I have a java application that is failing with

java.io.IOException: Too many open files
        at sun.nio.ch.ServerSocketChannelImpl.accept0(Native Method) ~[na:1.8.0-internal]
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:477) ~[na:1.8.0-internal]
        at sun.nio.ch.ServerSocketChannelImpl.accept(ServerSocketChannelImpl.java:287) ~[na:1.8.0-internal]
        at org.apache.tomcat.util.net.NioEndpoint$Acceptor.run(NioEndpoint.java:455) ~[tomcat-embed-core-8.5.27.jar!/:8.5.27]
        at java.lang.Thread.run(Thread.java:785) [na:1.8.0-internal]

my limit for open files is 30K

$ ulimit -a
open files                      (-n) 30480

I'm wondering now, what is the proper check...

lsof | grep 123 | wc -l (123 is pid of java application) returns number 45633.

How it could be over 30K?

On the other hand lsof -p 123| wc -l returns only 771 - it's not over the limit.

Can someone help me to understand what's going on here? What am I missing? Is the limit sum for all user processes (that's what I'd expect)?

This is RedHat 7, Lsof revision 4.87.

edit: ok, I believe I know what is the discrepancy - lsof -p ... shows open files for parent only while there are subprocesses

Thanks to a comment from @schily I found that limit per subprocess is 4K only (and not 30K).

  • If you were on a system with procfs support, you could use the command pfiles with the process ID of the failing process as argument to get the related rlimit, but it seems that you are on Linux. – schily Apr 28 at 10:42
  • pfiles/rlimit not available for me... – Betlista Apr 28 at 10:57
  • 1
    rlimit is not a command but a UNIX feature since 1979. pfiles needs procfs and since you are on Linux, you only have something that is remotely similar to procfs from it's inventor Roger Faulkner. But I just discovered that Linux has /proc/<pid>/limits. – schily Apr 28 at 11:01
  • Thank you very much - /proc/<pid>/limits helped, I can see there 4K max, I was not able so far to find (google it) how to increase it for subprocess... Seems the limits are not applied somehow... – Betlista Apr 28 at 12:33

Solution in my case, as I'm running it as a service (I didn't mention as I didn't know it's important), was to add


to my service file under /etc/systemd

That service file specifies, that it has to be run as some specific user, but still the limits were not used for this user.

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