I have the VM running with ubuntu(14.04.4). Sometimes, I just want to restart the VM by reboot command. When I execute the command, it prompts "success" but nothing happened.
I checked the syslog, no special logs found. Some services(like ssh) seem to be shut down.
My VM just run into docker hang issue(1.12.6) before reboot and I just removed the docker files under /var/lib/docker. The zombie processes still exist.
This VM can be restarted from VM web console. (I don't have the permission)
I want to know,
- What can I do when this happen?
- How can I get the clue for this issue, such as something found under /proc? reboot using "shutdown -r" which try to kill all the running processes, any condition causes "reboot" hangs?
- After first "reboot" command, can I run "reboot -f" again to shut down the system? I didn't try it since it's not safe.
Magic commands can be executed for this issue and the server reboot successfully and immediately,
echo 1 > /proc/sys/kernel/sysrq echo b > /proc/sysrq-trigger
I know reboot may do restart gracefully, such as sync dirty pages to disk, kill all running processes and so on.
When I run reboot, there were some zombie processes generated in special namespaces. Since the docker container removed, the namespaces also removed and only task_struct left in memory which needed to be released by wait4
The inheritance between processes were,
Processes after container removed,
- docker containered can be killed and then the children adopted by init 1
- entrypoint startup process can not be killed since the container removed
zombie always existed since parent was left in memory without wait4
- init 1(global ns) -> docker containered(global ns)(sleep) -> docker entrypoint startup(container ns)(sleep) -> java(container ns)(zombie)