The official documentation here talks about openhab:openhab
But some threads such as this are setting up permissions as openhab2:users
The default user for an apt-get installed OH is openhab:openhab.
That link is for a Synology install and it may require something different or they created a different user.
As already mentioned the openhab2 user is created on the Synology Diskstation, therefore I had to use this one.