Sometimes CRIU is unable to checkpoint or restore a process for various reasons. This article describes a way to check whether CRIU works or not for a given case.
It might be the case that a process can not be dumped at all (see what cannot be checkpointed), or that there are some problems which can be fixed. One way to check if checkpoint/restore will work is to run
criu dump with
--leave-running on the source system, copy the dump over, then run
criu restore on the destination.
The problems with the above approach are:
- If restore succeeds, one will have two sets of same processes running on two machines, which may have disastrous effects;
- A lot of memory is dumped to disk and transferred to the destination system, which is not necessary for a test run.
To solve these, an easier and faster way to test if dump/restore will work,
--check-only option was introduced.
# criu dump --check-only -D /tmp/cp -t <PID> Only checking if requested operation will succeed ... # rsync -a /tmp/cp dest-system:/tmp
# criu restore -D /tmp/cp Checking mode enabled ...
Upon restore, CRIU will see that the checkpoint is a check-only one, and will do restore in a check-only mode automatically, so there is no need to supply this option explicitly.
One can use the --check-only switch on a full checkpoint, to see if the restore will succeed, at the same time making sure the process will not start running:
# criu restore --check-only -D /tmp/cp Only checking if requested operation will succeed Checking mode enabled ...
Currently only the existing checks (e.g., check binary size) are run in check-only mode, but additional checks could be added, for example:
- checksums of binaries
- checksums of used libraries
- available memory