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UNIX Process Cryogenics?
shawarma asks: "Due to a recent
power outage, I've had to shut down a server running a process that had
been running for ages calculating something. The job it was doing would
have been done in a few days, I think, but I had to shut it down before the
UPS ran out of juice. This got me thinking: Why can't I freeze down the
process and thaw it back up at a later time? It ought to be possible to take
all the connected memory pages and save them in some way, preserve file
handles and pointers, and everything. Maybe net-connections would die,
but that's understandable. Has any work been done in this field? If not,
shouldn't there be? I'd like to contribute in some way, but I think it's a bit
over my head.." Laptops have been doing this in some form for years:
most laptops, when they run out of power, or when told by the user will
go into "suspend" mode which is similar to what the poster is describing,
however outside of laptops, I haven't seen this done. Sleeping processes
also do something similar, sending their memory pages into swap so other
running processes can use the memory. What, if anything, is preventing
someone from taking this a step further?
What you want is known as "checkpointing."
There have been a number of projects that do this under Unix over the years. Many of them do it for the purpose of process migration. Others do it just for recovery.
One such project that I used in the early 90s was Condor.
The typical approach is to do something along the lines of forcing a core dump and then doing some magic to restart the process from the core file.
This comment is far from (Score:4, Informative) ... it's not even relevant. We're not talking about the whole OS hibernating, we're talking about saving the execution state of an executing process so that it can be resurrected later and continued (ie. if a reboot is necessary).
----- rL