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−# 'Running' (ps tree is executed as usual)+# 'Stopped' (ps tree is stopped using SIGSTOP)+# 'Dead' (ps tree is destroyed using SIGKILL)+You can use --leave-stopped option with CRIU dump/restore commands to set process tree final state to 'Stopped'.
−Use --leave-running option to set final state to 'Running'.+== Process tree final state after CRIU dump command ==+By default final state of process tree after dump is 'Dead'.+So CRIU will kill process tree after it was dumped. But why? Suppose you leave your
−process tree running after it was dumped. What if it deleted some files it was using
−during its dump? What if it closed some tcp connections? After that CRIU won't be able
−to restore process tree from the dump it has created earlier.
−System simply won't have resources that this process tree requires at
−the moment captured in dump.
−If your process tree doesn't destroy resources it depended on before dump then you'll be able to restore it after dump with --leave-running option.+But be aware that your process tree left running after dump may modify some state (for example a file) in way not compatible on application level with process tree restored from this dump later.+What about leaving process tree stopped after dump was performed? When it is needed?+It may be needed for debugging of CRIU. If CRIU wasn't accurate during dump command+then it would leave some traces in dumped process tree. You can investigate such process tree in+stopped state. You'll probably find some other use cases for --leave-stopped option with CRIU dump command.+Leaving process tree running is necessary for predump command and currently --leave-stopped and+--leave-running options have on effect on it.+== Process tree final state after CRIU restore command ==+By default final state of process tree after restore is 'Running'. That's because you usually+want to immediately start execution of process tree after its restore. You can use --leave-stopped+option to restore process tree in 'Stopped' state.+
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Final state is the state that ps tree will have after its dump or restore.
+Final state is the state a process tree ends up in after CRIU dump or restore.
−There are 3 possible final states in CRIU:
+There are 3 possible final states:
−; Running : processes are running as usual
−; Stopped : processes are stopped using SIGSTOP
−; Dead : processes are destroyed using SIGKILL
−== CLI options for changing of process tree final state ==
+== Changing the default final states ==
−You can use the following command line options with CRIU dump and restore commands
+to change the default process tree final state:
−* <code>--leave-stopped</code>
+* <code>--leave-running</code>
−== criu dump ==
−By default, the final state of a process tree after <code>criu dump</code> is ''dead'',
−meaning CRIU kills the process tree right after dumping it.
−Such a default makes lot of sense. Suppose the process tree is left running after being dumped.
−If processes are left running, they will most probably change the filesystem state (for example,
−delete a file) and/or networking state (for example, close a TCP connection). After such changes
−CRIU won't be able to restore the process tree from the dump, as the system simply won't have
+resources that this process tree requires at the moment when it was captured.
−On the contrary, if a process tree does not destroy any resources it depended upon before dump,
−then it is possible to restore it after dump made with <code>--leave-running</code> option.
+Be aware, though, that the process tree left running after the dump may modify some state
+(for example, write to a file) in way that is not compatible on the application level with
+the process tree restored from this dump later.
−Now, let's consider leaving the process tree stopped after performing the dump.
−One possible use case for that is CRIU debugging. If CRIU was not quite accurate doing dump,
−then it would leave some traces in the dumped process tree. You can investigate such a process tree
−in its stopped state. Surely you might find some other cases to use <code>--leave-stopped</code>.
−== Moving process tree from 'Stopped' state to 'Running' ==
+Also, leaving the process tree running is naturally necessary for the <code>predump</code>
−After criu has dumped/restored process tree in 'Stopped' state we sometimes need to continue
+command, so currently <code>--leave-stopped</code> and <code>--leave-running</code> options
−its execution putting process tree into 'Running' state. For this purpose use this [https://github.com/xemul/criu-scripts/blob/master/pstree_cont.py script]. It has only single argument - PID of process tree root.
+are ignored for <code>predump</code>.
+== criu restore ==
+By default, the final state of a process tree after restore is ''running''. That's because one usually
+wants to immediately resume execution of the process tree after restore. One can use <code>--leave-stopped</code>
+option to restore the process tree and leave it in ''stopped' state.
+== Changing the state from stopped to running ==
+After criu dumped or restored a process tree and left it in ''stopped'' state,
+we may need to continue its execution, putting the process tree into ''running'' state.
+To do that, use the [https://github.com/xemul/criu-scripts/blob/master/pstree_cont.py pstree_cont.py]
+script. Its sole argument is the PID of a process tree root process.
[[Category: Under the hood]]
[[Category: Under the hood]]
[[Category: API]]
[[Category: API]]