Ok, I understood it now.
It was not easy because there was more to it than it seems at first sight.
I made some notes to myself that I share here, in case anyone has the same doubt.
one cpanel account has (only) one user and (only) one owner
and they are different, except if the cpanel account is a reseller account
so, that cpanel account can be access by (and simultaneously):
- cpanel account user
- cpanel account owner
you need to understand these different elements:
- WHM root user (owner)
- WHM reseller user (owner)
- cpanel account
- cpanel account user
- cpanel account owner
when you log with an account that is either the onwer of another account
you can switch between both accounts in the upper right menu switch, in cpanel
that menu is not visible if you login into cpanel with the cpanel user
except if that cpanel user is the owner of another account
this means that the cpanel user can switch between its cpanel account
(of which curiously he is not the onwer)
and the cpanel accounts that he is the owner of
usually, the cpanel account owner is not the cpanel account user
the cpanel account owner is either root or a reseller user
however, the cpanel account user can also be that cpanel account owner
if that is set when the cpanel account was being created
or later, by changing the ownership of that account
in a fresh WHM installation, there is only the root account
this means that there are no reseller users, nor cpanel users, nor cpanel accounts
but, each one of these three can be created at will
if you do not have a VPS with WHM, but instead a reseller account
you may or may not create sub-reseller accounts
depending on the hosting reseller package you have contracted with your hosting
you can login into MULTIPLE cpanel accounts simultaneously (using the switch cpanel account menu)
using only one user and password
by these 3 different ways:
1 - login into WHM with root, list accounts, click in the cpanel logo situated in the cpanel account line
2 - do exactly the same the same thing, but using a reseller account instead of the root user
3 - login into cpanel with a cpanel user that is the owner of another cpanel account
to accomplish point 3, this needs to be done:
- change an existing account from normal WHM cpanel account to WHM reseller account
- or create a new cpanel account with reseller permissions
- change the ownership of a second account from root to that reseller
so, the cpanel of this second account can now be accessed by its:
- cpanel account user or by its
- cpanel account owner
meaning, you can upgrade an existing cpanel account to reseller
and when you log into that cpanel account with it's user
you will also access the other cpanel accounts in which you changed its ownership to that of that cpanel's user that now is also a reseller
in WHM, it is not possible to have more than one admin user
there is only one admin user (which is the root user)
however, in WHMCS you can have admins beside root
in cpanel, the situation is the same as with WHM (and not as WHMCS)
it is not possible to have more than one admin user (the only admin is the root user)
but the cpanel account can be accessed both by the user and by the reseller
and those are two different logins:
- cpanel user account
- reseller user account
if a cpanel user is the owner of multiple cpanel accounts
he can switch easily between that a group of cpanel accounts
that includes its original cpanel account and the multiple cpanel accounts he owns
he can switch between them by using the upper right menu switch, inside cpanel
that menu is not visible if that cpanel user is not the owner of any account
curiously, by default the cpanel user is not the owner of its account
its account owner is either root or a reseller account
except if that cpanel account was defined as a reseller account
at its creation moment or changed later on
