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== DMTCP ==
DMTCP implements checkpoint/restore of a process on a library level. This means, that if you want to C/R some application you should launch one with DMTCP library (dynamically) linked from the very beginning. When launched like this, the DMTCP library intercepts a certain amount of library calls from the application, builds a shadow data-base of information about process' internals and bypasses the request further, to glibc/kernel. This information will be later used to create an image of the application. With this approach, one can only dump applications, that are known to run successfully with the DMTCP libraries, but the latter doesn't provide proxies for all kernel APIs. Another implication of this approach is potential performance issues that arise due to proxying of requests.
Restoration of process set is also tricky, as it frequently requires restoring an object with the predefined ID and kernel is known to provide no APIs for several of them. For example, kernel cannot fork a process with the desired PID. To address that, DMTCP fools a process, by intercepting the getpid() library call and providing fake PID value to the application. Such behavior is very dangerous, as application might see wrong files in the /proc filesystem if it will try to access one via its PID.