Final states - Revision history

Kir: /* Changing the state from stopped to running */ simplify a bit

2016-08-29T17:44:37Z

Changing the state from stopped to running: simplify a bit

Kir: reworked a bit

2016-08-29T17:43:07Z

reworked a bit

Xemul at 13:07, 29 August 2016

2016-08-29T13:07:30Z

Kir: don't use H1 headers, H1 is for the page title only

2016-08-26T18:43:39Z

don't use H1 headers, H1 is for the page title only

Ebatalov at 18:35, 26 August 2016

2016-08-26T18:35:39Z

Kir: created

2016-08-26T16:14:36Z

created

New page

@@ Line 49: / Line 49: @@
 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.
+we may need to continue its execution, changing the state to ''running''.
 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.

@@ Line 1: / Line 1: @@
-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' (ps tree is executed as usual)
+; Running : processes are running as usual
-# 'Stopped' (ps tree is stopped using SIGSTOP)
+; Stopped : processes are stopped using SIGSTOP
-# 'Dead' (ps tree is destroyed using SIGKILL)
+; Dead    : processes are destroyed using SIGKILL
-== CLI options for changing of process tree final state ==
+== Changing the default final states ==
-Use --leave-running option to set final state to 'Running'.
+You can use the following command line options with CRIU dump and restore commands
-== Process tree final state after CRIU dump command ==
+* <code>--leave-stopped</code>
-By default final state of process tree after dump is 'Dead'.
+== criu 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.
+By default, the final state of a process tree after <code>criu dump</code> is ''dead'',
-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.
+meaning CRIU kills the process tree right after dumping it.
-What about leaving process tree stopped after dump was performed? When it is needed?
+Such a default makes lot of sense. Suppose the process tree is left running after being dumped.
-It may be needed for debugging of CRIU. If CRIU wasn't accurate during dump command
+If processes are left running, they will most probably change the filesystem state (for example,
-then it would leave some traces in dumped process tree. You can investigate such process tree in
+delete a file) and/or networking state (for example, close a TCP connection). After such changes
-stopped state. You'll probably find some other use cases for --leave-stopped option with CRIU dump command.
+CRIU won't be able to restore the process tree from the dump, as the system simply won't have
-Leaving process tree running is necessary for predump command and currently --leave-stopped and
+On the contrary, if a process tree does not destroy any resources it depended upon before dump,
---leave-running options have on effect on it.
+then it is possible to restore it after dump made with <code>--leave-running</code> option.
-== Process tree final state after CRIU restore command ==
+Now, let's consider leaving the process tree stopped after performing the dump.
-By default final state of process tree after restore is 'Running'. That's because you usually
+One possible use case for that is CRIU debugging. If CRIU was not quite accurate doing dump,
-want to immediately start execution of process tree after its restore. You can use --leave-stopped
+then it would leave some traces in the dumped process tree. You can investigate such a process tree
-option to restore process tree in 'Stopped' state.
+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>.
 [[Category: Under the hood]]
 [[Category: API]]

← Older revision		Revision as of 13:07, 29 August 2016
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	[[Category: Under the hood]]		[[Category: Under the hood]]
		+	[[Category: API]]

@@ Line 1: / Line 1: @@
 Final state is the state that ps tree will have after its dump or restore.
@@ Line 8: / Line 6: @@
 # 'Dead' (ps tree is destroyed using SIGKILL)
-= CLI options for changing of process tree final state =
+== 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 =
+== Process tree final state after CRIU dump command ==
 By default final state of process tree after dump is 'Dead'.
@@ Line 34: / Line 32: @@
 --leave-running options have on effect on it.
-= Process tree final state after CRIU restore command =
+== 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' =
+== 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]]

← Older revision		Revision as of 18:35, 26 August 2016
Line 1:		Line 1:
−	~~{{FIXME\|~~this is for [[~~User~~:~~Ebatalov~~]] ~~to fill in}}~~	+	= 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]]