sysinstall(8) will first look for the file install.cfg on the root file system which sets installation parameters. This file can also be used to script sysinstall. When the execution exits, sysinstall will return to the interactive mode.
Hence, to automate the installation we need to create install.cfg and place it in the root of the memory filesystem we created. Remount the memory file system to create and store the installation configuration file.
The syntax, variables and commands are described in sysinstall(8), however not all variables and commands are documented, for theese, we need to take a look at the source code also. Also a sample install.cfg is given in the source code directory of sysinstall.