[ale] Lab Workstation Mystery

[Todor Fassl]

I posted about this problem a couple of weeks ago and still have not 
figured it out. The problem is that on a group of machines running 
ubuntu 15.10, after a period of time, mounting home directories via NFS 
hangs. Attempting to mount or unmount home directories via NFS simply 
hangs. Eventually, the root filesystem getsremounted read-only and the 
machine becomes unusable even as a local user. One thing I've discovered 
since my first post about this is that when end-users log out, some 
processes do not get killed off. The automounter can't umount the home 
directory because the user still has some processes running. Eventually, 
the machine has several home directories mounted via NFS for users who 
are no longer logged in. I am thinking that what is happening is that 
eventually this causes NFS to get wedged which in turn leads to the 
kernel freaking out. Or something. Here is an example of the output from 
listing the processes for a user who has logged out:

# ps -u enduser1
     PID TTY          TIME CMD
  101794 ?        00:00:00 systemd
  101795 ?        00:00:00 (sd-pam)
  103049 ?        00:00:00 ibus-daemon
  103057 ?        00:00:00 ibus-dconf


So frequently, even though a user has logged out days ago, the systemd 
and ibus-deamon might still be running. I am thinking after enough time, 
these things mess up the nfsv4 kernel module which eventually messes up 
the kernel itself.

But why would logging out *not* killoff all of an end-user's processes?