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−{{FIXME|this is for [[User:Ebatalov]] to fill in}}+
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= The concept of process tree final states =
+Final state is the state that ps tree will have after its dump or restore.
+There are 3 possible final states in CRIU:
+# 'Running' (ps tree is executed as usual)
+# 'Stopped' (ps tree is stopped using SIGSTOP)
+# 'Dead' (ps tree is destroyed using SIGKILL)
+= CLI options for changing of process tree final state =
+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.
+= Moving process tree from 'Stopped' state to 'Running' =
+After criu has dumped/restored process tree in 'Stopped' state we sometimes need to continue
+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.
+[[Category: Under the hood]]