I have nsenter set up on my local and remote Linux boxes. The remote box is a hosted virtual machine. The local box is a computer in my office. Both are running Ubuntu 12.0.4 LTS server version and both of them have the kernel patch to support docker. My local box is running Docker 1.0.1, the apt-get version for Docker. The remote box is running 1.4.1, the latest and greatest.
Here is the procedure I use to execute nsenter on both machines, shown with the remote machine details:
kelpmaster@external:~$ sudo docker inspect --format {{.State.Pid}} fluffy_cinnamon
32113
kelpmaster@external:~$ sudo nsenter --target 32113 --mount --ipc --net --pid
nsenter: cannot open /proc/32113/ns/pid: No such file or directory
I checked the process list on the remote box and 32113 is definitely in the process list. I checked the file structure and there definitely is a directory named /proc/32113/ns. However, on my remote box the file/directory named pid does not exist in the process namespace folder. On my local box it does.
Why is the pid file/directory missing from my remote box when it is being created properly on my local box? How can I fix this so I can nsenter my Docker container on the remote box like I can on my local box?
Use lxc-checkconfig to see if 'pid namespace: enabled' or else its the kernel.
you can also look for Cgroup: enabled Cgroup namespace: enabled
if not mount it appropriately.