When C/R fails

2020-08-03T09:25:56Z

Brlin: /* Restore "by hand" */ Fix typo

This page is the collection of typical situations when checkpoint or restore fails.

== PID mismatch on restore ==

If you see one of these lines in the failed restore logs

<pre>
Pid $number do not match expected $another_number
</pre>
<pre>
Thread pid mismatch $number1/$number2
</pre>

this means that while restoring a process tree, CRIU has failed to recreate a process (or a thread) with the PID (TID) value the proceess (thread) used to have on dump. Most likely, this is because the desired PID/TID is used by other task or thread. There are several possible solutions to this.

=== Restore "by hand" ===
One way is to restore the images into a separate pid namespace. This can be done by using the <code>unshare -p -m --fork --mount-proc</code> command and then doing the restore. In this case, you might also want to unshare the mount namespace and re-mount the /proc, so that the restored tasks can use it. This method effectively means restoring tasks in a container.

Note, however, that the most correct way is to run the tasks you plan to checkpoint in the pid namespace (with /proc tune-up if required) from the very beginning.

=== Kill the obstacle ===
Another solution to PID mismatch, which is not correct, but still efficient, is to kill the offending task :)

=== With CRIU help ===

There's a helper script called <code>criu-ns</code> that does restore in pseudo-container and also can dump again the restored tree. For more details see the "[[CR in namespace]]" article.

== Mount namespace with external dependences ==

The dump-time error in logs

<pre>
$nr:$path doesn't have a proper root mount
</pre>

indicates that the container (or just mount namespace) being dumped has some external dependences. CRIU knows how to work with it, you just need to tell CRIU about [[external bind mounts]] you have.

== External unix socket connection ==

If an application has an open unix connection to the external world, the dump will fail with

<pre>
"Cannot dump half of a stream unix connection
</pre>

In this case the socket should be explained as "OK to break" and reconnected back on restore. How to do it is described in [[external UNIX socket|here]]

[[Category:Using]]

CRIU - User contributions [en]

When C/R fails