Well, there is sort of, if you have a tcp-stack it will have a user database, also Envoy operated with user and groups, and even the amiga fast filesystem supports user and group flags.
But, first... try to just set a variabel USER to the username you want to use, for example in the shell "set USER blabla", you can see what USER is already by typing "echo $USER", or "get USER", or just type "set" to see all local shell variables and their content.
Notice that variables you set with the "set" command only exists within the shell they are set, if you want system wide variables you can use the command "setenv" instead, the resulting variable will be stored as a file in ENV:. For example "setenv USER blabla" will create the file ENV:USER which will contain "blabla", and if you then open a different shell and type "echo $USER" there, it will say "blabla".
Sometimes you even want such variables to survive boot, so you just copy them over to ENVARC: which normally is pointing to SYS:Prefs/Env-Archive. You do so simply with a "copy env:USER envarc:", newer setenv commands even have a "save" option that will create a variable and save it to envarc: in one go. With these global variables you can also use the command "getenv", f.ex "getent USER", and just running "setenv" will list out all global variables, but not their content (mostly because env:/envarc: is also used for system/program prefs as well).
If you havent already, you should get SnoopDOS from aminet to help you find out what mSQL is trying to do, what variables it looks for etc.
