CRIU

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CRIU
CRIU.svg
Checkpoint and Restore in Userspace
Developer(s) OpenVZ Team at Odin
Initial release 23 July 2012; 3 years ago (2012-07-23)[1]
Stable release 1.5 (March 2, 2015; 5 months ago (2015-03-02)[2]) [±]
Development status Active
Written in C and Assembler
Operating system Linux
Platform x86 64, ARM
Type Application checkpointing
License GNU GPL v.2
Website criu.org

Checkpoint/Restore In Userspace, or CRIU (pronounced kree-oo, /krɪʊ/), is a software tool for the Linux operating system. Using this tool, it is possible to freeze a running application (or part of it) and checkpoint it to persistent storage as a collection of files. One can then use the files to restore and run the application from the point it was frozen at. The distinctive feature of the CRIU project is that it is mainly implemented in user space, rather than in the kernel.

The project is currently under active development.

History[edit]

The initial version of CRIU software was presented to the Linux developers community by Pavel Emelyanov, the OpenVZ kernel team leader, on 15 July 2011.[3]

In September 2011, the project was presented at the Linux Plumbers Conference.[4] In general, most of the attendees took a positive view of the project, which is proven by the fact that a number of kernel patches required for implementing the project were included in the mainline kernel. Linus Torvalds, however, was a bit skeptical:

A note on this: this is a project by various mad Russians to perform c/r mainly from userspace, with various oddball helper code added into the kernel where the need is demonstrated... However I'm less confident than the developers that it will all eventually work! So what I'm asking them to do is to wrap each piece of new code inside CONFIG_CHECKPOINT_RESTORE. So if it all eventually comes to tears and the project as a whole fails, it should be a simple matter to go through and delete all trace of it.

—Linus Torvalds, [5]

Use[edit]

The CRIU tool is being developed as part of the OpenVZ project, with the aim of replacing the in-kernel checkpoint/restore. Though its main focus is to support the migration of containers, allowing users to check-point and restore the current state of running processes and process groups. The tool can currently be used on x86-64 and ARM systems and supports the following features:

No kernel patching is currently[when?] required, as all the needed functionality is already included since version 3.11 of the Linux kernel, which was released on September 2, 2013.[citation needed]

TCP connection migration[edit]

One of the initial project goals was to support the migration of TCP connections, the biggest challenge being to suspend and then restore only one side of a connection. This was necessary for performing the live migration of containers (along with all their active network connections) between physical servers, the main scenario of using the checkpoint/restore feature in OpenVZ. To cope with this problem, a new feature, "TCP repair mode", was implemented. The feature was included in the v3.5 mainline Linux kernel[6] and provides users with additional means to disassemble and reconstruct TCP sockets without the necessity of exchanging network packets with the opposite side of the connection.

Similar projects[edit]

The following projects provide functionality similar to CRIU:

References[edit]

External links[edit]