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Even an “uncatchable” signal may not terminate a process. For instance, a zombie is the remnant of a process that’s waiting to exit. (A zombie has Z in the ps STAT column.) A process that’s being traced can also be unkillable.
Unfortunately that article doesn't tell you what you can do about zombies, if anything.
You should find out what those parent processes are (like 21968 in the case of the last one). These processes are not waiting for their spawned df processes.
Maybe it helps to visualize what is going on if you install and use the program htop and use it to display the process structure as a tree. It will update the situation regularly and you can see what those processes spawning all those instances of df are. Normally df is too fast to even learn its process number, it just prints its results then exits. I suppose there is a badly written script or something which spawns these zombie processes.
There is no script spawning these processes - it's curious people like me who want to find out what the disk usage is and run df -kh. So even if I can kill these processes I'll still create a new one every time I run df -kh. I suppose I should try and find out the reason the df command is hanging - as per my last post, I think it's something to do with nfs....
Have you started all those df instances yourself or is there an automatism? All those ppids look as if they got created just to spawn a df instance. There must be a reason why df cannot read the nfs mount, so there's something wrong there.
If the NFS server (or the network connection thereto) becomes unavailable all processes that try to access any part of that share will be set into D state. (Use intr or soft mount options on NFS to avoid all that).
Thanks for your help and note the solution for future reference!
Yep, a little more info, state "D" is uninterruptible sleep. In that state a program is off in a driver call and cannot be interrupted even by kill -9. Fixing or removing the NFS mount, or mounting with different options, solves that as you saw.