How to Fix “java.io.FileNotFoundException Too many open files” Error

From your java application, under certain circumstances, you might be getting “java.io.FileNotFoundException: Too many open files” error message.

There are two typical solutions to it:

  1. Check your application logic and make sure it is not opening too many files unnecessarily (for example, In a loop there is file open, but it is not getting closed anywhere)
  2. Increase the open files limit on your system.


Don’t just blindly go with solution #2 and increase the total number of open files without understanding exactly what your application does, and how many files you are expecting the application to open.

If you are pretty sure that there is nothing wrong in the application logic, and it really needs to open more files, then you can increase the ulimit of the open files as explained in this article.

First, get the PID of the java application that is throwing this error message. In the following example, 4003 is the PID.

# ps -ef | grep java
tomcat  4003  00:26:20 /usr/bin/java -Dinstall4j.jvmDir=/usr

Next, count how many files this particular PID has opened. For this, go to /proc/PID/fd directory, and count the number of files there as shown below.

# cd /proc/4003/fd

# ls -l | wc -l
1020

Another way to view all the open files is using lsof command as shown below. Please note that there will be a slight difference in the count between the following output and the above output, as lsof will display few additional information.

# lsof -p 4003

In this case, the java application is started by the username “tomcat”.

To view the current hard limit and soft limit for the open files, execute the following command as the user who is running the java application. In this example, the following command is executed as user “tomcat”.

$ ulimit -Hn
1024

$ ulimit -Hs
unlimited

You can also execute ulimit -a to view all the current ulimit values as shown below:

$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 128365
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 1024
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

To increase the open files limit on Linux, as root, append the following lines to your /etc/security/limits.conf file. This will change the soft and hrad limit for the “open files” values for “tomcat” user.

# vi /etc/security/limits.conf
tomcat soft nofile 2048
tomcat hard nofile 10240

After you made that change, exit out of your current shell, and login again, you’ll see the new value for the open files. In this example, we’ve increased it from 1024 to 2048.

$ ulimit -a
core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 128365
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 2048
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 1024
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

After this change, you should restart your java application that was giving the “java.io.FileNotFoundException: Too many open files” error message.

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