Dynamic subsystem management (DSSM) of BS2000 links the POSIX subsystem from link and load modules supplied in the following platform-specific program libraries:
SYSLNK.POSIX-BC.<version> (/390)
- SKMLNK.POSIX-BC.<version> (X86)
The POSIX system kernel code - like the original UNIX system kernel code - contains various control parameters (tuning parameters) which a system administrator can set in the POSIX information file SYSSSI.POSIX-BC.010 in accordance with the specific application. These control parameters are used to configure the system kernel and to improve performance. In addition, the name of the root file system is entered in the POSIX information file.
In POSIX, the UNIX tuning mechanism is mapped to the parameter service of DSSM. The POSIX information file contains the name of the root file system in addition to the control parameters of the system kernel code, and other POSIX-specific control parameters. The contents of the POSIX information file are described in “POSIX information file”.
The POSIX information file is delivered to the customers together with other components. It is created as a SAM file and it already contains default values. The default values are selected so that the POSIX subsystem can operate in any environment without burdening the overall system by excessive use of resources. However, it may often be useful to adapt some control parameters, such as the maximum number of POSIX process, to the specific POSIX application and the resources available to the overall system.
If the system administrator enters an invalid parameter value in the POSIX information file, message POS1020 is returned. Instead of the invalid parameter value, the default value is entered in the internal subsystem parameter table.
If a POSIX information file is not available or if it cannot be opened when the POSIX subsystem starts, a corresponding message is returned and the subsystem is not started.
Some selected control parameters can also be modified using the priviledged POSIX command usp during an active POSIX session. The resources required are then available without the system needing to be rebooted.