[erlang-questions] Mnesia could not write core file: system_limit

Slobodan Miskovic <>
Wed Dec 9 23:03:08 CET 2009


On Wed, 2009-12-09 at 10:06 -0500, Bernard Duggan wrote:
> > How would I check the FD usage of a running system?
> Quick way to check on linux is to count the number of entries in
> /proc/<PID>/fd (excluding . and .. of course). 

Heh, thinking outside of the (VM) box - guess there is no query-able
interface in Erlang for this? Linux is then indeed simple enough:
{ok, FDList} = file:list_dir("/proc/self/fd"),
length(FDList)

What about other platforms, ie. Windows?

>  The command "lsof -p
> <PID>" will also show you (although it lists a bunch of other things too
> and I can't remember off the top of my head how to filter just to file
> descriptors that contribute to the processes limit).
> 

Would lsof (or similar mechanism) be preferable as I would get a list of
open sockets and network connections which as I understand all
contribute to the max open ports limit. Would I get all those in
the /proc/.../fd list as well?


> > Do open FDs get closed if a process dies? Perhaps that's where the leak is coming from.
> >   
> In general, yes they do.  However be aware that many operations in
> Erlang spawn a process, and they're not always cleaned up in the way you
> might expect (we found a particular case with long-lasting HTTP client
> connections where you have to explicitly shut them down, even if the
> process that initiated it had crashed).  Basically, what you need to be
> concerned about is process leaks, not FD leaks per se.


Hm, I have embedded Yaws running, and occasionally processes terminate
when invalid requests comes in. I would have thought those would have
been really dead. I'll have to keep an eye on the running system to see
if number of processes is rising.


Thanks,
Slobo




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