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The following instructions describe the process to build/insall components necessary to checkpoint/restart (C/R) LXC containers using the C/R implementation being pushed into mainline.

The three main components to be built/installed are:

  • C/R enabled Linux kernel
  • USERCR - the user-space component of checkpoint/restart
  • LXC

Note: This page is still under construction. Feel free to fix obvious mistakes or email

Commit id

The instructions below identify a commit-id or a git tag in each of the git trees and it is recommended that you create a branch on those commit ids and apply any of the listed patches on that branch, before building the component.

Basic debugging of C/R

There is a strong dependency between each of these components (USERCR and Linux kernel are tightly coupled as are USERCR and LXC) so it is important to ensure the versions match up correctly. Otherwise attempts to checkpoint/restart typically fail with terse -EINVAL or -EBUSY errors.

If this happens, usually more debug information is found in dmesg output. If lxc-checkpoint fails some additional error information can be found by running

  • $ /bin/ckptinfo -ev <checkpoint-statefile>


statefile / checkpoint-image - this refers to the file in which the application state is saved after a successful checkpoint.

USERCR - The user-space commands/library components that utilize the kernel system calls to checkpoint/restart applications. Specifically this refers to the git tree: git://

1. Build C/R-enabled Linux kernel

Get the C/R-enabled kernel sources

   $ cd /root
   $ git-clone  git:// linux-cr
   $ cd linux-cr
   $ git-checkout -b test-1 0fdca57255b8b5bc9a4f107bee7f1e47d2630cb3
   $ git-log --pretty=short HEAD^..
   commit 0fdca57255b8b5bc9a4f107bee7f1e47d2630cb3
   Author: Dan Smith <>
   Disable softirqs when taking the socket queue lock

Ensure following tokens are set in .config


Build, install, reboot on new kernel

After every reboot, ensure '-o newinstance' mount option to /dev/pts works (see Documentation/filesystems/devpts.txt for details). In short, run following commands on each reboot:

  $ rm /dev/ptmx
  $ ln -s pts/ptmx /dev/ptmx
  $ chmod 666 /dev/pts/ptmx

2. Build USERCR

Get latest USERCR sources

   cd /root
   $ git-clone git:// user-cr
   $ cd user-cr
   $ git-checkout -b test-1 fa382a1758ef395858b1bea530ccdb4e1360b76f
   $ git-log --pretty=short HEAD^..
   commit fa382a1758ef395858b1bea530ccdb4e1360b76f
   Author: Sukadev Bhattiprolu <>
   Date:   Tue Mar 30 23:14:53 2010 -0700

Build and install USERCR binaries

Build USERCR by pointing to corresponding kernel-source tree we used above and install binaries. This should create restart.o and checkpoint.o needed by LXC, which are left in the current directory (for now).

Note: You may need to compile checkpoint.o and restart.o with -fPIC compiler option.

   $ KERNELSRC=/root/linux-cr make 
   $ ls restart.o checkpoint.o
   restart.o   checkpoint.o
   $ make install

3. Build/install LXC

Get latest LXC sources

   $ cd /root
   $ git-clone git:// lxc.git
   $ cd lxc.git
   $ git-checkout -b test-1 f78a1f32f41f6acbbf0b78e6498736dbd22e2301
   $ git-log --pretty=short HEAD^
   commit f78a1f32f41f6acbbf0b78e6498736dbd22e2301
   Author: Daniel Lezcano <>
   Date:   Fri Apr 2 23:37:42 2010 +0200

Apply LXC patches

Get the patchset from Untar the file and apply each of the patches in the broken-out directory to the LXC git tree

   $ git-am -3 broken-out/0001-patch-1
   $ git-am -3 broken-out/0001-patch-2

Configure, build, install LXC binaries

   $ ./configure --with-libcr=/root/user-cr
   This will fail if /root/user-cr does not container checkpoint.o, restart.o and app-checkpoint.h files 
   $ make
   $ make install

4. Checkpoint/restart a simple LXC container

   $ lxc-execute --name foo --rcfile lxc-no-netns.conf -- /bin/sleep 1000
   $ lxc-checkpoint --name foo --statefile /root/lxc-foo.ckpt
   $ lxc-stop --name foo
   $ lxc-restart --name foo --statefile /root/lxc-foo.ckpt
   $ lxc-stop --name foo

5. Checkpoint/restart other LXC containers:

Similar to step 4 above checkpoint/restart other applications in containers. For example applications clone following git tree:

   cr-tests: git://

Then try checkpoint/restart of:

  • a file-io session (see run-fileio1 in cr-tests[1])
  • process-tree (see run-ptree1 in cr-tests[1])

6. Checkpoint/restart an LXC container running a VNC server

VI editing session in a VNC session

Run a "vi" editing session inside a VNC server using "twm" window manager

   $ cat /root/.vnc/xstartup
   xsetroot -solid grey||
   vncconfig -iconic &||
   xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &|
   twm &
   $ lxc-execute --name foo --rcfile lxc-no-netns.conf -- /usr/bin/vncserver :1
   $ vncviewer :1
   # Open a vi session in vnc viewer
   $ lxc-checkpoint --name foo  --statefile /root/vnc.ckpt
   $ lxc-stop --name foo
   $ lxc-restart --pause --name foo --statefile /root/vnc.ckpt
   # Leaves the server frozen due to --pause
   $ lxc-unfreeze --name foo
   $ vncviewer :1
   # Should bring up the old VNC session with vi window
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