So haven't had the opportunity to work with the Linux version of Tableau Server myself, but for the Windows version Tabcmd can be essentially copied to any machine. Because of this, the first thing that needs to be done is to login via Tabcmd to the Tableau Server environment you want to work with, even if you're running it from the environment you want to have the commands work. Whereas there's also a "Tabadmin" command (not in Linux version, replaced by TSM). Tabadmin can *only* be run on the Primary in a multi-node system or if it's standalone but basically if you can get to the box you can run it without having to specify the server.
Just to verify, did you already login to the one server with Tabcmd?
Well I found the issue yesterday. The thing is that if you use an AD identity store you have to use that AD user created for TS as initial user. I tried to create the initial user as if it was a local identity store and that failed( for obvious reasons) . So bear in mind that if you have other identity stored set up (AD, LDAP) you have to use that user in order to pass the initial user setup.
Hope this helps someone else also