Problem:
How do I start the InterBase 5.1 server for Linux 5.11?

I am looking a the InterBase 5 docs which talk about 
an ibmgr.

Solution:
The InterBase 5 documentation is based on the SuperServer architecture.

InterBase for Linux 5.11 is based on the Classic model.
This is the model where each user gets their own connection.
Inet deamon runs all the time and listens for users trying to connect

 Enter the following to start the server:
 ./isql
 You should receive an sql> prompt.