[CRIU] unclear CRIU and docker problems

[Cyrill Gorcunov]

On Tue, Jun 30, 2015 at 10:32:49AM +0200, Adrian Reber wrote:
> So I am trying Ross Boucher's docker branch to checkpoint/restore docker
> containers and I can successfully checkpoint a container. If I try to
> restore a container CRIU exists pretty early with following error:
> 
> (00.002935) Warn  (cr-restore.c:1029): Set CLONE_PARENT | CLONE_NEWPID but it might cause restore problem,because not all kernels support such clone flags combinations!
> (00.002938) Forking task with 1 pid (flags 0x6c028000)
> (00.002952) Saved netns fd for links restore
> (00.002962) Error (cr-restore.c:1134): Can't fork for 1: Invalid argument
> 
> I am not sure if I read the log correctly but it sounds like it wants to
> restore the process with the PID 1, which does sound wrong. Any ideas
> where I should look for further errors.
> 
> This is with CRIU 1.6 on an older kernel with backports. Could also be
> that some kernel changes are missing on my side.

I guess this is a because of CLONE_PARENT | CLONE_NEWPID. Do you have pid
namespace support compied into the kernel? What "criu check" shows?