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Created page with "This page describes the criu-ns script that has appeared in criu-dev branch after 2.5 and is aimed at 2.6. == Problem == When restoring a process tree without namespaces (i...."
This page describes the criu-ns script that has appeared in criu-dev branch after 2.5 and is aimed at 2.6.
== Problem ==
When restoring a process tree without namespaces (i.e. -- into the namespaces in which criu lives) one may frequently hit a "pid mismatch" problem. It is when a process we'd like to restore has a PID which is already owned by some other process living in this pid-namespace. There's no way one can restore a process tree in ''this'' namespace, so the only solution is to unshare the new pid namespace and restore the tree into it.
When doing so we have two problems
# In the new pid namespace someone has to become the "init" process
# In the new pid namespace we'd need to have new /proc mount which implies unsharing the mount namespace as well
And even if one solves the above problems, there will appear the third one -- when trying to dump the restore process tree ''again'' criu will likely refuse to dump the mount namespace, as it will be a complete clone of the original one and thus would likely contain many many unsupported mounts such as real devices, securityfs, trace/debug-fs etc. The latter can still be solved by nsenter-ing the process' pid and mount namespaces and doing the dump.
== Solution ==
All of the above -- the need to unshare stuff, getting pseudo-init, re-mounting /proc on dump and setns-ing on restore -- is solved by the scripts/criu-ns script. Just replace running one instead of regular criu run would do all of this, there's no need in doing anything with the CLI options, the API is fully compatible.
== Known issues ==
# The [[shell jobs]] are not supported
# The [[swrk mode]] is not supported
# Only the dump and restore is supported, so no [[Incremental dumps]] possible yet
== Problem ==
When restoring a process tree without namespaces (i.e. -- into the namespaces in which criu lives) one may frequently hit a "pid mismatch" problem. It is when a process we'd like to restore has a PID which is already owned by some other process living in this pid-namespace. There's no way one can restore a process tree in ''this'' namespace, so the only solution is to unshare the new pid namespace and restore the tree into it.
When doing so we have two problems
# In the new pid namespace someone has to become the "init" process
# In the new pid namespace we'd need to have new /proc mount which implies unsharing the mount namespace as well
And even if one solves the above problems, there will appear the third one -- when trying to dump the restore process tree ''again'' criu will likely refuse to dump the mount namespace, as it will be a complete clone of the original one and thus would likely contain many many unsupported mounts such as real devices, securityfs, trace/debug-fs etc. The latter can still be solved by nsenter-ing the process' pid and mount namespaces and doing the dump.
== Solution ==
All of the above -- the need to unshare stuff, getting pseudo-init, re-mounting /proc on dump and setns-ing on restore -- is solved by the scripts/criu-ns script. Just replace running one instead of regular criu run would do all of this, there's no need in doing anything with the CLI options, the API is fully compatible.
== Known issues ==
# The [[shell jobs]] are not supported
# The [[swrk mode]] is not supported
# Only the dump and restore is supported, so no [[Incremental dumps]] possible yet