Hercules V4.00.0 - User Reference Guide

8.170 SUSPEND (Suspend Hercules)

8.170.1 Function

This command lets you suspend the current Hercules session and shutdown the host machine. Subse-
quently the suspended session can be resumed (see “RESUME” command). The data necessary to be
saved for a later restart is saved in a packed (zipped) file called “hercules.srf.gz” which is located in the
current configuration path.

After entering the SUSPEND command the CPUs are put in a stopped state and the contents of the main
storage, CPU states, I/O device states and internal Hercules states are dumped onto the “Hercules.srf.gz”
file. After the SUSPEND command has finished writing to the suspend file, it schedules an immediate
shutdown of Hercules.

Currently device state is only fully saved for CKD disks. Each device class (e.g. TAPE, RDR, PUN, CTC)
will need code to save and restore their state. Some states may not be possible to restore (e.g. active
TCP/IP connections at the time of suspend). Currently the vector facility state is not saved, neither is the
ECPSVM state.

The created suspend file is designed to be HERCULES release independent and to be host architecture
independent. For example it is possible to take a suspend file created on HERCULES 3.05.0 on an Intel
machine and resume on a Sun machine running HERCULES 3.07.0.

Please note that there are some caveats with suspend / resume processing which can affect the guest
operating system running under Hercules. These caveats are described in the chapter about RESUME
processing (

8.137 , RESUME).

There are some caveats when suspending and 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.