-root owner creates and controls all other user accounts that can access the server installation. If user and group informix coexist with the non-root installation on the system, they have no administrative powers over the non-root database server.
You cannot run the CREATE USER command with a username of root or informix as that would defeat the purpose of a non-root (private) install and that is why you see error -26108.