Hercules V4.00.0 - User Reference Guide

8.137 RESUME (Resume Hercules)

8.137.1 Function

This command resumes a Hercules session that had been previously suspended with the SUSPEND
command (see section

8.170 for details). The data necessary to resume the session is read from a
packed (zipped) file called “hercules.srf.gz” located in the current configuration directory.

In order for an instance to be resumed HERCULES must be started with a configuration file describing
the configuration at suspend time. For example, MAINSIZE and XPNDSIZE must match and all devices
present at suspend time must be present at resume time.

Disk devices must be at the same state as they were at suspend time. They can however be a different
file type. For example a disk could be a CCKD disk at suspend time then a CKD disk could be created
using DASDCOPY and HERCULES resumed using the CKD disk instead.

HERCULES must also be configured similarly as at suspend time. For example if 4 emulated CPUs were
active at suspend time then the session cannot be resumed on a HERCULES with a maximum of two
CPUs. Similarly you will not be able to resume a session in z/Architecture mode for a HERCULES that
was built without z/Architecture.

After entering the RESUME command on the Hercules console the suspend file is re-imported and the
CPUs are put in the STARTED state again resuming guest program operations at the same point and in
the same state as the suspend file was created.

There are some caveats when resuming guest operating system processing:

As seen by the guest operating system, the TOD clock will appear to jump a large value. Some
guests may not cope very well with this. For example some guests may be dismayed because
certain interrupts will occur way past its due time. Also for S/370 an interval timer interrupt may
be lost if the guest is interrupted for more than half the Interval Timer wrap time (around 8 hours). Although some effort has been put in order to make this as transparent as possible (that is, it
should appear to the guest operating system that the STOP key was pressed for a large amount
of time), some state information may be missed. Some guest operating systems will fare better if the suspend state is prepared first. For MVS, as
an example, it seems to help when a QUIESCE command and a SYSTEM RESTART manual
operation are issued prior to suspend the system.